Touch sensing

• US 8,525,798 B2
• Filed: 02/29/2008
• Issued: 09/03/2013
• Est. Priority Date: 01/28/2008
• Status: Active Grant

• Current Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Birch, Robert, Peterson, Jonathan
• Primary Examiner(s): Shalwala, Bipin
• Assistant Examiner(s): CHOWDHURY, AFROZA Y
• Application Number:
  US12/040,387
• Publication Number:
  US 20120043140A1
• Time in Patent Office: 2,013 Days
• Field of Search: 451/73, 345/156, 345/173, 345/174
• US Class Current: 345/173
• CPC Class Codes: G06F 3/041 Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
• CPC Class Codes: G06F 3/04166 Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184
• 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
• CPC Class Codes: H03K 17/9622 using a plurality of detectors, e.g. keyboard
• CPC Class Codes: H03K 2217/960775 Emitter-receiver or "fringe" type detection, i.e. one or more field emitting electrodes and corresponding one or more receiving electrodes

Abstract

In one embodiment, an apparatus comprises a plurality of capacitors, each having a first electrode and a second electrode. The apparatus includes charging circuitry coupled to the first electrodes and sensing circuitry coupled to the second electrodes, the sensing circuitry configured to detect changes in capacitance across the capacitors responsive to movement of an input object relative to the apparatus. Interpolating circuitry identifies which one of the capacitors is nearest to the input object according to the detected capacitance changes.

Claims

1. An apparatus comprising:

a plurality of capacitors each having a first electrode and a second electrode;

signal generating circuitry coupled to the first electrodes;

sensing circuitry coupled to the second electrodes, the sensing circuitry configured to detect changes in capacitance across the capacitors responsive to movement of an input object related to the apparatus, the sensing circuitry comprising a pseudo random signal generator configured to provide a drive signal to the first electrodes, the pseudo random signal generator varying a frequency of the drive signal at intervals;

a demodulator coupled to the pseudo random signal generator and configured to receive the varying frequency therefrom and to select a passing frequency based on the varying frequency;

a low pass filter to filter an output of the sensing circuitry;

an analog to digital converter connected to the output of the low pass filter; and

interpolating circuitry to identify which one of the capacitors is nearest to the input object according to the detected capacitance changes,

wherein the demodulator dynamically varies the passing frequency to correspond with the varying frequency of the sensing circuitry output.

2. The apparatus of claim 1 wherein the electrodes form an electrode grid array, the first electrodes being non-parallel with the second electrodes.

3. The apparatus of claim 1 wherein the signal generating circuitry provides, to the first electrodes, an alternating current having an intermittently varying frequency.

4. The apparatus of claim 3 wherein the demodulator is electrically connected to the second electrodes and is further configured to dynamically vary the passing frequency to correspond with the intermittently varying frequency of the signal generating circuitry output.

5. The apparatus of claim 1 further comprising a touch panel arranged adjacent to the plurality of capacitors, the touch panel being at least one selecting from the group including a touch pad, a touch screen and a series of touch buttons.

6. An apparatus comprising:

a first set of electrodes;

a second set of electrodes arranged non-parallel with respect to the first set of electrodes;

a first insulating layer located between the sets of electrodes;

a second insulating layer adjacent to only one of the sets of electrodes;

charge generation circuitry coupled to the electrodes of the first set, the charge generation circuitry to electrically charge the electrodes of the first set thereby forming capacitance across the first insulating layer;

sensing circuitry coupled to the electrodes of the second set, the sensing circuitry configured to monitor for changes in the capacitance across the first insulating layer and comprising a pseudo random signal generator configured to provide a drive signal to the first set, the pseudo random signal generator varying a frequency of the drive signal at intervals;

a demodulator coupled to the pseudo random signal generator and configured to receive the varying frequency therefrom and to select a passing frequency based on the varying frequency;

a low pass filter to filter an output of the sensing circuit; and

an analog to digital converter connected to the output of the low pass filter,

wherein the demodulator dynamically varies the passing frequency to correspond with the varying frequency of the sensing circuitry output.

7. The apparatus of claim 6 wherein the second insulating layer is associated with a touchpad.

8. The apparatus of claim 6 further comprising:

multiplexing circuitry electrically interposed between the electrodes of the first set and the charge generation circuitry, the multiplexing circuitry alternating which one of the electrodes of the first set is electrically coupled to the charge generation circuitry according to a time division scheme.

9. The apparatus of claim 6 wherein

the demodulator is connected to the electrodes of the second set and receives a reference signal from the pseudo random signal generator and demodulates a signal corresponding to the electrodes of the second set according to the reference signal.

10. The apparatus of claim 6 further comprising an interpolating component to interpolate the position of an object relative to the second insulating layer according the monitored changes in capacitance across the first insulating layer.

11. The apparatus of claim 6 further comprising:

an interface to adjust at least one setting selected from the group comprising the center frequency of the pseudo random signal generator, the sampling rate of the analog to digital converter, and an operating characteristic of the low pass filter.

12. A method, comprising:

monitoring changes in capacitance across a plurality of capacitors using sensing circuitry, each of the capacitors having an electrode pair, only one of the electrodes of each pair being electrically coupled to signal generating circuitry;

providing a drive signal via a pseudo random signal generator to a first set of capacitors, the pseudo random signal generator varying a frequency of the drive signal at intervals;

selecting a passing frequency via a demodulator coupled to the pseudo random signal generator based on the varying frequency to provide an output of said sensing circuitry;

dynamically varying the passing frequency to correspond with the varying frequency of the output of said sensing circuitry;

filtering the output of said sensing circuitry using a low pass filter;

sampling an output of the sensing circuitry using an analog to digital converter; and

determining the position of at least one object on a touch device according to the monitored capacitance changes.

13. The method of claim 12, further comprising:

electrically charging the electrodes that are electrically coupled to the signal generating circuitry according to a time division multiplexing scheme; and

determining a plurality of contact positioned on the touch device, said plurality of contact positions determined within a same cycle of the time division multiplexing scheme.

14. The method of claim 12 further comprising:

electrically charging the electrodes that are electrically coupled to the signal generating circuitry using a pseudo random signal generator; and

adjusting the center frequency of the pseudo random signal generator between electrical chargings.

15. The method of claim 14 further comprising:

adjusting the sample rate of the analog to digital converter to correspond with the adjusted center frequency.

16. The method of claim 14 further comprising:

changing a cutoff frequency of the low pass filter according to the adjusted center frequency.

17. The method of claim 14 further comprising:

changing a cutoff frequency of the low pass filter according to a responsiveness of the position determination.

18. The method of claim 12 further comprising:

using a graphical user interface to dynamically adjust a characteristic of at least one circuit component used for said capacitance change monitoring.

19. The method of claim 12 wherein said sensing circuitry including a pull down resistor, and the method further comprises:

adjusting the resistance of the pull down resistor according to an accuracy of the position determination.