Measuring body capacitance effect in touch sensitive device

• US 9,444,453 B2
• Filed: 09/11/2009
• Issued: 09/13/2016
• Est. Priority Date: 09/11/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Krah, Christoph Horst, Hotelling, Steven Porter, Yousefpor, Marduke
• Primary Examiner(s): Chow, Van
• Application Number:
  US12/558,380
• Publication Number:
  US 20110061949A1
• Time in Patent Office: 2,559 Days
• US Class Current: 1/1
• 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 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;

and

determining the body capacitance effect based on the captured outputs wherein determining the body capacitance effect includes determining a body capacitance component of the captured outputs indicative of an amount of body capacitance associated with an object proximate to the panel.

2. The method of claim 1, further comprising:

determining whether the captured signals indicate poor object grounding; and

generating an indicator based on the determination.

3. The method of claim 1, further comprising:

programmably scaling the stimulation signal input to the sense channel.

4. The method of claim 1, 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.

5. The method of claim 1, 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.

6. The method of claim 1, 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.

7. The method of claim 1, 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.

8. An apparatus comprising:

a touch sensor panel couplable to a sense channel and a drive channel; and

one or more processors configured to;

enable a mode for measuring a body capacitance effect in the touch sensor;

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

capture outputs of the sense channel comprising signals from the touch sensor panel;

and

determine the body capacitance effect based on the captured outputs, wherein determining the body capacitance effect includes determining a body capacitance component of the captured outputs indicative of an amount of body capacitance associated with an object proximate to the panel.

9. The apparatus of claim 8, the processor further configured to:

determine whether the captured signals indicate poor object grounding; and

generate an indicator based on the determination.

10. The apparatus of claim 8, the processor further configured to:

programmably scale the stimulation signal input to the sense channel.

11. The apparatus of claim 8, the processor further configured to:

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

12. The apparatus of claim 8, the processor further configured to:

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

13. The apparatus of claim 8, the processor further configured to:

subtract 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.

14. The apparatus of claim 8, the processor further configured to:

subtract 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.