Capacitive touch sensor having code-divided and time-divided transmit waveforms
First Claim
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1. A method performed by a data processing apparatus associated with a sensor, the sensor comprising a plurality of trace lines oriented in a matrix configuration, a front end interface, a plurality of transmitters coupled with the front end interface, and a plurality of receivers, wherein respective transmitters correspond to and are coupled with a first location of respective trace lines, and respective receivers are coupled with a second location of the respective trace lines, the method comprising:
- determining orthogonal excitation waveforms having an orthogonal waveform sequence, wherein the orthogonal excitation waveforms are orthogonal to each other and define an integration period that is longer than a time constant of a feedback resistor and a feedback capacitor connected in parallel between an input of a transimpedance amplifier and an output of the transimpedance amplifier;
simultaneously transmitting, on each of at least two of the transmitters, one of the orthogonal excitation waveforms such that at least two of the transmitters are configured to transmit respective orthogonal waveform sequences for a duration equal to an integration time, wherein the transmitting occurs on less than all transmitters in the sensor, and wherein a length of the integration time is determined based on a number of transmitters simultaneously transmitting the one of the orthogonal excitation waveforms, the length of the integration time increasing as the number of transmitters simultaneously transmitting increases;
receiving at least two of the orthogonal excitation waveforms at least at two of the receivers, wherein each of the at least two orthogonal excitation waveforms are received at one of the respective receivers;
receiving information for at least an expected received waveform; and
for each of the at least two receivers, correlating the received excitation waveform against the expected received waveform.
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Abstract
Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for digital signal processing (DSP) techniques for generally improving a signal-to-noise ratio (SNR) of capacitive touch sensors.
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Citations
32 Claims
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1. A method performed by a data processing apparatus associated with a sensor, the sensor comprising a plurality of trace lines oriented in a matrix configuration, a front end interface, a plurality of transmitters coupled with the front end interface, and a plurality of receivers, wherein respective transmitters correspond to and are coupled with a first location of respective trace lines, and respective receivers are coupled with a second location of the respective trace lines, the method comprising:
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determining orthogonal excitation waveforms having an orthogonal waveform sequence, wherein the orthogonal excitation waveforms are orthogonal to each other and define an integration period that is longer than a time constant of a feedback resistor and a feedback capacitor connected in parallel between an input of a transimpedance amplifier and an output of the transimpedance amplifier; simultaneously transmitting, on each of at least two of the transmitters, one of the orthogonal excitation waveforms such that at least two of the transmitters are configured to transmit respective orthogonal waveform sequences for a duration equal to an integration time, wherein the transmitting occurs on less than all transmitters in the sensor, and wherein a length of the integration time is determined based on a number of transmitters simultaneously transmitting the one of the orthogonal excitation waveforms, the length of the integration time increasing as the number of transmitters simultaneously transmitting increases; receiving at least two of the orthogonal excitation waveforms at least at two of the receivers, wherein each of the at least two orthogonal excitation waveforms are received at one of the respective receivers; receiving information for at least an expected received waveform; and for each of the at least two receivers, correlating the received excitation waveform against the expected received waveform. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 32)
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16. A system comprising:
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a sensor, wherein the sensor comprises; a plurality of trace lines oriented in a matrix configuration, a front end interface, a front-end circuit comprising at least a two-stage circuit with a first stage comprising a first transimpedance amplifier configured to produce a transimpedance gain based on a first feedback resistor and a feedback capacitor and a second stage comprising a second transimpedance amplifier configured to produce a voltage gain based on a serially-connected resistor and a second feedback resistor, the first feedback resistor connected in parallel to the feedback capacitor and configured to provide a time constant that is less than an integration period, the serially-connected resistor connected in series to a serially-connected capacitor between the first transimpedance amplifier and the second transimpedance amplifier, the second feedback resistor connected between an input terminal and an output terminal of the second transimpedance amplifier, a plurality of transmitters coupled with the front end interface, and a plurality of receivers, wherein respective transmitters correspond to and are coupled with a first location of respective trace lines, and respective receivers are coupled with a second location of the respective trace lines, the system being configured to; determine orthogonal excitation waveforms having an orthogonal waveform sequence and wherein the orthogonal excitation waveforms are orthogonal to each other and the frequency of the orthogonal excitation waveforms define the integration period; simultaneously transmit, on each of at least two of the transmitters, one of the orthogonal excitation waveforms such that at least two of the transmitters are configured to transmit respective orthogonal waveform sequences, wherein the transmitting occurs on less than all transmitters in the sensor, the length of the integration period increasing as the number of transmitters simultaneously transmitting increases; receive at least two of the orthogonal excitation waveforms at at least two of the receivers, wherein each of the at least two orthogonal excitation waveforms are received at one of the respective receivers; receive information for at least an expected received waveform; and for each of the at least two receivers, correlate the received excitation waveform against the expected received waveform. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30)
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31. A system comprising:
a sensor, wherein the sensor comprises; a plurality of trace lines oriented in a matrix configuration, a front end interface, a plurality of transmitters coupled with the front end interface, and a plurality of receivers, wherein respective transmitters correspond to and are coupled with a first location of respective trace lines, and respective receivers are coupled with a second location of the respective trace lines, means for determining orthogonal excitation waveforms having an orthogonal waveform sequence including taking a noise spectrum associated with the sensor and taking a measurement of noise in the sensor by evaluating the noise spectrum associated with the sensor, and wherein the orthogonal excitation waveforms are orthogonal to each other and to the noise in the sensor; identifying the noise based on the evaluation of the noise spectrum; and determining the orthogonal excitation waveforms by making the orthogonal excitation waveforms orthogonal to the identified noise in the sensor; means for simultaneously transmitting, on each of at least two of the transmitters, one of the orthogonal excitation waveforms such that at least two of the transmitters are configured to transmit respective orthogonal waveform sequences for a duration equal to an integration time, wherein the transmitting occurs on less than all transmitters in the sensor, and wherein a length of the integration time is determined based on a number of transmitters simultaneously transmitting the one of the orthogonal excitation waveforms the length of the integration time increasing as the number of transmitters simultaneously transmitting increases; means for receiving at least two of the orthogonal excitation waveforms at at least two of the receivers, wherein each of the at least two orthogonal excitation waveforms are received at one of the respective receivers; means for receiving information for at least an expected received waveform; and for each of the at least two receivers, means for correlating the received excitation waveform against the expected received waveform.
Specification