Mutual capacitance sensing circuits, methods and systems

• US 9,013,195 B2
• Filed: 07/27/2011
• Issued: 04/21/2015
• Est. Priority Date: 08/23/2010
• Status: Active Grant

• Current Assignee: Parade Technologies, Ltd.
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Kremin, Victor, Maharyta, Andriy, Prendergast, Patrick
• Primary Examiner(s): Koval, Melissa
• Assistant Examiner(s): HOQUE, FARHANA AKHTER
• Application Number:
  US13/191,708
• Publication Number:
  US 20120043977A1
• Time in Patent Office: 1,364 Days
• Field of Search: 324658-690, 345/174
• US Class Current: 324/686
• 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 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• 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

A capacitance sensing system may include a first selection circuit that couples N electrodes of a first electrode set to a capacitance sense circuit; and a second selection circuit that couples M electrodes of a second electrode set, substantially simultaneously, to a signal generator circuit as a group to induce current in the N electrodes by mutual capacitance between the M and N electrodes; wherein N is at least one, and M>N.

Claims

1. A capacitance sensing system, comprising:

a first selection circuit that couples N electrodes of a first electrode set to a capacitance sense circuit, wherein the first selection circuit couples the N electrodes to the capacitance sense circuit in a first sense portion of a sensing operation, and further couples L electrodes of the first electrode set to a signal generator circuit in a second sense portion of the sensing operation; and

a second selection circuit that couples M electrodes of a second electrode set, substantially simultaneously, to the signal generator circuit as a group to induce current in the N electrodes by mutual capacitance between the M and N electrodes;

wherein N is at least one, and M>

N, wherein the second selection circuit couples the M electrodes of the second electrode to the signal generator circuit in the first sense portion, and further couples K electrodes of the second electrode set to the capacitance sense circuit in the second sense portion, and wherein K is at least one, and L>

K.

2. The capacitance sensing system of claim 1, wherein:

N is one and M is all electrodes of the second set.

3. The capacitance sensing system of claim 1, wherein:

the first selection circuit sequentially couples different groups of N electrodes of the first electrode set to the capacitance sense circuit while the second selection circuit couples the M electrodes to the signal generator circuit.

4. The capacitance sensing system of claim 1, wherein:

K is one and L is all electrodes of the first set.

5. The capacitance sensing system of claim 1, wherein:

the first set of electrodes are disposed substantially parallel to one another in a first direction; and

the second set of electrodes is disposed substantially parallel to one another in a second direction different from the first direction.

6. The capacitance sensing system of claim 1, wherein:

the sense circuit includes a current sense circuit that generates a read current that varies according to a sensed capacitance, and an ADC that converts the read current into a digital value.

7. A method, comprising:

in a first sense portion of a sensing operation,

coupling a subset of N electrodes of a first electrode set to a capacitance sense circuit, and

coupling a subset of M electrodes of a second electrode set, substantially simultaneously, to a signal generator circuit as a group to induce current in the N electrodes by mutual capacitance between the M and N electrodes;

in a second sense portion of the sensing operation,

coupling L electrodes of the first electrode set to the signal generator circuit, and

coupling K electrodes of the second electrode set to the capacitance sense circuit in the second sense portion, and wherein K is at least one, and L >

K, wherein N is at least one, and M >

N; and

generating first object position data by detecting change in mutual capacitance between the N electrodes and the M electrodes by sensing electrical changes induced in the N electrodes in response to electrical signals driven on the M electrodes substantially simultaneously.

8. The method of claim 7, further including:

generating second object position data by detecting change in mutual capacitance between subsets of second electrodes and a larger group of first electrodes.

9. The method of claim 7, wherein:

generating first object position data includes sequentially measuring mutual capacitance between each first electrode and all second electrodes.

10. The method of claim 7, wherein driving at least one first set of the second electrodes with a first time varying signal while driving a second group of the second electrodes with a second time varying signal that is different than the first periodic signal.

11. The method of claim 10, wherein:

detecting change in mutual capacitance further includes converting induced current into a digital value.

12. The method of claim 7, further including:

generating calibration values for multiple subsets of first electrodes by measuring a mutual capacitance between each of the multiple subsets of first electrodes and larger group of second electrodes while an object is not within a predetermined proximity of the electrodes.