Method and apparatus for reducing coupled noise influence in touch screen controllers

1. An apparatus comprising:

a detector configured to determine that noise from a display is present through a touch sensitive electrode that is not being scanned to detect a touch and produce an output that indicates the presence of the noise, in response to the determination; and

a state machine to synchronize signals produced in a touch screen controller and the noise, wherein synchronization is used to avoid an influence of the noise on the signals produced in the touchscreen.

2. The apparatus according to claim 1 further comprising a noise filter responsive to the noise to average the noise over a measurement interval.

3. The apparatus according to claim 2 further comprising a storage buffer responsive to the noise to store noise and signals in descending order from highest to lowest values, and wherein the noise filter comprises a median filter to discard the highest and lowest values and averaging remaining values there between.

4. The apparatus according to claim 1 wherein the detector comprises a threshold comparator responsively coupled to selected outputs of a display to produce the output indicative of the noise from the display.

5. The apparatus according to claim 4 wherein the touch screen has Rx outputs and Tx outputs, and the threshold comparator is coupled to at least one unused Tx electrode and at least one Rx electrode.

6. The apparatus according to claim 5 further comprising a gain control network for each selected Tx and Rx electrode to balance gain at each of the Tx and Rx electrodes.

7. The apparatus according to claim 4 wherein the detector is a digital circuit.

8. The apparatus according to claim 1 further comprising:

a delay line including a delay for each of first and second half cycles of a Tx excitation cycle;

a gate responsive to a noise event; and

a signal source selector responsively coupled to the gate to select a first half cycle and the second half cycle when noise is not present and to select a reference when a noise event is detected.

9. The apparatus according to claim 8 wherein the gate comprises a one shot to provide a fixed sampling time.

10. The apparatus according to claim 1 further comprising a timer responsive to the detector to measure a duration between a selected number of noise pulses in at least one of a first mode and a second mode when the noise is pulsed noise.

11. The apparatus according to claim 10 wherein the first mode is continuous.

12. The apparatus according to claim 11 wherein each selected number of noise pulses is configured to initiate a pause after a selected number of noise pulses.

13. The apparatus according to claim 1 further comprising a counter to produce output pulses coupled to the state machine to enable the state machine to produce a measurement in response to the output pulses, the counter responsive to the detector output to stop the counter when noise is present, the state machine being configured to be disabled when counter is stopped.

14. The apparatus according to claim 1 comprising a multiplexor to selectively connect one or more of Rx electrodes and Tx electrodes of the touch screen to the noise detector.

15. A method, comprising:

performing noise listening for detecting that noise from a display is present, the performing of the noise listening including determining that the noise is present through a touch sensitive electrode that is not being scanned to detect a touch;

detecting touch signals from a touch screen; and

synchronizing the noise and-the touch signals, wherein synchronizing the noise is used to avoid an influence of the noise on the touch signals.

16. The method according to claim 15 further including sensing inputs from selected Tx and Rx outputs of the panel.

17. The method according to claim 15 further including filtering the noise employing at least one of a window filter, an averaging filter and a median filter.

18. The method according to claim 15 further including delaying the noise and the touch signals for a selected interval.

19. The method according to claim 15 further including disabling noise and signal output for a fixed interval when noise is present and enabling signal output following the fixed interval.

20. An apparatus comprising:

a display to produce images and noise;

a touch screen overlying the display, the touch screen comprising touch sensitive electrodes to produce touch signals;

a touch screen controller responsively coupled to the touch screen including a processor and a noise detector, the noise detector to determine a presence of the noise operatively coupled to at least one touch sensitive electrode and a un-driven electrode while the at least one touch sensitive electrode is not producing a touch signal, the noise detector responsive to the processor and the detected presence of the noise to produce a synchronization signal when noise is present; and

a state machine operatively coupled to the processor and responsive to the touch signals and the synchronization signal to synchronize the touch signals with the noise, wherein synchronization is used to avoid an influence of the noise on the touch signals.