Apparatus and method for measuring capacitance in touch sensor

• US 8,829,927 B2
• Filed: 10/24/2011
• Issued: 09/09/2014
• Est. Priority Date: 10/24/2011
• Status: Active Grant

• Current Assignee: Zinitix Co., Ltd.
• Original Assignee: Zinitix Co., Ltd.
• Inventors: Kim, Tae Gyu
• Primary Examiner(s): Assouad, Patrick
• Assistant Examiner(s): Nemtzow, Alexander J
• Application Number:
  US13/280,079
• Publication Number:
  US 20130099804A1
• Time in Patent Office: 1,051 Days
• Field of Search: 324658-690, 345173-178
• US Class Current: 324/679
• 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
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 2217/960715 Rc-timing; e.g. measurement of variation of charge time or discharge time of the sensor

Abstract

An apparatus and method are provided to rapidly and accurately measure the variation of capacitance in a panel load of a touch sensor and thus increase touch sensitivity and noise resistance. The apparatus includes a panel driver configured to drive a panel load in the touch sensor according to a reference voltage, and a capacitive load detector configured to measure capacitance of the panel load by sensing a panel load driving current that is applied to the panel load by the panel driver.

Claims

1. An apparatus for measuring capacitance in a touch sensor, the apparatus comprising:

a panel driver configured to drive a panel load in the touch sensor according to a reference voltage; and

a capacitive load detector configured to measure capacitance of the panel load by sensing a panel load driving current that is applied to the panel load by the panel driver,

wherein the capacitive load detector includes;

a rising current detector configured to detect a rising current component of the panel load driving current; and

a falling current detector configured to detect a falling current component of the panel load driving current,

wherein the capacitive load detector further includes a sensing capacitor that is charged by the rising current component or the falling current component,

wherein the capacitive load detector is configured to measure the capacitance of the panel load when the sensing capacitor is fully charged by one of the rising and falling current components,

wherein the capacitance of the panel load is measured when there is no variation in a sensing voltage obtained by the capacitive load detector, and

wherein the capacitive load detector is configured to measure the capacitance of the panel load if a product of a load voltage for driving the panel load and capacitance of a load capacitor in the panel load is substantially the same as a product of the sensing voltage and capacitance of the sensing capacitor.

2. The apparatus of claim 1, wherein the panel driver includes:

a reference voltage generator configured to supply the reference voltage based on an external reference voltage; and

an amplifier configured to supply the panel load with the panel load driving current in response to the reference voltage.

3. The apparatus of claim 2, wherein the amplifier comprises:

an amplifying unit configured to amplify a voltage difference between the reference voltage and a voltage fed back from an output node of the amplifier; and

an output unit coupled to output nodes of the amplifying unit and configured to output the panel load driving current through its output node,

wherein the output unit includes a first PMOS transistor; and

a first NMOS transistor,

wherein the first PMOS transistor and the first NMOS transistor are coupled to each other and are provided between a supply voltage source and a ground source, and

wherein the first PMOS and NMOS transistors have gates coupled to the output nodes of the amplifying unit, respectively, and drains coupled to the output node of the output unit.

4. The apparatus of claim 3, wherein the capacitive load detector comprises:

a second PMOS transistor having a gate electrode coupled to a gate electrode of the first PMOS transistor;

a second NMOS transistor having a gate electrode coupled to a gate electrode of the first NMOS transistor, a drain electrode coupled to a drain electrode of the second PMOS transistor, and a source electrode coupled to the ground source;

a third NMOS transistor having a drain electrode and a gate, both of which are coupled to the drain electrode of the second NMOS transistor and a source electrode coupled to the ground source;

a fourth NMOS transistor having a gate electrode coupled to the gate electrode of the third NMOS transistor and a source electrode coupled to the ground source;

a third PMOS transistor having a drain electrode and a gate electrode both of which are coupled to a drain electrode of the fourth NMOS transistor;

a fourth PMOS transistor having a gate electrode coupled to the gate electrode of the third PMOS transistor; and

a sensing capacitor coupled to and disposed between a drain electrode of the fourth PMOS transistor and the ground source, and

wherein sources of the first to fourth PMOS transistors are coupled to the supply voltage source.

5. The apparatus of claim 4, wherein a first current flowing through the first PMOS transistor is substantially the same as a sum of a second current flowing to the ground source through the first NMOS transistor and the panel load driving current flowing into the panel load.

6. The apparatus of claim 4, wherein the current of the third PMOS transistor copied by the fourth PMOS transistor is charged in the sensing capacitor.

7. The apparatus of claim 4, wherein the first current flowing through the first PMOS transistor is substantially the same as the second current flowing to the ground via the first NMOS transistor when the sensing capacitor is fully charged.

8. The apparatus of claim 7, wherein the panel load driving current flowing into the panel load becomes zero (0) when the sensing capacitor is fully charged.

9. The apparatus of claim 1, wherein the capacitive load detector is configured to detect rising and falling current components of the panel load driving current after the touch sensor is initialized.

10. The apparatus of claim 1, wherein the rising current detector and the falling current detector are inversely activated in response to a selection signal, the rising current detector is activated to detect the rising current component of the panel load driving current when the selection signal has a low value, and the falling current detector is activated to detect the falling current component from the panel load driving current when the selection signal has a high value.

11. The apparatus of claim 10, wherein the rising current component is generated when the panel load is driven by a high voltage.

12. The apparatus of claim 10, wherein the falling current component is generated when the panel load is driven by a low voltage.