Touch sensing circuit and method

• US 9,261,546 B2
• Filed: 03/15/2013
• Issued: 02/16/2016
• Est. Priority Date: 11/16/2012
• Status: Active Grant

• Current Assignee: Princeton Technology Corporation
• Original Assignee: Princeton Technology Corporation
• Inventors: Tu, Chieh Yung, Tsai, Chien-Hsien, Lee, Wei-Lung
• Primary Examiner(s): LE, SON T
• Application Number:
  US13/842,563
• Publication Number:
  US 20140139242A1
• Time in Patent Office: 1,068 Days
• Field of Search: 324/686, 324/76.41
• US Class Current: 1/1
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: G06F 3/0202 Constructional details or processes of manufacture of the input device
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 2217/960725 Charge-transfer

Abstract

A touch sensing circuit is provided. The touch sensing circuit includes: a touch capacitor, for being touched; a touch capacitor frequency detection unit, coupled to the touch capacitor, for detecting an output frequency from the touch capacitor; a reference frequency generation unit, for generating a reference frequency; a calculation unit, coupled to the touch capacitor frequency detection unit and the reference frequency generation unit, for calculating the variation of the difference between the output frequency from the touch capacitor and the reference frequency; and a determination unit, coupled to the calculation unit, for determining whether the touch capacitor is being touched based on whether the variation of the difference is greater than a criterion value.

Claims

1. A touch sensing circuit, comprising:

a touch capacitor, for being touched;

a touch capacitor frequency detection unit, coupled to the touch capacitor, for detecting an output frequency from the touch capacitor;

a reference frequency generation unit, for generating a reference frequency;

a calculation unit, coupled to the touch capacitor frequency detection unit and the reference frequency generation unit, for obtaining a difference between the output frequency from the touch capacitor and the reference frequency and calculating a variation rate of the difference accordingly; and

a determination unit, coupled to the calculation unit, for determining whether the touch capacitor is being touched based on whether the variation rate of the difference is greater than a criterion value, wherein the touch capacitor frequency detection unit further comprises;

a Schmitt trigger having an input end for connecting to an input end of the touch capacitor in series; and

a switching capacitor network, wherein the switching capacitor network is coupled to the input end of the Schmitt trigger, and the switching capacitor network further comprises;

two switch transistors, both connected to a node, and alternatively turned on and off according to a switching frequency; and

a ground capacitor, connected to the node and a ground end.

2. The touch sensing circuit as claimed in claim 1, wherein the reference frequency is close to but not equal to the output frequency from the touch capacitor.

3. The touch sensing circuit as claimed in claim 1, wherein the reference frequency generation unit further comprises:

a reference capacitor; and

a reference capacitor frequency sampling unit, coupled to the reference capacitor, for detecting an output frequency from the reference capacitor, wherein the reference capacitor frequency sampling unit and the touch capacitor frequency detection unit have the same circuitry structure.

4. A touch sensing circuit, comprising:

a touch capacitor, for being touched;

a touch capacitor frequency detection unit, coupled to the touch capacitor, for detecting an output frequency from the touch capacitor;

a reference frequency generation unit, for generating a reference frequency;

a calculation unit, coupled to the touch capacitor frequency detection unit and the reference frequency generation unit, for obtaining difference between the output frequency from the touch capacitor and the reference frequency and calculating a variation rate of the difference accordingly; and

a determination unit, coupled to the calculation unit, for determining whether the touch capacitor is being touched based on whether the variation rate of the difference is greater than a criterion value, wherein the touch capacitor frequency detection unit further comprises a charging/discharging circuit, coupled to the touch capacitor for providing a charging voltage and a discharging voltage to the touch capacitor, and the reference frequency generation unit comprises a set of charging switches, coupled between the charging/discharging circuit and the touch capacitor, for controlling the charging/discharging circuit, and the charging/discharging circuit further comprises;

a current mirror, having an input end connected to a power, and an output end connected to a first resistor in series, wherein the first resistor is further connected to a second resistor in series, and the first resistor and the second resistor is connected to a node, wherein the node is used to receive an actual voltage of the capacitor, the first resistor is used to output the discharging voltage, and the second resistor is used to output the charging voltage.

5. The touch sensing circuit as claimed in claim 4, wherein the first resistor and the second resistor have the same resistance.