ELECTROSTATIC CAPACITY TYPE TOUCH SENSOR

• US 20110199331A1
• Filed: 02/17/2011
• Published: 08/18/2011
• Est. Priority Date: 02/18/2010
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: ON Semiconductor Trading, Ltd (ON Semiconductor Corporation)
• Inventors: Hasegawa, Kazuhiro, Ichikawa, Atsuhiro, OTAGAKI, Takayasu, Ito, Hiroya
• Granted Patent: US 9,041,683 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/044 by capacitive means

Abstract

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.

Claims

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 an input end connected to the sensor line and outputting an output voltage corresponding to a change of a capacitance of a capacitor that the touch sensor pad has;

a signal line disposed adjacent to the sensor line;

a parasitic capacitor formed between the sensor line and the signal line; and

a bias resistor biasing 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, further comprising a light emitting element connected to the signal line, and a drive transistor driving the signal line from the first potential to a second potential corresponding to the output voltage of the charge amplifier to light the light emitting element.

3. The electrostatic capacity type touch sensor of claim 2, wherein the light emitting element is an LED, and the signal line is connected to a cathode of the LED and the first potential is applied to an anode of the LED.

4. The electrostatic capacity type touch sensor of claim 2, wherein the light emitting element is an LED, and the signal line is connected to an anode of the LED and the first potential is applied to a cathode of the LED.

5. The electrostatic capacity type touch sensor of claim 1, further comprising a vibration motor connected to the signal line, and a drive transistor driving the signal line from the first potential to a second potential corresponding to the output voltage of the charge amplifier to operate the vibration motor.

6. An electrostatic capacity type touch sensor comprising:

a first touch sensor pad;

a second touch sensor pad;

a light emitting element;

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 corresponding to a difference between a capacitance of a first capacitor that the first touch sensor pad has and a capacitance of a second capacitor that the second touch sensor pad has;

a bias resistor biasing the first signal line to a first potential so as to avoid floating of the first signal line; 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 light the light emitting element.