CAPACITANCE CHANGE DETECTING CIRCUIT

• US 20110199329A1
• Filed: 06/02/2009
• Published: 08/18/2011
• Est. Priority Date: 11/14/2008
• Status: Abandoned Application

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Brown, Christopher, Kitakado, Hidehito
• Application Number:
  US12/998,336
• Publication Number:
  US 20110199329A1
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G02F 1/13338 Input devices, e.g. touch panels
• 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
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

When a surface of a liquid crystal panel is pressed, the capacitance value of a variable capacitor changes. In at least one embodiment, one electrode of the variable capacitor is connected to a voltage supply line to which a common voltage is applied, and the other electrode of the variable capacitor is connected to a gate electrode of a TFT. The TFT outputs a voltage generated according to the capacitance value of the variable capacitor. One electrode of a control capacitor is connected to the gate electrode of the TFT, and the other electrode of the control capacitor is connected to a control voltage line to which a control voltage is applied. By applying a control voltage to the gate electrode of the TFT through the control capacitor, while the load capacitance of the control voltage line is reduced and a change in capacitance is detected with a high sensitivity, the sensitivity can be adjusted according to the application, person, etc., when used. By this, a capacitance change detecting circuit is provided that can detect a change in capacitance with a high sensitivity and can control the sensitivity when used.

Claims

1. A capacitance change detecting circuit that detects a change in electrostatic capacitance, the capacitance change detecting circuit comprising:

a variable capacitor connected, at its one electrode, to a voltage supply line;

a detection transistor connected, at its gate electrode, to an other electrode of the variable capacitor and outputting an electrical signal generated according to a capacitance value of the variable capacitor; and

a capacitance element connected, at its one electrode, to the gate electrode of the detection transistor and connected, at its other electrode, to a control voltage line.

2. The capacitance change detecting circuit according to claim 1, wherein an insulating film is provided on at least one of the electrodes of the variable capacitor.

3. The capacitance change detecting circuit according to claim 2, wherein a minimum value of a distance between the electrodes of the variable capacitor is limited by the insulating film to between 0.05 μ

m and 0.2 μ

m inclusive.

4. The capacitance change detecting circuit according to claim 1, further comprising an output control switching element that switches whether to output the electrical signal or not, the output control switching element being provided in a path of a current passing through the detection transistor.

5. An image display device that can detect a touch position on a display screen, the image display device comprising:

a display panel including a plurality of pixel circuits and one or more capacitance change detecting circuits; and

a control circuit for the display panel, wherein

each capacitance change detecting circuit includes;

a variable capacitor connected, at its one electrode, to a voltage supply line;

a detection transistor connected, at its gate electrode, to an other electrode of the variable capacitor and outputting an electrical signal generated according to a capacitance value of the variable capacitor; and

a capacitance element connected, at its one electrode, to the gate electrode of the detection transistor and connected, at its other electrode, to a control voltage line.