Source: https://patents.google.com/patent/US9176633B2/en
Timestamp: 2019-04-23 11:17:09+00:00

Document:
A processing system configured to sense an input object in a sensing region of a sensing device including a transmitter module coupled to a first transmitter electrode and a second transmitter electrode and configured to simultaneously apply a first transmitter signal to the first transmitter electrode and a second transmitter signal to the second transmitter electrode, wherein the first transmitter signal is based on a first one of a plurality of distinct codes and the second transmitter signal is based on a second one of the plurality of distinct codes. The processing system also includes a receiver module including receiver circuitry coupled to a first receiver electrode and configured to receive a first resulting signal with the first receiver electrode, the first resulting signal comprising effects corresponding to the first and second transmitter signals and a noise component. The processing system is configured to determine an estimate of the noise component using a third one of the plurality of distinct codes which is not associated with a transmitter signal.
This invention generally relates to sensor devices using code division multiplexed (CDM) signaling, and more specifically relates to simultaneously measuring interference and touch sensing in hardware.
Presently known capacitive sensing devices temporarily suspend the application of drive signals onto transmitter electrodes in order to estimate system noise. However, suppressing drive signals can degrade device performance. This can limit the flexibility and usability of the sensor device, and negatively impact the user experience. Thus, there exists a need for capacitive sensing devices that overcome these shortcomings.
The embodiments of the present invention provide a device and method that facilitates improved device usability. Specifically, the device and method provide improved user interface functionality by measuring and estimating a noise component using a dedicated noise descrambler.
In various embodiments, a capacitive input sensor includes a processing system configured to sense an input object in a sensing region, the processing system drive circuitry coupled to a first transmitter electrode and a second transmitter electrode and configured to simultaneously apply a first transmitter signal to the first transmitter electrode and a second transmitter signal to the second transmitter electrode, wherein the first transmitter signal is based on a first one of a plurality of distinct codes and the second transmitter signal is based on a second one of the plurality of distinct codes. The processing system also includes a receiver module including receiver circuitry coupled to a first receiver electrode and configured to receive a first resulting signal with the first receiver electrode, the first resulting signal including effects (e.g., electrical effects) corresponding to the first and second transmitter signals and a noise component. The processing system is configured to determine an estimate of the noise component using a third one of the plurality of distinct codes which is not associated with a transmitter signal.
By configuring the processing system in this way, the input device and method can determine an up to date noise estimate and adjust operational parameters accordingly, thereby minimizing unnecessary performance degradation. Thus, the sensor device provides increased user interface flexibility.
FIG. 6 is a flow diagram of an exemplary method for estimating noise in a capacitive sensor environment in accordance with various embodiments.
According to various exemplary embodiments, spread spectrum techniques can be used in an input device such as a touchpad to improve noise immunity and/or to provide performance enhancements. Code division multiplexing (CDM), for example, can be used to create two or more distinct transmitterion signals that are applied to sensing electrode(s) within the sensor. The effect of noise on multiple signal channels may be more uniform so that a minimum signal-to-noise ratio (SNR) is maintained for each useful signal channel. This concept can be exploited even further by selecting digital codes to produce frequency-domain signals that avoid known sources of noise. Spread spectrum techniques can therefore apply increased power to the sensing region while reducing the effects of noise, thereby resulting in a significantly improved SNR for the sensor in comparison to conventional time-domain multiplexing techniques of a comparable sample period. Spread spectrum techniques applied within the sensor may enable other beneficial sensor designs and features as well.
In FIG. 1, a processing system 110 is shown as part of the input device 100. The processing system 110 is configured to operate the hardware of the input device 100 to detect input in the sensing region 120. The processing system 110 comprises parts of or all of one or more integrated circuits (ICs) and/or other circuitry components. For example, a processing system for a mutual capacitance sensor device may comprise transmitter circuitry configured to transmit signals with transmitter sensor electrodes, and/or receiver circuitry configured to receive signals with receiver sensor electrodes). In some embodiments, the processing system 110 also comprises electronically-readable instructions, such as firmware code, software code, and/or the like. In some embodiments, components composing the processing system 110 are located together, such as near sensing element(s) of the input device 100. In other embodiments, components of processing system 110 are physically separate with one or more components close to sensing element(s) of input device 100, and one or more components elsewhere. For example, the input device 100 may be a peripheral coupled to a desktop computer, and the processing system 110 may comprise software configured to run on a central processing unit of the desktop computer and one or more ICs (perhaps with associated firmware) separate from the central processing unit. As another example, the input device 100 may be physically integrated in a phone, and the processing system 110 may comprise circuits and firmware that are part of a main processing system of the phone. In some embodiments, the processing system 110 is dedicated to implementing the input device 100. In other embodiments, the processing system 110 also performs other functions, such as operating display screens, driving haptic actuators, etc.
It should be understood that while many embodiments of the invention are described in the context of a fully functioning apparatus, the mechanisms of the present invention are capable of being distributed as a program product (e.g., software) in a variety of forms. For example, the mechanisms of the present invention may be implemented and distributed as a software program on information bearing media that are readable by electronic processing systems (e.g., non-transitory computer-readable and/or recordable/writable information bearing media readable by the processing system 110). Additionally, the embodiments of the present invention apply equally regardless of the particular type of medium used to carry out the distribution. Examples of non-transitory, electronically readable media include various discs, memory sticks, memory cards, memory modules, and the like. Electronically readable media may be based on flash, optical, magnetic, holographic, or any other storage technology.
FIG. 2 shows a portion of an example sensor electrode pattern configured to sense objects in a sensing region associated with the pattern, according to some embodiments. For clarity of illustration and description, FIG. 2 shows a pattern (e.g., an array) 200 of represented schematically as rectangles. This sensor electrode pattern comprises a plurality of transmitter electrodes 220A-C and a plurality of receiver electrodes 210A-D.
Transmitter electrodes 220 and receiver electrodes 210 are typically ohmically isolated from each other. That is, one or more insulators separate the transmitter electrodes from the receiver electrodes and prevent them from electrically shorting to each other. In some embodiments, receiver electrodes 210 and transmitter electrodes 220 are separated by insulative material disposed between them at cross-over areas; in such constructions, the electrode junctions (or pixels) may be formed with jumpers connecting different portions of the same electrode. In some embodiments, the transmitter and receiver electrodes are separated by one or more layers of insulative material. In some other embodiments, the transmitter and receiver electrodes are separated by one or more substrates; for example, they may be disposed on opposite sides of the same substrate, or on different substrates that are laminated together. Moreover, one or more of the sensor electrodes can be used for both capacitive sensing and for updating the display. Alternatively, the sensor electrodes may be implemented in a single layer design where the sensor electrodes do not overlap in the sensing region.
With continued reference to FIG. 2, the transmitter electrodes 220 extend along the “X” direction, and the receiver electrodes 210 extend along the “Y” direction. When an input object is placed at or near the surface of the sensing region, for example, at location 214 (corresponding to the intersection of electrodes 220C and 210D), the sensor electrodes in pattern 200 capacitively sense the presence of the input object.
A capacitive image may be built from data received with the receiver electrodes. As noted above, the embodiments of the invention can be implemented with a variety of different types and arrangements of capacitive sensor electrodes. For example, the electrodes for sensing may be disposed in a first direction (e.g., the “X” direction), a second direction (e.g., the “Y” direction), or in any suitable orthogonal, parallel, or hybrid configuration such as polar coordinates (e.g., “Γ” and “θ”). In these embodiments the sensor electrodes themselves are commonly arranged in a circle or other looped shape to provide “θ”, with the shapes of individual sensor electrodes used to provide “r”. In other embodiments, the sensor electrodes may be formed on the same layer, or the input device can be implemented with electrode arrays that are formed on multiple substrate layers.
Also, a variety of different sensor electrode shapes can be used, including electrodes shaped as thin lines, rectangles, diamonds, wedge, etc. Finally, a variety of conductive materials and fabrication techniques can be used to form the sensor electrodes. As one example, the sensor electrodes are formed by the deposition and etching of conductive ink on a substrate.
With reference to FIGS. 2 and 3, FIG. 3 is a schematic diagram of exemplary time multiplexed waveforms used to modulate transmitter electrodes. More particularly, a first waveform 302 is applied to a first transmitter TX0 (analogous to transmitter 220A) in a first time period 308, a second waveform 304 is applied to a second transmitter TX1 (analogous to transmitter 220B) in a second time period 310, and a third waveform 306 is applied to a third transmitter TX2 (analogous to transmitter 220C) in a third time period 308. By driving only a single transmitter during a particular time period, the resulting signals on the receiver electrodes may be processed to determine the location (e.g., the X and Y coordinates) of an input object in the sensing region may be determined.
Those skilled in the art will appreciate that as the signal to noise ratio (SNR) of the resulting signals decreases due to increased system noise, errors can occur in detecting input objects. To compensate for the increased noise and reduce the likelihood of errors, various operating parameters may be adjusted in the presence of noise, such as decreasing the frame rate (which corresponds to increasing the length of a data sampling window). While this can reduce detection errors, it can also degrade device performance and negatively affect the quality of the user experience. Thus, it is desired to adjust system operating parameters only as and when necessary to compensate for high noise conditions. Accordingly, it is desirable to provide an up to date estimate of system noise.
One technique for estimating noise involves measuring resulting signals while suppressing drive signals. However, this technique can be error prone inasmuch as input objects can go undetected while drive signals are suppressed. In accordance with various embodiments, systems and methods are provided for estimating noise while simultaneously applying drive signals to transmitter electrodes and processing resulting signals received at receiver electrodes.
FIG. 4 is a schematic view of exemplary waveforms simultaneously applied to transmitter electrodes. More particularly, the processing system may be configured to simultaneously apply a first waveform 402 to a first transmitter TX0, a second waveform 404 to a second transmitter TX1, and a third waveform 406 to a third transmitter TX2.
The processing system may be configured to produce digital codes that can be used in generating the transmitter signals 402-406. The number, size and types of digital codes produced may vary significantly, but in various embodiments the codes may be strictly or substantially orthogonal to each other, and may be of sufficient length to apply a unique digital code to each transmitter electrode in the sensing region. Alternatively, the codes may be of sufficient length to apply a unique digital code to each of a subset of transmitter electrodes which are simultaneously driven.
The discrete codes may be binary, ternary, or generically multi-level, and may indicate both driven and un-driven states (tri-state). Various circuits, modules and techniques for generating digital codes based on pseudo-random codes, Hadamard codes, Walsh-Hadamard codes, m-sequences, Gold codes, Kasami codes, Barker codes, delay line multiple tap sequences, and/or the like. Alternatively, digital codes may be pre-determined and stored in a lookup table or other data structure associated with the processing system. Moreover, although FIG. 4 illustrates codes in the form of square waves, other modulation techniques (e.g., sine waves) are also contemplated by the present disclosure.
The term “substantially orthogonal” in the context of the distinct digital codes is intended to convey that the distinct codes need not be perfectly orthogonal from each other in the mathematical sense, so long as the distinct codes are able to produce meaningful independent results. Strict orthogonality may thus be traded off for various other properties such as correlation, spectra, or compressibility. Similarly, the term “sensing zone” is intended to convey that a single code could be applied to multiple transmitter electrodes to create a single zone of sensitivity that encompasses a larger portion of the sensing region than any of the individual transmitter electrodes. Also, more than one code could be applied to an electrode creating overlapping or spatially filtered “sensing zones”. For example phase delayed or “shifted” versions of the same code sequence can be distinct and substantially orthogonal such that they are readily distinguishable. In various cases, interpolation between phase shifts may even be possible.
FIG. 5 is a schematic block diagram of an exemplary receiver module 500 including receiver electrodes 504 and 508, and receiver circuitry comprising a plurality of descrambler modules corresponding to a plurality of transmitter signals, plus an additional descrambler module for noise estimation in accordance with various embodiments. More particularly, the receiver circuitry includes an integrator 515, a feedback capacitor 514, and a sampling module 516. In capacitive sensing devices, a change in measured capacitance is referred to as “delta C”. In the context of FIG. 5, the change in measured capacitance for a particular one of N transmitters is referred to as delta CTN, where N represents the number of transmitters processed by the receiver circuitry. That is, each one of M receiver electrodes has an associated receiver circuit, and each receiver circuit is configured to simultaneously measure the delta CT for each transmitter by multiplying the integrator output 517 by a unique sequence for each transmitter. As described in greater detail below, an estimate of the noise may be obtained by multiplying the integrator output 517 by a sequence 540 that is orthogonal to all of the distinct codes used to generate the transmitted waveforms. Estimating the noise in this manner (e.g., using hardware) simplifies the associated firmware and improves overall device performance.
More particularly and with continued reference to FIG. 5, a first transmitter signal 502 and a second transmitter signal 506 are simultaneously applied to a first transmitter electrode 504 and a second transmitter electrode 508, respectively. A first measured capacitance 510 embodies effects corresponding to the first transmitter signal 502, and a second capacitance 512 embodies effects corresponding to the second transmitter signal 506. The resulting signal 511 (corresponding to the combined delta CTN for N transmitters) is applied to the integrator 515, and the integrator output 519 is sampled by the continuous-to-discrete module 516. The sampled output 517 is applied to (N+1) descrambler circuits, corresponding to N descramblers for each of N transmitted signals, plus one (or more) additional descrambler(s) dedicated to noise estimation.
In the illustrated embodiment, the sampled integrator output 517 is multiplied by a unique sequence for each transmitter. In particular, output 517 is simultaneously applied to a first descrambler circuit 520 corresponding to the first transmitter signal 502, a second descrambler circuit 522 corresponding to the second transmitter signal 506, a noise descrambler circuit 524. In the illustrated embodiment, each descrambler circuit (sometimes referred to as a correlator or matched filter) may include a multiplier 532 and a summer 534. The summer may be implemented in any suitable manner, such as using an analog integrator or a digital accumulator. A first unique sequence 536 is applied to the multiplier associated with the first descrambler module 520 resulting in output 526 representing the variable capacitance due to the first transmitter signal 502 on the first transmitter 504. Similarly, a second unique sequence 538 is applied to the multiplier associated with the second descrambler module 522 resulting in output 528 representing the variable capacitance due to the second transmitter signal 506 on the second transmitter 508. Finally, a unique sequence 540 is applied to the multiplier associated with the noise descrambler module 524 resulting in output 530 representing the estimated system noise (also referred to herein as the interference component).
FIG. 6 is a flow diagram of an exemplary method for estimating noise in a capacitive sensor environment in accordance with various embodiments. More particularly, a method 600 for capacitive sensing includes simultaneously applying a first transmitter signal to a first transmitter electrode (Task 602) and a second transmitter signal to a second transmitter electrode (Task 604), wherein the first transmitter signal is based on a first one of a plurality of distinct digital codes and the second transmitter signal is based on a second one of the plurality of distinct digital codes. The method 600 further involves receiving resulting signals with a plurality of receiver electrodes (Task 606), wherein each resulting signal comprises effects corresponding to the first and second transmitter signals and an interference component. The method 600 further involves determining an estimate of the interference component using a third one of the plurality of distinct digital codes. More particularly, the method 600 involves multiplying the resulting signal (Task 608) by a unique digital code sequence for each of N transmitted signals to reveal the respective transmitted signals. Finally, the method 600 involves multiplying the resulting signal (Task 610) by an (N+1) digital code sequence orthogonal to the N digital codes to reveal the noise estimate.
wherein the processing system is configured to determine an estimate of the noise component using a third one of the plurality of distinct codes which is not associated with (or does not correspond to) a transmitter signal.
In an embodiment, the first, second, and third digital codes are mutually orthogonal digital codes.
In an embodiment, the processing system is further configured to demodulate the resulting signal using the first and second digital codes to determine indicia of the first and second transmitter signals, respectively.
In an embodiment, the processing system is further configured to demodulate the resulting signal to determine positional information for the input object based on the resulting signal.
In an embodiment, the processing system is further configured to compare the noise estimate to a predetermined threshold value.
In an embodiment, the processing system is further configured to select an operating mode based on whether the noise estimate exceeds the threshold value.
In an embodiment, selecting the operating mode may include adjusting a frame rate at which the input object is sensed in the sensing region.
In an embodiment, the receiver circuitry may include: a first descrambler circuit for determining the indicia of the first transmitter signal; a second descrambler circuit for determining the indicia of the second transmitter signal; a third descrambler circuit for determining a first attribute of the noise component; and a fourth descrambler circuit for determining a second attribute of the noise component, wherein the first attribute may correspond to a value of an estimated noise component, and the second attribute may correspond to a harmonic associated with the estimated noise component.
In an embodiment, the receiver circuitry may also include: a first multiplier circuit for applying the first digital code to the first descrambler circuit; a second multiplier circuit for applying the second digital code to the second descrambler circuit; and a third multiplier circuit for applying the third digital code to the third descrambler circuit. In various embodiments the multiplier function may be implemented in a correlator circuit.
In an embodiment, the transmitter module may be coupled to N ohmically isolated transmitter electrodes and configured to apply a unique one of N transmitter signals to each transmitter electrode, wherein the N transmitter signals are distinct digital codes; the receiver module may be coupled to M ohmically isolated receiver electrodes, each configured to receive a respective resulting signal; where N and M are positive integers; and the receiver circuitry comprises (N+1) discrete descrambler circuits for each of the M receiver electrodes.
In an embodiment, the processing system is configured to determine a respective estimated noise component for each of the M receiver electrodes.
In an embodiment, the receiver module may include a second receiver electrode configured to receive a second resulting signal, and the processing system may be further configured to determine positional information for at least two input objects in the sensing region based on the first and second resulting signals.
In an embodiment, the plurality of distinct digital codes may be based on Pseudo-Random codes, Hadamard codes, Walsh-Hadamard codes, m-sequences, Gold codes, Kasami codes, Barker codes, and/or delay line multiple tap sequences.
A sensing device is provided which includes: a plurality of transmitter electrodes; a plurality of receiver electrodes; and a processing system individually coupled to each of the plurality of transmitter electrodes and the plurality of receiver electrodes, the processing system configured to: simultaneously apply a first transmitter signal to a first transmitter electrode of the plurality of transmitter electrodes and a second transmitter signal to a second transmitter electrode of the plurality of transmitter electrodes, wherein the first transmitter signal is based on a first one of a plurality of distinct digital codes and the second transmitter signal is based on a second one of the plurality of distinct digital codes; receive resulting signals with the plurality of receiver electrodes, wherein each resulting signal comprises: i) effects corresponding to the first and second transmitter signals; and ii) a noise component; and determine an estimate of the noise component for each resulting signal using a third one of the plurality of distinct digital codes.
In an embodiment, the third one of the plurality of distinct digital codes is not associated with a transmitter signal.
In an embodiment, the first, second, and third digital codes are mutually orthogonal and each is based on at least one of: Pseudo-Random codes, Walsh-Hadamard codes, m-sequences, Gold codes, Kasami codes, Barker codes, and delay line multiple tap sequences.
In an embodiment, the processing system is further configured to: demodulate the resulting signals to determine positional information for an input object based on the resulting signals; and compare the noise estimates to a predetermined threshold value, and to select an operating mode based on whether at least one of the noise estimates exceeds the threshold value.
In an embodiment, the processing system may include, for each receiver electrode, a first filter for isolating indicia of the first transmitter signal, a second filter for isolating indicia of the second transmitter signal, and a noise filter for isolating a respective noise component.
A method for capacitive sensing is also provided, the method including: simultaneously applying a first transmitter signal to a first transmitter electrode and a second transmitter signal to a second transmitter electrode, wherein the first transmitter signal is based on a first one of a plurality of distinct digital codes and the second transmitter signal is based on a second one of the plurality of distinct digital codes; receiving resulting signals with a plurality of receiver electrodes, wherein each resulting signal comprises effects corresponding to the first and second transmitter signals and an interference component; and determining an estimate of the interference component using a third one of the plurality of distinct digital codes.
In an embodiment, the step of determining may include multiplying the resulting signal by the third digital code using a descrambler circuit.
wherein the processing system is configured to determine an estimate of the noise component using a third one of the plurality of distinct codes which is not associated with a transmitter signal.
2. The processing system of claim 1, wherein the first, second, and third digital codes are mutually orthogonal digital codes.
3. The processing system of claim 1, wherein the processing system is further configured to demodulate the first resulting signal using the first and second digital codes to determine indicia of the first and second transmitter signals, respectively.
4. The processing system of claim 1, wherein the processing system is further configured to demodulate the resulting signal to determine positional information for the input object based on the resulting signal.
5. The processing system of claim 1, wherein the processing system is further configured to compare the noise estimate to a predetermined threshold value.
6. The processing system of claim 5, wherein the processing system is further configured to select an operating mode based on whether the noise estimate exceeds the threshold value.
7. The processing system of claim 6, wherein selecting the operating mode comprises adjusting a frame rate at which the input object is sensed in the sensing region.
a fourth descrambler circuit for determining a second attribute of the noise component.
a third multiplier circuit for applying the third digital code to the third descrambler circuit.
the receiver circuitry comprises (N+1) discrete descrambler circuits for each of the M receiver electrodes.
11. The processing system of claim 10, wherein the processing system is configured to determine a respective estimated noise component for each of the M receiver electrodes.
12. The processing system of claim 1, wherein the receiver circuitry comprises a second receiver electrode configured to receive a second resulting signal, and the processing system is further configured to determine positional information for at least two input objects in the sensing region based on the first and second resulting signals.
13. The processing system of claim 1, wherein the plurality of distinct digital codes is based on one of a group consisting of Pseudo-Random codes, Hadamard codes, Walsh-Hadamard codes, m-sequences, Gold codes, Kasami codes, Barker codes, and delay line multiple tap sequences.
determine an estimate of the noise component for each resulting signal using a third one of the plurality of distinct digital codes.
15. The sensing device of claim 14, wherein the third one of the plurality of distinct digital codes is not associated with a transmitter signal.
16. The sensing device of claim 14, wherein the first, second, and third digital codes are mutually orthogonal and based on one of a group consisting of Pseudo-Random codes, Walsh-Hadamard codes, m-sequences, Gold codes, Kasami codes, Barker codes, and delay line multiple tap sequences.
compare the noise estimates to a predetermined threshold value, and to select an operating mode based on whether at least one of the noise estimates exceeds the threshold value.
18. The sensing device of claim 14, wherein the processing system comprises, for each receiver electrode, a first filter for isolating indicia of the first transmitter signal, a second filter for isolating indicia of the second transmitter signal, and a noise filter for isolating a respective noise component.
determining an estimate of the interference component using a third one of the plurality of distinct digital codes.
multiplying the resulting signal by the third digital code using a descrambler circuit.
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