Control circuit and control method for touch panel, and touch-type input device and electronic device using the same

• US 10,635,237 B2
• Filed: 10/10/2018
• Issued: 04/28/2020
• Est. Priority Date: 10/11/2017
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Shimada, Yuji
• Primary Examiner(s): Ahn, Sejoon
• Application Number:
  US16/156,420
• Publication Number:
  US 20190107920A1
• Time in Patent Office: 566 Days
• CPC Class Codes: G06F 2203/04104 Multi-touch detection in digitiser, i.e. details about the simultaneous detection of a plurality of touching locations, e.g. multiple fingers or pen and finger
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact
• CPC Class Codes: H03K 17/9645 Resistive touch switches

Abstract

There is provided a control circuit configured for a touch panel. The touch panel includes: a first resistive film and a second resistive film installed with a gap between the first resistive film and the second resistive film; and a first terminal and a second terminal that extend from two opposing sides of the first resistive film. The control circuit includes: a driving circuit configured to apply a driving voltage between the first terminal and the second terminal; and a current detection circuit configured to generate a digital current detection value that indicates a current amount obtained by subtracting a predetermined current from a panel current flowing between the first terminal and the second terminal.

Claims

1. A control circuit configured for a touch panel including a first resistive film, a second resistive film with a gap formed between the first resistive film and the second resistive film, and a first terminal and a second terminal that extend from two opposing sides of the first resistive film, control circuit comprising:

a driving circuit configured to apply a driving voltage between the first terminal and the second terminal;

a sense current generator configured to generate a sense current corresponding to a panel current flowing between the first terminal and the second terminal;

a subtraction circuit configured to subtract a predetermined current from the sense current to generate a corrected sense current in which a ratio of a fluctuation component to a constant component is increased for higher resolution of the fluctuation component upon quantization;

an analog amplification circuit configured to convert the corrected sense current into a current detection value for the quantization; and

a quantization circuit configured to quantize the current detection value.

2. The control circuit of claim 1, wherein the predetermined current is set based on the sense current generated in a non-touch state.

3. The control circuit of claim 1, wherein the sense current generator includes a current copy circuit configured to generate the sense current corresponding to the panel current,

wherein the subtraction circuit includes a variable current source configured to generate a correction current corresponding to the predetermined current,

wherein the analog amplification circuit includes an I/V conversion circuit configured to convert the corrected sense current into a sense voltage as the current detection value, and

wherein the quantization circuit includes an A/D converter configured to convert the sense voltage into a digital current detection value.

4. The control circuit of claim 3, wherein a gain of the I/V conversion circuit is adjustable.

5. The control circuit of claim 3, wherein an input range of the A/D converter is adjustable.

7. The control circuit of claim 3, wherein the I/V conversion circuit includes a transimpedance amplifier configured to receive the driving voltage by a first input and receive a difference between the sense current and the correction current by a second input.

8. The control circuit of claim 1, wherein the control circuit is integrated on a single semiconductor substrate.

6. A control circuit, for a touch panel,

wherein the touch panel comprises:

a first resistive film and a second resistive film installed with a gap between the first resistive film and the second resistive film; and

a first terminal and a second terminal that extend from two opposing sides of the first resistive film,

wherein the control circuit comprises;

a driving circuit configured to apply a driving voltage between the first terminal and the second terminal;

a panel current detector configured to detect a panel sense current flowing between the first terminal and the second terminal; and

a current detection circuit configured to generate a digital current detection value that indicates a current amount obtained by subtracting a predetermined current from the panel current,

wherein the current detection circuit includes;

a current copy circuit configured to generate a sense current corresponding to the panel current;

a variable current source configured to generate a correction current corresponding to the predetermined current;

an I/V conversion circuit configured to convert a difference between the sense current and the correction current into a sense voltage; and

an A/D converter configured to convert the sense voltage into the current detection value,

wherein the driving circuit has a push-pull output stage, and

wherein the current copy circuit is further configured to generate a first copy of a current flowing through a high-side transistor of the output stage and a second copy of a current flowing through a low-side transistor of the output stage, and to use a difference between the first copy and the second copy as the sense current.

9. A method of controlling a touch panel including a first resistive film, a second resistive film with a gap formed between the first resistive film and the second resistive film, and a first terminal and a second terminal that extend from two opposing sides of the first resistive film, the method comprising:

applying a driving voltage between the first terminal and the second terminal;

generating a sense current corresponding to a panel current flowing through the first terminal and the second terminal;

subtracting a predetermined current from the sense current to generate a corrected sense current in which a ratio of a fluctuation component to a constant component is increased for higher resolution of the fluctuation component upon quantization;

converting the corrected sense current into a current detection value;

quantizing the current detection value; and

detecting multi-touch based on the quantized current detection value.

10. The method of claim 9, further comprising determining the predetermined current based on the panel current in a non-touch state in a calibration process prior to detecting the multi-touch.

11. The method of claim 9, wherein quantizing the current detection value includes converting the current detection value into a digital current detection value by an A/D converter, and

wherein the method further comprises optimizing a measurement range of the A/D converter in a calibration process prior to detecting the multi-touch.