Hover sensing with multi-phase self-capacitance method
A capacitance sensing device includes a transmit (TX) generator for generating a sequence of receive (RX) signals by applying each TX signal pattern in a sequence of TX signal patterns to a set of sensor electrodes. For each TX signal pattern in the sequence of TX signal patterns, and for each subset of three or more contiguous sensor electrodes of the set of sensor electrodes, the TX generator applies to the subset one of a first excitation signal and a second excitation signal. The plurality of subsets includes at least half of the sensor electrodes in the set of sensor electrodes. The capacitance sensing device also includes a sequencer circuit coupled with the TX generator. For each TX signal pattern in the sequence of TX signal patterns, the sequencer circuit determines a next subsequent TX signal pattern in the sequence based on a circular rotation of the TX signal pattern. The capacitance sensing device also includes a processing block coupled with the TX generator. The processing block detects a presence of an object proximate to the set of sensor electrodes based on a measure of correlation between the sequence of RX signals and a predetermined function.
1. A capacitance sensing device, comprising:
a transmit (TX) generator configured to generate a sequence of receive (RX) signals by applying each TX signal pattern in a sequence of TX signal patterns to a set of sensor electrodes, the set of sensor electrodes comprising all of the sensor electrodes coupled to the transmit generator, wherein for each TX signal pattern in the sequence of TX signal patterns, the TX generator is configured to apply excitation signals to the set of sensor electrodes by, for each subset of a plurality of subsets each including three or more contiguous sensor electrodes of the set of sensor electrodes, applying the same one of a first excitation signal and a second excitation signal to each of the three or more contiguous sensor electrodes in the subset, wherein a magnitude of a sum of the excitation signals applied to the set of sensor electrodes is less than a magnitude of any one of the excitation signals applied to the set of sensor electrodes, and wherein the plurality of subsets comprises at least half of the sensor electrodes in the set of sensor electrodes;
a sequencer circuit coupled with the TX generator and configured to, for each TX signal pattern in the sequence of TX signal patterns, determine a next subsequent TX signal pattern in the sequence based on a circular rotation of the TX signal pattern; and
a processing block coupled with the TX generator and configured to detect a presence of an object proximate to the set of sensor electrodes based on a measure of correlation between the sequence of RX signals and a predetermined function.
2. The capacitance sensing device of claim 1 , wherein for each TX signal pattern in the sequence of TX signal patterns, for each sensor electrode in the set of sensor electrodes, an excitation signal applied to the sensor electrode corresponds to an excitation signal applied to a preceding sensor electrode in a circular sequence of the set of sensor electrodes during application of a preceding TX signal pattern in the sequence of TX signal patterns.
3. The capacitance sensing device of claim 1 , wherein
the second excitation signal is complementary to the first excitation signal; and
the sum of excitation signals includes, for each sensor electrode in the set of sensor electrodes, an excitation signal applied to the sensor electrode.
4. The capacitance sensing device of claim 1 , wherein the TX generator is further configured to, for each TX signal pattern in the sequence of TX signal patterns:
apply the first excitation signal to contiguous sensor electrodes that are contiguous in a circular sequence of the set of sensor electrodes, wherein the contiguous sensor electrodes include at least half of the set of sensor electrodes.
5. The capacitance sensing device of claim 1 , wherein:
the predetermined function is a sine function; and
the processing block is further configured to calculate the measure of correlation by calculating parameters for the sine function based on a least squares approximation of the sequence of RX signals.
6. The capacitance sensing device of claim 1 , wherein each RX signal in the sequence of RX signals represents a self capacitance measured from the set of sensor electrodes.
7. The capacitance sensing device of claim 1 , wherein:
the processing block is further configured to calculate a displacement based on a least squares approximation of the sequence of RX signals; and
the displacement indicates a position of the object relative to the set of sensor electrodes.
8. The capacitance sensing device of claim 1 , wherein:
the measure of correlation comprises a correlation coefficient; and
the processing block is further configured to
compare the correlation coefficient with a predetermined threshold; and
detect the presence of the object when the correlation coefficient exceeds the predetermined threshold.
9. The capacitance sensing device of claim 1 , further comprising:
an RX sensing channel coupled with the processing block and configured to, for each sensor electrode in the set of sensor electrodes, measure an RX signal of the sequence of RX signals after application to the sensor electrode of the one of the first excitation signal and the second excitation signal.
10. A method, comprising:
generating a sequence of RX signals by applying each TX signal pattern in a sequence of TX signal patterns to a set of sensor electrodes, the set of sensor electrodes comprising all of the sensor electrodes coupled to the transmit generator, wherein applying each TX signal pattern to the set of sensor electrodes comprises applying excitation signals to the set of sensor electrodes by, for each subset of a plurality of subsets each including three or more contiguous sensor electrodes of the set of sensor electrodes, applying the same one of a first excitation signal and a second excitation signal to each of the three or more contiguous sensor electrodes in the subset, wherein a magnitude of a sum of the excitation signals applied to the set of sensor electrodes is less than a magnitude of any one of the excitation signals applied to the set of sensor electrodes, and wherein the plurality of subsets comprises at least half of the sensor electrodes in the set of sensor electrodes;
for each TX signal pattern in the sequence of TX signal patterns, determining a next subsequent TX signal pattern in the sequence based on a circular rotation of the TX signal pattern; and
detecting a presence of an object proximate to the set of sensor electrodes based on a measure of correlation between the sequence of RX signals and a predetermined function.
11. The method of claim 10 , wherein applying each TX signal pattern to the set of sensor electrodes further comprises, for each sensor electrode in the set of sensor electrodes, applying an excitation signal to the sensor electrode corresponding to an excitation signal applied to a preceding sensor electrode in a circular sequence of the set of sensor electrodes during application of a preceding TX signal pattern in the sequence of TX signal patterns, wherein the preceding TX signal pattern is a TX signal pattern most recently applied to the set of TX sensor electrodes prior to applying the TX signal pattern.
12. The method of claim 10 , wherein
the second excitation signal is complementary to the first excitation signal; and
the excitation signals include the first excitation signal and the second excitation signal.
13. The method of claim 10 , further comprising, for each TX signal pattern in the sequence of TX signal patterns:
applying the first excitation signal to contiguous sensor electrodes that are contiguous in a circular sequence of the set of sensor electrodes, wherein the contiguous sensor electrodes include at least half of the set of sensor electrodes.
14. The method of claim 10 , further comprising:
calculating the measure of correlation by calculating parameters for the predetermined function based on a least squares approximation of the sequence of RX signals, wherein the predetermined function is a sine function.
15. The method of claim 10 , wherein each RX signal in the sequence of RX signals represents a self capacitance measured from the set of sensor electrodes.
16. The method of claim 10 , further comprising:
calculating a displacement based on a least squares approximation of the sequence of RX signals, wherein the displacement indicates a position of the object relative to the set of sensor electrodes.
17. The method of claim 10 , further comprising:
comparing the measure of correlation with a predetermined threshold; and
detecting the presence of the object when the measure of correlation exceeds the predetermined threshold, wherein the measure of correlation comprises a correlation coefficient.
18. A capacitance sensing system, comprising:
a host device;
a capacitive sensor array comprising a set of sensor electrodes, the set of sensor electrodes comprising all of the sensor electrodes coupled to a TX generator;
wherein the TX generator is configured to generate a sequence of RX signals by applying each TX signal pattern in a sequence of TX signal patterns to the set of sensor electrodes, wherein for each TX signal pattern in the sequence of TX signal patterns, the TX generator is configured to apply excitation signals to the set of sensor electrodes by, for each subset of a plurality of subsets each including three or more contiguous sensor electrodes of the set of sensor electrodes, applying the same one of a first excitation signal and a second excitation signal to each of the three or more contiguous sensor electrodes in the subset, wherein a magnitude of a sum of the excitation signals applied to the set of sensor electrodes is less than a magnitude of any one of the excitation signals applied to the set of sensor electrodes, and wherein the plurality of subsets comprises at least half of the sensor electrodes in the set of sensor electrodes;
a sequencer circuit coupled with the TX generator and configured to, for each TX signal pattern in the sequence of TX signal patterns, determine a next subsequent TX signal pattern in the sequence based on a circular rotation of the TX signal pattern; and
a processing block coupled with the host device and the TX generator and configured to detect a presence of an object proximate to the set of sensor electrodes based on a measure of correlation between the sequence of RX signals and a predetermined function.
19. The capacitance sensing system of claim 18 , wherein:
the second excitation signal is complementary to the first excitation signal;
the excitation signals include the first excitation signal and the second excitation signal; and
the processing block is further configured to:
calculate the measure of correlation by calculating parameters for the sine function based on a least squares approximation of the sequence of RX signals, and
detect the presence of the object when the measure of correlation exceeds a predetermined threshold.
20. The capacitance sensing system of claim 18 , wherein each RX signal in the sequence of RX signals represents a self capacitance measured from the set of sensor electrodes.
21. The capacitance sensing system of claim 18 , further comprising a display coupled with the host device, wherein the capacitive sensor array overlies the display, and wherein the host device is configured to update the display in response to the detected presence of the object.
22. The capacitance sensing system of claim 18 , wherein the processing block is further configured to detect a hover input by the object based on the sequence of RX signals, and wherein the host device is configured to execute a first subroutine in response to the hover input.