Capacitive sensor interference determination

• US 8,258,797 B2
• Filed: 06/24/2009
• Issued: 09/04/2012
• Est. Priority Date: 06/24/2009
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Synaptics Incorporated
• Inventors: Shahparnia, Shahrooz, Hargreaves, Kirk
• Primary Examiner(s): Vazquez, Arleen M
• Application Number:
  US12/491,102
• Publication Number:
  US 20100327882A1
• Time in Patent Office: 1,168 Days
• Field of Search: 324658-690, 345/174, 702/65
• US Class Current: 324/659
• CPC Class Codes: G01D 3/08 with provision for safeguarding the apparatus, e.g. against abnormal operation, against breakdown
• CPC Class Codes: G01D 5/24 by varying capacitance
• 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 2217/96058 Fail-safe touch switches, where switching takes place only after repeated touch
• CPC Class Codes: Y10T 29/49117 Conductor or circuit manufacturing

Abstract

In a method of determining interference in a capacitance sensor, a signal is transmitted on a transmitter sensor channel of the capacitive sensor. The signal is received on a receiver sensor channel of the capacitive sensor, the receiver sensor channel being coupled with an amplifier. Behavior of the amplifier is examined for non-linearity to determine if a level of interference has been received by the receiver sensor channel in conjunction with receipt of the signal.

Claims

1. A method of determining interference in a capacitance sensor device, said method comprising:

transmitting a signal on a transmitter sensor channel of said capacitive sensor;

receiving said signal on a receiver sensor channel of said capacitive sensor, wherein said receiver sensor channel is coupled with an amplifier; and

examining behavior of said amplifier for non-linearity to determine if a level of interference has been received by said receiver sensor channel in conjunction with receipt of said signal.

2. The method as recited in claim 1, further comprising:

setting an indicator in response to an occurrence of said non-linearity.

3. The method as recited in claim 1, wherein said examining behavior of said amplifier for non-linearity comprises:

determining if a saturation condition of said amplifier exists.

4. The method as recited in claim 1, wherein said examining behavior of said amplifier for non-linearity comprises:

determining if insufficient settling of an output current of said amplifier exists.

5. The method as recited in claim 1, wherein said examining behavior of said amplifier for non-linearity comprises:

using a current amplifier to examine a magnitude of an output current of said amplifier.

6. The method as recited in claim 5, wherein said examining behavior of said amplifier for non-linearity further comprises:

comparing said magnitude to a reference current to detect said non-linearity.

7. A capacitive sensor interference determining circuit, said circuit comprising:

an amplifier configured with a first input for receiving a signal from a receiver sensor channel of a capacitive sensor and a second input for a reference voltage;

a current differential amplifier coupled with said amplifier, said current differential amplifier configured to output two differential currents representing differentials of currents utilized in said amplifier; and

a current comparator coupled with said differential amplifier, said current comparator configured to compare said two differential currents to two reference currents to determine whether a non-linearity condition exists in said amplifier.

8. The circuit of claim 7, wherein said current comparator further comprises:

a first comparison output for outputting a result of comparing a first of said two differential currents to a first reference current of said two reference currents; and

a second comparison output for outputting a result of comparing a second of said two differential currents to a second reference current of said two reference currents.

9. The circuit of claim 8, further comprising:

an interference indicator associated with said first comparison output and said second comparison output, wherein said interference indicator is set when either of said first comparison output or said second comparison output is true.

10. The circuit of claim 7, wherein said amplifier comprises a transconductance amplifier.

11. The circuit of claim 7, wherein said non-linearity comprises:

an occurrence of a saturation condition of said output of said amplifier.

12. The circuit of claim 7, wherein said non-linearity comprises:

an occurrence of an insufficient settling of said output of said amplifier.

13. A method of fabricating an interference determining processor system for a capacitive sensor device, said method comprising:

coupling an amplifier with a receiver sensor channel of said processor system, said amplifier configured with a first input for receiving a signal from said receiver sensor channel and a second input for a reference voltage;

coupling a current differential amplifier with an output of said amplifier, said current differential amplifier configured to output two differential currents representing differentials of currents utilized in said amplifier; and

coupling a current comparator with said current differential amplifier, said current comparator configured to compare said two differential currents to two reference currents to determine whether a non-linearity exists in said amplifier.

14. The method as recited in claim 13, further comprising:

coupling a hardware interference indicator with said current comparator, said hardware interference indicator configured to output of an interference indication signal in response to comparisons of said reference currents and said differential currents indicating presence of said non-linearity.

15. The method as recited in claim 13, wherein said coupling an amplifier with a receiver sensor channel of said capacitive sensor comprises:

coupling an transconductance amplifier with said receiver sensor channel.

16. The method as recited in claim 13, wherein said coupling a current comparator with said current differential amplifier comprises:

coupling said current comparator with said current differential amplifier, said current comparator configured to compare said two differential currents to said two reference currents to determine whether an occurrence of a saturation condition of said output of said amplifier exists.

17. The method as recited in claim 13, wherein said coupling a current comparator with said current differential amplifier comprises:

coupling said current comparator with said current differential amplifier, said current comparator configured to compare said two differential currents to said two reference currents to determine whether an occurrence of an insufficient settling of said output of said amplifier exists.