Interference estimation and adaptive reconfiguration of a capacitive touch controller
Adaptive reconfiguration of a capacitive touch controller is implemented by estimating the interference spectrum of the signal received by the touch controller. The spectrum of the received signal is used to determine a desired frequency, and the touch panel transmitter is configured to use that desired frequency. The spectrum of the received signal is also used to determine an desired filter transfer function. A filter in the touch panel received signal path is configured to use that desired filter transfer function. The adaptive reconfiguration is focused on improving the signal to noise ratio of the received signal without the need for shielding the touch panel, performing additional scans of the touch panel, or using components that operate at higher power levels.
1. A method for reconfiguring a capacitive touch controller, the method comprising:
detecting a triggering event for reconfiguring the capacitive touch controller;
measuring a received signal from a capacitive touch panel;
determining an auto-correlation of the received signal;
determining a filter transfer function for rejecting interference from a subsequently received signal, where the filter transfer function is based on the auto-correlation of the received signal;
determining a transmit frequency for stimulating the capacitive touch panel, where the transmit frequency is based on the auto-correlation of the received signal, including determining an optimal transmit frequency from a range of available frequencies, where each available frequency has a mean square error (MSE), where the MSE is determined by the inner product of the auto-correlation of the received signal and auto-correlation of the filter transfer function, and where the optimal transmit frequency is the available frequency having the minimum MSE;
stimulating the capacitive touch panel using the transmit frequency by applying to the capacitive touch panel a time varying signal having the transmit frequency, and
subsequently receiving a signal from the capacitive touch panel, the subsequently received signal being indicative of a response of the capacitive touch panel to the time varying signal; and
filtering a subsequently received signal using the filter transfer function.
2. The method of claim 1 , where the triggering event occurs when signal to noise ratio (SNR) of the received signal is below a threshold SNR value.
3. The method of claim 1 , where the triggering event occurs when a period of time has elapsed.
4. The method of claim 1 , where determining the filter transfer function comprises determining a bandpass filter transfer function in series with a finite impulse response filter transfer function, wherein the filter transfer function is calculated to improve signal to noise ratio (SNR) of the subsequently received signal.
5. The method of claim 4 , where determining the filter transfer function for the finite impulse response filter comprises determining filter coefficients for a multi-tap digital filter.
6. The method of claim 1 , wherein determining the transmit frequency for stimulating the capacitive touch panel comprises determining the best linear unbiased estimator from the auto-correlation of the received signal.
7. A capacitive touch controller comprising:
a detector configured to detect a triggering event for reconfiguring the capacitive touch controller;
a signal processor configured to measure a received signal from a capacitive touch panel of the capacitive touch controller and determine auto-correlation of the received signal;
a filter processor configured to determine a filter transfer function for rejecting interference from a subsequently received signal, where the filter transfer function is based on the auto-correlation of the received signal;
a frequency processor configured to determine a transmit frequency for stimulating the capacitive touch panel, where the transmit frequency is an optimal transmit frequency selected from a range of available frequencies, where each available frequency has a mean square error (MSE), where the MSE is determined by the inner product of the auto-correlation of the received signal and the auto-correlation of the filter transfer function, and where the optimal transmit frequency is the available frequency having the minimum MSE;
a transmitter configured to stimulate the capacitive touch panel using the transmit frequency; and
a filter configured to apply the filter transfer function to a subsequently received signal.
8. The controller of claim 7 , where the triggering event occurs when signal to noise ratio (SNR) of the received signal is below a threshold SNR value.
9. The controller of claim 7 , where the triggering event occurs when a period of time has elapsed.
10. The controller of claim 7 , where the filter transfer function comprises a bandpass filter transfer function in series with a finite impulse response filter transfer function, wherein the filter transfer function is calculated to improve signal to noise ratio (SNR) of the subsequently received signal.
11. The controller of claim 10 , where the filter transfer function for the finite impulse response filter comprises a multi-tap digital filter.
12. The controller of claim 7 , wherein the filter processor comprises a circuit configured to determine the filter transfer by determining the best linear unbiased estimator from the auto-correlation of the received signal.
13. A portable data processing device comprising:
a video display;
a capacitive touch panel;
a control circuit operative to provide signals to the video display to produce images on the video display and operative to detect touch interactions with the capacitive touch panel, the control circuit including a capacitive touch controller comprising:
a detector configured to detect a triggering event for reconfiguring the capacitive touch controller;
a signal processor configured to measure a received signal from the capacitive touch panel of the portable data processing device and determine auto-correlation of the received signal;
a filter processor configured to determine a filter transfer function for rejecting interference from a subsequently received signal, where the filter transfer function is based on the auto-correlation of the received signal;
a frequency processor configured to determine a transmit frequency for stimulating the capacitive touch panel with a stimulation signal applied to the capacitive touch panel, where the transmit frequency is an optimal transmit frequency selected from a range of available frequencies, where each available frequency has a mean square error (MSE), where the MSE is determined by the inner product of the auto-correlation of the received signal and auto-correlation of the filter transfer function, and where the optimal transmit frequency is the available frequency having the minimum MSE;
a transmitter configured to stimulate the capacitive touch panel using the transmit frequency; and
a filter configured to apply the filter transfer function to a subsequently received signal.
14. The portable data processing device of claim 13 , where the triggering event occurs when signal to noise ratio (SNR) of the received signal is below a threshold SNR value or when a period of time has elapsed.
15. The portable data processing device of claim 13 , where the filter transfer function comprises a bandpass filter function in series with a finite impulse response filter function, wherein the filter transfer function is calculated to improve signal to noise ratio (SNR) of the subsequently received signal by filtering noise coupled to the received signal by the video display, the capacitive touch panel, and/or the touch controller.
16. The portable data processing device of claim 15 , where the filter transfer function for the finite impulse response filter comprises a multi-tap digital filter.
17. The portable data processing device of claim 13 , wherein the signal processor comprises a circuit configured to determine the auto-correlation of the received signal by determining the best linear unbiased estimator from the auto-correlation of the received signal.