Touch device and signal processing circuit as well as operating method thereof

Patent metadata

Field	Value
Publication number	US-10268314-B2
Application number	US-201715470055-A
Country	US
Kind code	B2
Filing date	Mar 27, 2017
Priority date	Mar 27, 2017
Publication date	Apr 23, 2019
Grant date	Apr 23, 2019

Abstract

A signal processing circuit of a touch device including an operational amplifier, a feedback resistor and a step current circuit is provided. The feedback resistor connects between a negative input and an output terminal of the operational amplifier. The step current circuit is coupled to the negative input of the operational amplifier and configured to provide or draw a step current to reduce the current flowing through the feedback resistor so as to compensate the voltage offset of the operational amplifier.

First claim

What is claimed is:

1. A signal processing circuit of a touch device, the signal processing circuit comprising:
an integrated programmable gain amplifier (IPGA), comprising:
a first operational amplifier having a positive input, a negative input and an output terminal;
a feedback resistor connecting between the negative input and the output terminal of the first operational amplifier;
a compensation capacitor connecting between the negative input and the output terminal of the first operational amplifier; and
an input resistor, a first terminal of the input resistor coupled to the negative input of the first operational amplifier;

an attenuation circuit coupled to a second terminal of the input resistor to split a current flowing through the input resistor;
a step current circuit, coupled to the negative input of the first operational amplifier, and configured to provide a step current to the IPGA or draw a step current from the IPGA, the step current circuit comprising a current mirror circuit which comprises a plurality of switching devices; and
a digital back end configured to store control codes for controlling on/off of the plurality of switching devices to determine the step current during a touch detection.

2. The signal processing circuit as claimed in claim 1 , wherein the current flowing through the input resistor is an offset current formed by an offset voltage difference between the IPGA and the attenuation circuit.

3. The signal processing circuit as claimed in claim 1 , wherein the digital back end is configured to
store the control codes in a calibration stage to cause a current flowing through the feedback resistor to have a smallest value, and
control, in a normal stage for the touch detection, the on/off of the plurality of switching devices according to the stored control codes.

4. The signal processing circuit as claimed in claim 1 , wherein the attenuation circuit comprises:
a second operational amplifier having a positive input, a negative input and an output terminal, and the output terminal of the second operational amplifier being coupled to the negative input of the second operational amplifier; and
a shunt resistor having a first terminal being coupled to the output terminal of the second operational amplifier, and a second terminal being coupled to the second terminal of the input resistor.

5. A touch device, comprising:
a capacitive touch panel comprising a plurality of sense electrodes each configured to output a detection signal;
a control chip, comprising:
a plurality of integrated programmable gain amplifiers (IPGAs) respectively coupled to the plurality of sense electrodes to amplify the detection signal, each of the IPGAs comprising:
a first operational amplifier having a positive input, a negative input and an output terminal;
a feedback resistor connecting between the negative input and the output terminal of the first operational amplifier;
a compensation capacitor connecting between the negative input and the output terminal of the first operational amplifier; and
an input resistor, a first terminal of the input resistor coupled to the negative input of the first operational amplifier;

a plurality of attenuation circuits each coupled to a second terminal of the input resistor of one of the IPGAs, and configured to split a current flowing through the input resistor;
a plurality of step current circuits each coupled to the negative input of the first operational amplifier of one of the IPGAs, and configured to provide a step current to the coupled IPGA or draw a step current from the coupled IPGA, each of the plurality of step current circuits comprising a current mirror circuit which comprises a plurality of switching devices; and
a digital back end configured to store control codes for controlling on/off of the plurality of switching devices of each of the plurality of step current circuits to determine the step current to be provided to or drawn from the coupled IPGA during a touch detection.

6. The touch device as claimed in claim 5 , wherein the control chip further comprises:
an analog-to-digital converter, coupled to the output terminal of the first operational amplifier of each of the IPGAs, and configured to convert the amplified detection signal to a digital signal, wherein
the digital back end is coupled to the analog-to-digital converter.

7. The touch device as claimed in claim 6 , wherein the digital back end is configured to
store the control codes in a calibration stage to cause a current flowing through the feedback resistor to have a smallest value, and
control, in a normal stage for the touch detection, the on/off of the plurality of switching devices according to the stored control codes.

8. The touch device as claimed in claim 7 , wherein the control chip further comprises a plurality of drive circuits configured to
output drive signals to the capacitive touch panel in the normal stage, and
not output the drive signals to the capacitive touch panel in the calibration stage.

9. The touch device as claimed in claim 5 , wherein the control chip further comprises a storage device configured to store the control codes respectively corresponding to each of the plurality of IPGAs.

10. The touch device as claimed in claim 5 , wherein each of the attenuation circuit comprises:
a second operational amplifier having a positive input, a negative input and an output terminal, and the output terminal of the second operational amplifier being coupled to the negative input of the second operational amplifier; and
a shunt resistor having a first terminal being coupled to the output terminal of the second operational amplifier, and a second terminal being coupled to the second terminal of the input resistor.

11. An operating method of a touch device, the touch device comprising a capacitive touch panel, an integrated programmable gain amplifier (IPGA), an attenuation circuit, a step current circuit, an analog-to-digital converter and a digital back end, the capacitive touch panel, the attenuation circuit, the step current circuit and the analog-to-digital converter being coupled to the IPGA, the attenuation circuit attenuating a gain of the IPGA, the step current circuit comprising a current mirror circuit which comprises a plurality of switching devices, and the analog-to-digital converter being coupled between the IPGA and the digital back end, the operating method comprising:
entering a calibration stage;
receiving, by the IPGA in the calibration stage, a detection signal outputted by the capacitive touch panel to output an amplified detection signal;
converting, by the analog-to-digital converter in the calibration stage, the amplified detection signal to a digital signal;
controlling, by the digital back end in the calibration stage, on/off of the plurality of switching devices of the step current circuit to provide a step current to the IPGA or draw a step current from the IPGA according to the digital signal to reduce an offset current value caused by an offset voltage difference between the IPGA and the attenuation circuit; and
storing a control code for controlling the on/off of the plurality of switching devices to cause the offset current value to have a smallest value.

12. The operating method as claimed in claim 11 , further comprising:
entering a normal stage; and
controlling, in the normal stage, the plurality of switching devices of the current mirror circuit according to the stored control code.

13. The operating method as claimed in claim 11 , wherein the IPGA comprises:
a first operational amplifier having a positive input, a negative input and a

Assignees

• Pixart Imaging Inc

Inventors

• Lim Wooi-Kip

Classifications

• G06F3/0418 Primary

  for error correction or compensation, e.g. based on parallax, calibration or alignment · CPC title

• G06F3/044

  by capacitive means · CPC title