Electrostatic capacity type touch sensor
The invention provides an electrostatic capacity type touch sensor that is not influenced by a parasitic capacitor formed between a sensor line connected to a touch sensor pad and other signal line and provides a stable sensor output. A sensor line connected to a touch sensor pad is connected to a non-inverting input terminal (+) of a charge amplifier. An LED is disposed in the touch sensor pad, and the cathode of the LED is connected to an LED signal line. Since the LED signal line is disposed adjacent to the sensor line, a parasitic capacitor is formed between the LED signal line and the sensor line. In order to keep the capacitance of this parasitic capacitor constant, a pull-up resistor is connected to the LED signal line. The LED signal line is biased to a power supply potential Vdd by the pull-up resistor.
1. An electrostatic capacity type touch sensor, comprising:
a touch sensor pad;
a sensor line connected to the touch sensor pad;
a charge amplifier having a first input connected to the sensor line and outputting an output voltage corresponding to a change of a capacitance at the touch sensor pad;
a signal line disposed adjacent to the sensor line that connects a vibration motor associated with the touch sensor pad that indicates touch detection to a drive transistor that drives the signal line between a first potential and a second potential in correspondence with the output voltage of the charge amplifier, wherein the vibration motor is connected between the first potential and the signal line;
a parasitic capacitor formed between the sensor line and the signal line; and
a bias resistor connected in parallel with the vibration motor associated with the touch sensor pad that biases the signal line to a first potential so as to avoid floating of the signal line.
2. The electrostatic capacity type touch sensor of claim 1 , wherein the bias resistor and the drive transistor, serially connected to each other, are coupled between the first potential and the second potential.
3. The circuit of claim 1 , wherein upon a change of capacitance of the first touch sensor pad occurring, the output of the charge amplifier changes such that the drive transistor activates the vibration motor.
4. An electrostatic capacity type touch sensor, comprising:
a first touch sensor pad having two sub touch sensor pads;
a second touch sensor pad;
a light emitting element disposed between the two sub touch sensor pads of the first touch sensor pad;
a first sensor line connected to the first touch sensor pad;
a second sensor line connected to the second touch sensor pad;
a first signal line connected to the light emitting element and disposed adjacent to the first sensor line;
a parasitic capacitor formed between the first sensor line and the first signal line;
a charge amplifier having a first input end connected to the first sensor line and a second input end connected to the second sensor line, the charge amplifier outputting an output voltage responsive to a difference between a capacitance of the first touch sensor pad and a capacitance of the second touch sensor pad;
a bias resistor connected in parallel with the light emitting element that biases the first signal line to a first potential so as to maintain the parasitic capacitance constant; and
a drive transistor driving the first signal line from the first potential to a second potential corresponding to the output voltage of the charge amplifier to turn on the light emitting element.
5. The electrostatic capacity type touch sensor of claim 4 , wherein each of the two sub touch sensor pads is surrounded by the common voltage line, and wherein the component associated with the touch sensor pad is disposed between the two sub touch sensor pads.
6. The electrostatic capacity type touch sensor of claim 4 , wherein each of the sub touch sensor pads is surrounded by, and electrically shielded from, a common voltage line.
7. The electrostatic capacity type touch sensor of claim 6 , wherein the common voltage line is driven with an alternating current (AC) power supply.
8. An electrostatic capacity type touch sensor comprising:
a touch sensor pad that comprises two sub touch sensor pads;
a sensor line connected to the touch sensor pad;
a charge amplifier having a first input connected to the sensor line and outputting an output voltage corresponding to a change of a capacitance at the touch sensor pad;
a signal line disposed adjacent to the sensor line that connects a component associated with the touch sensor pad that indicates touch detection to a drive transistor that drives the signal line between a first potential and a second potential in correspondence with the output voltage of the charge amplifier, wherein the component is connected between the first potential and the signal line, and wherein the component associated with the touch sensor pad is disposed between the two sub touch sensor pads;
a parasitic capacitor formed between the sensor line and the signal line; and
a bias resistor connected in parallel with the component associated with the touch sensor pad that biases the signal line to a first potential so as to avoid floating of the signal.
9. The electrostatic capacity type touch sensor of claim 8 , wherein the component associated with the touch pad sensor is a light emitting diode (LED).
10. The electrostatic capacity type touch sensor of claim 9 , wherein the signal line is connected to a cathode of the LED and the first potential is applied to an anode of the LED.
11. The electrostatic capacity type touch sensor of claim 9 , wherein the signal line is connected to an anode of the LED and the first potential is applied to a cathode of the LED.
12. The electrostatic capacity type touch sensor of claim 8 , wherein the bias resistor and the drive transistor, serially connected to each other, are coupled between the first potential and the second potential.
13. The electrostatic capacity type touch sensor of claim 8 , wherein the touch sensor pad is surrounded by, and electrically shielded from a common voltage line.
14. The electrostatic capacity type touch sensor of claim 13 , wherein the common voltage line is driven with an alternating current (AC) power supply.
15. The electrostatic capacity type touch sensor of claim 8 , wherein the charge amplifier has a second input that is connected to a different touch sensor pad.
16. A circuit for a touch sensor, comprising:
a first touch sensor pad and a second touch sensor pad, wherein the first touch sensor pad comprises two sub touch sensor pads;
a component associated with the first touch sensor pad to indicate touch detection at the first touch sensor pad and having a first terminal coupled to a first potential, wherein the component is a light emitting diode disposed between the two sub touch sensor pads;
a first sensor line connected to the first touch sensor pad and a second sensor line connected to the second touch sensor pad;
a first signal line connected to a second terminal of the component and disposed adjacent to the first sensor line, forming a parasitic capacitor between the first sensor line and the first signal line;
a charge amplifier having a first input connected to the first sensor line and a second input connected to the second sensor line, the charge amplifier outputting an output voltage corresponding to a difference between a capacitance of the first touch sensor pad and a capacitance of the second touch sensor pad wherein the capacitance of the second touch sensor pad acts as a reference;
a bias resistor connected in parallel with the component that biases the first signal line to the first potential so as to maintain the parasitic capacitance constant; and
a drive transistor driving the first signal line from the first potential to a second potential in correspondence with the output voltage of the charge amplifier.
17. The circuit of claim 16 , further comprising a common voltage line surrounding and electrically shielded from each of the sub touch sensor pads.
18. A circuit for a touch sensor, comprising:
a first touch sensor pad and a second touch sensor pad;
a vibration motor associated with the first touch sensor pad to indicate touch detection at the first touch sensor pad and having a first terminal coupled to a first potential;
a first sensor line connected to the first touch sensor pad and a second sensor line connected to the second touch sensor pad;
a first signal line connected to a second terminal of the vibration motor and disposed adjacent to the first sensor line, forming a parasitic capacitor between the first sensor line and the first signal line;
a charge amplifier having a first input connected to the first sensor line and a second input connected to the second sensor line, the charge amplifier outputting an output voltage corresponding to a difference between a capacitance of the first touch sensor pad and a capacitance of the second touch sensor pad wherein the capacitance of the second touch sensor pad acts as a reference;
a bias resistor connected in parallel with the component that biases the first signal line to the first potential so as to maintain the parasitic capacitance constant; and
a drive transistor driving the first signal line from the first potential to a second potential in correspondence with the output voltage of the charge amplifier.