NOISE REJECTION CIRCUIT FOR TOUCH SENSITIVE DISPLAY

• US 20130069904A1
• Filed: 09/15/2011
• Published: 03/21/2013
• Est. Priority Date: 09/15/2011
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Christoph Horst Krah
• Inventors: KRAH, Christoph Horst
• Granted Patent: US 9,436,315 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• 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: H03K 2217/960705 Safety of capacitive touch and proximity switches, e.g. increasing reliability, fail-safe

Abstract

A noise rejection circuit for a touch sensitive display is disclosed. The noise rejection circuit can reject noise introduced by the touch sensitive display'"'"'s display device into its touch panel. The noise rejection circuit can be integrated into the touch circuitry of the touch sensitive display and can include a resistor to sense the noise and an amplifier to isolate the sensed noise for rejection.

Claims

1. A touch sensitive display comprising:

a touch panel configured to sense an object proximate to the panel;

a display device configured to display data; and

a noise rejection circuit integrated with touch circuitry to reject noise introduced by the display device into the touch panel, the noise being caused by a voltage layer of the display device capacitively coupling with the touch circuitry of the touch panel.

2. The touch sensitive display of claim 1, wherein the touch circuitry comprises at least one touch buffer configured to transmit a stimulation signal to the touch panel to cause the panel to sense the proximate object, and

wherein the noise rejection circuit comprises a resistor disposed in a feedback loop of the touch buffer and configured to sense the noise.

3. The touch sensitive display of claim 2, wherein the resistor is variable so as to adjust a gain of the touch buffer to sense the noise.

4. The touch sensitive display of claim 1, wherein the touch circuitry comprises at least one touch buffer configured to transmit a stimulation signal to the touch panel to cause the panel to sense the proximate object, and

wherein the noise rejection circuit comprises a resistor disposed between the touch buffer and the touch panel and configured to sense the noise.

5. The touch sensitive display of claim 1, wherein the touch circuitry is configured to generate a coupled signal of a first stimulation signal having a first polarity and including the noise and a second stimulation signal having an opposite polarity and including the noise, the coupling canceling out the first and second stimulation signals, and

wherein the noise rejection circuit comprises an amplifier configured to receive the coupled signal and isolate the noise in the coupled signal.

6. The touch sensitive display of claim 1, wherein the touch circuitry comprises:

a multiplexor configured to select a stimulation signal having a first polarity from among multiple stimulation signals, and

a stimulation matrix configured to control the selection by the multiplexor based on a drive pattern of the touch panel,

wherein the touch circuitry is configured to generate a coupled signal of the selected stimulation signal and another stimulation signal having an opposite polarity, the coupling canceling out the selected and other stimulation signals, and

wherein the noise rejection circuit comprises an amplifier configured to receive the coupled signal and isolate the noise in the coupled signal.

7. The touch sensitive display of claim 1, wherein the noise rejection circuit is configured to isolate the noise, and

wherein the touch circuitry is configured to couple the isolated noise from the noise rejection circuit with a sense signal including the noise from the touch panel, the coupling canceling out the noise with the isolated noise.

8. The touch sensitive display of claim 1, wherein the noise rejection circuit is configured to isolate the noise, and

wherein the touch circuitry is configured to couple the isolated noise received from the noise rejection circuit with a stimulation signal including the noise being transmitted to the touch panel, the coupling canceling out the noise with the isolated noise.

9. The touch sensitive display of claim 1, wherein the touch panel is configured to generate sense signals having variable amounts of the noise, and

wherein the noise rejection circuit is configured to isolate the noise and to vary the amounts of isolated noise so as to cancel out the variable noise amounts in the sense signals.

10. The touch sensitive display of claim 1, wherein the touch panel comprises:

a first set of conductive lines configured to drive the panel to sense the proximate object; and

a second set of conductive lines configured to transmit a sense signal indicative of the sensed proximate object for further processing,

wherein the voltage layer couples to the second set of conductive lines to introduce the noise into the sense signal.

11. The touch sensitive display of claim 1, wherein the display device comprises:

a transistor layer configured to be driven by the voltage layer to display the data.

12. The touch sensitive display of claim 1 incorporated into at least one of a mobile telephone, a digital media player, or a portable computer.

13. A circuit for rejecting noise in a touch sensitive display, comprising:

multiple touch buffers configured to output stimulation signals to drive the display, the signals including noise; and

an amplifier configured to isolate the noise from the signals,

wherein at least two of the stimulation signals are coupled together to form a coupled signal, the coupling canceling the signals and leaving the noise in the coupled signal, and

wherein the amplifier is configured to receive the coupled signal to isolate the noise in the coupled signal for rejection.

14. The circuit of claim 13, wherein the amplifier comprises an adjustable capacitor configured to adjust a gain of the amplifier to isolate the noise.

15. The circuit of claim 13, comprising:

a multiplexor configured to select at least one of the stimulation signals having a first polarity; and

a stimulation matrix configured to send a selection signal to the multiplexor to make the selection,

wherein the at least one stimulation signal is coupled with at least another of the stimulation signals having a second polarity opposite the first polarity so as to cancel the at least one stimulation signal and the at least another stimulation signals.

16. A circuit for rejecting noise in a touch sensitive display, comprising:

multiple touch buffers configured to output stimulation signals to drive the display, the stimulation signals including noise;

a noise amplifier coupled to the outputs of the touch buffers and configured to isolate the noise from the stimulation signals to form a noise signal; and

a sense amplifier configured to receive sense signals generated from the stimulation signals with the noise rejected therefrom, the noise being rejected by applying the noise signal in the display.

17. The circuit of claim 16, wherein the noise is rejected by applying the noise signal to the sense signals so as to remove the noise from the sense signals.

18. The circuit of claim 16, wherein the noise is rejected by applying the noise signal to the stimulation signals so as to remove the noise from the stimulation signals.

19. A method for rejecting noise in a touch sensitive device, comprising:

driving the device with stimulation signals, the stimulation signals including capacitively coupled noise;

sensing the noise in the stimulation signals;

isolating the noise in the stimulation signals to produce a noise signal;

generating sense signals from the stimulation signals, the sense signals including the noise; and

applying the noise signal to the sense signals so as to reject the noise in the sense signals.

20. The method of claim 19, wherein isolating the noise comprises coupling at least two of the stimulation signals having opposite polarity so as to cancel the stimulation signals and leave the noise.

21. The method of claim 19, wherein applying the noise signal comprises subtracting the noise signal from the sense signal.

22. A touch sensitive device comprising:

a touch panel configured to sense an object proximate to the panel;

a voltage circuit proximate to the panel; and

a noise rejection circuit integrated with touch circuitry to reject noise introduced by the voltage circuit into the touch panel, the noise being caused by the voltage circuit capacitively coupling with the touch circuitry of the touch panel.

23. The device of claim 22, wherein the noise rejection circuit comprises a resistor configured to sense the noise.

24. The device of claim 22, wherein the noise rejection circuit comprises a common mode amplifier configured to isolate the noise.

25. The device of claim 22, wherein the touch panel is configured to generate sense signals indicative of the proximate object and the noise rejection circuit is configured to reject the noise from the sense signals.