ELECTROSTATIC CAPACITY TYPE TOUCH SENSOR

• US 20110199105A1
• 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 8,618,818 B2
• Time in Patent Office: Days
• US Class Current: 324/679
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/0445 using two or more layers of sensing electrodes, e.g. using two layers of electrodes separated by a dielectric layer
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes

Abstract

This invention offers an electrostatic capacity type touch sensor that can be calibrated in a short period of time at a moment when a finger of operator or the like does not touch a touch pad. An absolute value of a difference (AD0−AD2) between a first output voltage AD0 and a third output voltage AD2 is compared with a first threshold value Vtr1 in step S10. When the difference (AD0−AD2) between the output voltages is smaller than the first threshold value Vtr1, it is judged that the finger of operator or the like does not touch the touch pad, and it is judged which of an offset in a second output voltage AD1 and an offset in the third output voltage AD2 is smaller than the other. When the offset in the second output voltage AD1 is smaller than the offset in the third output voltage AD2, the modification to the second calibration data X1 is permitted.

Claims

1. An electrostatic capacity type touch sensor comprising:

a sensor circuit detecting a change in a capacitance of a touch pad;

a calibration register to adjust an offset in an output value of the sensor circuit; and

a control circuit that makes the sensor circuit operate to obtain a first output value of the electrostatic capacity type touch sensor based on calibration data stored in the calibration register, modifies the calibration data depending on the first output value, makes the sensor circuit operate to obtain a second output value of the electrostatic capacity type touch sensor based on the modified calibration data, makes the sensor circuit operate to obtain a third output value of the electrostatic capacity type touch sensor based on the calibration data before the modification, and judges whether an offset in the second output value is larger than an offset in the third output value when a difference between the first output value and the third output value is smaller than a first threshold value.

2. The electrostatic capacity type touch sensor of claim 1, wherein the control circuit permits the modification of the calibration data when the offset in the second output value is smaller than the offset in the third output value, but does not permit the modification of the calibration data when the offset in the third output value is smaller than the offset in the second output value.

3. The electrostatic capacity type touch sensor of claim 1, wherein the control circuit judges whether the offset in the second output value is smaller than the offset in the third output value when the difference between the first output value and the third output value is smaller than the first threshold value and a rate of change in an output value of the sensor circuit is smaller than a second threshold value.

4. The electrostatic capacity type touch sensor of claim 1, wherein the first threshold value is one tenth of a maximum output value of the sensor circuit.

5. The electrostatic capacity type touch sensor of claim 1, wherein the control circuit does not permit the modification of the calibration data when the difference between the first output value and the third output value is larger than the first threshold value.