SIGNAL PROCESSING CIRCUIT FOR ELECTROSTATIC CAPACITY TYPE TOUCH SENSOR

• US 20110012863A1
• Filed: 07/15/2010
• Published: 01/20/2011
• Est. Priority Date: 07/15/2009
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Inventors: Suzuki, Tatsuya, Kaneta, Yasuhiro, KOBAYASHI, Kazuyuki, Fukai, Kumiko
• Granted Patent: US 8,878,812 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G06F 3/03547 Touch pads, in which fingers can move on a surface
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes

Abstract

There is offered a signal processing circuit for an electrostatic capacity type touch sensor capable of detecting a larger number of locations with a smaller number of touch pads as well as improving noise immunity. A selection circuit selects either a signal from a combination of the first and second kinds of touch pads outputted through the first and second output terminals CO1 and CO2 in a touch panel or a signal from a combination of the third and fourth kinds of touch pads outputted through the third and fourth output terminals CO3 and CO4. An electric charge amplifier outputs first and second output voltages V1 and V2 corresponding to a difference between capacitances of the touch pads on the touch panel based on the signals from the selected combination. A delta sigma type A/D converter converts the first and second output voltages V1 and V2 into digital signals.

Claims

1. A signal processing device comprising:

a touch panel comprising,

a plurality of pairs of touch pads, each of the touch pads being a first kind of touch pad, a second kind of touch pad, a third kind of touch pad or a fourth kind of touch pad, and each of the pairs of touch pads comprising two touch pads of a single kind or two touch pads of two different kinds, and

an excitation pad disposed between neighboring two of the pairs of touch pads; and

a signal processing circuit for the touch panel comprising,

an alternating current power supply providing the excitation pad with an alternating voltage,

an electric charge amplifier generating a first output voltage corresponding to a difference between a capacitance of a first capacitor formed between the excitation pad and the first kind of touch pad and a capacitance of a second capacitor formed between the excitation pad and the second kind of touch pad and generating a second output voltage corresponding to a difference between a capacitance of a third capacitor formed between the excitation pad and the third kind of touch pad and a capacitance of a fourth capacitor formed between the excitation pad and the fourth kind of touch pad; and

a delta sigma type A/D converter converting each of the first and second output voltages generated by the electric charge amplifier into a digital value.

2. The signal processing circuit of claim 1, further comprising a selection circuit selecting the first and second kinds of touch pads in a first phase and the third and fourth kinds of touch pads in a second phase, the electric charge amplifier generating the first output voltage in the first phase and generating the second output voltage in the second phase.

3. The signal processing circuit of claim 1, further comprising a voltage amplifier amplifying the first and second output voltages outputted from the electric charge amplifier, an output of the voltage amplifier being inputted to the delta sigma type A/D converter.

4. The signal processing circuit of claim 3, wherein each of the voltage amplifier and the delta sigma type A/D converter comprise a switched capacitor circuit.

5. The signal processing circuit of claim 1, further comprising an arithmetic circuit performing a calculation so as to find the touch position based on a correlation between the touch position and a ratio of the second output voltage to the first output voltage converted into the digital values by the delta sigma type A/D converter.

6. The signal processing circuit of claim 1, wherein the plurality of pairs of touch pads comprises a first pair of touch pads comprising the first kind of touch pad, a second pair of touch pads comprising the first kind of touch pad and the third kind of touch pad, a third pair of touch pads comprising the third kind of touch pad, a fourth pair of touch pads comprising the third kind of touch pad and the second kind of touch pad, fifth pair of touch pads comprising the second kind of touch pad, sixth pair of touch pads comprising the second kind of touch pad and the fourth kind of touch pad, a seventh pair of touch pads comprising the fourth kind of touch pad and a eighth pair of touch pads comprising the fourth kind of touch pad and the first kind of touch pad.