METHOD AND APPARATUS FOR REDUCING COUPLED NOISE INFLUENCE IN TOUCH SCREEN CONTROLLERS

• US 20110115729A1
• Filed: 10/20/2010
• Published: 05/19/2011
• Est. Priority Date: 10/20/2009
• Status: Active Grant

• Current Assignee: Parade Technologies, Ltd.
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Konovalov, Anton, Kremin, Victor
• Granted Patent: US 8,947,373 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• CPC Class Codes: G02F 1/13338 Input devices, e.g. touch panels
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/04184 Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally
• CPC Class Codes: G06F 3/0445 using two or more layers of sensing electrodes, e.g. using two layers of electrodes separated by a dielectric layer
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes

Abstract

A method and apparatus for reducing influence of noise for touch screen controllers employing noise listening synchronization, delay lines, filtering and sensing selected touch screen electrodes.

Claims

1. Apparatus for reducing noise influence on signals produced in touch screen controllers, the apparatus comprising:

a detector to produce an output in response to noise; and

a state machine to synchronize the signals and the noise.

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 an 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.

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 noises 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.

9. The apparatus according to claim 9 wherein the gate comprises a one shot to provide a fixed sampling 1 time.

15. A method, comprising:

performing noise listening for detecting noise and signal from a touch screen; and

synchronizing the noise and the signal.

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 signal 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 signals; and

a touch screen controller responsively coupled to the touch screen including,

a processor,

a noise detector operatively coupled to the processor and to at least one touch sensitive electrode and a un-driven electrode, the noise detector responsive to the processor and the noise to produce a synchronization signal when noise is present; and

a state machine operatively coupled to the processor and responsive to the signals and the synchronization signal to synchronize the signals with the noise.