Generating a baseline compensation signal based on a capacitive circuit

A capacitance-sensing circuit may include a plurality of channel inputs associated with measuring a capacitance of a unit cell of a capacitive sense array. The capacitance-sensing circuit may also include a baseliner component that is coupled to the plurality of channel inputs. The baseliner component may generate a baseline compensation signal using a capacitive circuit and may provide the baseline compensation signal to each of the plurality of channel inputs of the capacitive sense array.

TECHNICAL FIELD

The present disclosure generally relates to sensing systems, and more particularly to generating a baseline compensation signal based on a capacitive circuit.

BACKGROUND

Capacitance sensing systems can sense electrical signals generated on electrodes that reflect changes in capacitance. Such changes in capacitance can indicate a touch event (e.g., the proximity of an object to particular electrodes). Capacitive sense elements may be used to replace mechanical buttons, knobs and other similar mechanical user interface controls. The use of a capacitive sense element allows for the elimination of complicated mechanical switches and buttons, providing reliable operation under harsh conditions. In addition, capacitive sense elements are widely used in modern customer applications, providing user interface options in existing products. Capacitive sense elements can range from a single button to a large number arranged in the form of a capacitive sense array for a touch-sensing surface.

Transparent touch screens that utilize capacitive sense arrays are ubiquitous in today's industrial and consumer markets. They can be found on cellular phones, GPS devices, set-top boxes, cameras, computer screens, MP3 players, digital tablets, and other such devices. The capacitive sense arrays work by measuring the capacitance of a capacitive sense element, and looking for a delta in capacitance indicating a touch or presence of a conductive object. When a conductive object (e.g., a finger, hand, or other object) comes into contact or close proximity with a capacitive sense element, the capacitance changes and the conductive object is detected. The capacitance changes of the capacitive touch sense elements can be measured by an electrical circuit. The electrical circuit converts the measured capacitances of the capacitive sense elements into digital values.

There are two typical types of capacitance: 1) mutual capacitance where the capacitance-sensing circuit has access to both electrodes of the capacitor; 2) self-capacitance where the capacitance-sensing circuit has only access to one electrode of the capacitor where the second electrode is tied to a DC voltage level or is parasitically coupled to Earth Ground.

DETAILED DESCRIPTION

Aspects of the present disclosure relate to providing a baseline compensation signal for a capacitive sense channel associated with a capacitive sense array. A baseline capacitance may be used by the capacitive sense channel for touch detection. For example, the baseline capacitance may represent a capacitance when no touch object is present at a corresponding sense channel associated with a unit cell of the capacitive sense array. The baseline capacitance may be compared to a subsequently measured capacitance value to determine if a touch object is present at the unit cell associated with the corresponding sense channel. For example, a change or difference between the subsequently measured capacitance value and the value of the baseline capacitance may indicate the presence of a touch object at the unit cell of the capacitive sense array.

The capacitive sense array may be associated with a spurious capacitance that may reduce the sensitivity for touch detection. For example, a spurious charge or current or a noise signal may be received by the capacitive sense array when providing the baseline capacitance. A baseliner component may be provided to generate a baseline compensation signal to compensate for the spurious current or noise signal that is received by the capacitive sense array when the baseline capacitance is provided. For example, the baseliner component may generate the baseline compensation signal and transmit the baseline compensation signal to the capacitive sense channels of the capacitive sense array that are used for touch detection.

The baseliner component may be implemented with a sensor model and a current conveyor. The sensor model may include multiple capacitors. For example, the sensor model may include a first capacitor corresponding to the operation of the capacitive sense array in a mutual capacitance mode and a second capacitor corresponding to the operation of the capacitive sense array in a self-capacitance mode. The current conveyor may include a differential amplifier and current mirrors that may be used to generate multiple baseline compensation signals based on an output of the sensor model and a voltage reference input signal. The outputs of the current conveyor may be coupled to each sense channel of the capacitive sense array so that the baseline compensation signals may be used to compensate for the spurious current or noise signal that is received by each of the sense channels of the capacitive sense array.

As previously described, the baseliner component may generate the baseline compensation signal that is received by each of the sense channels of the capacitive sense array. The current conveyor of the baseliner component may also receive the current from the sensor model, which may be referred to as a capacitive circuit, and may provide a splitting and scaling function to the current from the sensor model to generate the baseline compensation signals for each of the sense channels of the capacitive sense array.

FIG. 1is a block diagram illustrating one embodiment of an electronic system having a processing device, including a baseliner component. The electronic system may correspond to a capacitive sense array system. Details regarding the baseliner component120are described in more detail with respect toFIGS. 3-8. In some embodiments, the baseliner component120may be located in the capacitive sense array125and/or the baseliner component120of the processing device110may be used to configure components (e.g., a gain component) of the baseliner component as described in further detail below. The processing device110is configured to detect one or more touches detected proximate to a touch-sensing device, such as capacitive sense array125. The processing device110can detect conductive objects, such as touch objects140(fingers or passive styluses, an active stylus130, or any combination thereof). The capacitance-sensing circuit101can measure touch data created by a touch using the capacitive sense array125. The touch may be detected by a single or multiple sensing cells, each cell representing an isolated sense element or an intersection of sense elements (e.g., electrodes) of the capacitive sense array125. In one embodiment, when the capacitance-sensing circuit101measures mutual capacitance of the touch-sensing device (e.g., using capacitive sense array125), the capacitance-sensing circuit101acquires a 2D capacitive image of the touch-sensing object and processes the data for peaks and positional information. In another embodiment, the processing device110is a microcontroller that obtains a capacitance touch signal data set from application processor150, such as from capacitive sense array125, and finger detection firmware executing on the microcontroller identifies data set areas that indicate touches, detects and processes peaks, calculates the coordinates, or any combination therefore. The microcontroller can report the precise coordinates to an application processor, as well as other information.

Electronic system100includes processing device110, capacitive sense array125, stylus130, and application processor150. The capacitive sense array125may include capacitive sense elements that are electrodes of conductive material, such as copper. The sense elements may also be part of an indium-tin-oxide (ITO) panel. The capacitive sense elements can be used to allow the capacitance-sensing circuit101to measure self-capacitance, mutual capacitance, or any combination thereof. In the depicted embodiment, the electronic system100includes the capacitive sense array125coupled to the processing device110via bus122. The capacitive sense array125may include a multi-dimension capacitive sense array. The multi-dimension sense array includes multiple sense elements, organized as rows and columns. In another embodiment, the capacitive sense array125is non-transparent capacitive sense array (e.g., PC touchpad). The capacitive sense array125may be disposed to have a flat surface profile. Alternatively, the capacitive sense array125may have non-flat surface profiles. Alternatively, other configurations of capacitive sense arrays may be used. For example, instead of vertical columns and horizontal rows, the capacitive sense array125may have a hexagon arrangement, or the like, as would be appreciated by one of ordinary skill in the art having the benefit of this disclosure. In one embodiment, the capacitive sense array125may be included in an ITO panel or a touch screen panel.

The operations and configurations of the processing device110and the capacitive sense array125for detecting and tracking the touch object140and stylus130are described herein. In short, the processing device110is configurable to detect a presence of the touch object140, a presence of a stylus130on the capacitive sense array125, or any combination thereof. If the touching object is an active stylus, in one embodiment, the active stylus130is configurable to operate as the timing “master,” and the processing device110adjusts the timing of the capacitive sense array125to match that of the active stylus130when the active stylus130is in use. In one embodiment, the capacitive sense array125capacitively couples with the active stylus130, as opposed to other inductive stylus applications. It should also be noted that the same assembly used for the capacitive sense array125, which is configurable to detect touch objects140, is also used to detect and track a stylus130without an additional PCB layer for inductively tracking the active stylus130.

In the depicted embodiment, the processing device110includes analog and/or digital general purpose input/output (“GPIO”) ports107. GPIO ports107may be programmable. GPIO ports107may be coupled to a Programmable Interconnect and Logic (“PIL”), which acts as an interconnect between GPIO ports107and a digital block array of the processing device110(not shown). The digital block array may be configurable to implement a variety of digital logic circuits (e.g., DACs, digital filters, or digital control systems) using, in one embodiment, configurable user modules (“UMs”). The digital block array may be coupled to a system bus. Processing device110may also include memory, such as random access memory (“RAM”)105and program flash104. RAM105may be static RAM (“SRAM”), and program flash104may be a non-volatile storage, which may be used to store firmware (e.g., control algorithms executable by processing core109to implement operations described herein). Processing device110may also include a memory controller unit (“MCU”)103coupled to memory and the processing core109. The processing core109is a processing element configured to execute instructions or perform operations. The processing device110may include other processing elements as would be appreciated by one of ordinary skill in the art having the benefit of this disclosure. It should also be noted that the memory may be internal to the processing device or external to it. In the case of the memory being internal, the memory may be coupled to a processing element, such as the processing core109. In the case of the memory being external to the processing device, the processing device is coupled to the other device in which the memory resides as would be appreciated by one of ordinary skill in the art having the benefit of this disclosure.

In one embodiment, the processing device110further includes processing logic102. Some or all of the operations of the processing logic102may be implemented in firmware, hardware, or software or some combination thereof. The processing logic102may receive signals from the capacitance-sensing circuit101, and determine the state of the capacitive sense array125, such as whether an object (e.g., a finger) is detected on or in proximity to the capacitive sense array125(e.g., determining the presence of the object), resolve where the object is on the sense array (e.g., determining the location of the object), tracking the motion of the object, or other information related to an object detected at the touch sensor. In another embodiment, processing logic102may include capacitance-sensing circuit101. In another embodiment, processing logic102may perform some or all the functions of capacitance-sensing circuit101and/or processing device110.

The processing device110may also include an analog block array (not shown) (e.g., field-programmable analog array). The analog block array is also coupled to the system bus. Analog block array may also be configurable to implement a variety of analog circuits (e.g., ADCs or analog filters) using, in one embodiment, configurable UMs. The analog block array may also be coupled to the GPIO107.

As illustrated, capacitance-sensing circuit101may be integrated into processing device110. Capacitance-sensing circuit101may include analog I/O for coupling to an external component, such as touch-sensor pad (not shown), capacitive sense array125, touch-sensor slider (not shown), touch-sensor buttons (not shown), and/or other devices. The capacitance-sensing circuit101may be configurable to measure capacitance using mutual-capacitance sensing techniques, self-capacitance sensing technique, charge-coupling techniques, charge balancing techniques or the like. In one embodiment, capacitance-sensing circuit101operates using a charge accumulation circuit, a capacitance modulation circuit, or other capacitance sensing methods known by those skilled in the art. In an embodiment, the capacitance-sensing circuit101is of the Cypress TMA-3xx, TMA-4xx, or TMA-xx families of touch screen controllers. Alternatively, other capacitance-sensing circuits may be used. The mutual capacitive sense arrays, or touch screens, as described herein, may include a transparent, conductive sense array disposed on, in, or under either a visual display itself (e.g. LCD monitor), or a transparent substrate in front of the display. In an embodiment, the transmit (TX) and receive (RX) electrodes are configured in rows and columns, respectively. It should be noted that the rows and columns of electrodes can be configured as TX or RX electrodes by the capacitance-sensing circuit101in any chosen combination. In one embodiment, the TX and RX electrodes of the sense array125are configurable to operate as a TX and RX electrodes of a mutual capacitive sense array in a first mode to detect touch objects, and to operate as electrodes of a coupled-charge receiver in a second mode to detect a stylus on the same electrodes of the sense array. The stylus, which generates a stylus TX signal when activated, is used to couple charge to the capacitive sense array, instead of measuring a mutual capacitance at an intersection of a RX electrode and a TX electrode (a sense element) as done during mutual-capacitance sensing. An intersection between two sense elements may be understood as a location at which one sense electrode crosses over or overlaps another, while maintaining galvanic isolation from each other. The capacitance associated with the intersection between a TX electrode and an RX electrode can be sensed by selecting every available combination of TX electrode and RX electrode. When a touch object, such as a finger or stylus, approaches the capacitive sense array125, the object causes a decrease in mutual capacitance between some of the TX/RX electrodes. In another embodiment, the presence of a finger increases the capacitance of the electrodes to the environment (Earth) ground, typically referred to as self-capacitance change. Utilizing the change in mutual capacitance, the location of the finger on the capacitive sense array125can be determined by identifying the RX electrode having a decreased coupling capacitance between the RX electrode and the TX electrode to which the TX signal was applied at the time the decreased capacitance was measured on the RX electrode. Therefore, by sequentially determining the capacitances associated with the intersection of electrodes, the locations of one or more touch objects can be determined. It should be noted that the process can calibrate the sense elements (intersections of RX and TX electrodes) by determining baselines for the sense elements. It should also be noted that interpolation may be used to detect finger position at better resolutions than the row/column pitch as would be appreciated by one of ordinary skill in the art having the benefit of this disclosure. In addition, various types of coordinate interpolation algorithms may be used to detect the center of the touch as would be appreciated by one of ordinary skill in the art having the benefit of this disclosure.

The capacitance-sensing circuit101includes the baseliner component120. In addition, the baseliner component120may be used in conjunction with various components to provide a baseline compensation signal for sense channels of the capacitive sense array. Additional details of the baseliner component120are described below with respect toFIGS. 3-8. The baseliner component may be implemented on or off chip.

Processing device110may include internal oscillator/clocks106and communication block (“COM”)108. In another embodiment, the processing device110includes a spread-spectrum clock (not shown). The oscillator/clocks block106provides clock signals to one or more of the components of processing device110. Communication block108may be used to communicate with an external component, such as an application processor150, via application interface (“I/F”) line151.

Processing device110may reside on a common carrier substrate such as, for example, an integrated circuit (“IC”) die substrate, a multi-chip module substrate, or the like. Alternatively, the components of processing device110may be one or more separate integrated circuits and/or discrete components. In one exemplary embodiment, processing device110is the Programmable System on a Chip (PSoC®) processing device, developed by Cypress Semiconductor Corporation, San Jose, Calif. Alternatively, processing device110may be one or more other processing devices known by those of ordinary skill in the art, such as a microprocessor or central processing unit, a controller, special-purpose processor, digital signal processor (“DSP”), an application specific integrated circuit (“ASIC”), a field programmable gate array (“FPGA”), or the like.

It should also be noted that the embodiments described herein are not limited to having a configuration of a processing device coupled to an application processor, but may include a system that measures the capacitance on the sensing device and sends the raw data to a host computer where it is analyzed by an application. In effect, the processing that is done by processing device110may also be done in the application processor.

Capacitance-sensing circuit101may be integrated into the IC of the processing device110, or alternatively, in a separate IC. Alternatively, descriptions of capacitance-sensing circuit101may be generated and compiled for incorporation into other integrated circuits. For example, behavioral level code describing the capacitance-sensing circuit101, or portions thereof, may be generated using a hardware descriptive language, such as VHDL or Verilog, and stored to a machine-accessible medium (e.g., CD-ROM, hard disk, floppy disk, etc.). Furthermore, the behavioral level code can be compiled into register transfer level (“RTL”) code, a netlist, or even a circuit layout and stored to a machine-accessible medium. The behavioral level code, the RTL code, the netlist, and the circuit layout may represent various levels of abstraction to describe capacitance-sensing circuit101.

It should be noted that the components of electronic system100may include all the components described above. Alternatively, electronic system100may include some of the components described above.

In one embodiment, the electronic system100is used in a tablet computer. Alternatively, the electronic device may be used in other applications, such as a notebook computer, a mobile handset, a personal data assistant (“PDA”), a keyboard, a television, a remote control, a monitor, a handheld multi-media device, a handheld media (audio and/or video) player, a handheld gaming device, a signature input device for point of sale transactions, an eBook reader, global position system (“GPS”) or a control panel. The embodiments described herein are not limited to touch screens or touch-sensor pads for notebook implementations, but can be used in other capacitive sensing implementations, for example, the sensing device may be a touch-sensor slider (not shown) or touch-sensor buttons (e.g., capacitance sensing buttons). In one embodiment, these sensing devices include one or more capacitive sensors or other types of capacitance-sensing circuitry. The operations described herein are not limited to notebook pointer operations, but can include other operations, such as lighting control (dimmer), volume control, graphic equalizer control, speed control, or other control operations requiring gradual or discrete adjustments. It should also be noted that these embodiments of capacitive sensing implementations may be used in conjunction with non-capacitive sensing elements, including but not limited to pick buttons, sliders (ex. display brightness and contrast), scroll-wheels, multi-media control (ex. volume, track advance, etc.) handwriting recognition, and numeric keypad operation.

FIG. 2illustrates a capacitive touch-sensing system, according to one embodiment. Capacitive touch-sensing system200includes a sense array220. Sense array220may be a capacitive sense array. Sense array220includes multiple row electrodes231-240and multiple column electrodes241-248. The row and column electrodes231-248are connected to a processing device110, which may include the functionality of capacitance-sensing circuit101, as illustrated inFIG. 1. In one embodiment, the processing device110may perform mutual capacitance measurement scans and/or self capacitance measurement scans of the sense array220to measure a mutual capacitance value or a self capacitance value associated with each of the intersections between a row electrode and a column electrode in the sense array220. The measured capacitances may be further processed to determine centroid locations of one or more contacts of conductive objects proximate to the sense array220.

In one embodiment, the processing device110is connected to an application processor150which may receive the measured capacitances or calculated centroid locations from the processing device110.

The sense array220illustrated inFIG. 2includes electrodes arranged to create a pattern of interconnected diamond shapes. Specifically, the electrodes231-248of sense array220form a single solid diamond (SSD) pattern. In one embodiment, each intersection between a row electrode and a column electrode defines a unit cell. Each point within the unit cell is closer to the associated intersection than to any other intersection. For example, unit cell250contains the points that are closest to the intersection between row electrode234and column electrode246. Thus, the unit cell may be considered to include a pair of electrodes, or may alternatively include a single electrode.

In one embodiment, capacitive touch-sensing system200may collect data from the entire touch-sensing surface of sense array220by performing a scan to measure capacitances of the unit cells that comprise the touch-sensing surface, then process the touch data serially or in parallel with a subsequent scan. For example, one system that processes touch data serially may collect raw capacitance data from each unit cell of the entire touch-sensing surface, and filter the raw data. Based on the filtered raw data, the system may determine local maxima (corresponding to local maximum changes in capacitance) to calculate positions of fingers or other conductive objects, then perform post processing of the resolved positions to report locations of the conductive objects, or to perform other functions such as motion tracking or gesture recognition.

In one embodiment, capacitive touch-sensing system200may be configured to perform both of self-capacitance sensing and mutual capacitance sensing. In one embodiment, capacitive touch-sensing system200is configured to perform self-capacitance sensing, in sequence or in parallel, to measure the self-capacitance of each row and column electrode of the touch-sensing surface (e.g., sense array220), such that the total number of sense operations is N+M, for a capacitive-sense array having N rows and M columns. In one embodiment, capacitive touch sensing system200may be capable of connecting individual electrodes together to be sensed in parallel with a single operation. For example, multiple row (e.g., electrodes231-240) and or column electrodes (e.g., electrodes241-248) may be coupled together and sensed in a single operation to determine whether a conductive object is touching or near the touch-sensing surface. In an alternate embodiment, the capacitive touch-sensing system200may be capable of connecting each row electrode to it is own sensing circuit such that all row electrodes may be sensed in parallel with a single operation. The capacitive touch-sensing system200may also be capable of connecting each column electrode to its own sensing circuit such that all column electrodes may be sensed in parallel with a single operation. The capacitive touch-sensing system200may also be capable of connecting all row and column electrodes to their own sensing circuits, such that all row and column electrodes may be sensed in parallel with a single operation.

In one embodiment, the capacitive touch-sensing system200may perform mutual capacitance sensing of the touch-sensing surface (e.g., sense array220) by individually sensing each intersection between a row electrode and a column electrode. Thus, a total number of sense operations for a capacitive-sense array (e.g., sense array220) having X rows and Y columns is X×Y. In one embodiment, performing a mutual capacitance measurement of a unit cell formed at the intersection of a row electrode and a column electrode includes applying a signal (TX) to one electrode and measuring characteristics of the signal on another electrode resulting from the capacitive coupling between the electrodes.

In one embodiment, multiple capacitance-sensing circuits may be used in parallel to measure a signal coupled to multiple column electrodes simultaneously, from a signal applied to one or more row electrodes. In one embodiment, for a capacitive-sense array (e.g., sense array220) having X rows, Y columns, and N columns that can be sensed simultaneously, the number of mutual capacitance sensing operations is the smallest whole number greater than or equal to X×Y/N.

In one embodiment, each update of the touch locations may include a sensing portion and a non-sensing portion. The sensing portion may include measurement of capacitance associated with intersections between electrodes, while the non-sensing portion may include calculation of touch locations based on the capacitance measurements and reporting of the calculated touch locations to a host device. In one embodiment, capacitive touch-sensing system200includes baseliner component120.

FIG. 3is a block diagram of a baseliner component associated with sense channels of a capacitive touch-sensing system. In general, the baseliner component310may correspond to the baseliner component120ofFIGS. 1 and 2.

As shown inFIG. 3, a capacitive touch-sensing system300may include a baseliner component310(also referred to as a baseliner circuit) that may provide multiple output signals (i.e., a baseline compensation signals or currents) to sense channels of the capacitive touch-sensing system. For example, a first output of the baseliner component310that corresponds to a first output current or baseline compensation signal may be coupled to a first sense channel (e.g., an RX sense channel or RX channel) of the capacitive touch-sensing system and a second output of the same baseliner component310that corresponds to a second output current or baseline compensation signal may be coupled to a second sense channel of the same capacitive touch-sensing system. The baseliner component310may generate the output currents or baseline compensation signals based on a TX signal (e.g., from a TX driver). The output currents of the baseliner component310may be referred to as baseline compensation signals that are used to compensate for spurious charge or noise signals received from the capacitive touch sensor320in the capacitive touch-sensing system300(e.g., associated with transmitting of the TX signal to electrodes of the capacitive touch sensor320). In some embodiments, the baseliner component310may generate multiple baseline compensation signals to each of the sense channels of the capacitive touch-sensing system300. For example, a first output311of the baseliner component310may be coupled to a first sense channel360of the capacitive touch-sensing system and a second output312of the baseliner component310may be coupled to a second sense channel361. The first output311and the second output312of the baseliner component310may be a similar or identical signal. The baseliner component310may generate the baseline compensation signals based on a combination of the TX signal and a voltage input from a digital to analog converter (DAC) associated with the receive (RX) sense channel. Further details with regard to the architecture and circuitry of the baseliner component310are described in relation toFIGS. 4-5.

Referring toFIG. 3, the capacitive touch-sensing system300may include a capacitive touch sensor320that may correspond to the sense array220ofFIG. 2. The capacitive touch sensor320may be coupled to the sensing system through a multiplexor330. For example, the capacitive touch sensor320may be coupled to the multiplexor330that may receive RX signals from the capacitive touch sensor320and may transmit TX signals to the capacitive touch sensor320. The RX signals from the capacitive touch sensor320may be received by the multiplexor330which may transmit the RX signals to corresponding sense channels of the capacitive touch-sensing system300. For example, a first RX signal321may be transmitted to the first sense channel360and a second RX signal322may be transmitted to the second sense channel361.

The sense channels of the capacitive touch-sensing system300may perform a charge conversion function based on the RX signals that are received from the capacitive touch sensor320. In some embodiments, each of the sense channels may receive a first input corresponding to a current (e.g., a corresponding RX signal) based on the capacitive touch sensor320and a second input corresponding to a reference input signal. A sense channel may include an integrator component that receives the first input corresponding to the RX signal and the second input corresponding to the reference input signal and may collect or accumulate a charge from the capacitive touch sensor320after excitation represented by the RX signal. The accumulated charge may be represented by a voltage on the output of the integrator and may be converted to a digital signal by an analog to digital converter (ADC). In some embodiments, the ADC of the sense channel may perform the conversion from the analog signal to the digital signal by comparing the accumulated charge of the integrator with the reference input signal. The digital representation of the accumulated charge may then be transmitted to a microcontroller.

As shown inFIG. 3, the capacitive touch-sensing system300may further include TX drivers340that may provide the TX signals to the capacitive touch sensor320via the multiplexor330. In some embodiments, the TX drivers340may transmit TX signals based on TX control logic345. The TX control logic345may control the TX drivers340to generate the TX signals for drive alternation of excitation voltages across the electrodes of the capacitive touch sensor320. In some embodiments, the TX control logic345may be synchronized by a clock signal that may correspond to a capacitive touch-sensing system300clock signal. In the same or alternative embodiments, the excitation of the electrodes of the capacitive touch sensor320(e.g., by the TX signals) may be directly applied to the electrodes when operating in a mutual capacitance sensing mode or through an RX digital to analog converter (DAC), also referred to as an RxDAC350) to inputs of the sense channels (e.g., the reference input signal) when operating in a self-capacitance measuring mode. Furthermore, when operating in the mutual capacitance measuring mode, the Rx DAC350may generate a constant voltage corresponding to the midpoint of the supply voltage used by the capacitive touch-sensing system300.

In some embodiments, the TX signal received by the baseliner component310(e.g., via the TX control logic345) may have the same frequency, shape, and amplitude of the TX signals transmitted from the TX drivers340to the capacitive touch sensor320. The TX signal received by the baseliner component310may be received each time that one of the TX drivers340transmits another TX signal to the capacitive touch sensor320. Thus, the TX signal received by the baseliner component310may be received each time that the TX drivers340transmits another TX signal to the capacitive touch sensor320. For example, the TX signal from the TX drivers340may be transmitted to electrode of the capacitive touch sensor320in a sequential manner in time according to a scanning procedure and the TX signal may further be transmitted to the baseliner component310each time that a TX signal is transmitted from the TX drivers to the electrodes of the capacitive touch sensor320.

As such, the capacitive touch-sensing system300may include a baseliner component310that may generate baseline compensation signals. The sense channels of the capacitive touch-sensing system300may receive an input signal based on the RX signals of the capacitive touch sensor320of the capacitive touch-sensing system300. The sense channels may further receive a reference input signal that may be used when converting the analog signal corresponding to the accumulated charge at an integrator to a digital value. The baseline compensation signals may be combined with the RX signals based on a capacitive circuit that generates an output based on a TX signal and the reference input signal.

FIG. 4is a block diagram of an example architecture of a baseliner component400. In general, the baseliner component400may correspond to the baseliner component120ofFIGS. 1 and 2or the baseliner component310ofFIG. 3.

As shown inFIG. 4, the architecture of the baseliner component400may include a buffer420, a sensor model430(also referred to as a capacitive circuit), and a current conveyor440. The baseliner component400may receive a TX input signal410that is received by the buffer420. The output of the buffer420(e.g., the TX input signal410) may be coupled to the sensor model430. In some embodiments, the sensor model430may include one or more capacitive circuits or capacitors that may be used to approximate a current that is detected or generated by the capacitive circuits in response to the TX input signal410. The output signal435of the sensor model430may be coupled to an input of the current conveyor440. For example, the output signal435of the sensor model430may be received by an X input of the current conveyor440.

The current conveyor440(also referred to as a current to current convertor) may receive the output signal435of the sensor model430as a first input (e.g., an X input) and a second input (e.g., a Y input) corresponding to the reference voltage input signal437that is generated from an DAC based on a TX control signal as described with relation to the RxDAC350. The current conveyor440may then generate multiple output signals (i.e., baseline compensation signals) for each sense channel. For example, the current conveyor440may generate multiple baseline compensation signals450and451to different sense channels. The X input of the current conveyor440may be associated with a zero impedance current and the Y input may be associated with a convertor operation point. The voltages corresponding to the X and Y inputs may be similar. In some embodiments, the current conveyor may be a second generation current conveyor (CCII) that may provide an output (e.g., the output signals or baseline compensation signals) from the output of the sensor model430. Further details with regard to the sensor model430and the current conveyor440are described in relation toFIGS. 5 and 6.

FIG. 5is a block diagram of an example circuit of a baseliner component500. In general, the baseliner component500may correspond to the baseliner component120ofFIGS. 1 and 2, the baseliner component310ofFIG. 3, or the baseliner component400ofFIG. 4.

As shown inFIG. 5, the baseliner component500may include a sensor model or capacitive circuit510that may correspond to the sensor model430. The sensor model or capacitive circuit510may include a first capacitor511corresponding to a capacitor used for a mutual capacitance measuring mode and a second capacitor512corresponding to another capacitor that is used for a self-capacitance measuring mode.

The baseliner component500may further include a current conveyor520that may correspond to the current conveyor440. As shown, the current conveyor520may include a differential amplifier521and current mirrors522. The differential amplifier521may receive the output of the sensor model or capacitive circuit510and a reference input signal530and may generate an output current that is received by the current mirrors522. In some embodiments, the differential amplifier521may amplify the difference between two input voltages. Thus, the differential amplifier521may amplify the voltage difference between the first input to the current conveyor that corresponds to a voltage corresponding to an output of the sensor model or capacitive circuit and the second input to the current conveyor that corresponds to an output of a DAC that corresponds to a reference input signal. Furthermore, each of the current mirrors522may receive the output of the differential amplifier521and may copy or reproduce (i.e., split) the output current from the differential amplifier521to generate a mirrored output current (or mirrored current output). Furthermore, in some embodiments, the output current from the current mirrors522may be modified. For example, a gain factor (i.e., a scaling) may be applied to the output currents from the current mirrors522to increase the amplitude or magnitude of the output currents relative to the output of the differential amplifier521. In some embodiments, the gain factor may be applied based on a gain component. Thus, the current mirrors522may receive the output signal of the differential amplifier521and may reproduce the output signal and/or may reproduce the output signal and apply a gain factor to the output signal. Each of the current mirrors522may further be coupled to a sense channel of a capacitive sense array.

Thus, the baseliner component may include a capacitive circuit or sensor model and a current conveyor. A differential amplifier of the current conveyor may generate an output signal based on a difference between the output of the capacitive circuit and a reference input signal. Current mirrors of the current conveyor may reproduce or copy the output signal of the differential amplifier and each current mirror may provide an output signal to a different sense channel. The output signals of each of the current mirrors may be referred to as the baseline compensation signal that is received by each of the sense channels of the capacitive sense array. Furthermore, the current conveyor may receive a gain control input signal. Each of the current mirrors may apply a gain factor to the output of the differential amplifier based on the gain control input. In some embodiments, the current mirror may correspond to an inverting current amplifier that may reverse a current direction. In some embodiments, the current conveyor may correspond to an operational amplifier with a feedback where the X input with the feedback loop corresponds to approximately a zero impedance.

FIG. 6illustrates an example method600to provide a baseline compensation signal. The method600may be performed by processing logic that may include hardware (circuitry, dedicated logic, etc.), software (such as is run on a general purpose computing system or a dedicated machine), firmware (embedded software), or any combination thereof. In general, the baseliner component120,310,400, or500ofFIGS. 1-5may perform the method600.

As shown inFIG. 6, the method600may begin with the processing logic receiving a first signal from a sensor model that corresponds to a capacitive circuit (block610). The first signal may be received by a current conveyor or a differential amplifier of the current conveyor. In some embodiments, the first signal may be based on a TX signal as previously described. The processing logic may further receive a second signal from a digital to analog converter (block620). For example, the second signal may be received by the differential amplifier of the current conveyor from the Rx DAC as previously described. In some embodiments, the second signal may be a reference input signal (e.g., a voltage reference signal from a voltage source) that is further received by sense channels of the capacitive sense array. The processing logic may subsequently generate an output signal based on the first signal and the second signal (block630). For example, the differential amplifier of the current conveyor may generate an output signal based on a difference between the first signal and the second signal. Subsequently, a gain factor may be applied to the output signal to generate a modified output signal (block640). For example, a gain factor input signal may be received by the current conveyor and the power or amplitude of the output signal may be increased or modified based on the gain factor to generate the modified output signal. Subsequently, the processing logic may reproduce or copy the modified output signal (block650). For example, current mirrors of the current conveyor may receive the modified output signal and may reproduce or copy the modified output signal. In some embodiments, the number of current mirrors may correspond to or equal the number of sense channels of the capacitive sense array. Furthermore, the processing logic may provide the mirrored outputs to the sense channels of the capacitive sense array (block660). For example, each sense channel may receive one output from one of the current mirrors where each current mirror provides its output to one of the sense channels.

FIG. 7illustrates an example timing diagram700of signals associated with the capacitive sense array in a mutual capacitance measuring mode. The timing diagram700may correspond to an output signal of a baseliner component120,310,400, or500ofFIGS. 1-5.

As shown inFIG. 7, the timing diagram700illustrates the baseline compensation signal730(e.g., Ibl), the input to a sense channel720(e.g., Irx) that is received through the capacitive touch sensor, and the TX signal that is transmitted to a capacitive touch sensor and/or the sensor model or capacitive circuit (e.g., a TX signal). In operation, an output voltage of the Rx DAC that is received by the current conveyor may be constant. The TX drivers of the capacitive sense array may alternate a voltage on the sensor model of the baseliner component as well as the electrodes of the capacitive touch sensor. The alternation of the voltage on the sensor model and the sensor electrodes may lead to a mutual capacitance of the sensor and the sensor model recharging. The capacitive recharging may result in the generation of a current in a sense channel as well as the current conveyor of the baseliner component (e.g., the output of the sensor model). The current conveyor may repeat the direction of the received current and the output of the current mirrors of the current conveyor may be the opposite to the current that is received in the sense channel.

FIG. 8illustrates an example timing diagram800of signals associated with the capacitive sense array in a self-capacitance measuring mode. The timing diagram800may correspond to an output signal of a baseliner component120,310,400, or500ofFIGS. 1-5.

As shown inFIG. 8, the timing diagram800illustrates the baseline compensation signal830(e.g., Ibl), the input to a sense channel820(e.g., Irx), and a reference signal810(e.g., Uref) that is received by both the baseliner component (e.g., the Y input of the current conveyor) as well as a sense channel as a reference input signal. In some embodiments, the TX signal as illustrated inFIG. 7may be set to zero in the self-capacitance measuring mode. The Rx DAC may swing the reference signal810in a reference range. The swinging or changing of the reference signal810may be controlled by a TX control signal corresponding to the TX drivers of the capacitive sense array. The reference signal810may be repeated on the X input of the current conveyor and may lead to the recharging of the capacitive touch sensor of the capacitive sense array and the sensor model.

Correlation of Components of a Capacitive Touch Sensing System to Reduce Noise

Aspects of the present disclosure may further correlate components of a capacitive touch sensing system. For example, a first signal from a first component may be correlated with a second signal from a second component. As an example, a baseline compensation signal may be provided with digitally controlled current sources. However, the use of the current sources may result in a variation in the current source that may contribute to noise or a spurious signal in the capacitive sense array. The introduction of the noise or spurious signal may reduce the sensitivity of the capacitive sense array for touch detection. Aspects of the present disclosure may establish a correlation between components of a capacitive touch sensing system to reduce the noise impact of the variation of the current source.

FIG. 9is a block diagram of a capacitive touch sensing system900with a correlation implementation.

As shown inFIG. 9, the capacitive touch sensing system900may include a sense channel that includes an integrator component942and an analog to digital converter (ADC)943. The sense channel of the capacitive touch sensing system900may correspond to the operations of the sense channel360. A first input to the sense channel may be received from a current source (ISRC) component910via a multiplexor944(or switch) that is controlled by a pulse width control signal. For example, the ISRC component910may include two outputs for each sense channel of the capacitive sense array. For a sense channel, a first output (e.g., In) and a second output (e.g., Ip) may be coupled to the multiplexor944so that one of the output currents of the ISRC component910are applied to the input of the integrator component942of the sense channel. In some embodiments, the integrator component942may be based on an operational amplifier. A measured charge may be represented from a voltage in the integration capacitor (e.g., Cint) associated with the integrator component942. Furthermore, the output of the integrator component942may be coupled to the ADC943that may convert the output into digital form as previously described. In the same or alternative embodiments, the time in which each of the first input and the second input are applied to the input of the integrator component942are determined by the pulse width control signal of the multiplexor944. The use of the pulse width control signal in combination with the current source component910may provide a baseline compensation signal to the sense channel to reduce noise or spurious signals that may be received by the sense channel.

However, the current source component910that is used with the pulse width control signal may introduce noise into the sense channel. A correlation between the ISRC component910and a digital to analog converter (e.g., UDAC) used to generate a reference input signal to the sense channel may be implemented to reduce the impact of the noise that is introduced in to the sense channel from the ISRC component910.

As shown inFIG. 9, the reference voltage source of the UDAC component940is coupled to a current to voltage (I/U) convertor component930. The I/U convertor component930may be coupled to the ISRC component910via a signal path920. For example, an input of the I/U convertor component940may be coupled to an output of the ISRC component910. Thus, the I/U convertor component940may be considered to be sourced by a current from the ISRC component910via the signal path920. The current that is used to source the I/U converter component940may be the same current that is used to input signal to the sense channel (e.g., via multiplexor or switch944). In some embodiments, the I/U convertor component930may further include a digitally controlled gain component to generate a voltage on the output of the I/U convertor component930which may be approximate to the value of a reference voltage used by a sense channel. Thus, the UDAC component940that generates the reference signal for the sense channel is sourced by the same current from the ISRC component910that generates the current for the input signal of the same sense channel. As such, any variation introduced by the ISRC component910may be correlated or introduced to the output of the UDAC component940.

FIG. 10is a block diagram of an architecture1000associated with correlating signals of the capacitive touch sensing system. In general, the architecture1000may include a UDAC component1030that may correspond to the UDAC component940ofFIG. 9, an I/U convertor component1020that may correspond to the I/U convertor component930ofFIG. 9, and an ISRC component1010that may correspond to the ISRC component910ofFIG. 9.

As shown inFIG. 10, the architecture1000may include an ISRC component1010, an I/U convertor component1020, and a UDAC component1030. The ISRC component1010may receive an input reference current source1011and provide multiple output currents. The ISRC component1010may include a current to current convertor (IDAC) component1002that is digitally controlled via a control signal1005. The IDAC component1002may include current mirrors that may scale (e.g., apply a gain factor to) the input current from the input reference current source1011based on the control signal1005. Furthermore, as shown, the current mirrors of the IDAC component1002may be coupled to a set of switches that may be operated based on the control signal1005. Thus, the output current of the IDAC component1002may be based on the switches that are controlled by the control signal1005. The output current may be distributed to current mirrors of the ISRC component1010. For example, the output current from the IDAC component1002may be distributed to sense channels by a first set of current mirrors1007(e.g., n-current mirrors) where one of the first set of current mirrors are used to distribute the output current of the IDAC component1002to a second set of current mirrors1008(e.g., p-current mirrors) where the second set of current mirrors may distribute the output current of the IDAC component1002in a reverse direction (relative to the n-current mirrors) to the sense channels. In some embodiments, the second set of current mirrors (e.g., the p-current mirrors) may include an additional current mirror1003that generates the input current for the I/U convertor component1020.

As shown inFIG. 10, the I/U convertor component1020may include a series of resistors1022and a multiplexor (or switch)1023. The multiplexor1023may receive the output current of the ISRC component1010(e.g., from the current mirror1003) and may couple the received output current to the series of resistors1022based on a gain control signal1021. For example, the gain control signal1021may determine whether to couple the input of the I/U convertor component1020to a first number of resistors of the series of resistors1022or a second number of resistors of the series of resistors1022. The output of the I/U convertor component1020may be coupled to a non-inverting amplifier of the UDAC component1030. For example, the output of the I/U convertor component1020may be a reference voltage signal that is received by the positive terminal of a non-inverting amplifier of the UDAC component1030. The output of the non-inverting amplifier may be coupled to another series of resistors which is coupled to a first multiplexor and a second multiplexor that are each controlled by a UDAC control signal.

As such, the output voltage of the UDAC component1030may be correlated with the output current of the ISRC component1010. Thus, when the sense channel of a capacitive sense array receives the output current of the ISRC component1010(e.g., for an input signal), the reference signal of the same sense channel that is received from the UDAC component1030may be correlated with the output current of the ISRC component1010.

FIG. 11is a block diagram of a capacitive touch sensing system1100. In general, the capacitive touch sensing system1100may correspond to the capacitive touch sensing system900ofFIG. 9with a modified ISRC component and a modified UDAC component.

As shown inFIG. 11, the capacitive touch sensing system1100, a current generated by the ISRC component1110may be used to provide the input source to the UDAC component1140via the signal path1120. As such, the capacitive touch sensing system1100does not include an I/U convertor component as described with regard toFIGS. 9 and 10. Further details with regard to the ISRC component1110and the UDAC component1140are described in relation toFIG. 12.

FIG. 12is a block diagram of components associated with another implementation for correlation of the capacitive touch sensing system in accordance with some embodiments.

FIG. 12is a block diagram of an architecture1200associated with correlating signals of a capacitive touch sensing system. In general, the architecture of the capacitive touch sensing system1100may include a UDAC component1230that may correspond to the UDAC component1130ofFIG. 11and an ISRC component1210that may correspond to the ISRC component1110ofFIG. 11.

As shown inFIG. 12, the ISRC component1210may include the IDAC component with an additional current mirror1215that is used to generate a current based on the input reference current source. In some embodiments, the additional current mirror1215may repeat or copy (e.g., mirror) the current from the input reference current source. In the same or alternative embodiments, the additional current mirror1215may correspond to the current mirror with the greatest weight of the current mirrors of the IDAC component. The output current1220of the additional current mirror1215may be coupled to the UDAC component1230. For example, the series of resistors of the UDAC component1230may directly receive the output current1220from the additional current mirror1215of the IDAC component of the IRSC component1210.

In the description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be evident, however, to one skilled in the art that the present disclosure may be practiced without these specific details. In other instances, well-known circuits, structures, and techniques are not shown in detail, but rather in a block diagram in order to avoid unnecessarily obscuring an understanding of this description.

Reference in the description to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. The phrase “in one embodiment” located in various places in this description does not necessarily refer to the same embodiment.

For simplicity of explanation, the above methods are depicted and described as a series of acts. Although the operations of the methods herein are shown and described in a particular order, such order does not mean that such operations are necessarily performed in that order. Operations in accordance with this disclosure can occur in various orders and/or concurrently, and with other acts not presented and described herein. Certain operations may be performed, at least in part, concurrently with other operations and certain operations may be performed in an inverse order to that shown or described.

The methods described above regarding capacitance to code conversion can be implemented by the baseliner component120, which may be implemented in a capacitive touch screen controller. In one embodiment, the capacitive touch screen controller is the TrueTouch® capacitive touchscreen controller, such as the CY8CTMA3xx family of TrueTouch® Multi-Touch All-Points touchscreen controllers, developed by Cypress Semiconductor Corporation of San Jose, Calif. The TrueTouch® capacitive touchscreen controllers sensing technology to resolve touch locations of multiple fingers and a stylus on the touch-screens, supports operating systems, and is optimized for low-power multi-touch gesture and all-point touchscreen functionality. Alternatively, the touch position calculation features may be implemented in other touchscreen controllers, or other touch controllers of touch-sensing devices. In one embodiment, the touch position calculation features may be implemented with other touch filtering algorithms as would be appreciated by one of ordinary skill in the art having the benefit of this disclosure.

The embodiments described herein may be used in various designs of mutual-capacitance sensing arrays of the capacitance sensing system, or in self-capacitance sensing arrays. In one embodiment, the capacitance sensing system detects multiple sense elements that are activated in the array, and can analyze a signal pattern on the neighboring sense elements to separate noise from actual signal. The embodiments described herein are not tied to a particular capacitive sensing solution and can be used as well with other sensing solutions, including optical sensing solutions, as would be appreciated by one of ordinary skill in the art having the benefit of this disclosure.

It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the above discussion, it is appreciated that throughout the description, discussions utilizing terms such as “integrating,” “comparing,” “balancing,” “measuring,” “performing,” “accumulating,” “controlling,” “converting,” “accumulating,” “sampling,” “storing,” “coupling,” “varying,” “buffering,” “applying,” or the like, refer to the actions and processes of a computing system, or similar electronic computing device, that manipulates and transforms data represented as physical (e.g., electronic) quantities within the computing system's registers and memories into other data similarly represented as physical quantities within the computing system memories or registers or other such information storage, transmission or display devices.

Embodiments described herein may also relate to an apparatus for performing the operations herein. This apparatus may be specially constructed for the required purposes, or it may comprise a general-purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a non-transitory computer-readable storage medium, such as, but not limited to, any type of disk including floppy disks, optical disks, CD-ROMs and magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, flash memory, or any type of media suitable for storing electronic instructions. The term “computer-readable storage medium” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database and/or associated caches and servers) that store one or more sets of instructions. The term “computer-readable medium” shall also be taken to include any medium that is capable of storing, encoding or carrying a set of instructions for execution by the machine and that causes the machine to perform any one or more of the methodologies of the present embodiments. The term “computer-readable storage medium” shall accordingly be taken to include, but not be limited to, solid-state memories, optical media, magnetic media, any medium that is capable of storing a set of instructions for execution by the machine and that causes the machine to perform any one or more of the methodologies of the present embodiments.