Noise reduction for touch controller

• US 8,743,062 B2
• Filed: 12/03/2010
• Issued: 06/03/2014
• Est. Priority Date: 12/03/2010
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Krah, Christoph Horst, Motamed, Ali
• Primary Examiner(s): SHERMAN, STEPHEN G
• Application Number:
  US12/960,371
• Publication Number:
  US 20120139846A1
• Time in Patent Office: 1,278 Days
• Field of Search: 345173-178, 178 1801- 1809, 178/18.11
• US Class Current: 345/173
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/044 by capacitive means

Abstract

A touch controller having noise reduction circuitry is disclosed. The touch controller can include a transmit section for generating stimulation signals to drive a touch display to sense a touch or hover event. The touch controller can also include a receive section for processing touch signals from the touch display indicative of the touch or hover event. The touch controller can reduce noise introduced into the stimulation signals and propagated through the touch display into the touch signals, thereby interfering with touch and hover sensing. To reduce the noise, the transmit section'"'"'s noise reduction circuitry can isolate and subtract some or all of the noise from the stimulation signals. In addition or alternatively, the receive section'"'"'s noise reduction circuitry can isolate and subtract some or all of the noise from the touch signals.

Claims

1. A touch controller comprising:

a transmit section configured to reduce noise, the transmit section including

a digital-to-analog converter (DAC) configured to output a first stimulation signal and a second stimulation signal, the stimulation signals including the noise, and

multiple output buffers, a first output buffer configured to convert the noise to first differential noise and output the first stimulation signal with the first differential noise to a touch sensor panel, and a second output buffer configured to convert the noise to second differential noise and output the second stimulation signal with the second differential noise to the touch sensor panel; and

a receive section configured to receive a touch signal generated from the first and second stimulation signals, the received touch signal having the first and second differential noise canceled therefrom.

2. The touch controller of claim 1, wherein the received touch signal comprises a first touch signal generated from the first stimulation signal with the first differential noise and a second touch signal generated from the second stimulation signal with the second differential noise, the first and second touch signals being coupled together to cancel out the first and second differential noise.

3. The touch controller of claim 1, wherein the first output buffer receives the first stimulation signal as a first input and the second stimulation signal as a second input so as to convert the noise in the first and second stimulation signals into the first differential noise, and the second output buffer receives the second stimulation signal as a first input and the first stimulation signal as a second input so as to convert the noise in the first and second stimulation signals into the second differential noise.

4. The touch controller of claim 3, wherein the first output buffer receives a bias voltage coupled with the second stimulation signal as the second input to the first output buffer, and the second output buffer receives a bias voltage coupled with the first stimulation signal as the second input to the second output buffer.

5. The touch controller of claim 4, wherein the bias voltage is coupled with the first stimulation signal through one or more voltage dividers.

6. The touch controller of claim 4, wherein the bias voltage is coupled with the second stimulation signal through one or more voltage dividers.

7. The touch controller of claim 4, wherein the bias voltage introduces a second noise into the first and second stimulation signals.

8. The touch controller of claim 7, wherein the second noise is canceled out by using the bias voltage as a reference.

9. The touch controller of claim 1, wherein the first and second stimulation signals have opposite phases, one having a positive phase and the other having a negative phase.

10. The touch controller of claim 1, wherein the converter induces the noise in the stimulation signals.

11. The touch controller of claim 1, wherein the noise comprises common mode noise.

12. The touch controller of claim 1, wherein the transmit section further comprises:

multiple DAC buffers, a first DAC buffer configured to transmit the first stimulation signal with the noise for generating a first touch signal and a second DAC buffer configured to transmit the second stimulation signal with the noise for generating a second touch signal.

13. A touch sensitive device comprising:

a touch sensor panel; and

a touch controller comprising;

a transmit section configured to reduce noise, the transmit section including

a digital-to-analog converter (DAC) configured to output a first stimulation signal and a second stimulation signal, the stimulation signals including the noise, and

multiple output buffers, a first output buffer configured to convert the noise to first differential noise and output the first stimulation signal with the first differential noise to the touch sensor panel, and a second output buffer configured to convert the noise to second differential noise and output the second stimulation signal with the second differential noise to the touch sensor panel; and

a receive section configured to receive a touch signal generated from the first and second stimulation signals, the received touch signal having the first and second differential noise canceled therefrom.

14. The touch sensitive device of claim 13, wherein the received touch signal comprises a first touch signal generated from the first stimulation signal with the first differential noise and a second touch signal generated from the second stimulation signal with the second differential noise, the first and second touch signals being coupled together to cancel out the first and second differential noise.

15. The touch sensitive device of claim 13, wherein the first output buffer receives the first stimulation signal as a first input and the second stimulation signal as a second input so as to convert the noise in the first and second stimulation signals into the first differential noise, and the second output buffer receives the second stimulation signal as a first input and the first stimulation signal as a second input so as to convert the noise in the first and second stimulation signals into the second differential noise.

16. The touch sensitive device of claim 15, wherein the first output buffer receives a bias voltage coupled with the second stimulation signal as the second input to the first output buffer, and the second output buffer receives a bias voltage coupled with the first stimulation signal as the second input to the second output buffer.

17. The touch sensitive device of claim 16, wherein the bias voltage is coupled with the first stimulation signal through one or more voltage dividers.

18. The touch sensitive device of claim 16, wherein the bias voltage is coupled with the second stimulation signal through one or more voltage dividers.

19. The touch sensitive device of claim 16, wherein the bias voltage introduces a second noise into the first and second stimulation signals.

20. The touch sensitive device of claim 19, wherein the second noise is canceled out by using the bias voltage as a reference.

21. The touch sensitive device of claim 13, wherein the first and second stimulation signals have opposite phases, one having a positive phase and the other having a negative phase.

22. The touch sensitive device of claim 13, wherein the converter induces the noise in the stimulation signals.

23. The touch sensitive device of claim 13, wherein the noise comprises common mode noise.

24. The touch sensitive device of claim 13, wherein the transmit section further comprises:

multiple DAC buffers, a first DAC buffer configured to transmit the first stimulation signal with the noise for generating a first touch signal and a second DAC buffer configured to transmit the second stimulation signal with the noise for generating a second touch signal.