Gain Correction for Fast Panel Scanning

• US 20140022201A1
• Filed: 09/28/2012
• Published: 01/23/2014
• Est. Priority Date: 07/17/2012
• Status: Active Grant

• Current Assignee: Parade Technologies, Ltd.
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Boychuk, Yuriy, Finch, David P., Karpin, Oleksandr, Mandziy, Vasyl
• Granted Patent: US 9,069,399 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• 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

Abstract

Settling time for high-impedance conductive materials in capacitance touchscreen may be overcome by employed a series of mathematical or hardware implemented correction factors. Correction factors may allow for faster mutual capacitance measurement and enable greater noise performance for mutual capacitance panels.

Claims

1. A method comprising:

calculating a correction factor for at least one of a plurality of capacitance sensors;

measuring capacitance of the at least one of the plurality of capacitance sensors;

applying the correction factor the measured capacitance of the at least one of the plurality of capacitance sensors to generate a corrected measured capacitance value;

determining a position of at least one conductive object in proximity to the plurality of capacitance sensors based on the corrected measured capacitance values.

2. The method of claim 1, wherein the calculating a correction factor comprises:

measuring a mutual capacitance of the plurality of capacitance sensors at a first transmit frequency;

measuring the mutual capacitance of the plurality of capacitance sensors as a second transmit frequency;

comparing the measured mutual capacitances of the first and second transmit frequencies.

3. The method claim 2, wherein the comparison of the measured mutual capacitances of the first and second transmit frequencies occurs during manufacturing of the plurality of capacitance sensors.

4. The method claim 2, wherein the comparison of the measured mutual capacitances of the first and second transmit frequencies occurs at device start up.

5. The method claim 2, wherein the comparison of the measured mutual capacitances generates a curve fit corresponding to differences between the measured mutual capacitances at each of the plurality of capacitance sensors.

6. The method claim 5, wherein the curve fit is an exponential relationship.

7. The method claim 5, wherein the applying the correction factor the measured capacitance of the at least one of the plurality of capacitance sensors comprises multiplying the measured capacitance by the calculated correction factor.

8. The method of claim 2, wherein the correction factor is a value of an integration capacitor of a capacitance measurement circuit.

9. The method of claim 2, wherein the correction actor is an attenuation ratio on an input of a capacitance measurement circuit.

10. An apparatus comprising:

a plurality of mutual capacitance sensors;

signal transmit circuitry coupled to each of the plurality of mutual capacitance sensors, the transmit circuit configurable to generate a plurality of signals, the plurality of signals having different frequencies;

signal receive circuitry coupled to each of the plurality of mutual capacitance sensors, the receive circuitry configurable to output a digital value representative of the transmit signal and the mutual capacitance of the sensor; and

processing circuitry configurable to;

receive the digital value representative of the transmit signal and the mutual capacitance of the sensor,

apply a correction factor the measured capacitance of the at least one of the plurality of capacitance sensors, and

determine a position of at least one conductive object in proximity to the plurality of capacitance sensors based on the corrected measured capacitance values.

11. The apparatus of claim 10, wherein the processing circuitry is further configured to calculate the correction factor based on a comparison on digital value from at least two transmit frequencies.

12. The apparatus of claim 11, wherein the correction factor is calculated from a curve fit of the differences between the digital values at the least two transmit frequencies.

13. The apparatus of claim 12, wherein the curve fit is an exponential relationship.

14. The apparatus of claim 13, wherein the correction factor is calculated during device manufacturing and stored in a memory.

15. The apparatus of claim 10, wherein the correction factor is a value of an integration capacitor of a capacitance measurement circuit.

16. The apparatus of claim 10, wherein the correction actor is an attenuation ratio on an input of a capacitance measurement circuit.

20. The system of claim 12, wherein the correction factor is a value of an integration capacitor of a capacitance measurement circuit.

17. A system comprising:

a mutual capacitance sensing array configurable to be driven at a plurality of frequencies;

mutual capacitance measurement circuitry configured to output digital values representative of the mutual capacitance of each of a plurality of nodes in the mutual capacitance sensing array; and

processing circuitry configurable to;

receive the digital value representative of the transmit signal and the mutual capacitance of the sensor,

apply a correction factor the measured capacitance of the at least one of the plurality of capacitance sensors, and

determine a position of at least one conductive object in proximity to the plurality of capacitance sensors based on the corrected measured capacitance values.

18. The system of claim 17, wherein the processing circuitry is further configured to calculate the correction factor based on a comparison on digital value from at least two transmit frequencies.

19. The system of claim 17, wherein the correction factor is calculated from a curve fit of the differences between the digital values at the least two transmit frequencies.

21. The system of claim 17, wherein the correction factor is an attenuation ratio on an input of a capacitance measurement circuit.