Signal processing circuit for electrostatic capacitor type touch sensor
View Patent ↗The invention realizes certainly detecting two or more positions on a touch panel that are touched at the same time. A drive circuit selects one from X lines, and supplies an alternating drive voltage to the selected line. A multiplexer selects a first sense line and a second sense line from Y lines that extend to cross the X lines. A charge amplifier outputs an output voltage corresponding to a difference between a first capacitance between the first sense line and the X line selected by the drive circuit and a second capacitance between the second sense line and the X line selected by the drive circuit. A touch position is then detected based on the output voltage of the charge amplifier.
1. A signal processing circuit for an electrostatic capacitor type touch sensor comprising a plurality of drive lines disposed on a substrate and a plurality of sense lines disposed on the substrate and intersecting the drive lines, the signal processing circuit comprising:
a drive circuit selecting one of the drive lines and supplying a first alternating drive voltage to the selected drive line;
a multiplexer selecting a first sense line and a second sense line from the sense lines; and
a charge amplifier outputting an output voltage corresponding to a difference between a first capacitance of a first capacitor and a second capacitance of a second capacitor, the first capacitor being formed between the first sense line selected by the multiplexer and the drive line selected by the drive circuit, and the second capacitor being formed between the second sense line selected by the multiplexer and the drive line selected by the drive circuit, wherein the charge amplifier comprises a third capacitor, a fourth capacitor, and a differential amplifier,
the first capacitor and the third capacitor are connected to each other through a first connecting node,
the second capacitor and the fourth capacitor are connected to each other through a second connecting node,
the differential amplifier comprises first and second input terminals, the first input terminal being connected directly to the first connecting node, and the second input terminal being connected directly to the second connecting node,
the third capacitor and the fourth capacitor are connected to each other through a third connection node, and
the signal processing circuit further comprising a power supply configured to supply a second alternating drive voltage to the third connection node, the first and second alternating drive voltages being opposite in phase to each other.
2. The signal processing circuit of claim 1 , wherein the processing circuit is configured so that the output voltage is fed to an external device for determining a touch position.
3. The signal processing circuit of claim 1 , wherein the drive circuit comprises a power supply generating the first alternating drive voltage, a plurality of switches connected between the power supply and the drive lines, and a selection circuit turning on and off the switches sequentially.
4. The signal processing circuit of claim 1 , wherein the first sense line and the second sense line are disposed next to each other.
5. The signal processing circuit of claim 1 , further comprising an AD converter converting the output voltage of the charge amplifier to a digital value.