CURRENT-MODE COARSE-BASELINE-CORRECTION

• US 20150115977A1
• Filed: 10/30/2013
• Published: 04/30/2015
• Est. Priority Date: 10/30/2013
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Synaptics Incorporated
• Inventors: BOHANNON, Eric Scott, HARGREAVES, Kirk, OZBAS, Murat, SMALL, Jeffrey A., BELL, Marshall J. Jr.
• Granted Patent: US 9,541,588 B2
• Time in Patent Office: Days
• US Class Current: 324/601
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: G01R 35/005 Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references G01R33/0035, G01R35/002 take precedence
• 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

The embodiments herein are generally directed to using a current-mode CBC circuit to maintain a voltage bias setting at a receiver when performing capacitive sensing. To do so, the CBC circuit may compensate for the change in voltage at a receiver by providing a current at the input of the receiver. Instead of using a passive CBC capacitor for each receiver, the input device may use a single CBC capacitor and a plurality of current mirrors to source and sink the current required to correct the input voltage at a plurality of receivers. As a result, the current-mode CBC circuit includes only one passive capacitor (or bank of capacitors) and a plurality of current mirrors which may provide space and cost benefits relative to a CBC circuit that uses a passive capacitor (or bank of capacitors) for each receiver channel.

Claims

1. A system comprising:

a sensor comprising a transmitter electrode and a receiver electrode; and

a coarse-baseline-correction (CBC) circuit, the CBC circuit comprising;

a capacitor coupled to the transmitter electrode, and

a current mirror where an input of the current mirror is electrically coupled to the capacitor and an output of the current mirror is coupled to the receiver electrode.

2. The system of claim 1, wherein the current mirror is configured to mirror a current at the input based on a programmable scaling factor.

3. The system of claim 1, wherein the current mirror is part of a current conveyor in the CBC circuit.

4. The system of claim 1, wherein the CBC circuit includes a plurality of current mirrors each comprising a respective input coupled to the capacitor and a respective output coupled to a respective receiver electrode, wherein the sensor includes a plurality of a receiver electrodes.

5. The system of claim 4, wherein each of the plurality of current mirrors are configured to output a current that compensates for a change of charge at the respective receiver electrodes resulting from a transmitter signal driven onto the transmitter electrode.

6. The system of claim 1, wherein the capacitor comprises a programmable bank of capacitors.

7. The system of claim 1, wherein the CBC further comprises a resistance in series with the capacitor, the resistance is configured to synchronize the charge transfer through the sensor and the charge transfer through the CBC circuit.

8. The system of claim 1 further comprising a plurality of receiver circuits, each receiver circuit comprises a first output and a second output, wherein the second outputs from the receiver circuits are summed and the first output and second output have different scaling factors.

9. A processing system comprising:

a transmitter circuit configured to drive a modulated signal on a transmitter electrode;

a receiver circuit configured to receive a resulting signal from a receiver electrode based on the modulated signal; and

a coarse-baseline-correction (CBC) circuit, the coarse-baseline-correction circuit comprising;

a capacitor coupled to an output of the transmitter circuit, and

a current mirror where an input of the current mirror is electrically coupled to the capacitor and an output of the current mirror is coupled to an input of the receiver circuit.

10. The processing system of claim 9, wherein the transmitter circuit, receiver circuit, and the CBC circuit are located on the same integrated circuit.

11. The processing system of claim 9, wherein the current mirror is configured to mirror a current at the input based on a programmable scaling factor.

12. The processing system of claim 9, wherein the current mirror is part of a current conveyor in the CBC circuit.

13. The processing system of claim 9, wherein the CBC circuit includes a plurality of current mirrors each comprising a respective input coupled to the capacitor and a respective output coupled to a respective receiver circuit, wherein the processing system includes a plurality of a receiver circuits.

14. The processing system of claim 13, wherein each of the plurality of current mirrors are configured to output a current that compensates for a change of charge at the inputs of the respective receiver circuits resulting from the modulated signal driven by the transmitter circuit on the transmitter electrode.

15. The processing system of claim 9, wherein the capacitor comprises a programmable bank of capacitors.

16. The processing system of claim 9, wherein the CBC further comprises a resistance in series with the capacitor, the resistance is configured to synchronize the charge transfer through the sensor and the charge transfer through the CBC circuit.

17. The processing system of claim 9 further comprising a plurality of receiver circuits, each receiver circuit comprises a first output and a second output, wherein the second outputs from the receiver circuits are summed and the first output and second output have different scaling factors.

18. A coarse-baseline-correction (CBC) circuit, comprising:

a resistance element;

a capacitor coupled to the resistance element; and

a plurality of current mirrors where each input of the plurality of current mirrors are electrically coupled to the capacitor and each output of the plurality of current mirrors are coupled to an input of respective receiver circuits, wherein the plurality of current mirrors generate respective currents that compensate for a change of charge at the input of the respective receiver circuits.

19. The CBC circuit of claim 18, wherein each of the plurality of currents mirrors include an adjustable scaling factor that varies the respective currents.

20. The CBC circuit of claim 18, wherein a current associated with the capacitor and the resistance element sets the respective currents generated by the plurality of current mirrors.