Detector and detection method for a capacitive touchpad to identify a real touch point

• US 8,519,975 B2
• Filed: 06/21/2010
• Issued: 08/27/2013
• Est. Priority Date: 06/25/2009
• Status: Active Grant

• Current Assignee: Elan Microelectronics Corporation
• Original Assignee: Elan Microelectronics Corporation
• Inventors: Huang, Chun-Chung, Wang, Tsun-Min, Chiu, Te-Sheng
• Primary Examiner(s): Bibbins, Latanya
• Application Number:
  US12/819,477
• Publication Number:
  US 20100328262A1
• Time in Patent Office: 1,163 Days
• Field of Search: 345/173, 345/174
• US Class Current: 345/174
• 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 3/04166 Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184
• CPC Class Codes: G06F 3/041662 using alternate mutual and self-capacitive scanning
• CPC Class Codes: G06F 3/04186 Touch location disambiguation
• 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

A two-step detection for a capacitive touchpad to identify a real touch point first detects the self capacitances from multiple capacitance sensor traces of the capacitive touchpad to identify any touch point on the capacitive touchpad and then, if multiple touch points are detected, further detects the mutual capacitance at one of the detected touch points to identify whether it is a real touch point.

Claims

1. A detection method for a capacitive touchpad including a plurality of capacitance sensor traces, the detection method comprising the steps of:

(A) detecting self capacitances from the plurality of capacitance sensor traces for identifying any touch point on the capacitive touchpad; and

(B) if a plurality of touch points are detected in the step (A), detecting a mutual capacitance at one of the plurality of touch points for identifying whether it is a real touch point;

wherein the step (A) comprises the steps of;

applying a first voltage to charge a detected capacitance sensor trace selected from the plurality of capacitance sensor traces;

setting a voltage across a gain control capacitor array;

connecting the detected capacitance sensor trace to a first terminal of the gain control capacitor array under compensating the self capacitor of the detected capacitance sensor trace;

extracting a first sense signal from a second terminal of the gain control capacitor array;

applying a second voltage to charge the detected capacitance sensor trace, wherein a voltage difference between the first voltage and a voltage on the first terminal of the gain control capacitor array, and a voltage difference between the second voltage and the voltage on the first terminal of the gain control capacitor array, are equal in magnitude but opposite in polarity;

resetting the voltage across the gain control capacitor array;

connecting the detected capacitance sensor trace to the first terminal of the gain control capacitor array under compensating the self capacitor of the detected capacitance sensor trace;

extracting a second sense signal from the second terminal of the gain control capacitor array; and

extracting an average from the first and second sense signals to determine whether the detected capacitance sensor trace has a touch point thereon.

2. The detection method of claim 1, wherein each touch point detected from the step (A) is at an intersection of two of the plurality of capacitance sensor traces.

3. A detection method for a capacitive touchpad including a plurality of capacitance sensor traces, the detection method comprising the steps of:

(A) detecting self capacitances from the plurality of capacitance sensor traces;

(B) detecting mutual capacitances at intersections of the plurality of capacitance sensor traces; and

(C) identifying a touch point according to the self capacitances and the mutual capacitances;

wherein the step (B) comprises the steps of;

(a) during a first time phase, setting a voltage across a mutual capacitor between two of the plurality of capacitance sensor traces, and a voltage across a capacitor array; and

(b) during a second time phase, switching the voltage on one of the two capacitance sensor traces from a first voltage to a second voltage and connecting the other of the two capacitance sensor traces to a first terminal of the capacitor array, to thereby cause a variation of the voltage on a second terminal of the capacitor array.

4. The detection method of claim 3, wherein the step (a) comprises the step of applying a third voltage to the first and second terminals of the capacitor array for setting the voltage across the capacitor array.

5. The detection method of claim 4, wherein the third voltage is equal to the second voltage.

6. The detection method of claim 5, wherein the step (b) comprises the steps of:

applying the second voltage to a first input terminal of an operational amplifier;

connecting the other of the two capacitance sensor traces and the first terminal of the capacitor array to a second input terminal of the operational amplifier; and

connecting the second terminal of the capacitor array to an output terminal of the operational amplifier.

7. The detection method of claim 4, wherein the third voltage is equal to the first voltage.

8. The detection method of claim 7, wherein the step (b) comprises the steps of:

applying the first voltage to a first input terminal an operational amplifier;

connecting the other of the two capacitance sensor traces and the first terminal of the capacitor array to a second input terminal of the operational amplifier; and

connecting the second terminal of the capacitor array to an output terminal of the operational amplifier.

9. A detector for a capacitive touchpad including two capacitance sensor traces which have a mutual capacitor therebetween at an intersection thereof, the detector comprising:

a self negative capacitance compensator for compensating a self capacitor of a first one of the two capacitance sensor traces;

a first switch connected between the self negative capacitance compensator and the first capacitance sensor trace;

a switching circuit connected to the first capacitance sensor trace for applying one of a plurality of supply voltages to the first capacitance sensor trace;

a mode switching device connected to the two capacitance sensor traces;

a second switch connected between the first capacitance sensor trace and the mode switching device; and

a sensing circuit connected to the mode switching device, for detecting the self capacitance of the first capacitance sensor trace or the mutual capacitance at the intersection, to thereby generate a sense signal;

wherein the mode switching device connects the first capacitance sensor trace to the sensing circuit in a first mode to detect a variation of the self capacitance from the first capacitance sensor trace, and connects the second capacitance sensor trace to the sensing circuit in a second mode to detect a variation of the mutual capacitance at the intersection.

10. The detector of claim 9, wherein the sensing circuit comprises:

an operational amplifier having a first input terminal to receive a second one of the plurality of supply voltages, a second input terminal connected to the mode switching device, and an output terminal to provide the sense signal;

a third switch connected between the second input terminal and the output terminal of the operational amplifier;

a first capacitor array connected between the second input terminal and the output terminal of the operational amplifier; and

a second capacitor array connected to the output terminal of the operational amplifier for storing the sense signal.

11. The detector of claim 10, wherein the switching circuit comprises:

a fourth switch connected between the first capacitance sensor trace and a node having a third one of the plurality of supply voltages;

a fifth switch connected between the first capacitance sensor trace and a node having a fourth one of the plurality of supply voltages; and

a sixth switch connected between the first capacitance sensor trace and a node having a fifth one of the plurality of supply voltages, wherein a voltage difference between the third supply voltage and a voltage on the first input terminal of the operational amplifier, and a voltage difference between the fifth supply voltage and the voltage on the first input terminal of the operational amplifier, are equal in magnitude but opposite in polarity.

12. The detector of claim 9, wherein the sensing circuit comprises:

an operational amplifier having a first input terminal to receive a second one of the plurality of supply voltages, a second input terminal connected to the mode switching device, and an output terminal to provide the sense signal;

a third switch connected between the second input terminal and the output terminal of the operational amplifier;

a first capacitor array having a first terminal connected to the second input terminal of the operational amplifier, and a second terminal;

a second switching circuit connected to the second terminal of the first capacitor array, for connecting the second terminal of the first capacitor array to the output terminal of the operational amplifier or a node having the second supply voltage; and

a second capacitor array connected to the output terminal of the operational amplifier for storing the sense signal.

13. The detector of claim 12, wherein the second switching circuit comprises:

a fourth switch connected between the second terminal of the first capacitor array and the node having the second supply voltage; and

a fifth switch connected between the second terminal of the first capacitor array and the output terminal of the operational amplifier.

14. The detector of claim 9, further comprising:

an analog-to-digital converter connected to the sensing circuit, for converting the sense signal from analog to digital; and

a microprocessor control unit connected to the analog-to-digital converter, for processing the digital signal.