Active Stylus Self-Capacitance Measurement

• US 20140043279A1
• Filed: 08/09/2012
• Published: 02/13/2014
• Est. Priority Date: 08/09/2012
• Status: Active Grant

• Current Assignee: Wacom Co Limited (Wacom)
• Original Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Inventors: Pedersen, Trond Jarle, Bakken, Vemund Kval
• Granted Patent: US 9,354,737 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G06F 3/03545 Pens or stylus
• 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 3/0441 using active external devices, e.g. active pens, for receiving changes in electrical potential transmitted by the digitiser, e.g. tablet driving signals
• CPC Class Codes: G06F 3/0442 using active external devices, e.g. active pens, for transmitting changes in electrical potential to be received by the digitiser
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes
• 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

In one embodiment, a method includes modifying an amount of charge of a capacitance of a touch sensor. The modified amount of charge results in a voltage at the capacitance being a first pre-determined voltage level. The method also includes applying a first pre-determined amount of charge to the capacitance. The application of the first pre-determined amount of charge to the capacitance modifies the voltage at the capacitance from the first pre-determined voltage level to a first charging voltage level. The method also includes determining a first voltage at a sampling capacitor. The first voltage is proportional to a difference between the first charging voltage level and a reference voltage level. The method also includes determining whether a touch and stylus input to the touch sensor has occurred based on the first voltage and a second voltage.

Claims

1. A method comprising:

modifying an amount of charge of a capacitance of a touch sensor, the modified amount of charge resulting in a voltage at the capacitance being a first pre-determined voltage level;

applying a first pre-determined amount of charge to the capacitance, the application of the first pre-determined amount of charge to the capacitance modifying the voltage at the capacitance from the first pre-determined voltage level to a first charging voltage level;

determining a first voltage at a sampling capacitor, the first voltage being proportional to a difference between the first charging voltage level and a reference voltage level; and

determining whether a touch and stylus input to the touch sensor has occurred based on the first voltage and a second voltage, the second voltage being proportional to a second pre-determined amount of charge applied to the sampling capacitor by a first edge of a signal transmitted a stylus.

2. The method of claim 1, further comprising:

modifying the amount of charge of the capacitance, the modified amount of charge resulting in the voltage at the capacitance being a second pre-determined voltage level;

applying a third pre-determined amount of charge to the capacitance, the application of the third pre-determined amount of charge to the capacitance modifying the voltage at the capacitance from the second pre-determined voltage level to a second charging voltage level;

determining a third voltage at the sampling capacitor, the third voltage being proportional to a difference between the second charging voltage level and the reference voltage level; and

determining whether a touch and stylus input to the touch sensor has occurred based on the first voltage, the second voltage, the third voltage, and a fourth voltage, the fourth voltage being proportional to a fourth pre-determined amount of charge applied to the sampling capacitor by a second edge of a signal transmitted a stylus.

3. The method of claim 2, wherein the first pre-determined amount of charge comprising applying a first amount of current to the capacitance prior to receiving the first edge and applying the third pre-determined amount of charge comprising applying a second amount of current to the capacitance prior to receiving the second edge, the second current having an inverse polarity than the first current relative to the capacitance.

4. The method of claim 2, further comprising:

inverting a sign of the third and fourth voltages; and

subtracting a sum of the first and second voltages from a sum of the third and fourth voltages, the subtraction substantially suppressing low-frequency noise in the first, second, third and fourth voltages.

5. The method of claim 1, wherein determining the first and second voltage comprises integrating an amount of charge on the sampling capacitor associated with the first and second voltage.

6. The method of claim 1, further comprising:

detecting the first edge of the signal; and

determining a frequency of the signal based at least in part on the detection of the first edge.

7. The method of claim 6, wherein a timing of the application of the second pre-determined amount of charge and the determination of the first voltage is based at least in part on the determination of the frequency.

8. A computer-readable non-transitory storage medium embodying logic configured when executed to:

modify an amount of charge of a capacitance of a touch sensor, the modified amount of charge resulting in a voltage at the capacitance being a first pre-determined voltage level;

apply a first pre-determined amount of charge to the capacitance, the application of the first pre-determined amount of charge to the capacitance modifying the voltage at the capacitance from the first pre-determined voltage level to a first charging voltage level;

determine a first voltage at a sampling capacitor, the first voltage being proportional to a difference between the first charging voltage level and a reference voltage level; and

determine whether a touch and stylus input to the touch sensor has occurred based on the first and a second voltage, the second voltage being proportional to a second pre-determined amount of charge applied to the sampling capacitor by a first edge of a signal transmitted a stylus.

9. The medium of claim 8, wherein the logic is further configured to:

modify the amount of charge of the capacitance, the modified amount of charge resulting in the voltage at the capacitance being a second pre-determined voltage level;

apply a third pre-determined amount of charge to the capacitance, the application of the third pre-determined amount of charge to the capacitance modifying the voltage at the capacitance from the second pre-determined voltage level to a second charging voltage level;

determine a third voltage at the sampling capacitor, the third voltage being proportional to a difference between the second charging voltage level and the reference voltage level; and

determine whether a touch and stylus input to the touch sensor has occurred based on the first voltage, the second voltage, the third voltage, and a fourth voltage, the fourth voltage being proportional to a fourth pre-determined amount of charge applied to the sampling capacitor by a second edge of a signal transmitted a stylus.

10. The medium of claim 9, wherein the logic is further configured to apply a first amount of current to the capacitance prior to receiving the first edge and a second amount of current to the capacitance prior to receiving the second edge, the second current having an inverse polarity than the first current relative to the capacitance.

11. The medium of claim 9, wherein the logic is further configured to:

invert a sign of the third and fourth voltages; and

subtract a sum of the first and second voltages from a sum of the third and fourth voltages, the subtraction substantially suppressing low-frequency noise in the first, second, third and fourth voltages.

12. The medium of claim 8, wherein the logic is further configured to integrate an amount of charge on the sampling capacitor associated with the first and second voltage.

13. The medium of claim 8, wherein the logic is further configured to:

detect the first edge of the signal; and

determine a frequency of the signal based at least in part on the detection of the first edge.

14. The medium of claim 13, wherein a timing of the application of the second pre-determined amount of charge and the determination of the first voltage is based at least in part on the determination of the frequency.

15. A device comprising:

a measurement circuit; and

a computer-readable non-transitory storage medium coupled to the measurement circuit and embodying logic configured when executed to;

modify an amount of charge of a capacitance of a touch sensor, the modified amount of charge resulting in a voltage at the capacitance being a first pre-determined voltage level;

apply a first pre-determined amount of charge to the capacitance, the application of the first pre-determined amount of charge to the capacitance modifying the voltage at the capacitance from the first pre-determined voltage level to a first charging voltage level;

determine a first voltage at a sampling capacitor, the first voltage being proportional to a difference between the first charging voltage level and a reference voltage level; and

determine whether a touch and stylus input to the touch sensor has occurred based on the first and a second voltage, the second voltage being proportional to a second pre-determined amount of charge applied to the sampling capacitor by a first edge of a signal transmitted a stylus.

16. The device of claim 15, wherein the logic is further configured to:

modify the amount of charge of the capacitance, the modified amount of charge resulting in the voltage at the capacitance being a second pre-determined voltage level;

apply a third pre-determined amount of charge to the capacitance, the application of the third pre-determined amount of charge to the capacitance modifying the voltage at the capacitance from the second pre-determined voltage level to a second charging voltage level;

determine a third voltage at the sampling capacitor, the third voltage being proportional to a difference between the second charging voltage level and the reference voltage level; and

determine whether a touch and stylus input to the touch sensor has occurred based on the first voltage, the second voltage, the third voltage, and a fourth voltage, the fourth voltage being proportional to a fourth pre-determined amount of charge applied to the sampling capacitor by a second edge of a signal transmitted a stylus.

17. The device of claim 16, wherein the logic is further configured to apply a first amount of current to the capacitance prior to receiving the first edge and a second amount of current to the capacitance prior to receiving the second edge, the second current having an inverse polarity than the first current relative to the capacitance.

18. The device of claim 16, wherein the logic is further configured to:

invert a sign of the third and fourth voltages; and

subtract a sum of the first and second voltages from a sum of the third and fourth voltages, the subtraction substantially suppressing low-frequency noise in the first, second, third and fourth voltages.

19. The device of claim 15, wherein the logic is further configured to:

detect the first edge of the signal; and

determine a frequency of the signal based at least in part on the detection of the first edge.

20. The device of claim 19, wherein a timing of the application of the second pre-determined amount of charge and the determination of the first voltage is based at least in part on the determination of the frequency.