Touch switches and practical applications therefor

A touch switch apparatus for detecting the presence of an object such as a human appendage, the apparatus having a touch pad, an electric field generated about the touch pad and also having a preferably integrated and local control circuit connected to the touch pad and to a controlled device. Practical applications for touch switch apparatus, including use of touch switch apparatus in connection with other structure to emulate mechanical switches.

FIELD OF THE INVENTION

The present invention relates to touch switches (i.e., switches that are operated, for example, by touching a finger to or about a touch pad; also referred to herein as touch sensors or field effect sensors) and related control circuits and practical applications therefor.

BACKGROUND OF THE INVENTION

Mechanical switches have long been used to control apparatus of all types, including household appliances, machine tools, automobiles and related systems, and all sorts of other domestic and industrial equipment. Mechanical switches are typically mounted on a substrate and require some type of penetration through the substrate. These penetrations, as well as penetrations in the switch itself, can allow dirt, water and other contaminants to pass through the substrate or become trapped within the switch, thus leading to electrical shorts and other malfunctions.

Touch switches are often used to replace conventional mechanical switches. Unlike mechanical switches, touch switches contain no moving parts to break or wear out. Moreover, touch switches can be mounted or formed on a continuous substrate sheet, i.e. a switch panel, without the need for openings in the substrate. The use of touch switches in place of mechanical switches can therefore be advantageous, particularly in environments where contaminants are likely to be present. Touch switch panels are also easier to clean than typical mechanical switch panels because they can be made without openings in the substrate that would allow penetration of contaminants.

Known touch switches typically comprise a touch pad having one or more electrodes. The touch pads communicate with control or interface circuits which are often complicated and remote from the touch pads. A signal is usually provided to one or more of the electrodes comprising the touch pad, creating an electric field about the affected electrodes. The control/interface circuits detect disturbances to the electric fields and cause a response to be generated for use by a controlled device.

Although touch switches solve many problems associated with mechanical switches, known touch switch designs are not perfect. For example, many known touch switches can malfunction when contaminants such as water or other liquids are present on the substrate. The contaminant can act as a conductor for the electric fields created about the touch pads, causing unintended switch actuations. This presents a problem in areas where such contaminants are commonly found, such as a kitchen and some factory environments.

Existing touch switch designs can also suffer from problems associated with crosstalk, i.e., interference between the electric fields about adjacent touch pads. Crosstalk can cause the wrong touch switch to be actuated or can cause two switches to be actuated simultaneously by a touch proximate a single touch pad.

Many known touch switch designs are also susceptible to unintended actuations due to electrical noise or other interferences affecting a touch pad itself, or the leads extending from the touch pad to its associated control circuit. This problem can be aggravated in applications where the touch pad is a relatively large distance away from the control circuitry, as is frequently the case with conventional touch switch designs.

Existing touch switch designs commonly require complicated control circuits in order to interface with the devices they control. These control circuits are likely to be comprised of a large number of discrete components which occupy considerable space on a circuit board. Because of their physical size, the control circuits are typically located at a substantial distance from the touch pads themselves. The physical size of the control/interface circuits and their remoteness from the touch pads can aggravate many of the problems discussed above, such as crosstalk and susceptibility to electrical noise and interference. The size and remoteness also complicate the overall touch switch panel design, resulting in increased production cost and complexity.

Some known touch switch designs require a separate grounding lead from the touch pad to the interface/control circuit or to the controlled device. Certain apparatus utilizing conventional mechanical switches do not require, and may not readily accommodate, such grounding leads. Adapting such apparatus for use with such touch switches can require the addition of special grounding provisions, thus increasing design and production time, complexity, and cost. These ground lead requirements can preclude simple, direct replacement of conventional mechanical switch panels with touch switch panels.

Recent improvements in touch switch design include techniques which lower the input and output impedance of the touch switch itself, thereby making it highly immune to false actuations due to contaminants and external noise sources. U.S. Pat. No. 5,594,222 describes a low impedance touch switch design which is less susceptible to malfunction in the presence of contaminants and electrical noise than many previous designs. Even though this approach has several advantages over the prior art, there are some attributes that may limit its application. For instance, the resulting touch switch may be sensitive to temperature variations. As long as the temperature variations at the output are small relative to legitimate signal changes and are small relative to signal variations induced by transistor variations, then a single transistor or other amplifying device will be quite satisfactory. However, this technique may require the use of additional circuitry to interface with the controlled device, thus increasing cost and complexity to the overall touch switch design. In applications where there is little dynamic range to allow for compensation, and where temperature changes are significant relative to legitimate signal changes, a different approach may be better able to eliminate or reduce the effects of temperature.

Also, even though the low impedance approach of this technique can differentiate between contaminants with some finite amount of impedance and a human touch with some finite amount of impedance, this technique may not be enough to differentiate between extremely low levels of impedance. Such a situation could exist when an entire touch switch (i.e., both the inner and outer electrode) is covered with a large amount of contaminant. A similar, essentially zero-impedance, situation could exist when a conductive material, such as a metal pan, entirely covers a touch switch.

U.S. Pat. No. 6,310,611, assigned to the same assignee as the present application, and hereby incorporated by reference herein, discloses a touch switch apparatus having a differential measuring circuit which addresses many of the problems related to common mode disturbances affecting touch switches. For example, a touch switch having a two-electrode touch pad can be configured to generate an electric field about each electrode. A common mode disturbance, such as a contaminant substantially covering both electrodes, is likely to affect the electric field about each of the electrodes substantially equally. Each electrode provides a signal proportional to the disturbance to the differential measuring circuit. Since the signals from the electrodes are therefore contemplated to be substantially equal, the differential measuring circuit does not sense a differential and does not respond to the common mode disturbance. On the other hand, if the field about only one of the electrodes is disturbed, the signal provided by that electrode to the differential measuring circuit will likely be substantially different than that provided by the other, non-affected electrode. The differential circuit can respond by providing an output based on the different degrees of stimulation at the first and second electrodes, which can cause a switch actuation based upon the particular stimulation state of the electrodes or can provide information based on many stimulation states at the electrodes.

Although the differential measuring circuit approach addresses many problems known in the prior art, it is relatively complex and can be costly to design and manufacture. A differential measuring circuit typically comprises many more parts than a more conventional control circuit. The additional parts are likely to take up more space on a touch switch panel. As such, the control circuit is likely to be even farther from the touch pad than it might be with a non-differential circuit design, requiring long leads between the touch pad and its control circuit. This can actually aggravate concerns related to electrical interference. Furthermore, when building a differential measuring circuit, matching of components becomes important. Proper component matching presents an additional manufacturing burden and is likely to add cost. Also, when using differential sensing techniques, the resulting signals are relatively small compared to the dynamic range of absolute signal changes of the electrodes, especially in low impedance applications. The resulting signal therefore can be affected by noise and other environmental effects. Proper buffering of the differential signal would typically require the use of additional components to construct a switch or a buffer. Further, when a stimulus such as a pulse signal is applied from a remote control circuit, the pulse signal may be affected. Stimulus generating circuits such as pulse generating circuits typically require many components and occupy physical space that could interfere with the sensing electrodes. Therefore, the signal generating circuits need to be physically located remote from the sensing electrodes if they occupy physical space that can inadvertently affect or bias the sensing electrodes, which would effectively reduce the signal to noise ratio performance of the sensor.

Although the foregoing improvements can reduce unintended switch actuations as a result of crosstalk between switches and the effects of electrical interference on their control circuits, they do not eliminate these problems completely. Also, they do not address the need for separate grounding circuits in certain touch switch applications or resolve the concerns related thereto. Furthermore, it would be advantageous if the aforementioned features could be implemented using as small a physical structural form as possible.

Typically, actuation of a field effect sensor requires neither application of force nor physical displacement of a structural member by a user, as would be the case with, for example, a mechanical push button, toggle, or rotary switch. While this is a desirable attribute in many applications, in other applications it can be desirable for a user to apply force to or physically displace a switch member in order to give the user the physical perception that the switch has changed state. In certain application, it would be desirable to provide a switching mechanism having the advantages offered by field effect sensors, while retaining the mechanical feel of a conventional mechanical switch.

SUMMARY OF INVENTION

The present invention provides a touch switch apparatus comprising a touch pad and a control circuit located near the touch pad. The touch pad and control circuit may be mounted on a dielectric substrate. The control circuit is small compared to the overall size of the apparatus. In a preferred embodiment, the control circuit is substantially reduced to one or more integrated circuits. The physical compactness of the control circuit in the integrated circuit embodiment reduces the touch switch's susceptibility to common mode interference and to crosstalk and interference between adjacent touch switches. The integrated circuit approach also provides for better matching and balancing of the control circuit components.

The touch switch of the present invention can be configured in a variety of preferred embodiments. In some embodiments, the touch switch can emulate a conventional, maintained-contact type of mechanical switch. In other embodiments, the touch switch can emulate a momentary-contact type of mechanical switch. Also, in other embodiments the touch switch can provide multiple outputs relative to the sensing at the sensing electrodes.

In a preferred embodiment, the touch pad has a first electrode and a second electrode proximate the first electrode. At least one of the electrodes is electrically coupled to the local control circuit. The first and second electrodes and the local control circuit are typically placed on the same surface of a substrate, opposite the side of the substrate to be used as the touch surface. However, they need not be coplanar, and may be placed on opposite sides of a substrate.

In an alternate embodiment, the touch pad has a single electrode which is electrically coupled to the local control circuit. In other alternate embodiments, the touch pad can have more than two electrodes.

In a preferred embodiment, the control circuit includes means for generating a signal and providing it to the touch pad to create an electric field about one or more of the electrodes comprising the touch pad. Alternatively, such a signal may be generated elsewhere and provided to one or more of the electrodes to create one or more electric fields thereabout. The control circuit detects disturbances to the electric fields in response to stimuli thereto, such as a user's fingertip contacting or approaching the substrate adjacent the touch switch. The control circuit selectively responds to such field disturbances by generating a control signal for use by a controlled device, such as a household appliance or an industrial machine.

In a preferred embodiment, the control circuit detects and responds to differences in electrical potential between the first and second electrodes in response to the introduction of a stimulus in proximity to either the first electrode, the second electrode, or both. Such differential measuring circuit provides for the rejection of common mode signals (i.e., signals that would tend to affect both electrodes approximately equally) such as temperature, electrical noise, power supply variations, and other inputs. The differential measuring circuit also provides for the rejection of common mode signals resulting from the application of contaminants to the substrate adjacent the touch switch.

In a preferred embodiment, a signal is applied to a first electrode and to a second electrode. The signal may be generated from within the control circuit or from elsewhere. An electric potential is developed at each electrode, and, consequently, an electric field is generated about each of the electrodes. Two matched transistors are arranged in a differential measuring circuit, with the first transistor connected to the first electrode and the second transistor connected to the second electrode. Each transistor's output is connected to a peak detector circuit, and the output of each peak detector circuit is in turn provided to a decision circuit.

Each transistor's output is altered when the electric field about its corresponding electrode is altered, such as when the electrode is touched or approached by a user. The peak detector circuits respond to changes in the transistors' outputs and provide signals corresponding to the peak potentials from the transistors to the decision circuit. The decision circuit uses the peak potentials in a predetermined manner to provide an output for use by other portions of the control circuit.

In a preferred embodiment, the inner and outer electrodes are operably associated with the inputs to the decision circuit such that when a disturbance to an electric field about a first electrode is greater than the degree of disturbance of an electric field about a second electrode, the decision circuit will provide a high level output. Conversely, the decision circuit will provide a low level output when a disturbance to the electric field about the second electrode is greater than the degree of disturbance of an electric field about the first electrode. When the fields about both electrodes are disturbed more or less equally, the decision circuit will provide a low level output.

The first condition can be created, for example, when a fingertip substantially covers the first electrode but not the second electrode. The second condition can be created, for example, when a fingertip or contaminant substantially covers the second electrode but not the first electrode. The third condition can be created, for example, when a contaminant or an object, such as a metal pan, covers both the first and second electrodes.

The decision circuit output is provided to other circuit components, such as an electrical latch, which selectively cause a control signal to be output from the control circuit, depending on the decision circuit output state. In a preferred embodiment, a high level output from the decision circuit ultimately causes a control signal to be output from the control circuit, while no control signal will be output in response to a low level output. In an alternate embodiment, a low level output from the decision circuit causes a control signal to be output from the control circuit, while no control signal will be output in response to a high level output.

The touch switch apparatus of the present invention can be used to perform almost any function which can be performed by a mechanical switch, such as turning a device on or off, adjusting temperature, or setting a clock or timer. It can be used in place of, and solve problems associated with, existing touch switches. It can also be used as a direct replacement for mechanical membrane-type switches. The touch switch apparatus of the present invention is well suited for use in environments where temperature variations are extreme, where substantial amounts of contaminants can be present or where metal objects may be placed on or over the touch pad.

The present invention provides input circuit portions for more effectively communicating signals between touch pad electrodes and logic and decision circuits. In a preferred embodiment, these input portions of the control circuit include active devices and peak detection circuits in various configurations to convert high frequency transient pulses to DC signals. These embodiments can eliminate the need for more complicated AC processing circuitry and can allow for the use of DC processing circuitry which will reduce the size and cost of the integrated circuits of the touch switch assemblies. Also, these preferred embodiments can be capable of discharging the electric fields associated with the peak detection circuits, which correspond to the electric fields at the input electrodes.

In other preferred embodiments, the negative effects of stray capacitance caused by bonding pad and wire bonding configuration are compensated for by incorporating swamping capacitance in the input portions of the control circuits mentioned above. Swamping according to these embodiments of the present invention can eliminate imbalances in the differential measuring circuit caused by the stray capacitance and can thereby provide for more consistent electrical information going into the decision circuit.

In other preferred embodiments, protection of the control circuitry from damage caused by stray current and the sometimes high electrostatic potential of the input electrodes of the touch pad is provided by active blocking device configurations in the input portions of the control circuit.

Other preferred embodiments can provide for statistical filtering and sampling in high noise and other environments. Also, other preferred embodiments provide for the linearization of input signals sent to decision circuits using differential measuring techniques.

The present invention also provides dual connection latch circuits, which facilitate the direct replacement of membrane and other mechanical switches with touch sensing switches. In preferred embodiments, this latch circuit configuration can provide isolation from inherent leakage current paths that develop from the doped substrates used to fabricate the control and integrated circuits of touch switch assemblies. It is also an object of the present invention to provide for an analog output that exploits the advantages of the input configurations of the circuits utilized by the invention. It is a further object of the invention to provide ways to sense capacitive inputs.

The present invention also is directed to practical applications for touch switches. While the touch switches described herein are particularly well-suited for use in connection with many of the applications discussed herein, other touch switches and sensors, for example, capacitive sensors and field effect sensors as disclosed in U.S. Pat. Nos. 5,594,222 and 6,310,611, the disclosures of which are incorporated herein by reference, may be used in such applications as well.

DETAILED DESCRIPTION OF THE DRAWINGS

The disclosures of U.S. Pat. Nos. 5,594,222, 5,856,646, 6,310,611, 6,320,282, 6,713,897, and 6,897,390, and U.S. patent application Ser. No. 10/271,933 entitled Intelligent Shelving System, Ser. No. 10/272,047, entitled Touch Sensor with Integrated Decoration, and Ser. No. 10/850,272, entitled Integrated Touch Sensor and Light Apparatus, all filed on Oct. 15, 2002 all assigned to the assignee of the present invention, are hereby incorporated herein by reference.

The invention pertains to a touch switch apparatus comprising a touch pad having one or more electrodes and a control circuit. Many of the drawings illustrating the control circuit depict the circuit as large in relation to the touch pad for clarity. In typical applications, however, the control circuit may be small compared to the touch pad, and is preferably in the form of one or more integrated circuit chips.

FIG. 1is a perspective representation of one preferred embodiment of a touch switch apparatus20of the present invention. Touch switch apparatus20comprises a touch pad22, a control circuit24comprising an integrated circuit (IC) chip26having eight output terminals PIN1-PIN8, and first and second resistors R1and R2. In the embodiment shown, touch pad22comprises a first electrode E1and a second electrode E2, although the touch pad may also be comprised of more or fewer than two electrodes. Although control circuit24could be fabricated using discrete electronic components, it is preferable to embody control circuit24in a single integrated circuit chip, such as IC chip26.

Control circuit24, via terminals PIN1-PIN8of IC chip26, is electrically coupled to, and communicates with, first and second resistors R1and R2, first and second electrodes E1and E2, and an input line30which is configured to supply a control and/or power signal from a remote device (not shown). Control circuit24also communicates with a remote device (not shown) using a first output line32. In some embodiments, a second output line34is also used for communication with the remote device (not shown).

FIG. 2is a partial cross-sectional view of a typical touch switch20of the present invention in which the components comprising touch switch apparatus20are mounted on a dielectric substrate35having a front surface36and an opposing rear surface37. In the embodiment shown, first and second electrodes E1and E2are mounted on rear surface37of substrate35. IC chip26is also mounted on rear surface37of substrate35, proximate first and second electrodes E1and E2. As can be seen from bothFIGS. 1 and 2, in the preferred embodiment it is contemplated that IC chip26comprising control circuit24be mounted in close proximity to touch pad22.

Substrate35is typically comprised of a relatively rigid dielectric material, such as glass, plastic, ceramic, or any other suitable dielectric material. However, substrate35may also comprise any other suitable dielectric material, including flexible materials. Consolidated Graphics No. HS-500, Type 561, Level 2, a 0.005 inch thick polyester material, is an example of a suitable flexible substrate. In embodiments where the touch switch apparatus components are mounted on a flexible substrate, the flexible carrier is often subsequently applied to another, generally more rigid, substrate.

In a preferred embodiment, substrate35is made of glass having a uniform thickness of about 3 mm. In other embodiments, the thickness of substrate35may vary, depending on the type of material used, its mechanical and electrical properties, and the physical strength and electrical sensitivity required for a particular application. The maximum functional thickness for glass and plastic substrates is on the order of several inches. However, in most practical applications, glass substrates range in thickness from about 1.1 mm to about 5 mm, while plastic substrates can be even thinner.

In a preferred embodiment, as shown inFIGS. 1 and 2, second electrode E2substantially surrounds first electrode E1. A space28is located between first electrode E1and second electrode E2. First electrode E1may be dimensioned such that it may be “covered” by a user's fingertip or other human appendage when the user touches the corresponding portion of front surface36of substrate35. In one preferred embodiment, first electrode E1is square and second electrode E2is arranged in a square pattern about and conforming to the shape of first electrode E1.

Although the touch pad geometry illustrated inFIGS. 1 and 2represents a preferred arrangement of first and second electrodes E1and E2, it should be recognized that the electrode arrangement can be varied extensively to accommodate a wide variety of applications. For example, the electrode size, shape, and placement may be varied to accommodate the size of the appendage or other stimulus contemplated to actuate touch switch20. For example, a particular application might require that a hand, rather than a finger, provide the stimulus to actuate touch switch20. In such an application, first and second electrodes E1and E2would be much larger and spaced farther apart.

First electrode E1may take any number of different geometric shapes, including, but not limited to, rectangles, trapezoids, circles, ellipses, triangles, hexagons, and octagons. Regardless of the shape of first electrode E1, second electrode E2can be configured to at least partially surround first electrode E1in a spaced-apart relationship. However, it is not necessary for second electrode E1to surround the first electrode even partially in order to obtain the benefits of the invention. For example, first and second electrodes E1and E2can be adjacent to each other, as shown inFIG. 3. In alternative embodiments, second electrode E2may be omitted.

Furthermore, the electrode configuration need not be co-planar, but can be three dimensional to conform to a sphere, a cube, or other geometric shape. This design flexibility allows the invention to be used in a wide variety of applications, with substrates of varying shapes and composition. In some applications, it may not be necessary to actually touch substrate35upon or within which touch pad22and control circuit24are situated. For example,FIG. 8illustrates a touch switch apparatus20wherein first and second electrodes E1and E2are mounted on an exterior surface113of a first pane111of a thermopane window110and which can be actuated by a user bringing a suitable stimulus115proximate an exterior surface114of an opposing pane112of the window.

As noted above, first and second electrodes E1and E2need not be coplanar; they can be mounted on different sides or surfaces of a substrate, or on different substrates altogether. For example,FIG. 9illustrates a touch switch apparatus20wherein first electrode E1is mounted on a first surface36of a substrate35and second electrode E2and IC chip26are mounted on a second, opposing surface37of substrate35. In applications where first and second electrodes E1and E2are on the same side of a substrate, IC chip26can be mounted on the same side of the substrate as the electrodes, or on another side of the substrate. If the first and second electrodes are mounted on different surfaces of a substrate or on different substrates altogether, IC chip26can be mounted on the same surface as either of the electrodes, or on a different surface or substrate altogether. However, it is preferred that the IC chip26be mounted in close proximity to the electrodes.

Preferably, first electrode E1is a solid conductor. However, first electrode E1may also have a plurality of apertures or may have a mesh or grid pattern. In some embodiments, second electrode E2will take the form of a narrow ribbon partially surrounding first electrode E2. In other embodiments, such as where first and second electrodes E1and E2are merely adjacent each other, second electrode E2may also be a solid conductor or may have a mesh or grid pattern.

Control circuit24may be designed in many different ways, and it may be used with a variety of power sources, such as AC, periodically varying DC (such as a square wave), continuous DC, or others.FIGS. 4-7illustrate a preferred control circuit design which may be easily adapted for use with a variety of power supplies, in a variety of operating modes. TheFIG. 4embodiment uses square wave DC power in a differential input, strobed mode of operation; theFIG. 5embodiment uses continuous DC power in a differential input, continuous DC mode; theFIG. 6embodiment uses square wave DC power in a single-ended input, strobed mode; and theFIG. 7embodiment uses continuous DC power in a single-ended input, continuous DC mode.

It is apparent fromFIGS. 4-7that control circuit24can be readily adapted for various different operating modes. The foregoing four operating modes will be described in detail to demonstrate the design flexibility allowed by the invention. However, it should be recognized that the invention is by no means limited to these four operating modes. The particular operating mode and power source used in a specific application depends primarily on the requirements and specifications of the controlled device.

Boxed areas B1and B2onFIGS. 4-7indicate the demarcation between components contemplated to be located on IC chip26and components located off of IC chip26, such as electrodes E1and E2, resistors R1and R2, the controlled device (not shown), and input and output lines30and32, respectively. The portions ofFIGS. 4-7which are outside boxed areas B1and B2are contemplated to be located on IC chip26and are identical for all four figures and operating modes depicted therein. Boxed area B6contains the input portion of the control circuit. Various configurations of the input portion contained in boxed area B6are discussed with reference toFIGS. 11A-18E, below.

FIGS. 4-7illustrate a control circuit24comprising a startup and bias section40, a pulse generator and logic section50, a decision circuit section60, and a self-holding latch section70, the functions of which will be described below. Each of the foregoing circuit sections40,50,60and70may be designed in a number of different ways, as would be known to those skilled in the art of electronic integrated circuit design.

Control circuit24also comprises first, second, and third transistors P1, P2, and P3. In the embodiments described herein, transistors P1-P3are P-MOS devices, although N-MOS devices, bipolar devices, or other transistor types can also be used. Control circuit24further comprises an inverter I1, first, second, and third diodes D1-D3, first and second capacitors C1and C2, first, second, third, and fourth transistor switches SW1-SW4, and third and fourth resistors R3and R4. It should be recognized that third and resistors R3and R4may be replaced with current sources or active loads.

In each of the embodiments illustrated inFIGS. 4-7, source terminal77of third transistor P3and power input terminals41,51,61, and71of startup and bias section40, pulse generator and logic section50, decision circuit60, and self-holding latch section70, respectively, are electrically coupled to terminal PIN8of IC chip26. Terminal PIN8is in turn electrically coupled to control circuit24power input line30, which is in turn electrically coupled to a power source25. Typically, power source25is located at the controlled device (not shown).

A biasing output terminal43from startup and bias section40is electrically coupled to gate terminals G2and G4of second and fourth transistor switches SW2and SW4, respectively. In the preferred embodiment and as described herein with respect toFIGS. 4-7, first through fourth transistor switches SW1-SW4are N-MOS devices, although other transistor types and combinations may be used, as well, as shown inFIGS. 11A-18E.

A power-on reset output44from startup and bias section40is electrically coupled to a power on reset input54at pulse generator and logic section50. Power on reset output44of startup and bias section40is also electrically coupled to gate terminals G1and G3of first and third transistor switches SW1and SW3.

Internal ground reference output42from the startup and bias section40is electrically coupled to low potential plates102and103of first and second capacitors C1and C2, source terminals S1, S2, S3, and S4of first through fourth transistor switches SW1-SW4, respectively, internal ground reference output52of the pulse generator and logic section50, internal ground reference output62of decision circuit60, anode98of third diode D3, low potential ends96and97of third and fourth resistors R3and R4, and to terminal PIN6of IC chip26. The node thus described will hereinafter sometimes be referred to as the internal ground reference CHIP VSS.

A pulse output53from pulse generator and logic section output50is electrically coupled to source terminals80and81of first and second transistors P1and P2, respectively, and to terminal PIN2of IC26. Gate terminal82of first transistor P1is electrically coupled to terminal PIN1of IC26. Gate terminal83of second transistor P2is electrically coupled to terminal PIN3of IC26.

Drain terminal84of first transistor P1is electrically coupled to anode90of first diode D1and to high potential end94of third resistor R3. Drain terminal85of second transistor P2is electrically coupled to anode91of second diode D2and to high potential end95of fourth resistor R4.

Cathode92of first diode D1is electrically coupled to PLUS input terminal64of decision circuit60, to drain terminals86and87of first and second transistor switches SW1and SW2, and to high potential plate100of first capacitor C1. Cathode93of second diode D2is electrically coupled to MINUS input terminal66of decision circuit60, to drain terminals88and89of third and fourth transistor switches SW3and SW4, and to high potential plate101of second capacitor C2.

In the illustrated embodiments, decision circuit section60is designed so that its output63is at a low potential when its PLUS and MINUS inputs64and66, respectively, are at substantially equal potentials or when MINUS input66is at a substantially higher potential than PLUS input64. Decision circuit section60output63is at a high potential only when PLUS input64, is at a substantially higher potential than MINUS input66.

Self-holding latch section70is designed so that no current flows through latch section70from the control circuit24power supply25to internal ground reference CHIP VSS and through third diode D3when decision circuit section60logic output63is at a low potential. However, when decision circuit60section logic output63is at a high potential, latch trigger input73is at a high potential, thus triggering latch circuit70and enabling current to flow through latch section70from control circuit24power supply25to internal ground reference CHIP VSS and through third diode D3, by way of latch70power input and output terminals71and72, respectively. Once latch70has been triggered, it remains triggered, or sealed in, until power is removed from control circuit24. The design and construction of a latch section which operates in this manner is known to those skilled in the art and need not be described in detail herein.

Third diode D3is provided to prevent back-biasing of control circuit24when touch switch apparatus20is used in multiplexed applications. It can be omitted in applications where only a single touch pad22is used, or where multiple touch pads22are used, but not multiplexed.

The foregoing description of the basic design of control circuit24is identical for each of the four operating modes depicted inFIGS. 4-7. The distinctions in overall apparatus configuration among the four operating modes lie primarily in the external terminal connections of IC26, as will be described in detail below.FIG. 4illustrates a touch switch apparatus20configured for operation in differential input strobed mode, as described below. Control circuit24for operation in this mode is configured as described hereinabove forFIGS. 4-7generally. Terminal PIN2of IC26is electrically coupled to high potential ends104and105of first and second resistors R1and R2, respectively. Terminal PIN1of IC26is electrically coupled to both low potential end106of first resistor R1and to first electrode E1. Terminal PIN3of IC26is electrically coupled to both low potential end107of second resistor R2and to second electrode E2.

The circuit elements represented as C3and C4inFIGS. 4-7are not discrete electrical components. Rather, reference characters C3and C4represent the capacitance-to-ground of first and second electrodes E1and E2, respectively.

Terminal PIN8of IC26is electrically coupled to input line30, which is in turn electrically coupled to a power signal source25at, for example, the controlled device (not shown). Terminal PIN4of IC26is electrically coupled to terminal PIN6of IC26, thereby electrically coupling output terminal72of latch70to the internal ground reference CHIP VSS and anode98of third diode D3. Terminal PIN7of IC chip26is not externally terminated in this embodiment. Terminal PIN5of IC26is electrically coupled to output line32, which is in turn electrically coupled to high potential end108of fifth resistor R5and to output line120, which is connected to the controlled device (not shown), either directly or by way of a processor or other intermediate device (not shown). Low potential end109of resistor R5is electrically coupled to the system ground. In a typical application, resistor R5will be at a substantial distance from the other components comprising touch switch apparatus20. That is, in the preferred embodiment, resistor R5is contemplated not to be near touch pad22and control circuit24.

FIG. 5illustrates a typical touch switch control circuit24configured for operation in differential input continuous DC mode, as described below. The overall control circuit and apparatus is identical to that described forFIG. 4hereinabove, with three exceptions. First, in theFIG. 5embodiment, terminal PIN7of IC26is electrically coupled to high potential end108of resistor R5and to output line120, which is connected to the controlled device (not shown) either directly or by way of a processor or other intermediate device (not shown), whereas terminal PIN7is not externally terminated in theFIG. 4embodiment. Second, in theFIG. 5embodiment, terminals PIN4and PIN6of IC26are not electrically coupled to each other or otherwise externally terminated, whereas they are in theFIG. 4embodiment. Third, in theFIG. 5embodiment, terminal PIN5of IC26is electrically coupled to low potential end109of resistor R5, whereas in theFIG. 4embodiment, terminal PIN5of IC26is electrically coupled to high potential end108of fifth resistor and to the controlled device (not shown). As in theFIG. 4embodiment, fifth resistor R5will typically be at a substantial distance from the other components comprising touch switch apparatus20.

FIG. 6illustrates a typical touch switch control circuit configured for operation in single-ended input strobed mode, as described below. Control circuit24is configured as described hereinabove forFIGS. 4-7generally. Terminal PIN2of IC26is electrically coupled to high potential ends104and105of first and second resistors R1and R2, respectively. Terminal PIN1of IC26is electrically coupled to both low potential end106of first resistor R1and to first electrode E1. Terminal PIN3of IC26is electrically coupled to both low potential end107of second resistor R2and to high potential end110of sixth resistor electrode R6, such that second resistor R2and sixth resistor R6form a voltage divider. Low potential end111of sixth resistor R6is electrically coupled to internal ground reference CHIP VSS, typically at a point proximate terminal PIN5of IC26. InFIG. 6, the electrical connection of sixth resistor R6to the internal ground reference CHIP VSS is represented by broken line “A-A” for clarity.

Terminal PIN8of IC26is electrically coupled to input line30, which is in turn electrically coupled to a power signal source25. Terminal PIN5of IC26is electrically coupled to output line32, which is in turn electrically coupled to high potential end108of fifth resistor R5and to output line120. Output line120is electrically coupled to the controlled device (not shown), either directly or by way of a processor or other intermediate device. Terminal PIN4of IC26is electrically coupled to terminal PIN6of IC26. Terminal PIN7of IC26is not externally terminated in this embodiment. In a typical application, fifth resistor R5will be at a substantial distance from the other components comprising touch switch apparatus20.

FIG. 7illustrates a typical touch switch control circuit configured for operation in single ended input continuous DC mode, as described below. Control circuit24is configured as described hereinabove forFIGS. 4-7generally. The overall control circuit and apparatus is identical to that described forFIG. 6hereinabove, with three exceptions. First, in theFIG. 7embodiment, terminal PIN7of IC26is electrically coupled to high potential end108of fifth resistor R5and to output line120, which is in turn connected to the controlled device (not shown), typically by way of a microprocessor or other controller (not shown). Terminal PIN7of IC26is not externally terminated in theFIG. 6embodiment. Second, in theFIG. 7embodiment, terminals PIN4and PIN6of IC26are not electrically coupled or otherwise externally terminated, whereas they are in theFIG. 6embodiment. Third, in theFIG. 7embodiment, terminal PIN5of IC26is electrically coupled to low potential end109of fifth resistor R5, whereas in theFIG. 6embodiment, terminal PIN5of IC26is electrically coupled to high potential end108of fifth resistor and to output line120. In a typical application, fifth resistor R5will be at a substantial distance from the other components comprising touch switch apparatus20. InFIG. 7, the electrical connection of sixth resistor R6to the internal ground reference CHIP VSS is represented by broken line “A-A” for clarity.

A touch switch apparatus20configured for the differential input strobed mode operates as follows. Referring toFIG. 4, a power/control signal25is provided to terminal PIN8of IC26and, in turn, to power input terminals41,51,61, and71of start up and bias section40, pulse generator and logic section50, decision circuit section60, and self-holding latch section70, respectively.

Upon becoming powered, and after a suitable delay interval to allow for stabilization (approximately25microseconds is sufficient but may be either shorter or longer depending on the application), start up and bias section40outputs a short duration power-on reset signal from output terminal44to gate terminals G1and G3of first transistor switch SW1and third transistor switch SW3, respectively, causing first and third transistor switches SW1and SW3to turn on, and thus providing a current path from high potential plates100and101of first and second capacitors C1and C2, respectively, to the internal ground reference CHIP VSS. The power on reset signal duration is sufficient to allow any charge present on first and second capacitors C1and C2to be substantially completely discharged to the internal ground reference CHIP VSS. In this manner, PLUS and MINUS inputs64and66to decision circuit section60attain an initial low-potential state.

At substantially the same time, start up and bias circuit40sends a power on reset signal from output44to input54of pulse generator and logic section50, thus initializing it. After a suitable delay to allow pulse generator and logic section50to stabilize, pulse generator and logic section50generates a pulse and outputs it from pulse output terminal53to first and second electrodes E1and E2by way of first and second resistors R1and R2, and to source terminals80and81of first and second transistors P1and P2, respectively. The pulse may be of any suitable waveform, such as a square wave pulse.

Startup and bias circuit40also outputs a bias voltage from bias output43to gate terminals G2and G4of second and fourth transistor switches SW2and SW4, respectively. The bias voltage is out of phase with the pulse output to first and second electrodes E1and E2. That is, when the pulse output is at a high state, the bias voltage output is at a low state and when the pulse output is at a low state, the bias voltage output is at a high state.

When a pulse is applied to first and second electrodes E1and E2through first and second resistors R1and R2, respectively, the voltage at gate terminals82and83of first and second transistors P1and P2is initially at a lower potential than that at source terminals80and81of first and second transistors P1and P2, respectively, thus biasing first and second transistors P1and P2and causing them to turn on. With first and second transistors P1and P2turned on, current will flow through third and fourth resistors R3and R4, thus creating a peak potential at anode terminals90and91of first and second diodes D1and D2, respectively.

If the peak potential at anodes90and91of first and second diodes D1and D2is higher than the potential across first and second capacitors C1and C2, a peak current is established through first and second diodes D1and D2, causing first and second capacitors C1and C2to become charged, and establishing a peak potential at each of PLUS and MINUS inputs64and66to decision circuit section60. This situation will occur, for example, following the first pulse after control circuit24has been initialized because first and second capacitors C1and C2will have become discharged upon startup, as described above.

As is evident to one skilled in the art, the biasing of first and second transistors P1and P2, the current through third and fourth resistors R3and R4, the peak potential created at anodes90and91of first and second diodes D1and D2, and the peak potential created at each of PLUS and MINUS inputs64and66to decision circuit60are proportional to the condition of the electric field at first and second electrodes E1and E2. The condition of the electric field proximate electrodes E1and E2will vary in response to stimuli present proximate the electrodes.

With control circuit24activated, as described above, and with no stimuli present proximate either first and second electrodes E1and E2, the potentials at each of PLUS and MINUS inputs64and66to decision circuit60are in what may be termed a neutral state. In the neutral state, the potentials at each of PLUS and MINUS inputs64and66may be substantially equal. However, in order to prevent unintended actuations, it may be desirable to adjust control circuit24so that the neutral state of MINUS input66is at a somewhat higher potential than the neutral state of PLUS input64. This adjustment may be effected by varying the configurations of first and second electrodes E1and E2and the values of first and second resistors R1and R2to achieve the desired neutral state potentials. Regardless of the neutral state potentials, it is contemplated that decision circuit60output63will be at a low potential unless PLUS input64is at a substantially higher potential than

With decision circuit60output63at a low potential, inverter I1causes the potential at gate terminal78of third transistor P3to be at a high level, substantially equal to the potential at source terminal77. In this state, third transistor P3is not biased and will remain turned off. However, in this embodiment, terminal PIN7of IC26is not terminated. Drain terminal79of third transistor P3is therefore in an open-circuit condition, and the state of third transistor P3is of no consequence to the function of the apparatus. Also, with decision circuit60output63, and consequently latch trigger input73, at a low state, self holding latch circuit70will not be triggered, and no current will flow through latch70from power supply25to the internal ground reference CHIP VSS and through third diode D3.

Over a period of time which is determined by the pulse voltage, the values of first and second resistors R1and R2, and the capacitance to ground of first and second electrodes E1and E2(represented in the figures as virtual capacitors C3and C4), the potential at first and second electrodes E1and E2eventually rises to substantially equal the pulse voltage and thus the voltage at source terminals80and81of first and second transistors P1and P2, thus unbiasing first and second transistors P1and P2. When this state is reached, first and second transistors P1and P2turn off, and the potentials at anodes90and91of first and second diodes D1and D2begin to decrease at a substantially equal rate towards the internal ground reference CHIP VSS level. Eventually, the anode potential at each of first and second diodes D1and D2is likely to fall below the respective cathode potential. At this point, diodes D1and D2become reverse biased and prevent first and second capacitors C1and C2from discharging.

When the pulse on output53goes to a low state, the bias voltage output goes to a high state relative to the internal ground reference CHIP VSS, and applies the elevated bias voltage to gate terminals G2and G4of second and fourth transistor switches SW2and SW4. In this state, second and fourth transistor switches SW2and SW4become slightly biased and turn on sufficiently to effect a slow, controlled discharge of first and second capacitors C1and C2to the internal ground reference CHIP VSS. When the pulse next goes to a high state, the bias voltage will return to a low state, second and fourth transistor switches SW2and SW4will turn off, and the circuit will respond as described initially.

If a stimulus is present at or near second electrode E2when the pulse from pulse generator and logic section50goes to a high potential, first transistor P1will operate as described hereinabove. That is, first transistor P1will be initially biased and will allow some current to flow through third resistor R3, creating a peak potential at anode90of first diode D1, and allowing a peak current to flow through first diode D1, thereby charging first capacitor C1, and establishing a peak potential at PLUS input64to decision circuit60. Once the voltage at first electrode E1has stabilized in response to the incoming pulse, first transistor P1will become unbiased and will turn off.

Second transistor P2operates in much the same way, except that the presence of the stimulus proximate second electrode E2will alter the RC time constant for that circuit segment, thus lengthening the time required for the potential at second electrode E2to stabilize. As a consequence, second transistor P2will remain biased on for a longer period of time than first transistor P1, allowing a greater peak current to flow through fourth resistor R4than flows through third resistor R3, thus generating a peak potential at anode91of second diode D2which is greater than the peak potential present at anode90of first diode D1. Consequently, a peak current will flow through second diode D2, causing second capacitor C2to become charged, ultimately resulting in a peak potential at MINUS input66to decision circuit60which is greater than the peak potential at PLUS input64to decision circuit. Since decision circuit60is configured so that its output will be at a low potential when the potential at MINUS input66is greater than or substantially equal to the potential at the PLUS input64, decision circuit60output terminal63will be at a low potential.

With decision circuit60output terminal63, and consequently latch trigger input terminal73, at a low potential, self holding latch70will not be triggered. Inverter I1and third transistor P3will operated as described previously, although, again, the state of third transistor P3is inconsequential in this configuration.

In the event that a contaminant or foreign object, or other stimulus, substantially covers, or is applied to, both first and second electrodes E1and E2, the system will respond much in the same way as it would when no stimulus is present at either the first electrode or second electrode. However, with contaminants or a foreign object present proximate both electrodes E1and E2, the RC time constant for those segments of the circuit will be altered such that it will take longer for the voltage at both first and second electrodes E1and E2, respectively, to substantially equalize with the pulse voltage. Consequently, both first and second transistors P1and P2will turn on and will allow more current to flow through third and fourth resistors R3and R4than they would in a condition where neither first nor the second electrode E1or E2is affected by a stimulus. However, first and second transistors P1and P2will be substantially equally biased. Therefore, a substantially equal peak potential will be developed at anodes90and91of both first and second diodes D1and D2, causing a substantially equal peak current to flow through first and second diodes D1and D2, charging first and second capacitors C1and C2, and establishing a substantially equal peak potential at both PLUS and MINUS inputs64and66to decision circuit60. In this state, decision circuit section60output terminal63will be at a low potential, latch trigger input terminal73of self holding latch70will be at a low potential, and latch70will remain untriggered. As previously described, the state of inverter I1and third transistor P3is inconsequential in this embodiment.

In the situation where a stimulus is applied proximate first electrode E1, but not second electrode, second transistor P2will be initially biased and will turn on, establishing a current through fourth resistor R4, and generating a peak potential at anode terminal90of second diode D2. A peak current will flow through second diode D2, charging second capacitor C2, and establishing a peak potential at MINUS input66of decision circuit section60. As the voltage at gate terminal81of second transistor P2rises to the level of the pulse voltage, second transistor P2will become unbiased and will turn off. Second diode D2will then become reverse biased, and will prevent second capacitor C2from discharging.

As is evident to one skilled in the art, the presence of a stimulus proximate first electrode E1will lengthen the time required for the potential at first electrode E1to stabilize. As a consequence, first transistor P1will remain biased on for a longer period of time than second transistor P2, allowing a greater peak current to flow through third resistor R3than through fourth resistor R4, thus generating a peak potential at anode90of first diode D1which is greater than the potential present at anode91of second diode D2. Consequently, a peak current of greater magnitude and/or duration will flow through first diode D1than through second diode D2, causing first capacitor C1to become charged, ultimately resulting in a peak potential at PLUS input64to decision circuit60which is substantially greater than the peak potential at MINUS input66to decision circuit60. Since decision circuit60is configured so that output terminal63will be at a high state when the potential at PLUS input64is greater than the potential at MINUS input66, decision circuit60output63will be at a high potential.

With decision circuit60output63at a high potential, inverter I1will cause potential at gate terminal78of third transistor P3to be low relative to the potential at source terminal77, thus biasing third transistor P3, and causing it to turn on. However, since terminal PIN7of IC26is not terminated in this embodiment, the state of third transistor P3is of no consequence.

With decision circuit60output terminal63at a high potential, self holding latch circuit70trigger input terminal73will also be at a high potential, thus triggering latch70. When self holding latch70is triggered, a current path is established from power supply25to internal ground reference CHIP VSS and through third diode D3, effectively short circuiting the remainder of control circuit24, including startup and bias section40, pulse generator and logic section50, and decision circuit section60. In this state, those sections of control circuit24become substantially de-energized and cease to function.

Once triggered, self holding latch70will remain triggered, regardless of the subsequent state of stimuli proximate either or both of electrodes E1and E2. Latch70will reset when the power from the power supply25goes to a near zero state, such as when the square wave strobe signal from power supply25of this example falls to zero.

While self holding latch70is in the triggered state, a steady state signal will be supplied through fifth resistor R5and back to the controlled device (not shown). In this manner, touch switch apparatus20emulates the change of state associated with a maintained-contact mechanical switch.

Referring now toFIG. 5, the operation of a touch switch apparatus20configured for the differential input continuous DC mode is as follows. The control circuit24, up to and including decision circuit60, performs in substantially the same manner as when configured for the differential input strobed mode of operation, as described above with reference toFIG. 4. That is, with no stimulus present proximate either first or second electrodes E1and E2, with a stimulus present proximate both first and second electrodes E1and E2, or with a stimulus present proximate second electrode E2, but not first electrode E1, the decision circuit60output63will be at a low potential. With a stimulus present proximate first electrode E1, but not second electrode E2, the decision circuit60output63will be at a high level.

As can be readily seen inFIG. 5, self holding latch circuit70output72is not terminated in this embodiment, and the self holding latch70is therefore inoperative in differential input DC mode. However, drain terminal79of third transistor P3is electrically coupled to internal ground reference CHIP VSS and to output line32in this embodiment, and it therefore becomes an operative part of control circuit24. When decision circuit60output63is at a low potential, inverter I1causes the potential at gate terminal78of third transistor P3to be at a high potential, substantially equal to the potential source terminal77. In this state, third transistor P3is not biased and does not turn on. When decision circuit60output63is at a high potential, inverter I1causes the potential at gate terminal78of third transistor P3to be at a low potential compared to the potential at source terminal77. In this state, third transistor P3is biased and turns on, allowing current to be established through third transistor P3and fifth resistor R5. Output line resistor R5limits the current through third transistor P3such that the balance of control circuit24is not short circuited and remains operative.

In the DC mode shown inFIG. 5, control circuit24also responds to the removal of the stimulus from the proximity of first electrode E1. So long as a stimulus remains present proximate first electrode E1, but not second electrode E2, each time the pulse goes to a high state, a peak potential will be created at anode90of first diode D1which is higher than the peak potential at anode91of second diode D2. Consequently, the peak potential at PLUS input64to decision circuit60will be at a higher level than the peak potential at MINUS input66and control circuit24will behave as described above. When the stimulus is removed, however, and no stimulus is present proximate either first electrode E1or second electrode E2, the charge on first capacitor C1will eventually discharge to a neutral state by means of the biasing function of second transistor switch SW2. At this point, the potential at PLUS input64of decision circuit60will no longer be higher or substantially higher than the potential at MINUS input66, and decision circuit60output63will return to a low state.

In this manner, touch switch apparatus20operating in differential input DC mode emulates a momentary contact, push-to-close and release-to-open, mechanical switch. It should be recognized that, with minor revisions, the control circuit could be configured to emulate a push-to-open and release-to-close mechanical switch.

Referring now toFIG. 6, touch switch apparatus20configured for the single ended input strobed mode of operation operates as follows. When a pulse is applied to first electrode E1and first and second resistors R1and R2, current flows through second resistor R2and sixth resistor R6. Second and sixth resistors R2and R6are configured as a voltage divider; that is, when the pulse output is in a high state, gate terminal83of second transistor P2will be at a lower potential than source terminal81of second transistor P2. Therefore, when pulse output53is in a high state, second transistor P2will be continuously biased and will allow a constant current to flow through fourth resistor R4, thus creating a reference potential at anode91of second diode D2. The reference potential at anode91of second diode D2will establish a current through second diode D2, causing second capacitor C2to become charged, and thus creating a reference potential at MINUS input66to decision circuit60. When the reference potential at MINUS input66becomes substantially equal to the reference potential at anode91of second diode D2, the current through second diode D2will cease.

Concurrently, with no stimulus present at first electrode E1, the pulse applied to source terminal80of first transistor P1and to first electrode E1will initially cause first transistor P1to become biased and to turn on. A current will thus be established through third resistor R3and a peak potential will be created at anode90of first diode D1. The peak potential will establish a peak current through first diode D1, charging first capacitor C1and creating a peak potential at PLUS input64of the decision circuit. Resistors R1, R2, R3, R4, and R6are selected so that when no stimulus is present proximate first electrode E1, the reference potential at MINUS input66of decision circuit60will be greater than or equal to the peak potential at to PLUS terminal64of decision circuit60.

In this state, output63of the decision circuit60will be at a low potential and self holding latch70will not be triggered. Also, inverter I1will cause the potential at gate terminal78of third transistor P3to be at a high state, substantially equal to the source terminal77potential, so that third transistor P3is unbiased and remains turned off. However, this is of no consequence since drain terminal79of third transistor P3is in an open-circuit condition in this embodiment.

This embodiment does not require a second electrode, although a two-electrode touch pad may be adapted for use in this mode. In the event a two-electrode touch pad is adapted for use in this mode of operation, the presence or absence of a stimulus proximate the second electrode has no effect on the operation of the circuit.

In the event that a stimulus is present proximate first electrode E1, the operation of second transistor P2is the same as described hereinabove for this embodiment. However, the presence of the stimulus proximate first electrode E1will cause a greater time to be required for the voltage at gate terminal82of first transistor P1to become equalized with source terminal80potential at first transistor. Consequently, first transistor P1will be turned on and will allow a relatively greater current to flow through third resistor R3, compared to the current that second transistor P2allows to flow through fourth resistor R4. As a result, the peak potential at anode90of first diode D1will be greater than the reference potential at anode91of second diode D2. As a result, the peak potential at PLUS input64of decision circuit60will be greater than the reference potential at MINUS input66of decision circuit60, and output63from decision circuit60will therefore be at a high state. With output63of decision circuit60at a high state, inverter I1causes the potential at gate terminal78of third transistor P3to be at a low state, thus turning transistor P3on. However, since drain terminal79of third transistor P3is effectively not terminated, this is of no consequence.

With output63of decision circuit60at a high state, latch trigger input73is at a high state, and self holding latch70is triggered, thus establishing a current path through latch section70, from power supply25to internal ground reference CHIP VSS and through third diode D3, thereby effectively short circuiting the balance of control circuit24. Self holding latch70will remain in this state until power to latch input terminal71is removed. Until latch70is thus reset, a continuous digital control signal is output to the controlled device (not shown). In this manner, touch switch apparatus20emulates a change of state associated with a mechanical switch.

Referring now theFIG. 7, a touch switch apparatus20configured for operation in the single ended input continuous DC mode operates as follows. The operation and functionality of control circuit24is substantially the same as described for the single ended input, strobed mode as described hereinabove with reference toFIG. 6. However, in the single ended input, DC mode, self holding latch output72is open circuited and self holding latch70is therefore not operative.

With no stimulus applied to first electrode E1, output63of decision circuit60is at a low potential. Consequently, inverter I1output76to gate terminal78of third transistor P3is at a high potential. With gate terminal78of third transistor P3at a high potential, similar to the potential at source terminal77, third transistor P3is unbiased and does not turn on, and therefore no current flows through third transistor P3or through fifth resistor R5.

With a stimulus proximate first electrode E1, output63of decision circuit60, and consequently input75to inverter I1, is at a high state. Inverter I1changes the high level input to a low level output, and provides output76to gate terminal78potential of third transistor P3. With gate terminal78at a low potential compared to source terminal77, third transistor P3is biased, it turns on, and current flows through third transistor P3and fifth resistor R5. This creates an elevated potential at anode108of fifth resistor R5which may be used as an input to the controlled device (not shown) via output line120.

In the continuous DC mode ofFIG. 7, the control circuit responds to the removal of the stimulus from the proximity of first electrode E1. So long as the stimulus remains present proximate first electrode E1, each time the pulse goes to a high state, a peak potential will be created at anode90of first diode D1which is higher than the reference potential at anode91of second diode D2. Consequently, the peak potential at PLUS input64to the decision circuit60will be at a higher level than the reference potential at the MINUS input66and control circuit24will behave as described above. When the stimulus is removed from first electrode E1, the charge on first capacitor C1will eventually discharge to a neutral state by means of the biasing function of second transistor switch SW2. At this point, the peak potential at PLUS input64of decision circuit60will no longer be higher or substantially higher than the reference potential at MINUS input66, and decision circuit60output63will return to a low state.

In this manner, touch switch apparatus20operating in single-ended input DC mode emulates a momentary contact mechanical switch. With minor revisions, the control circuit could be configured to emulate a push-to-open and release-to-close mechanical switch.

Thus far, this specification has described the physical construction and operation of a single touch switch. Typical touch switch applications frequently involve a plurality of touch switches which are used to effect control over a device.FIG. 10shows a switch panel comprising nine touch switches20, where the nine touch switches20are arranged in a three-by-three matrix. Box B4represents components at the touch panel, while box B5represents components at the controlled device. Although any number of touch switches could theoretically be laid out in any manner, matrix layouts such as this one are readily multiplexable, reducing the number of necessary input and output lines from the controlled device, and are preferred.

Box B6inFIG. 4depicts an input portion of a touch switch control circuit, which includes active devices P1and P2, diodes D1and D2, resistors R3and R4and capacitors C1-C2.FIGS. 11A-18Edepict other configurations for the input portion of a touch switch control circuit involving active devices and peak detector circuits that fulfill some of the above described objects of the present invention, including providing for low impedance buffering, reducing the size and cost of the integrated circuit, linearizing input signals, swamping stray capacitance and blocking damaging current paths. The configurations depicted inFIGS. 11A-18Ecorrespond basically to the configuration in boxed area B6ofFIG. 4as will be understood by those skilled in the art of circuit design. Specifically, active devices M1and M2inFIG. 11A, for instance, correspond to active devices P1and P2inFIG. 4; active devices Q1and Q2inFIGS. 11A-18Ecorrespond to diodes D1and D2inFIG. 4; resistances R7and R8inFIG. 11A, for instance, correspond to resistors R3and R4inFIG. 4; and capacitances C9and C10inFIGS. 11A-18Ecorrespond to capacitors C1and C2inFIG. 4. Further, electrodes E1and E2and resistors R1and R2are the same inFIG. 4as in those ofFIGS. 11A-18Ewhere they occur. Pins OSCB, I_RNG and O_RNG in those ofFIGS. 11A-18Ewhere they occur correspond to pins PIN2, PIN1and PIN3ofFIG. 4. Switches SW2and SW4inFIG. 4correspond to active devices M3and M4inFIG. 11A, for instance. Discharge signal DSCHGB inFIGS. 11A-18Ecorresponds to current bias on trace43from startup and bias circuitry40ofFIG. 4. Traces POS and NEG ofFIGS. 11A-18Ecorresponds to traces64and66ofFIG. 4, respectively. Finally, trace OSCB inFIGS. 11A-18Ecorresponds to trace53from pulse generator and logic circuitry50ofFIG. 4. Thus, the input portions ofFIGS. 11A-18Ecan be understood to be compatible with the circuit configurations described with reference toFIGS. 4-7.

FIG. 11Aillustrates inner electrode E1and outer electrode E2, electrically coupled to oscillating signal generator OSCB through pin OSCB and resistors R1and R2, respectively.FIG. 11Afurther shows inter-electrode capacitance C6. Capacitances C7and C8, which represent the bond pad and wiring bond capacitances inherent when electrical components are coupled to an integrated control circuit, are also shown. Capacitances C7and C8can also represent other capacitances owing to under-bump-metallization, redistribution traces and the like, in flip chip and other applications not involving bonding pad wires as would be known to those skilled in the art.

InFIG. 11A, electrodes E1and E2are electrically coupled to the input portion of the touch switch control circuit at the gates of active devices M1and M2, respectively, through pins I_RNG and O_RNG, respectively. InFIG. 11A, active devices M1and M2are shown as N-type MOSFET devices. The drains of active devices M1and M2are electrically coupled to voltage source VDD through resistors R7and R8, respectively and their sources to oscillating signal OSCB.

The drains of active devices M1and M2are also electrically coupled to respective peak detection circuits consisting of active devices M3, M4, Q1and Q2and capacitors C9and C10, which, as discussed above, correspond to the peak detection circuits shown inFIG. 4, having components switches SW2and SW4, diodes D1and D2, and capacitors C1and C2, except that, since the input active devices M1and M2are N-MOS active devices, where active devices P1and P2inFIG. 4are P-MOS devices, capacitances C9and C10and the sources of active devices M1and M2, through resistances R7and R8, are coupled to signal VDD, instead of to voltage signal VSS. The peak detection circuit inFIG. 11Aassociated with active device M1includes active device Q1, the base of which is electrically coupled to the source of active device M1through trace SNEG and also, through resistor R7, to voltage signal VDD, the emitter of which is electrically coupled to the drain of active device M3and to capacitor C9, and the collector of which is coupled to voltage signal VSS; capacitance C9, one terminal of which is electrically coupled to voltage source VSS and the other terminal of which is electrically coupled to the emitter of active device Q1and the drain of active device M3; and active device M3, the drain of which is electrically coupled to the emitter of active device Q1, the source of which is coupled to voltage source VDD and the base of which is electrically coupled to discharge signal DCHGB. The configuration of the peak detection circuit associated with active device M2is analogous and involves active devices Q2and M4and capacitance C10. InFIG. 11A, active devices Q1and Q2are P-type bipolar transistors, and active devices M3and M4are P-type MOSFET devices. The emitters of active devices Q1and Q2are electrically coupled as inputs to the decision circuit component (not shown) of the control circuit through traces NEG and POS, respectively. The operation of the decision circuit component is as described above with respect toFIGS. 4-7.

InFIG. 11A, resistors R7and R8serve to convert drain currents to voltages at the drains of active devices M1and M2, respectively. These voltages are related to changes in the electric fields of electrodes E1and E2caused by touch or other stimuli. The voltage potential at the respective nodes of the drains of active devices M1and M2is communicated to the peak detectors through traces SNEG and SPOS, respectively. The peak detectors can convert the peak negative value of very fast transient pulses on traces SPOS and SNEG to DC signals on traces POS and NEG, respectively, which are easier for the decision circuit to process. Thus,FIG. 11Aillustrates a dual input system having negative pulse peak detecting circuits. A similar positive pulse peak detecting system is described in U.S. Pat. No. 5,594,222 for a single channel. The sensing circuit that generates these negative pulses could include an N-type MOSFET device that would be capable of pulling low at a high rate and a current source pulling high in a softer manner.

Active devices M1and M2inFIG. 11Awill be turned on and off, by oscillating signal OSCB communicated through both electrodes E1and E2and pins I_RNG and O_RNG, to provide transient, negative-going pulses on traces SNEG and SPOS, respectively. The negative maximum peak levels of these pulses will be proportional to the strength of the electric fields at input electrodes E1and E2, which can change when electrodes E1and E2are stimulated by touch or otherwise.

The signals on traces SNEG and SPOS are then communicated to the respective bases of active devices Q1and Q2of the peak detection circuits corresponding to active devices M1and M2. A low signal communicated to the bases of active devices Q1and Q2will bias them on and present the maximum negative voltage at the drains of active devices M1and M2to traces NEG and POS, respectively. Capacitors C9and C10, initially charged at VDD, slow the rate of this voltage change on traces POS and NEG and thereby convert the transient pulses of traces SPOS and SNEG to DC pulses on traces POS and NEG, as shown in the timing diagram ofFIG. 11A. Active devices Q1and Q2then isolate capacitors C9and C10from charging once the transient signal is over. Active devices M3and M4, controlled by discharge signal DCHGB, can then reset the initial charge VDD of capacitors C9and C10, respectively.

Using short duration pulses advantageously allows the touch sensor to maintain a low impedance. Also, the control circuit consumes low average power. For instance, the peak current through the input electrode capacitance may be as high as several milliamps. This would correspond to a very low impedance during the time period that the peak current persists. If each pulse were active for even 20 nanoseconds and were sampled once every 50 microseconds, then the continuous average current would be 0.8 microamps for each channel, and 1.6 microamps for both channels. In addition, the input portion provides statistical filtering and periodic sampling of the sensing signals when discharge signal DCHGB is not active.

These low impedance and low average power consumption characteristics can enhance the stimulus interpretation performance of the touch sensor, as described in U.S. Pat. No. 5,594,222 and can be advantageous when replacing mechanical switches, membrane switches and the like with touch sensing devices. Mechanical and other true switches do not allow current to pass when they are open. A low impedance and low power solid-state switch mimics this characteristic of true switches and can thereby allow for direct replacement of mechanical switches without risking the passage of unacceptable amounts, of leakage current through an “open” solid-state switch. Also, the peak detector circuits of low impedance and low average power touch switches are compatible with the use of relatively low gain and low bandwidth product amplifiers and op amps in the decision and other circuits and DC and relatively low gain and low bandwidth devices for the signal generating circuits.

FIG. 11Bshows an input portion of an integrated control circuit wherein active devices M1and M2are P-type MOSFET devices, active devices M3and M4are N-type MOSFET devices and active devices Q1and Q2are N-type bipolar devices.FIG. 11Botherwise has the same configuration ofFIG. 11A, except that resistors R7and R8and the sources of active devices M3and M4are coupled to voltage signal VSS and the collectors of active devices Q1and Q2are coupled to voltage source VDD.FIG. 11Bthus illustrates an embodiment using positive-going transient and DC pulses, as shown in the timing diagram ofFIG. 11B.FIGS. 11C and 11Dshow input portions wherein the active devices M1and M2ofFIG. 11Ahave been replaced by active devices Q3and Q4, which are N-type inFIG. 11Cand P-type inFIG. 11D.FIG. 11Cshows the peak detection circuit ofFIG. 11A, which involves P-type active devices Q1, Q2, M3and M4, andFIG. 11Dshows the peak detection circuit ofFIG. 11B, the active devices of which are all N-type devices. The operation of these input portion configurations parallel the operation described above with respect toFIG. 11Aand will be understood by those skilled in the art of circuit design.

FIGS. 11A-11Dall show the use of resistors R7and R8which provide for the conversion of drain or collector currents (of either active devices M1and M2or Q3and Q4, respectively) to voltages proportional to the current at the drain or collector. Thus, inFIGS. 11A-11D, this drain or collector voltage will be equal to V−(Ir)(R). Other ways to provide for this voltage conversion are shown inFIGS. 12A-15D. In these drawings, resistors R7and R8have been replaced with active devices.

Use of active devices as current to voltage converters, as shown inFIGS. 12A-12D, for example, allows for high gain outputs with replacement of resistive components and conserves integrated circuit space.FIGS. 12A-12Dgenerally correspond toFIGS. 11A-11D, respectively. InFIGS. 12A-12B, resistors R7and R8ofFIGS. 11A-11Bhave been replaced by MOSFET devices M5and M6, where inFIGS. 12C-12D, resistors R7and R8ofFIGS. 11C-11Dhave been replaced by bipolar devices Q5and Q6.FIGS. 13A-13Dgenerally correspond toFIGS. 12A-12Dexcept that the P-type active device current sources ofFIGS. 12A-12Dhave been replaced with N-type active device current sources inFIGS. 13A-13D(and, similarly, the N-type active device current sources ofFIGS. 12A-12Dbeen replaced with P-type active device current sources inFIGS. 13A-13D). Since the active loads are the same type as the input devices inFIGS. 13A-13D, these active devices can be incorporated into the integrated circuit during the same manufacturing step. This provides for better matching. The output gain is determined by the size of the device and the voltage reference, Vref, used. Vref can be set by a bias circuit that allows for currents to be mirrored by scaling the sizes of gate widths, when using MOSFET devices, or emitter areas, when using bipolar devices.

In the embodiments depicted inFIGS. 12E-12Hand13E-13H, resistors R7and R8ofFIGS. 11A-11Dhave been replaced with the active devices M5and M6(FIGS. 12E-12Fand13E-13F) or Q5and Q6(FIGS. 12G-12Hand13G-13H) as well as cascoding active devices M7and M8(FIGS. 12E-12Fand13E-13F) or Q7and Q8(FIGS. 12G-12Hand13G-13H). Cascode biasing in this manner helps immunize the control circuit against power supply and process variations.

FIGS. 14A-14Dshow embodiments using complementary device types. For example, inFIG. 14A, the active square root extraction devices M9and M10are P-type MOSFET devices and the input active devices M1and M2are N-type MOSFET devices.FIGS. 14B-14Dshow embodiments using complementary device types which correspond toFIGS. 11B-11D. InFIGS. 14C-14D, active square root extraction devices Q9and Q10are bipolar devices. The embodiments depicted inFIGS. 14A-14Dprovide for better stability despite changes in temperature, power supply, common mode noise, and process variations during manufacturing of the integrated circuit.FIGS. 15A-15Ddepict embodiments using active square root extraction devices and active input devices of the same type. Thus, inFIG. 15A, active square root extraction devices M9and M10are N-type MOSFET devices, as are input devices M1and M2. Similar configurations are shown inFIGS. 15B(using N-type MOSFET devices),15C (using N-type bipolar devices) and15D (using P-type bipolar devices). Output linearity can be maximized when matched MOSFET devices, i.e., MOSFET devices of the same type, are used for both the input and the active square root extraction devices, as shown inFIGS. 15A-15B.

FIGS. 11A-15Dall show input capacitances C7and C8on the integrated circuit pin input connections I_RNG and O_RNG. These input capacitances can vary from part to part owing to manufacturing tolerances and processes and the variations can compromise circuit performance. These variations tend to add to the electric field capacitance of the electrodes and can cause variations and offsets in the performance of the control circuit. Since typical applications often require the input detection circuit to resolve very small changes in the electric field at the electrodes where the input capacitance at the bonding pad input nodes can be relatively large compared to the input field effect capacitance signal level, minimizing stray capacitance C7and C8can be advantageous. One method to minimize the effects of this stray capacitance variation is to add “swamping” capacitors to the input circuit. While this may tend to desensitize the control circuit, it can stabilize the input against variations owing to the input capacitance associated with the bond wires, under-bump-metallization, redistribution traces in flip chip configurations and the like. Use of swamping capacitance is shown inFIG. 16, which generally corresponds toFIG. 15A. InFIG. 16, swamping capacitors C11and C12exist in parallel equivalent with stray capacitance C7and C8, respectively, and are electrically coupled to voltage signal VSS. It will be understood that swamping capacitors C11and C12are compatible with all of the embodiments of the present invention described herein, and are not limited to use with the embodiment depicted inFIG. 16.

Though swamping capacitors C11and C12may improve the control circuit's performance, they will tend to require additional physical space. Space is conserved in the embodiment depicted inFIG. 17A, showing the addition of swamping capacitance that results from the depletion capacitance of diodes D4-D7at the control circuit input, here, the gates of active devices M1and M2. InFIG. 17A, diodes D4and D6replace swamping capacitor C12ofFIG. 16and diodes D5and D7replace swamping capacitor C11ofFIG. 16. The amount of capacitance per unit surface area is much greater for diode configurations of the sort depicted inFIG. 17Acompared to the capacitance per unit area of poly or metal type capacitors. Also, diodes D4-D7can be used for protection of both positive and negative high voltage potential discharges. This protection is especially advantageous for touch input applications. Human input devices, such as keyboards, single input switches, and others, are exposed to electrostatic discharge transients and can include components, such as MOSFET and other devices, to protect their sensitive input circuits. This problem is aggravated when, as shown inFIG. 17B, sensing electrodes E1and E2are located very close to the input circuits ICC.

FIGS. 18A- 18Eshow other possible configurations of the input circuitry for touch switches with integrated control circuits.FIGS. 18A-18Cshow various alternatives to the common mode stimulation of active devices M1and M2.FIG. 18Ashows generally the configuration ofFIG. 17Aand also includes active devices M1-M14. InFIG. 18A, active devices M11-M14are electrically coupled to the sources of input active devices M1and M2. The gates of active devices M13and M14are coupled to oscillating signal OSCB and their drains are coupled to the gate of active device M12. The gate of active device M11is coupled to a current source bias signal CSBS and its drain is coupled to the source of active device M12. The configuration depicted inFIG. 18Acan provide negative feedback at the input stage to active devices M1and M2.

FIG. 18Bshows an input circuit portion including active devices M15and M16, here shown as N-type devices, the sources of which are electrically coupled to input pins I_RNG and O_RNG, respectively, and the gates of which are electrically coupled to oscillating signal OSCB. The drains of active devices M15and M16are coupled to the sources of active square root extraction devices M9and M10, respectively, and to the bases of peak detection circuit active devices Q1and Q2, respectively. InFIG. 18B, active devices M15and M16, which are stimulated by oscillating signal OSCB through their gates and accept input signals through their sources, take the place of active devices M1and M2, which have previously been depicted as being stimulated through their sources and accepting inputs through their gates.

FIG. 18Cshows generally the configuration ofFIG. 18Band also includes swamping diodes D4-D7as also shown inFIG. 17A. The configuration ofFIG. 18Ccan also be employed in single input mode with one electrode and can offer all the benefits of employing input diodes that provide depletion mode swamping capacitance.

FIG. 18Dshows the configuration ofFIG. 16, including swamping capacitors C11and C12, which balance the inputs to active devices M1and M2, but in single electrode mode with no outer electrode E2or input pin O_RNG.FIG. 18Eshows the configuration ofFIG. 18D, except that swamping capacitance is provided by diodes D4-D7, as also shown inFIG. 17A, minimizing the space needed to provide the benefits of swamping capacitance, as discussed above.

FIG. 19is an electrical schematic representation of a possible configuration for an output circuit portion of the integrated circuits of the present invention showing various output features and their possible configurations, including latch output LCH_O and its components, which can function as self-holding latch70inFIGS. 4-7. These output features allow the touch cell to duplicate the responses of conventional membrane or mechanical switches.

Output pins NDB_O, NE_O and ND_O are outputs of the touch cell and integrated circuit assembly that will pull the output electrically low through active devices. The integrated control circuit can be configured to pull the output electrically low through active devices when there is a stimulus applied (for example, a human touch stimulus) or can be configured to pull the output electrically low through active devices when there is a lack of stimulus (for example, no human touch stimulus).

As shown inFIG. 19, output pin NDB_O is electrically coupled to the drain of active device M18, whose source is coupled to voltage signal VSS and whose gate is coupled to the input of inverter U2, the output of inverter U2, the gate of active device M17and voltage signal TP_O. Output pin NE_O is electrically coupled to the emitters of active devices Q13and Q14, the bases of which are coupled to the drain of active device M20and the collectors of which are coupled to voltage signal VSS. Active device M20is in turn coupled at its gate to the output of inverter U2and at its source to voltage signal VSS. Output pin ND_O is electrically coupled to the bases of active devices Q13and Q14and to the drain of active device M20. Active device M20can act as a negative pull down device for output NE_O and can bias on the gates of active devices Q13and Q14for output ND_O.

Output pins PDS_O, PD_O and PE_O are outputs of the touch cell and integrated circuit assembly that will pull the output electrically high through active devices. The integrated control circuit can be configured to pull the output electrically high through the active devices when the there is stimulus applied (for example, a human touch stimulus) or can be configured to pull the output electrically high through the active devices when there is a lack of stimulus (for example, no human touch stimulus).

InFIG. 19, output pin PDS_O is electrically coupled to Schotky diode SD1, which is in turn coupled to output pin PD_O. Output pin PD_O is electrically coupled to the base of active device Q12and the drain of active device M17, whose source is coupled to voltage signal VDD and whose gate is coupled to the output of inverter U1and the input of inverter U2. The collector of active device Q12is coupled to the emitter of active device Q11, whose collector and base both are coupled to voltage signal VDD. Also shown inFIG. 19, the emitter of active device Q12is coupled to output pin PE_O.

The integrated control circuit can be applied in conventional DC mode, DC matrix, pulsed DC matrix mode or latch matrix mode.FIG. 20Aillustrates applications where the integrated control circuit is applied in touch cell configurations for DC mode. In all applications using DC mode, each integrated control circuit is continuously connected to system voltage signals VDD and VSS. In some cases, the outputs of several touch cells are connected in electrical OR logic (for example, touch cells TC1-TC3using PE_O outputs and TC7-TC9using NE_O outputs). The rest of the touch cells (TC4-TC6and TC10-TC13) show the use of the various outputs, namely, PD_S, PD_O, PD_E, NDB_O, NE_O and ND_O. For touch cells TC4-TC6, which can pull electrically high outputs, output pins are coupled through a resistor to ground, where for touch cells TC10-TC13, which can pull electrically low outputs, output pins are coupled through a resistor to voltage signal VDD.

FIG. 20Billustrates the application of touch sensors in negative pulsed DC matrix mode. Each touch cell's integrated control circuit has its voltage signal VDD connected to system voltage supply Vsupply. Also shown are the VSS connections of each touch cell's integrated control circuit to a row select signal, ROW SELECT1or ROW SELECT2. InFIG. 20B, output pins NE_O of each touch cell's integrated control circuit connect to a column return, either COLUMN RETURN1(touch sensors TS1and TS2) or COLUMN RETURN2(touch sensors TS3and TS4). As can be seen fromFIG. 20B, ROW SELECTS and COLUMN RETURNS can activate a single touch sensor, a row of touch sensors or a column of touch sensors. This is also illustrated in the timing diagram ofFIG. 20B.

P-type active devices Q13and Q14, shown inFIG. 19, will pull NE_O low when there is an active stimulus applied to the associated input. The input can also be configured such that these P-type active devices on the output will pull NE_O low when there is no stimulus applied to the associated input. The emitter base junction of active devices Q13and Q14will block current back through VSS to other devices in the matrix when any one device goes active low. Whenever any one particular touch cell's integrated control circuit pulls low, there will be a reduced output (as measured from Vsupplyto NE_O) to the forward biased voltage drop of the base-emitter junction of the output active devices Q13and Q14. One device can be used in place of or in lieu of the two active devices Q13and Q14, depending on the application.

When it is desirable to avoid the Vbedrop of the P-type device or devices, then the NDB_O or ND_O outputs, which employ MOSFET devices as shown inFIG. 19, can be used. A negative pulsed DC matrix mode configuration of touch sensors with ND_O outputs is shown inFIG. 20Cand is substantially similar to that shown inFIG. 10B. The voltage drop across the N-type MOSFET devices M18or M20will be relatively low at low current levels and is dependent on the RDSon resistance multiplied by the current through the MOSFET device channel. This current will therefore be predominantly set by the external load resistance. At lower current levels, the voltage drop will be less, relative to the corresponding voltage drop for P-type bipolar transistors. On the other hand, at higher current levels the bipolar transistors will tend to drop the forward bias of the base emitter junction (0.6 to 0.7 volts) while the N-type MOSFET devices will tend to have an increased voltage drop owing to the approximate linear relationship of RDSon to drain current: Vdrop=(RDSon)(Idrain). Thus, in typical logic circuits where lower current levels are present, an N-type MOSFET output will tend to drop less voltage than would a bipolar device. This makes MOSFET devices more generically appropriate for other logic circuits.FIG. 20Dshows a positive pulsed DC matrix configuration with touch sensors having PD_O outputs using P-type MOSFET device M17, as shown inFIG. 19, to which these observations also apply.

MOSFET devices, however, do not have any inherent blocking features as do bipolar devices.FIG. 21Aillustrates a cross sectional view of a typical P-type substrate with doped N and P type materials used in the construction of typical CMOS circuits.FIG. 21Bis a schematic representations of an N-type MOSFET device, N1, which can be used as an output pull down device for output pin NBD_O (active device M18inFIG. 19) or for output pin ND_O (active device M20inFIG. 19).FIG. 21Cis a schematic representation of a blocking device, N2, connected in series with the output device N1to prevent the development of leakage currents from parasitic devices associated with N1, which can occur as an unintended consequence of MOSFET device construction because of the depletion regions that surround the device.

FIGS. 21A-21Cillustrate how the construction of an N-type MOSFET device results in the creation of a parasitic drain to source bipolar diode PD1and how to block leakage current from VSS to the substrate. Typical CMOS integrated circuits make use of P or N type substrates. These substrates are typically electrically connected to the integrated circuit VSS or VDD. In the case of P type substrates, the substrate is tied to VSS and in the case of N type substrates, the substrate is tied to VDD. Note that, inFIG. 21B, the source of N-type MOSFET device N1is tied to voltage signal VSS and that the anode of parasitic diode PD1is also tied to the source node of device N1. The cathode of parasitic diode PD1is tied to the drain of device N1. As a result of this, when the integrated control circuit is implemented in negative pulsed DC matrix mode with active electrical pull down, using N-type MOSFET devices (as shown inFIG. 20C, with ND_O outputs), there exists an inherent path for reverse current through parasitic diode PD1through the P substrate. When the pulses for the strobe rows are applied to the matrix and are at a potential that is greater than the potential at the output of ND_O, a current will flow through parasitic diode PD1from VSS to ND_O. This current path will affect the operation of the matrix and the power supply; and this low current path will provide a low impedance path that connects VSS to VDD through the strobe drivers. A bipolar diode connected in series with the N-type MOSFET pull down device will prevent reverse current flow but would also negate the advantage of the N-type MOSFET pull down device, namely, low voltage drop at the output. A bipolar diode would also tend to drop the Vbeof a base emitter junction. To block this unwanted current path, a way to implement a blocking device is needed that preferably is compatible with conventional integrated circuit manufacturing and has a minimum voltage drop. By making appropriate connections between the N-type MOSFET devices N1and N2, the leakage current path can be blocked such that the P substrate and voltage signal VSS are isolated from leakage paths of current through the ND_O device N1; at the same time the voltage drop of the control circuit output is minimized.

Device N2inFIG. 21Ais the blocking device and is represented schematically inFIG. 21C. The drain and source of blocking device N2are connected to VSS and VSS1, respectively, as shown inFIGS. 21A and 21C. The gate of blocking device N2is coupled to voltage signal VDD, which can, but need not, be 3-5 volts so as to be compatible with most microprocessors. When the source of device N2is at a low potential, such as ground, the channel resistance will be very low so long as the gate voltage is slightly higher than he threshold voltage of the device. Since the gate of device N2is at VDD, which can be on the order of 3 to 5 volts (Vsupply), its source is at zero volts during the active pulse period, and its threshold voltage is less than a volt, the channel resistance will be very low and therefore the channel drop of the device will also be very low (i.e., less than a standard bipolar diode). When the source of device N2is at a voltage equal to (or higher than) VDD, the gate to source voltage (VGS) will be less than the threshold voltage of the device. This will cause the channel resistance to increase significantly, thereby blocking substantial current through the channel. Also, the voltage across the depletion junction of the source of device N2to parasitic diodes PD of substrate PS will be less than the barrier potential (about 0.6 to 0.7 volts) of the source-drain parasitic diode PD1. Parasitic diode PD1will therefore block substantial current through the substrate.

Also, blocking device N2can be used for reverse voltage protection in standard integrated circuit applications and provide all of the benefits stated above. When used in this way, blocking device N2would be connected to the integrated circuit's VSS in the same way as described and would protect the circuit from reverse current or voltage damage.

FIGS. 21D-21Fdepict a blocking device BDP2for the electrically high pull devices having outputs PDS_O, PD_O and PE_O, shown inFIG. 19. The device depicted inFIGS. 21D-21Fis complementary to the device depicted inFIGS. 21A-21Cand will be understood by those skilled in the art in light of the discussion referencingFIGS. 21A-21C. In all DC mode configurations described, there are three connections to each touch cell's integrated control circuit. VDD and VSS for each touch cell's integrated control circuit need to be connected to a source of power for some amount of time, in order to process the input stimuli. The output of the integrated control circuit is found at PDS_O, PD_O, PE_O NDB_O, ND_O, and NE_O, depending on the configuration desired. These outputs form the third connection required by the integrated control circuit. In some cases, however, it would be advantageous to have an integrated circuit requiring only two connections. For example, since typically only two connections per switch are used in applications involving membrane switches, having a touch sensing switch and integrated control circuit requiring only two connections would facilitate direct replacement of the membrane switches with touch switches.

A schematic representation of a matrix of two-terminal membrane switches MS1-MS4is shown inFIG. 22.FIG. 22shows one way to address and read switches within a matrix. The matrix ofFIG. 22could, of course, also be modified to include more rows, more columns, more switches, and alternative connections. In all cases, the interface to each switch typically would include two types of signal lines: ROW SELECT and COLUMN RETURN. Each ROW SELECT line is a source of potential to allow current to flow through each switch MS1-MS4as they are closed (in the case of membrane switches, by finger pressure causing closure) through the COLUMN RETURN lines. The terminating resistors COLR1and COLR2on the COLUMN RETURN lines1and2, respectively, are used to develop the voltage to be processed by return logic circuits and for limiting current through the switch devices. The strobe lines can be sequenced in such a manner that only one row of switches (MS1and MS3or MS2and MS4) is active at a given time. When a particular row is selected, the voltage generated through each terminating resistor COLR will indicate which switches on the selected row are electrically closed. The COLUMN RETURN lines are generally processed simultaneously. Matrix schemes are efficient in terms of the number of interconnections used to process the number of switch inputs. For example, sixty four switches can be read with an eight by eight matrix using eight ROW SELECT lines and eight COLUMN RETURN lines. Typically, some sort of logic device is connected to the strobe and return lines to determine the status of all the switches over a short period of time. This is a typical matrix scheme that one skilled in the art would know how to implement. It can be used in controllers, keyboards for computers, telephones, and other devices that are widely available in the market.

A solid-state type sensing device that can detect stimuli and act as a two-terminal switch could be advantageous in that it would allow conventional matrix strobe and read circuits to be built without additional software, logic circuits, and/or microprocessors, which are susceptible to resets and other failures.FIG. 23illustrates the implementation of such devices, arranged in a matrix and having only two integrated circuit connections. Thus, the touch sensors TS1-TS4ofFIG. 23have replaced the membrane switches MS1-MS4ofFIG. 22. InFIG. 23, each touch sensor TS1-TS4senses electric field potential differences. According to the presence or absence of an appropriate stimulus, the device (depending on the specific application) will move from a high impedance state (open switch equivalent) to a low impedance state (closed switch equivalent), thereby mimicking a conventional membrane or other mechanical switch. The chief advantage of these devices is their ability to mimic the attributes of two terminal switches.

FIGS. 24A and 24Bshow possible circuitry for the touch sensors TS1-TS4ofFIG. 23. The circuits depicted inFIGS. 24A and 24Bare based on the latch circuit portion of the circuit depicted inFIG. 19. InFIG. 19, the latch circuit depicted includes active devices M19and Q15-Q19as well a resistor R9. Latch circuit output pin LCH_O is shown coupled to the emitter of active device Q19. Active device Q19is in turn coupled at its base to the output of inverter U2, to the drain of active device Q15and the gate of active device M20; and at its collector to the emitter of active device Q18, whose base is coupled to voltage signal VDD and whose collector is coupled to resistor R9, which in turn is coupled to voltage signal VDD. The collector of active device Q18is also shown coupled to the bases of active device Q15and Q16, the emitters of which are coupled to voltage signal VDD, and the base of active device Q17, the collector of which is coupled to voltage signal VSS and the emitter of which is coupled to the collector of active device Q15. The collector of active device Q18is also coupled to the drain of active device M19, the gate of which is coupled to output pin INITB of the control circuit and the source of which is coupled to voltage signal VDD.

FIGS. 24A and 24Bshow various embodiments of the latch circuit ofFIG. 19. Both of these embodiments omit optional active devices Q16-Q18.FIG. 24Ashows the implementation of bipolar components Q15and Q19in the latch circuit, as shown inFIG. 19, andFIG. 24Bshows the implementation of MOSFET components in the latch circuit. Other configurations can be implemented in keeping with the spirit and functionality of a two terminal device.

FIG. 24Ashows a bipolar latch circuit operating in conjunction with a control circuit, which provides the functions needed to detect an input stimulus, make decisions, and trigger the bipolar latch circuit. The control circuit can also provide for power on reset functions, initializing and sequencing of various internal blocks and features. Inputs into the control circuit include those associated with the input sensing connections, namely, OSCB, +(PLUS), and −(NEGATIVE); those associated with the power supply of the control circuit, namely, voltage signals VDD and VSS; and those associated with the latch circuit, namely, INIT and TRIGGER. The latch output is through output pin LCH_O.

When there exists a path for current from a system Vsupplyto GND through the active pull P-type MOSFET device on the ROW SELECT line, the strobe line ROW SELECT inFIG. 24Ais active. With power supplied, the control circuit would be operational. When the strobe pulse is first applied, the control circuit would apply a gate signal, via the INIT line, to turn on active device M19. This will ensure that the base emitter voltage of active device Q15is essentially at zero volts, keeping it from conducting (except for leakage current). With Q15off, there is no current available for the base of Q19and, therefore, Q19will also be off. With Q19off, the voltage at the base of Q15would be essentially VDD, even after the INIT signal is removed and M19is off. With the latch essentially off (i.e., no current flow), the control circuit will be allowed to operate. When operational, the integrated control circuit is in the high impedance mode and simulates an open switch. The output voltage developed across resistor Rcolumnis equal to Vsupply×R(integrated control circuit)/([R(integrated control circuit)+Rcolumn]. The greater the effective resistance of the integrated control circuit, the less the percentage of Vsupplythat will be dropped across Rcolumn, and the greater the percentage that will be dropped across integrated control circuit.

A perfect switch would have infinite resistance and zero current when open and therefore Vsupplywould be dropped across the switch during a strobe pulse and zero voltage would be dropped across Rcolumnbecause of zero current flow. Since an integrated circuit is not a switch, it is important to design the integrated control circuit to have as little current as possible when Vsupplyis applied by the strobe pulse to more accurately replicate an open switch's characteristics.

An input electrode can be configured to cause the integrated control circuit to stay in this high impedance mode with a stimulus applied or without a stimulus applied. When the integrated control circuit is in the high impedance mode, most of Vsupplywill be applied across the integrated control circuit. This will allow the circuit to operate in a floating mode since the internal VDD and VSS is sufficient to operate the integrated circuit as a whole and the internal control circuit as well. The electrode configuration can also be such as to cause the control circuit to generate a trigger pulse to the latch circuit when a stimulus is applied or, alternatively, when a stimulus is not applied. When the control circuit generates a trigger pulse, the latch will turn on. The trigger pulse inFIG. 24Awould be a positive pulse moving towards VDD from VSS. This trigger pulse would be allowed after the INIT signal resets, causing M19to turn off. This positive pulse would forward bias the base emitter junction of N-type bipolar device Q19, causing it to turn on. With the flow of base current and the gain transfer of active device Q19, current will flow at the collector of active device Q19and therefore through resistor R9. The current flow across resistor R9will generate a voltage potential that will cause the base of active device Q15to drop towards VSS—enough to forward bias the emitter base junction of active device Q15to cause it to turn on. The current gain of active device Q15will cause substantial current to flow at the collector of active device Q15and will also cause the voltage to increase at the base of active device Q19sufficiently to forward bias the emitter base junction of active device Q19, even after the removal of the trigger pulse. The trigger pulse will be removed, owing to the voltage drop across the control circuit, sufficiently to disable the operation of the control circuit. The latch current will stay on after the trigger pulse is removed owing to the positive current feedback loop between the Q15and Q19. The voltage drop of the latch will be determined by the saturation voltage, the junction resistances, the gains of active devices Q15and Q19and the resistance of Rcolumn. The latch circuit inside the integrated control circuit has to stay on once the trigger is removed since the control circuit is inoperable and it is important that the latch drop as little voltage as possible across a range of currents. In this low impedance mode, it is desirable to obtain these attributes as much as possible to replicate a closed switch. A perfect closed switch would pass infinite current and drop zero volts at all current levels. To best replicate a perfect switch, e.g., one with a low voltage drop, the latch circuit can preferably make use of bipolar transistors with increased emitter areas and low Vbedrops and MOSFETS with high W/L channel ratios, low thresholds and devices with high gains.

FIG. 24Bshows the latch circuit ofFIG. 24Awhere the bipolar active devices Q15and Q19have been replaced by MOSFET devices M21and M22. The operation of the integrated control circuit inFIG. 24Bparallels the operation of the integrated control circuit ofFIG. 24A. The operation of the latch portion depicted inFIG. 14Bis described below.

When the INIT pulse is applied, active device M19is turned on. This will allow VDD to be applied to the gate of active device M21. In this condition, the gate source voltage of active device M21will be less than the threshold voltage of the P-type MOSFET device M21, essentially zero volts, and, therefore, active device M21will be off. With the drain current of active device M21at essentially zero amps (other than leakage current), there will be no voltage developed across resistor R10. With the gate of active device M22at essentially zero volts, its gate source voltage will be substantially less than the threshold voltage of the device. The drain current of active device M22will be essentially zero with its gate source voltage well below the threshold voltage. The zero current through resistor R9will cause the voltage on the gate of active device M21to be at, or very close to, VDD, and, therefore, the gate source voltage of active device M21will be essentially zero also, even after the INIT signal is removed. This condition will place the latch circuit in the high impedance state. When a trigger pulse approaching VDD is applied to the gate of active device M22, after removal of the INIT pulse, its gate source voltage will exceed the threshold voltage of active device M22, causing M22to turn on. The drain current of active device M22will increase, developing a voltage drop across resistor R9. With voltage drop across resistor R9, the gate source voltage of active device M21will exceed its threshold voltage, causing active device M21to turn on. The drain current of active device M21will increase also causing the voltage drop across resistor R10to increase above the threshold voltage of active device M22, even after the trigger pulse is removed. The latch will therefore move into a low impedance state and the voltage drop across it will be dependent on the characteristics of active devices M21and M22, values of resistors R9and R10, and the resistance of Rcolumn. The rest of the operation of the integrated control circuit inFIG. 24Bis similar to that of the integrated control circuit ofFIG. 24A. Also shown in both FIGS. are the blocking diodes ofFIGS. 21A-21C, labeled D8and D9inFIGS. 24A and 24B, respectively.

FIG. 25Aillustrates the latch circuit portion ofFIG. 19comprising active devices Q15-Q19in a possible configuration built into substrate PS.FIG. 25Bshows the latch circuit portion schematically. InFIG. 25A, active devices Q15and Q16share a P-doped well EMITTERQ15/EMITTERQ16as an emitter and the collector of active device Q15and emitter of active device Q17are the same P-doped well COLLECTORQ15/EMITTERQ17, which is coupled to the gate of active device Q15. Active devices Q15, Q16and Q17also share the same N-doped well as their bases BASEQ15, BASEQ16and BASEQ17, respectively. Substrate PS forms the collectors of active devices Q16and Q17, COLLECTORQ16and COLLECTORQ17, respectively. Active device Q19is shown in a separate N-doped well in substrate PS, and is coupled at its N-doped well collector COLLECTORQ19to resistance R9, at its P-doped well base BASEQ19to P-doped well COLLECTORQ15/EMITTERQ17, and at its N-doped well emitter EMITTERQ19to voltage signal VSS at the anode of diode D10. InFIG. 25A, active device M19is coupled in parallel with resistance R9. Operation of the configuration depicted inFIGS. 25A and 25Bwill be understood by those skilled in the art of active device and circuit design and from the discussion of the latch circuit with reference toFIG. 24A. Active devices Q16-Q18will enhance the signal delivered to output LCH_O. The configuration shown inFIG. 25Awill benefit from a reduced latch ON voltage drop, as compared with the voltage drop associated with a standard latch, owing to the dynamic impedance of active device Q17and the shunting of VSS current through substrate PS. Diode D10, coupled at its cathode to output LCH_O and at its anode to the emitter of active device Q19and to voltage signal VSS, can prevent feedback into the latch portion of the integrated circuit depicted inFIG. 25B.FIG. 25Cshows diode D10coupled at it anode to voltage signal VSS and the collectors of active devices Q17and Q18and at its cathode to the emitter of active device Q19and output LCH_O. The configuration inFIG. 25Cthus changes the voltage signal on the emitter of active device Q19, which can be biased on by output TRIG, from VSS, inFIG. 25B, to VSS1. This latch circuit configuration can advantageously reduce the voltage drop since, in this case, the voltage drop across diode D10is not in series with the base emitter voltage of active device Q19. Optional active device Q18inFIGS. 25B and 25Cis useful to increase the reverse breakdown voltage of the latch circuit.

The integrated circuits of the present invention can respond to capacitive inputs that change in a variety of ways. For example,FIGS. 26A-26Cshow a capacitive input sensing apparatus compatible with the integrated circuit of the present invention, wherein the capacitive input changes as a result of a change in the distance d between electrodes GE and SE that form capacitance Csense, shown schematically inFIG. 26D. Capacitance Csenseis a function of the capacitive constant of the electrodes Eo, relative dielectric constant Er, surface area of the electrodes s and the distance between them d. The apparatus depicted inFIG. 26A, having sensor electrodes SE and integrated control circuit ICC on one side143of substrate144and grounded electrode GE configured into buttons122creating cavities121on the other side145.FIGS. 26B and 26Bshow the separate layers of the apparatus shown inFIG. 26A. Cavities121inFIG. 26Aallow buttons122to be depressed, for instance, by a human finger or other probe, so as to alter the distance d between electrodes GE and SE. The control circuit depicted inFIG. 26D, can respond to the changed capacitance that results from the changed distance d. The control circuit ofFIG. 26Dcorresponds to the control circuit depicted inFIG. 18D, except that capacitance C3inFIG. 18Dhas been renamed CsenseinFIG. 26D.

Thus far, this specification generally has described various preferred embodiments of touch sensors (or field effect sensors) according to the present invention. Following are descriptions of various preferred embodiments of practical applications for such sensors. Although it generally is preferred that these applications be practiced using the touch sensors described above, these applications generally also may be practiced using other types of touch sensors, for example, the sensors described in U.S. Pat. Nos. 5,594,222 and 6,310,611, conventional capacitive sensors, and other types of sensors, as would be known to one skilled in the art.

FIGS. 27A-27Dshow a capacitive input liquid level sensing apparatus compatible with the integrated circuit of the present invention, wherein the capacitive input changes as a result of a change in the dielectric constant Erbetween two electrodes. This change can occur, for instance, when liquid replaces air between two electrodes GE and SE1forming capacitance Csense. Thus, inFIG. 27A, grounded electrode GE on substrate123is separated from sensor electrode SE1through an air gap that can be filled by liquid125.FIG. 27Bshows substrate124forming a reservoir for liquid125and substrate123adapted to allow liquid125to fill the air gap between grounded electrode GE and sensor electrode SE1when liquid125reaches a certain level.FIGS. 27C and 27Dillustrate one possible advantageous configuration of grounded electrode GE and sensor electrode SE1, coupled to integrated control circuit ICC. In bothFIGS. 27C and 27D, electrodes GE and SE1are long and disposed horizontally, i.e., with their longitudinal axes parallel with the surface of liquid125, such that a small increase in the level of liquid125will significantly change capacitance Csense, shown schematically inFIG. 27D. The control circuit shown inFIG. 27Eis the same as that shown inFIG. 26D, and it is equally compatible with the apparatus depicted inFIG. 27A-27D.

FIGS. 28A-28Bshow a capacitive input sensing apparatus compatible with the integrated circuit of the present invention, wherein the capacitive input changes as a result of a change in the surface area ss3of sensor electrode SE3. InFIG. 28A, substrate126bears a grounded electrode GE and movable substrate127bears two sensors electrodes SE2and SE3coupled to integrated control circuit ICC. Sensor electrode SE3has a surface area ss2that varies along the direction in which substrate127is adapted to be moved. Thus,FIG. 28Bshows substrate127moved upward relative to its position inFIG. 28A. Surface area ss3of sensor electrode SE3seen by grounded electrode GE therefore decreases. This change in surface area corresponds to a change in capacitance Csense3, which is shown schematically inFIG. 28C. The control circuit depicted inFIG. 28Cis similar to the circuit depicted inFIG. 18E, but has the dual electrode structure depicted inFIG. 11A, where electrodes E1and E2have been renamed sensor electrodes SE2and SE3and capacitance C6has been renamed capacitance C23. The operation of the circuit will be understood by those skilled in the art and from the preceding discussion ofFIGS. 11A and 18E.

FIGS. 29A-29Dshow a capacitive input sensing dial apparatus compatible with the integrated circuit of the present invention, wherein input pulse widths and sequence can determine the integrated control circuit response.FIGS. 29A-29Dshow sensor electrode SE4coupled to integrated control circuit ICC on substrate128and grounded electrodes GE1and GE2on rotating disc129. InFIGS. 29A-29D, grounded electrodes GE1and GE2(including the space between them) together occupy only about one half the area of rotating disc129and are spaced apart. This, and other, similar configurations, can allow a control circuit to distinguish between clockwise and counterclockwise rotation of the dial device.FIGS. 29B-29Cshow the movement of rotating disc129relative to stationary substrate128.FIGS. 29E and 29Fshow the output pulses of the dial apparatus depicted inFIGS. 29A-29D, which can create a response in an input portion of an integrated control circuit, as shown inFIG. 29G.FIG. 29Eshows the relatively wide and spaced apart input pulses that result from counterclockwise rotation of rotating disc129at one speed andFIG. 29Fshows the relatively narrow and close input pulses that result from clockwise rotation of rotating disc129at a faster speed. Changes in capacitance Csense, formed between electrodes SE4and either GE1and GE2and shown schematically inFIG. 29G(which is similar to the configuration shown inFIG. 27E), can be detected by embodiments of the integrated control circuits of the present invention.

FIGS. 30A-30Eshow another capacitive sensing dial apparatus compatible with the integrated circuit of the present invention, wherein a coupling to ground is provided by the user.FIG. 30Ashows rotating disc130having transfer electrodes TE1-TE8of various sizes, which can correspond to input pulse widths of various sizes when they are coupled to ground.FIG. 30Bshows the transfer electrodes TE1-TE8of rotating disc130coupled to coupling electrode CE borne on cylinder131.FIG. 30Cshows cylinder132, adapted to fit within cylinder131ofFIG. 30B, having sensor electrodes SE5and SE6coupled to integrated control circuit ICC.FIG. 30Dshows the components depicted inFIGS. 30A-30Cassembled together as a rotary capacitive input device.FIG. 30Eshows hand133grasping cylinder131. Hand133couples coupling electrode CE and transfer electrodes TE1-TE8to a virtual ground. Each sensor electrode SE5and SE6, as shown inFIG. 30C, is adapted to receive capacitive input from one transfer electrode at a time. As shown inFIGS. 30F-30H, two input pulses can be fed to integrated control circuit ICC at a time. Both the direction and arc length of a user's turn of the dial comprising rotating disc130and cylinder131can be determined from the inputs shown inFIGS. 30F and 30G.FIG. 30Fshows the pulse train resulting from two full turns of the dial device in a counterclockwise direction, whereFIG. 30Gshows the pulse train resulting from two turns in a clockwise direction.FIG. 30Hshows a schematic representation of the dial device ofFIG. 30E, including grounding hand133, coupling electrode CE connected to transfer electrodes TE, which form a capacitance with sensor electrodes SE5and SE6, coupled to resistances RIN1and RIN2, respectively. Integrated control circuit ICC provides oscillating signal OSC to sensor electrodes SE5and SE6through resistances RIN1and RIN2, respectively, and provides outputs OUT1and OUT2to a decision circuit (not shown). The various components of the dial device, including rotating disc130and cylinders131and132can be formed according to the invention described in U.S. Pat. No. 6,897,390, entitled Molded/Integrated Touch Switch/Control Panel Assembly and Method for Making Same, or in other ways.

FIGS. 31A-31Fshow the separate layers and construction of a touch switch assembly having an integrated control circuit according to the present invention.FIGS. 31A-31Eshow the individual layers of the assembled touch switch depicted inFIG. 31F.FIG. 31Ashows the backside of substrate133including opaque area135and window area136. Opaque area135can be decorative frit, decorative epoxy, ultraviolet cured ink or any other decorative layer material.FIG. 31Bshows the electrodes134of the touch switch borne on the backside of substrate133at window area136. Electrodes134are shown overlapping opaque area135and can be composed of a transparent conductive material including indium tin oxide or other suitable material.FIG. 31Cshows the bottom conductive layer of the touch switch assembly, as viewed from the backside, including circuit traces138, which can be composed of silver loaded frit, silver epoxies, copper epoxies, electroplated conductors, and the like, as well as combinations of the above.FIG. 31Dshows the dielectric layer of the touch switch having dielectric layer areas140, which can be insulated ceramic frits, ultraviolet inks, epoxies and the like.FIG. 31Eshows the crossover layer of the touch switch assembly, as viewed from the backside, including crossover conductors137, which can be composed of the materials described with reference toFIG. 31C.FIG. 31Fshows the separate layers depicted inFIGS. 31A-31Eassembled together as a finished touch switch assembly.FIG. 31Fprovides a view from the backside of the assembly as well.

While the embodiments depicted above have been described as being in DC mode, the integrated control circuits of the present invention are also compatible with AC inputs and can therefore also operate in AC mode. The AC situation is depicted inFIG. 32.FIG. 32shows a touch switch with integrated control circuit adapted to receive an AC input. InFIG. 32, AC signal AC is coupled to rectifier bridge RB, including diodes D11-D14, through resistances R10and RLOAD. Rectifier bridge RB diodes D11-D14are coupled in parallel with zener diode Z1and capacitance C15. AC signal AC can stimulate the touch switch with integrated control circuit, including the latch portion shown inFIG. 24Awith diode D8removed. This configuration can be advantageous in that the integrated circuit can be designed to draw relatively little current and in that the circuit is characterized by low sensing impedance, which provides for a floating circuit that is not so ground dependent.

Although the embodiments of the present invention described above have been described as providing a digital output, many of the benefits of the touch switch with integrated control circuit configurations described above can also accrue where the integrated control circuit provides an analog output. In the digital output situation, the output reflects information provided by input to the electrodes for only two states, e.g., stimulated or not stimulated. In some applications it is desirable to provide output that can correspond to more than two states. For example, in liquid sensing applications, similar to the situation described with reference toFIGS. 27A-27D, it can be desirable to provide output that reflects not two states, but many states that can correspond to many liquid levels. An analog output can correspond to many input states.FIG. 33Ashows possible circuitry for an analog electric field sensor with integrated control circuit. The circuit configuration ofFIG. 33Acorresponds to the circuit depicted inFIG. 4, and includes startup and bias circuit40providing a current bias to the gates of switches SW2and SW4and pulse generator and logic circuitry providing a power on reset signal POR to the gates of switches SW1and SW3. The configuration ofFIG. 33Aalso includes an input portion, including active devices M1, M2, M5and M6, similar to the input portion described with reference toFIG. 12A. The drains of active devices M1and M2are coupled to traces INPUT1and INPUT2and, through diodes D1and D2to traces PKOUT1and PKOUT2, which provide input to differential amplifying circuit160. The operation of this circuit can be understood from the description provided with reference toFIGS. 4-7. The configuration depicted inFIG. 33Acan provide the benefits of the configurations depicted inFIGS. 4-7, including sensor electrode and strobe signal buffering, common mode rejection of electrical interference at the electrodes and circuitry, temperature stability and the like.FIGS. 33B and 33Cshow timing diagrams for the circuitry depicted inFIG. 33A.FIGS. 33B and 33Cshow the oscillating signal OSC and the signals provided on traces IN1, IN2, INPUT1and INPUT2.FIG. 33Bshows the signals as a function of time in microseconds andFIG. 33Cshows the signals as a function of time in nanoseconds.

FIG. 34shows a two-by-two matrix of the field sensors ofFIG. 33Athat accept analog input and provide analog output. The multiplexed system ofFIG. 34is similar to that shown inFIG. 10. Trace ROWSELECT1, having a signal provided by control circuit141, will go high for a time period in which analog switches ATS1and ATS3have power applied to them. Analog outputs AOUT of analog switches ATS1and ATS3will provide an output, provided to trace COLUMNRETURN1and fed into analog interface circuit142, that is proportional to the stimulus provided at the electrodes of analog switches ATS1and ATS3. These outputs will be temperature stable, exhibit good signal to noise performance characteristics owing to the low impedance of the circuitry, and exhibit common mode rejection properties, as well. The analog signals could be processed in a manner similar to that described in U.S. Pat. No. 5,594,222, or using other analog processing techniques as will be understood by those skilled in the art of electrical circuit design.

FIGS. 35A-35Billustrate an embodiment1100of the present invention wherein a field effect sensor is used in connection with other structure to emulate a mechanical pushbutton switch. Embodiment1100includes dielectric substrate1102, which can be embodied in any suitable form. Preferably, substrate1102is substantially rigid. For example, substrate1102can be a conventional printed wiring board or a panel or portion of a larger assembly or component, for example, the door panel or dashboard of an automobile or an interior panel of a refrigerator. Alternatively, substrate1102can be a flexible circuit carrier. In such an embodiment, the flexible circuit carrier preferably is applied to a substantially rigid secondary substrate (not shown). Substrate1102can take any other suitable form, as would be recognized by one skilled in the art.

Substrate1102defines aperture1104. Field effect sensor1106A is disposed on substrate1102, in proximity to aperture1104. Field effect sensor1106A is shown inFIG. 35Aas disposed on one side of substrate1102. Alternatively, field effect sensor1106A could be disposed on the other side of substrate1102. Further, in embodiments where field effect sensor1106A includes two or more electrodes, one or more such electrodes can be disposed on one side of substrate1102and the other electrode(s) can be disposed on the other side of substrate1102. In other embodiments, field effect sensor1106A can be encapsulated within substrate1102, as shown with respect to field effect sensor1106E inFIG. 1D, discussed further below.

Shaft1108is inserted in sliding engagement through aperture1104. A sleeve, bushing, or the like (not shown) can be provided in connection with aperture1104to better enable shaft1108to slide through aperture1104without wobbling. Shaft1108preferably includes knob1110. In the illustrated embodiment, shaft1108is a threaded plastic bolt, the head of which forms knob1110. In other embodiments, shaft1108can take any suitable form and can be made of any suitable material, as would be recognized by one skilled in the art. Preferably, shaft1108is made of a non-conductive material, such as plastic or resin.

Electric field stimulator1112is attached to shaft1108at a predetermined location. Electric field stimulator1112is made of a material that readily stimulates or disturbs an electric field, as discussed above. Preferably, electric field stimulator1112is made of metal or other conductive material, but other materials are suitable as well, as would be known to one skilled in the art. In theFIG. 35Aembodiment, electric field stimulator1112is a metal washer secured to shaft1108with a threaded plastic washers1116on each side of electric field stimulator1112. In other embodiments, electric field stimulator1112can take other forms, be made of other materials, and be attached to shaft1108by any suitable means, as would be known to one skilled in the art.

Plastic washer1116installed between substrate1102and electric field stimulator1112preferably is sufficiently thick to prevent electric field stimulator1112from contacting the electrode(s) of field effect sensor1106A. Alternatively, other structures (not shown) can be provided to prevent electric field stimulator1112from making contact with the electrode(s) of field effect sensor1106A, as would be known to one skilled in the art.

FIG. 35Ashows electric field stimulator1112located on the same side of substrate1102as field effect sensor1106A and on the opposite side of substrate1102as head1110. Alternatively, electric field stimulator1112and field effect sensor1106A can be located on opposite sides of substrate1102, and electric field stimulator1112and head1110can be located on the same side of substrate1102.

Shaft1108is biased longitudinally so that electric field stimulator1112normally is in a predetermined position relative to field effect sensor1106A. Shaft1108and, therefore, electric field stimulator1112, can be displaced from their normal positions by applying an appropriate force to head1110. In theFIG. 35Aembodiment, biasing is provided by coil spring1114installed about shaft1108between knob1110and a corresponding surface of substrate1102, such that electric field stimulator1112is normally near field effect sensor1106A. Electric field stimulator1112is displaced away from field effect sensor1106A when a longitudinal force is applied to shaft1108. In alternative embodiments, shaft1108can be biased so that electric field stimulator1112normally is distant from field effect sensor1106A and is displaced nearer field effect sensor1106A when a suitable force is applied to shaft1108, as would be recognized by one skilled in the art. In further alternative embodiments, coil spring1114can be replaced with any suitable structure for biasing shaft1108. For example, a layer of flexible and/or resilient material (not shown) might be disposed on substrate1102about aperture1104, or substrate1102itself might be comprised of a flexible and/or resilient material that deforms when knob1110is pressed against it and returns to its original position when released, thus returning knob1110, shaft1108and electric field stimulator1112to their original positions. Any number of other structures can be used to bias shaft1108, as would be known to one skilled in the art

In operation, an electric field is generated about field effect sensor1106A, as discussed above. With shaft1108in the normal position as shown inFIG. 35A, electric field stimulator1112is coupled to this electric field. Detection circuitry (not shown) associated with field effect sensor1106A detects this coupling, as discussed above. When shaft1108is displaced longitudinally in response to, for example, a user pressing down on knob1110, electric field stimulator1112moves away from field effect sensor1106A and decouples from the electric field about field effect sensor1106A. The corresponding detection circuitry (not shown) detects this decoupling and provides a signal to a control circuit, which, in turn, can provide a control signal to a controlled device, as discussed above. In this manner, embodiment1100emulates a mechanical pushbutton switch.

FIG. 35Cillustrates an alternate embodiment1140of the present invention emulating a mechanical pull switch. Embodiment1140is structurally similar to embodiment1100, except that shaft1108is biased so that electric field stimulator1112normally is positioned at a predetermined distance from field effect sensor1106A. As such, electric field stimulator1112normally is decoupled from the electric field about field effect sensor1106A. In order to actuate field effect sensor1106A, a user would pull on knob1110, thus drawing electric field stimulator1112near field effect sensor1106A and causing electric field stimulator1112to couple with the electric field about field effect sensor1106A. Preferably, a mechanical stop, for example, mechanical stop1119attached to shaft1108at a predetermined location, is provided to limit the travel of shaft1108by coil spring1114or other biasing means.

FIG. 35Dillustrates another alternate embodiment1160of the present invention emulating a mechanical pushbutton switch. Embodiment1160includes post1118disposed on substrate1102. Field effect sensor1106E is encapsulated within substrate1102in proximity to post1118. In other embodiments, field effect sensor1106E can be disposed on either surface of substrate1102in the manner of field effect sensor1106A, as illustrated in and discussed in connection withFIG. 35A.

Push button1120having a bearing surface1122is slidingly engaged with post1118. Electric field stimulator1112is associated with a lower portion of push button1120nearest substrate1102. Push button1120and electric field stimulator1112can, but need not be, separate structures. Indeed, push button1120and electric field stimulator1112can be embodied as a single, monolithic structure.

Coil spring1114biases push button1120so that field effect stimulator1112normally is located at a predetermined distance from field effect sensor1106E. Application of an appropriate force to bearing surface1122displaces field effect stimulator1112toward field effect sensor1106E. Field effect sensor1106E and the associated detection circuitry respond as discussed above. Significantly, this embodiment1160does not include an aperture in substrate1102. As such, embodiment1160may be particularly preferable for use in applications where it is desirable to preclude intrusion of fluids or contaminants through substrate1102. Embodiment1160readily could be modified to function as a pull switch, as would be recognized by one skilled in the art.

More than one field effect sensor can be used in connection with any of the foregoing embodiments.FIG. 35Eillustrates an embodiment using four field effect sensors1106A-1106D arranged about aperture1104of embodiments1100and1140. Embodiment1160could be similarly modified. Other embodiments could use more or fewer than four field effects sensors.

In embodiments using plural field effect sensors1106A-1106n, the sensors and corresponding detection and control circuits can be configured so that electric field stimulator1112couples to or decouples from the electric field or fields about each individual field effect sensor1106isubstantially simultaneously as electric field stimulator1112is moved toward or away from the field effect sensors1106A-1106n. Alternatively, such embodiments can be configured (through, for example, sensor and/or stimulator geometry) so that electric field stimulator1112couples to or decouples from the electric field or fields about each field effect sensor1106ias electric field stimulator1112reaches different points in its travel toward or away from field effect sensors1106A-1106n.

Other modifications to the foregoing embodiments are possible. For example, the biasing means could be omitted from any of the foregoing embodiments so that shaft1108or push button1120remain in the last position in which placed by a user. Also, while shaft1108and post1118are shown as substantially perpendicular to substrate1102, shaft1108and post1118could be configured at other angles to substrate1102, as would be known to one skilled in the art.

FIGS. 36A-36Billustrate an embodiment1200of the present invention emulating a mechanical toggle switch. Embodiment1200includes substrate1202defining aperture1204. Field effect sensor1206A is disposed on substrate1202in proximity to aperture1204. Shaft1208extends through and is pivotally connected to substrate1202at aperture1204. Shaft1208can, but need not, include knob1210. A bearing (not shown), for example, a cylindrical or spherical bearing, or other means (not shown) can be provided at aperture1204to provide support for and/or restrict the degree and direction of movement of shaft1208. For example, in an embodiment intended for use as a simple on-off switch, it might be desirable to restrict shaft1208so that it can be moved only in a single plane, for example, to the left and right in theFIG. 36Aembodiment.

Electric field stimulator1212is attached to shaft1208at a predetermined location, as discussed above in connection with embodiment1100. In theFIGS. 36A-36Bembodiment, coil spring1214is inserted between head1210and substrate1202, biasing shaft1208to a centered position where shaft1208is substantially perpendicular to substrate1202. In other embodiments, other means can be used to bias shaft1208to a centered position or another desired position, as would be recognized by one skilled in the art. Alternatively, such biasing means can be omitted so that shaft1208normally rests in the last position to which it was moved.

In operation, an electric field is generated about field effect sensor1206A, as discussed above. With shaft1208in the centered position, electric field stimulator1212is sufficiently removed from this electric field so that electric field stimulator1212does not disturb this electric field. When shaft1208is displaced, for example, by a user applying a perpendicular force to shaft1208, electric field stimulator1212is displaced so that at least a portion of electric field stimulator1212moves closer to field effect sensor1206A, thus disturbing the electric field about field effect sensor1206A. Detection circuitry associated with field effect sensor1206A detects this disturbance and, in turn, sends an output signal to corresponding control circuitry, as discussed above.

Embodiment1200can be readily modified to yield a combination toggle/pushbutton embodiment (not shown) by adapting the connection between shaft1208and aperture1204such that shaft1208can both toggle about and slide through aperture1204, as would be understood by one skilled in the art.

FIG. 36Cillustrates an alternate embodiment including four field effect sensors1206A-1206D located in proximity to aperture1204and spaced from each other about aperture1204at 90° intervals. Each field effect sensor1206A-1206D includes corresponding field generation and detection circuitry. A particular field effect sensor1206iis actuated when, in response to toggling of shaft1208, electric field stimulator1212comes sufficiently close to such field effect sensor1206ias to disturb the electric field about field effect sensor1206i. Typically, only one field effect sensor1206iis actuated at any time. However, field effect sensors1206A-1206D (and their corresponding field generation and detection circuits) can be adapted so that two (or more) adjacent field effect sensors1206iare simultaneously actuated when electric field stimulator1212is positioned near them. For example, in theFIG. 36Cembodiment, electric field stimulator1212could couple to both field effect sensors1206A and1206B when shaft1208is toggled in a manner that positions at least a portion of electric field stimulator1212between field effect sensors1206A and1206B. In alternate embodiments, more or fewer than four field effect sensors can be arranged on substrate1202about aperture1204in any desired arrangement, as would be recognized by one skilled in the art.

FIG. 36Dillustrates another embodiment1240of the present invention emulating a mechanical toggle switch. Embodiment1240includes shaft1208connected to substrate1202at pivot point1224. In this embodiment, shaft208does not penetrate substrate1202. Electric field stimulator1212is attached to shaft1208at a predetermined distance from pivot point1224. Biasing means (not shown) can be provided to bias shaft1208to any desired position.

FIGS. 37A-37Dillustrate an embodiment1300of the present invention emulating a mechanical rotary switch. Substrate1302defines aperture1304. Inner field effect sensor1306A and outer field effect sensor1306B are disposed on a surface of substrate1302at first and second predetermined distances, respectively, from aperture1304. Shaft1308is inserted through and free to rotate within aperture1304. A bushing, bearing, or other means (not shown) can be provided to better enable shaft1308to rotate within aperture1304and preclude shaft1308from sliding through aperture1304. Preferably, shaft1308includes knob1310to facilitate grasping and rotation of shaft1308by a user.

Electric field stimulator mounting plate1330is attached to shaft1308at a predetermined distance from substrate1302by any suitable means, as would be known to one skilled in the art. Inner electric field stimulators1332are mounted on electric field stimulator mounting plate1330in an annular arrangement at a predetermined distance from the center of electric field stimulator mounting plate1330. This predetermined distance corresponds to and preferably is equal to the predetermined distance from the center of aperture1304to inner field effect sensor1306A. Similarly, outer electric field stimulators1334are mounted on electric field stimulator mounting plate1330in an annular arrangement at a predetermined distance from the center of electric field stimulator mounting plate1330corresponding to and preferably equal to the predetermined distance from the center of aperture1304to outer field effect sensor1306B. Preferably, the angular spacing between adjacent inner electric field stimulators1332is equal. Similarly, the angular spacing between adjacent outer electric field stimulators1334also preferably is equal.

In operation, a user rotates knob1310, in turn rotating shaft1308and electric field stimulator mounting plate1330. As electric field stimulator mounting plate1330rotates, each inner electric field stimulator1332alternately couples with and decouples from the electric field about inner field effect sensor1306A. Similarly, each outer electric field stimulator1334alternately couples with and decouples from the electric field about outer field effect sensor1306BA. Detection circuits associated with field effect sensors1306A,1306B detect this coupling and decoupling and provide corresponding output signals to a control circuit (not shown). The control circuit can be adapted to recognize the degree and rate of rotation of knob1310based on these signals.

Preferably, inner electric field stimulators1332are neither radially aligned with nor angularly centered between adjacent outer electric field stimulators1334. As such, inner electric field stimulators1332will couple to and decouple from the electric field about inner field effect sensor1306A at certain angular displacements of knob1310and outer electric field stimulators1334will couple to and decouple from the electric field about outer field effect sensor1306B at different angular displacements of knob1310.FIG. 37Eillustrates typical streams of output signals from the detection circuits associated with field effect sensors1306A,1306B as knob1310is turned in a particular direction. Based on these signals, a microprocessor can determine whether knob1310is being turned clockwise or counterclockwise, as would be recognized by one skilled in the art.

In alternate embodiments, one of inner field effect sensor1306A and outer field effect sensor1306B can be omitted. In such embodiments, the corresponding inner electric field stimulators1332or outer electric field stimulators1334preferably also would be omitted.

In other alternate embodiments, shaft1308can be adapted to slide longitudinally through, as well as rotate within, aperture1304, and means can be provided to bias shaft1308longitudinally, as discussed above in connection with the mechanical pushbutton switch emulation embodiments, thus yielding a combination rotary/push and/or pull switch emulation embodiment. Such embodiments can include one or more additional field effect sensors and/or electric field stimulators to facilitate such push and/or pull switch functionality, as would be understood by one skilled in the art.

FIG. 37Fillustrates an alternate rotary switch emulation embodiment1350of the present invention. Embodiment1350includes a second substrate1340in predetermined spatial relationship with substrate1302. Second inner and outer field effect sensors1306C,1306D are disposed on second substrate1340. Second inner and outer electric field stimulators1342,1344are disposed on a second surface of electric field stimulator mounting plate1330, opposite the surface on which inner and outer electric field stimulators1332,1334are disposed. Shaft1308is free to slide through, as well as rotate within, aperture1304.

FIG. 37Fillustrates electric field stimulator mounting plate1330in a first position where inner and outer electric field stimulators1332,1334are in relatively close proximity to substrate1302(and, therefore, the annuli in which inner and outer field effect sensors1306A,1306B are located) and second inner and outer electric field stimulators1342,1344are relatively far from second substrate1340. In this position, rotation of knob1310causes inner and outer electric field stimulators1332,1334to alternately couple to and decouple from the electric fields about inner and outer field effect sensors1306A,1306B, respectively. In this position, second inner and outer electric field stimulators1332,1334remain sufficiently far from second inner and outer field effect sensors1306C,1306D so that second inner and outer electric field stimulators1342,1344do not couple to and decouple from the electric fields about respective field effect sensors1306C,1306D.

By pressing on knob1310, a user can displace electric field stimulator mounting plate1330to a second position where inner and outer electric field stimulators1332,1334are relatively far from substrate1302and second inner and outer electric field stimulators1332,1334are in relatively close proximity to second substrate1340(and, therefore, the annuli in which second inner and outer field effect sensors1306C,1306D are located). In this position, rotation of knob1310causes second inner and outer electric field stimulators1342,1344to alternately couple to and decouple from the electric fields about second inner and outer field effect sensors1306C,1306D, respectively. In this position, inner and outer electric field stimulators1332,1334remain sufficiently far from inner and outer field effect sensors1306A,1306B so that inner and outer field effect sensors1306A,1306B do not couple to and decouple from the electric fields about respective field effect sensors1306A,1306B.

Coil spring1314can be provided to-bias electric field stimulator mounting plate1330to a “normal” position, as illustrated inFIG. 37F. In other embodiments, electric field stimulator mounting plate1330can be biased to a different “normal” position. In further embodiments, coil spring1314can be omitted, so that electric field stimulator mounting plate1330remains in any desired position between substrate1302and second substrate1340. Further, embodiment1350can be adapted so that both sets of inner and outer electric field stimulators1332,1334and1342,1344can couple to the electric fields about respective field effect sensors1306A,1306B,1306C,1306D when electric field stimulator mounting plate1330is positioned substantially midway between substrate1302and second substrate1340. Alternatively, embodiment1350can be adapted so that no electric field stimulator can couple to its respective field effect sensor when electric field stimulator mounting plate is so positioned.

All of the foregoing embodiments are suitable for use in connection with analog or digital detection and control circuitry, as would be understood by one skilled in the art.FIG. 37Gillustrates an alternate embodiment1360of the present invention emulating a mechanical rotary switch that is particularly well-suited for use in connection with analog detection and control circuitry. Embodiment1360includes substrate1302defining aperture1304. Field effect sensor1306is disposed on substrate1302in proximity to aperture1304. Shaft1308is inserted through and free to rotate within aperture1304. In the illustrated embodiment, shaft1308is fixed longitudinally. In other embodiments, shaft1308can be adapted to slide through aperture1304. Shaft1308preferably includes knob1310at one end. Electric field stimulator1328is attached to shaft1308at a predetermined distance from substrate1302. Electric field stimulator1328preferably is tapered like a propeller blade so that the distance between field effect sensor1306and electric field stimulator1328varies with rotation of knob1310and shaft1308. Alternatively, electric field stimulator1328could be substantially planar and parallel to substrate1302, and having a width or thickness that varies with distance from shaft1308, as illustrated inFIG. 371. As such, the degree of coupling of electric field stimulator1328with the electric field about field effect sensor1306varies with rotation of knob1310as a function of the distance between electric field stimulator1328and field effect sensor1306and/or the effective area of electric field stimulator1328in proximity to field effect sensor1306. Through use of appropriate analog detection and control circuitry, embodiment1360could emulate, for example, a potentiometer.

FIG. 37Hillustrates another alternate embodiment1380of the present invention that is particularly well-suited for use in connection with analog detection and control circuitry. Embodiment1380includes substrate1302defining aperture1304having internal threads1305. Field effect sensor1306is disposed on substrate1302in proximity to aperture1304. Threaded shaft1308having knob1310at one end is screwed into aperture1304. Electric field stimulator1312is attached to shaft1308at a predetermined location. As knob1310is rotated clockwise, electric field stimulator1312moves farther away from field effect sensor1306. Conversely, as knob1310is rotated counter-clockwise, electric field stimulator1312moves closer to field effect sensor1306. As such, rotation of knob1310affectively changes the coupling between electric field stimulator1312and field effect sensor1306. These coupling changes readily can be detected and processed by analog detection and control circuitry, as would be known to one skilled in the art.

FIGS. 38A-38Dillustrate yet another embodiment1400of the present invention emulating a rotary switch. Embodiment1400includes substrate1402. Inner and outer knobs1450,1452are attached to substrate1402by any suitable means such that each knob1450,1452can rotate about an axis substantially perpendicular to substrate1402, as would be recognized by one skilled in the art. One or more electric field stimulators1412are disposed in the base of each of inner and outer knobs1450,1452. Inner and outer field effect sensors1406A,1406B are disposed on substrate1402substantially in alignment with electric field stimulators1412disposed in respective inner and outer knobs1450,1452so that each electric field stimulator1412alternately couples to and decouples from the electric field about respective field effect sensor1406A,1406B upon rotation of respective inner or outer knob1450,1452. Electric field stimulators1412can be embodied in various ways. For example, each electric field stimulator1412could be a conductive mass1413, for example, a ball bearing, set into the bottom of respective knob1450,1452. Alternatively, each electric field stimulator1412could be a bump1417in a ring1415inset into the bottom of respective knob1450,1452, as shown inFIG. 38D. In a preferred embodiment, ring1415is made of beryllium copper having stamped bumps1517.

FIGS. 39A-39Billustrate an alternate embodiment1500of the present invention emulating a rotary switch. This embodiment is particularly well-suited for angular position sensing applications. These embodiment uses a single field effect sensor with multiple sensing electrodes. This embodiment includes substrate1502onto which are disposed in a generally circular arrangement detection1503and a string of sensing electrodes1505A-1505H interspersed with resistors R1-R7. In alternate embodiments, detection circuit1503can be located remotely and more or fewer sensing electrodes and resistors than shown can be used.

Knob1510is connected to substrate1502such that knob1510can rotate about an axis substantially perpendicular to substrate1502. In theFIG. 39Aembodiment, shaft1508is inserted into and free to rotate within aperture1504defined by substrate1502, and knob1510is fixed to shaft1508. In other embodiments, shaft1508could be fixed to substrate1502and knob1510could rotate about shaft1508. Field effect stimulator1512is embedded within or otherwise associated with knob1510such that field effect stimulator1512rotates with knob1510through an arc that substantially corresponds to the circular arrangement in which electrodes1505A-1505H and resistors R1-R7are disposed on substrate1502.

In operation, as a user rotates knob1510, electric field stimulator1512alternately couples to and decouples from the electric fields about corresponding electrodes1505A-1505H. Analog detection circuitry could be adapted to determine the extent, rate, and direction of rotation of knob1510, as would be understood by one skilled in the art. In a preferred embodiment, detection circuit1503can take the form shown inFIG. 33A, with electrodes1505A and1505H of theFIG. 39Aembodiment taking the place of electrodes E2and E1, respectively, shown inFIG. 33A. The strengths of the signals at the (+) and (−) inputs, and, therefore, the output of, summer160will have unique, predetermined values for each position of electric field stimulator1512with respect to electrodes1505A-1505H, as would be recognized by one skilled in the art. (A detection circuit of the form shown inFIG. 33Aalso could be used to detect variations in distance between two conductive sheets, as would be recognized by one skilled in the art. As such, theFIG. 33Adetection circuit could be used in connection with a pair of conductive sheets arranged as a vibration sensor, sound pressure sensor, air pressure sensor, position sensor, and the like. In certain embodiments, a layer of conductive foam could be disposed between the conductive sheets.)

Conductor1507having varying impedance over its length, as shown inFIG. 39B, can be used in place of the electrode-resistor string shown inFIG. 39A. The continuously varying impedance of conductor1507provides a continuously varying output to detection circuit1503as field effect stimulator1512changes position in response to rotation of knob1510. As such, use of conductor1507might be preferred where fine resolution of, for example, angular position is required.

TheFIGS. 39A-39Bembodiment can easily be adapted for use as an angular position sensor, as would be recognized y one skilled in the art. The principles of theFIGS. 39A-39Bembodiment can easily be adapted to provide a slide switch or slide potentiometer by simply arranging field effect sensors1505A-1505H and resistors R1-R7linearly and replacing knob1510with a slide, as shown in, for example,FIG. 42A. These principles can be further extended to detect position of a stimulus in an x-y array by creating an array of detection circuit and electrode-resistor strings, as shownFIG. 42E.

FIG. 40illustrates yet another embodiment1600of the invention emulating a rotary switch. Embodiment1600includes substrate1602and shaft1608having a outer knob1610and inner knob1611. Substrate1602is formed, for example, by molding, to capture inner knob1611and encapsulate field effect sensor1606. Electric field coupling element1612is encapsulated or otherwise embedded within outer knob1610. Alternatively, electric field coupling element1612could be encapsulated or otherwise embedded within inner knob1611. Light emitting device1621can be encapsulated within substrate1602. By selecting transparent or translucent materials for at least portions of substrate1602, inner and outer knobs1610,1611, and shaft1608, light emitting deice1621can be used to selectively illuminate at least a portion of outer knob1610.

FIG. 41Aillustrates an embodiment1700of the present invention emulating a mechanical rocker switch. Embodiment1700includes a substrate1702, two field effect sensors1706A,1706B disposed on a surface of substrate1702, and electric field stimulators1713A,1713B in the form of rocker1713attached to substrate1702. In the illustrated embodiment, rocker1713is a piece of curved spring steel fixed to substrate1702, and electric field stimulators1713A,1713B are monolithic portions of rocker1713. In alternate embodiments, rocker1713can be made of other materials and take other forms, and electric field stimulators1713A,1713B could be separate elements, for example, ball bearings, embedded within rocker1713, as would be recognized by one skilled in the art.

In operation, a user depresses either electric field stimulator1713A corresponding to the left side of rocker1713or electric field stimulator1713B corresponding to the right side of rocker1713toward substrate1702. As electric field stimulator1713A,1713B approaches or contacts substrate1702, electric field stimulator1713A,1713B couples to corresponding field effect sensor1706A,1706B. In the illustrated embodiment, both electric field stimulators1713A,1713B could be moved toward substrate1702at the same time. Preferably, rocker1713is configured so that only one of electric field stimulators1713A,1713B can be moved toward substrate1702at any time.

FIG. 41Billustrates another embodiment1750of the present invention emulating a mechanical rocker switch. Embodiment1750is similar to embodiment1700, except that embodiment1750uses a rigid rocker1713. In certain embodiments, rocker1713might be made of a material that does not provide sufficient coupling to field effect sensors1706A,1706B when depressed. In such embodiments, conductive masses1715can be embedded at appropriate locations in rocker1713to enhance such coupling, as would be recognized by one skilled in the art. In other embodiments, rocker1713can be shaped and sized so that a user's finger on rocker1713provides coupling to the electric field about field effect sensor1706A,1706B when the user presses the corresponding portion of rocker1713towards substrate1702.

Biasing means can be provided to bias rocker1713to a predetermined “normal” position. InFIG. 41B, the biasing means is embodied as a pair of plastic tabs1725attached to substrate1702. Plastic tabs1725are sufficiently flexible to deflect when rocker1713is pressed, and sufficiently resilient to return rocker1713to the “normal” position when rocker1713is released. Any other suitable biasing means could be used, as would be recognized by one skilled in the art.

Alternatively, as illustrated inFIG. 41C, rocker1713and tabs can be adapted to secure rocker1713in a particular position until repositioned by a user. In such an embodiment, tabs1725preferably include nubs1725projecting toward the ends of rocker1713and rocker1713preferably includes concavities1727at its ends for receiving nubs1725.

FIG. 42Aillustrates an embodiment1800of the present invention emulating a mechanical slide switch. Embodiment1800includes substrate1802. One or more field effect sensors1806are disposed on substrate1802. Electric field stimulator1812, for example, a conductive cylinder or ball bearing, is attached to slide1811. Slide1811engages with rails1803attached to substrate1802. In operation, a user slides slide1811back and forth along substrate1802. As electric field stimulator1812comes into proximity with a particular field effect sensor1806, electric field stimulator1812couples to the electric field about such field effect sensor1806. Likewise, when electric field stimulator1812is moved away from a particular field effect sensor1806, electric field stimulator1812decouples from the electric field about such field effect sensor1806.

In an alternate embodiment, slide1811can be replaced with slide1817having a cutout1819designed to accommodate a user's finger. In this embodiment, the user's finger functions as electric field stimulator1812. In a further alternate embodiment, slide1811can be eliminated altogether. The same principles can be applied to a rotary switch emulation by arranging field effect sensors1806about the periphery of a cylinder (not shown) or frustum of a cone1807, as illustrated inFIG. 42D.

In certain embodiments, portions of slide1811can be illuminated. Such embodiments preferably include light pipe1821and a light source (not shown) for illuminating light pipe1821in connection with substrate1802, such that light channel1823disposed on slide1811can receive light from light pipe1821. In other embodiments, other means can be used to illuminate slide1811or portions thereof.

FIG. 42Billustrates another embodiment1850of the present invention emulating a slide switch. Embodiment1850is similar to embodiment1800, except that embodiment eliminates slider1811altogether. Flexible sheet1827under rails1803so as to overlay substrate1802. Preferably, sheet1827is easily replaceable and can include graphics indicating, for example, the location of field effect sensors (not shown) disposed on substrate1802beneath sheet1827. Normally, an air gap exists between sheet1827and a field effect sensor (not shown) disposed on substrate1802beneath sheet1827. When a user touches sheet1827to actuate such field effect sensor, the air is displaced from this air gap, allowing and enhancing coupling of the user's finger to the electric field about the field effect sensor.

FIG. 42Cillustrates an alternate embodiment1860of the present invention emulating a slide switch. Field effect sensor1806is disposed on substrate1802. Substrate1802includes rails1803. Slide1811is slidingly engaged with substrate1802via rails1803. Electric field stimulator1812preferably is a conductive mass disposed on slide1811. In theFIG. 41Cembodiment, the cross sectional area of electric field stimulator1812varies from one end of slide1811to the other. With slide1811in the position shown inFIG. 42C, electric field stimulator1812is distant from field effect sensor1806and does not couple to the electric field about field effect sensor1806. As slide1811is moved to the right by, for example, a user's finger, electric field stimulator eventually moves sufficiently close to field effect sensor1806to couple to the electric field about field effect sensor1806. Initially, such coupling is small due to the small area of electric field stimulator1812that is in proximity to field effect sensor1806and the corresponding electric field. As slide1811is moved farther to the right, a greater portion of electric field stimulator1812comes into proximity with field effect sensor1806and the corresponding electric field and the coupling of electric field stimulator1812to the electric field increases. Analog detection circuitry can discern the varying state of coupling and provide a corresponding analog output to a corresponding control circuit. Biasing means, for example, coil spring1814, can be provided to maintain slide1811in a “normal” position in the absence of a force displacing slide1811from such “normal” position.

FIG. 43illustrates an embodiment1900of the present invention emulating a mechanical spherical switch or track ball. Embodiment1900includes a substrate1902forming a housing1962for ball1960. One or more field effect sensors1906are arranged on the surface or embedded within substrate1902. The perimeter of ball1960includes electric field stimulators1912arranged in a unique, non-repetitive pattern. In operation, as ball1960rotates within housing1962, electric field stimulators couple to and decouple from the electric fields about field effect sensors1906. Detection and control circuitry associated with field effect sensors1906can be adapted to determine the degree and direction of rotation of ball1960, as would be recognized by one skilled in the art. In an alternate embodiment, ball1960can be fixed and substrate1902and housing1962can be permitted to rotate or otherwise move about housing1962. This embodiment could be used, for example, to detect tilt or vibration.

FIG. 44illustrates an application specific embodiment2000of a mechanical switch emulation according to the present invention, in particular, a throttle for a snowmobile or personal watercraft. A field effect sensor2006is disposed in or encapsulated within handle2002. Electric field stimulator2012in the form of a conductive mass is disposed on throttle lever2016. As a user depresses and releases throttle lever2016, electric field stimulator2012moves closer to and farther from field effect sensor2006, respectively. An analog detection and control can be used to determine throttle position based on signals received from field effect sensor2006. In preferred embodiments, additional field effect sensors2031,2033, and2035can be disposed on handle2002. These additional sensors can include, for example, a redundant sensor2031for throttle control, a hand position sensor2033that disables the throttle unless it detects a rider's hand on handle2002, and a water sensor2035that disables the throttle when immersed in water due to, for example, inversion of a watercraft.

FIGS. 45A-45Billustrate an application specific embodiment of a tire pressure sensor2100according to the present invention. In preferred embodiments, a compressible and preferably conductive foam substrate2104is disposed on a surface of substrate2102. A plurality of field effect sensors2106are arranged in a matrix array on the other surface of substrate2102. In operation, tire2108of, for example, an automobile (not shown), is placed upon foam substrate2104, thereby compressing the portion of foam substrate2104in contact with tire2108. The compressed portion of foam substrate2104couples with the electric fields about corresponding field effect sensors2106, thus actuating these sensors, as would be understood by one skilled in the art. A microprocessor (not shown) programmed with the weight of the load on tire2108can determine the air pressure in tire2108based on the signals it receives from field effect sensors2106corresponding to the area of foam compressed by tire2108. In other embodiments, foam substrate2104can be omitted, such that tire2108itself effects the coupling to field effect sensors2106.

FIG. 46illustrates automobile passenger seat2202having seat portion2202A and back portion2202B. Seat2202preferably is stuffed or padded using compressible foam2204in which are embedded a plurality of field effect sensors2206A for detecting weight placed on seat2202and a plurality of field effect sensors2206B for sensing the physical dimensions of a person or item placed on seat2202. Field effect stimulators2212, embodied as seat support posts in the illustrated embodiment, are located in predetermined spatial relation to field effect sensors2206A.

With seat2202empty, field effect sensors2206A are a predetermined distance from field effect stimulators2212such that field effect sensors2206A are not actuated. When a load, for example, a person or package, is placed on seat2202, foam2204in seat portion2202A is compressed, moving field effect sensors2206A closer to field effect stimulators2212, causing field effect stimulators2212to disturb the electric field about field effect sensors2206A. The heavier the load placed on seat2202, the greater the compression of foam2204in seat portion2202B and corresponding displacement of field effect sensors2206A. An analog detection and control circuit (not shown) receiving output signals from field effect sensors2206A can determine from these signals the displacement of field effect sensors2206A in response to the load placed on seat2202. The control circuit can determine the weight of the person sitting or article placed on seat2202based on this displacement data and the compressibility characteristics of foam2204.

Also, with seat2202empty, no stimulus couples to the electric fields about field effect sensors2206B. When a person sits or a package is placed on seat2202, the portions of the person or package in proximity to any of field effect sensors2206B couple to the electric fields about these sensors. An analog or digital detection and control circuit receiving the output signals from field effect sensors2206B can determine the physical outline of the load (person or package) on seat2202. The control circuit could use this data in connection with the weight data derived from the signals received from field effect sensors2206A, as discussed above, to determine whether the load on seat2202was a person or package. If the control circuit determined the load was a package and not a person, it might deactivate the passenger airbag. If the control circuit determined the load was a person and not a package, it might tailor the air bag deployment speed and force to the size and weight of the person occupying seat2202.

While several embodiments of the present invention have been shown, it will be obvious to those skilled in the art that numerous modifications may be made without departing from the spirit of the claims appended hereto.