MEASURING BODY CAPACITANCE EFFECT IN TOUCH SENSITIVE DEVICE

• US 20110061949A1
• Filed: 09/11/2009
• Published: 03/17/2011
• Est. Priority Date: 09/11/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Hotelling, Steven Porter, Yousefpor, Marduke, KRAH, Christoph Horst
• Granted Patent: US 9,444,453 B2
• Time in Patent Office: Days
• US Class Current: 178/18.06
• CPC Class Codes: G02F 1/13338 Input devices, e.g. touch panels
• CPC Class Codes: G06F 2203/04104 Multi-touch detection in digitiser, i.e. details about the simultaneous detection of a plurality of touching locations, e.g. multiple fingers or pen and finger
• 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
• 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 17/962 Capacitive touch switches
• CPC Class Codes: H03K 2217/960705 Safety of capacitive touch and proximity switches, e.g. increasing reliability, fail-safe

Abstract

Measuring an effect of body capacitance in a touch sensitive device is disclosed. This effect can be caused by poor grounding of a user or other objects touching the device or of the device itself. The device can operate in a stray capacitance mode to measure a body capacitance effect and in a normal mode to detect a touch on the device. During the stray capacitance mode, the device can obtain a body capacitance measurement from the device. During the normal mode, the device can obtain a touch measurement from the device. The device can calculate a body capacitance factor based on a ratio between the body capacitance measurement and the touch measurement and use the body capacitance factor to compensate for erroneous or distorted touch output values from the device. Various components of the device can be switchably configured according to the particular mode.

Claims

1. A circuit comprising:

a sense channel having a switchable input;

a drive channel associated with the sense channel; and

switching circuitry coupled to at least the sense channel and configured to operate the circuit in

a first mode for measuring a body capacitance effect of an object proximate to the circuit by transmitting a stimulation signal through the input of the sense channel, and

a second mode for measuring a touch of the object at the circuit by transmitting a reference signal through the input of the sense channel.

2. The circuit of claim 1, wherein the first mode includes transmitting a common voltage signal from the drive channel.

3. The circuit of claim 1, wherein the second mode includes transmitting a second stimulation signal from the drive channel.

4. The circuit of claim 1, further comprising a processor configured to measure the body capacitance effect.

5. The circuit of claim 1 incorporated into at least one of a mobile telephone, a digital media player, or a personal computer.

6. A circuit comprising:

multiple sense channels, each sense channel having at least two inputs;

multiple drive channels associated with the sense channels, each drive channel associated with a first of the at least two inputs of a corresponding sense channel; and

switching circuitry coupled to at least the sense channels and configured to operate the circuit in

a first mode for measuring a body capacitance effect of an object proximate to the circuit by transmitting a stimulation signal from each drive channel to the first input of a corresponding sense channel and by transmitting the stimulation signal to a second of the at least two inputs of at least one of the sense channels, and

a second mode for measuring a touch of the object at the circuit by transmitting a reference voltage to the second input of the at least one of the sense channels.

7. The circuit of claim 6, wherein the first mode includes transmitting the reference voltage to the second input of the remainder of the sense channels.

8. The circuit of claim 6, further comprising:

multiple sense lines, each sense line associated with a corresponding sense channel, wherein the first mode includes

the stimulation signal to the second input of the at least one of the sense channels stimulating a corresponding sense line,

the stimulated sense line injecting charge from a first circuit location associated with the stimulated sense line to a second circuit location associated with another sense line, and

the another sense line transmitting the injected charge to the first input of a corresponding sense channel for measurement.

9. The circuit of claim 8, wherein the injected charge measurement is associated with the body capacitance effect.

10. The circuit of claim 6, wherein the second mode includes transmitting a second stimulation signal from each drive channel to the first input of a corresponding sense channel.

11. The circuit of claim 6, wherein the switching circuitry comprises a switch configured to switch the second input of a sense channel based on the mode.

12. A method comprising:

enabling a mode for measuring a body capacitance effect in a touch sensor panel couplable to a sense channel and a drive channel;

switching the sense channel from a reference signal input to a stimulation signal input;

capturing outputs of the sense channel comprising signals from the touch sensor panel indicative of the body capacitance of an object proximate to the panel; and

measuring the body capacitance effect based on the captured outputs.

13. The method of claim 12, further comprising:

determining whether the captured signals indicate poor object grounding; and

generating an indicator based on the determination.

14. The method of claim 12, further comprising:

programmably scaling the stimulation signal input to the sense channel.

15. The method of claim 12, further comprising:

receiving at the drive channel the stimulation signal input, the received drive channel input configured to compensate for a capacitance formed at the panel.

16. The method of claim 12, further comprising:

transmitting the stimulation signal input downstream of the sense channel, the transmitted stimulation signal configured to improve a dynamic range of the sense channel.

17. The method of claim 12, further comprising:

subtracting the stimulation signal input from the captured outputs in order to at least one of increase a dynamic range of the captured outputs or increase a signal-to-noise ratio of the captured outputs.

18. The method of claim 12, further comprising:

subtracting the stimulation signal input from the captured outputs in order to reduce a dependency of the captured outputs on a frequency-dependent phase shift of the stimulation signal input.

19. A method comprising:

obtaining a first capacitance measurement from a device during a first mode of the device;

obtaining a second capacitance measurement from the device during a second mode of the device;

calculating a ratio between the first and second capacitance measurements; and

calculating a capacitance factor based on the calculated ratio.

20. The method of claim 19, wherein obtaining the first capacitance measurement comprises:

enabling the first mode of the device;

capturing outputs from the device associated with a capacitance change indicative of a object touch at the device; and

obtaining the first capacitance measurement from the captured outputs.

21. The method of claim 19, wherein obtaining the second capacitance measurement comprises:

enabling the second mode of the device;

capturing outputs from the device associated with a capacitance indicative of poor grounding of an object proximate to the device; and

obtaining the second capacitance measurement from the captured outputs.

22. The method of claim 19, further comprising:

applying the capacitance factor to outputs of the device to correct for poor grounding.

23. A touch sensitive device comprising:

a touch sensor panel configured to sense an object proximate thereto;

scan logic couplable to the touch sensor panel and configured to perform a first scan sequence on the panel to measure a touch by the object at the panel during a first mode and to perform a second scan sequence on the panel to measure grounding of the object during a second mode; and

a processor configured to compensate touch measurements according to grounding measurements.

24. The device of claim 23, wherein the second scan sequence is further performed to determine an occurrence of the touch by the object at the panel and wherein the device switches to the first mode if the touch is determined to have occurred.

25. The device of claim 23, wherein the scan logic concurrently performs the first scan sequence and the second scan sequence or the scan logic alternates between performing the first scan sequence and the second scan sequence.