Capacitance sensor for detecting a charge voltage of a multi-capacitor circuit

• US 8,283,934 B2
• Filed: 03/10/2009
• Issued: 10/09/2012
• Est. Priority Date: 03/10/2008
• Status: Active Grant

• Current Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Original Assignee: Fujitsu Semiconductor Limited (Fujitsu Limited)
• Inventors: Nishizono, Kazunori
• Primary Examiner(s): NATALINI, JEFF WILLIAM
• Application Number:
  US12/401,174
• Publication Number:
  US 20090224775A1
• Time in Patent Office: 1,309 Days
• Field of Search: 324/658
• US Class Current: 324/658
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 2017/9613 using two electrodes per touch switch
• CPC Class Codes: H03K 2217/96072 Phase comparison, i.e. where a phase comparator receives at one input the signal directly from the oscillator, at a second input the same signal but delayed, with a delay depending on a sensing capacitance
• CPC Class Codes: H03K 2217/960745 Capacitive differential; e.g. comparison with reference capacitance
• CPC Class Codes: H03K 2217/960755 Constructional details of capacitive touch and proximity switches

Abstract

A capacitance sensor includes a first charging voltage detector configured to detect a change in a voltage loaded into a first capacitor between an electrode and a ground terminal a second charging voltage detector configured to detect a change in a voltage loaded into a second capacitor among a plurality of electrodes and a determiner configured to generate a determination signal based on a detection voltage transmitted from each of the first charging voltage detector and second charging voltage detector.

Claims

1. A capacitance sensor comprising:

a first charging voltage detector configured to detect a change in a voltage loaded into a first capacitor between a first electrode and a ground terminal;

a second charging voltage detector configured to detect a change in a voltage loaded into a second capacitor between the first electrode and a second electrode; and

a determiner configured to generate a determination signal based on a detection voltage transmitted from each of the first charging voltage detector and second charging voltage detector,

wherein the first charging voltage detector includes;

a first comparator configured to compare a first detection voltage obtained from the first detection operation of the detection circuit with a first threshold;

a first counter configured to count an output from the first comparator,

the second charging voltage detector includes;

a second comparator configured to compare a second detection voltage obtained from the second detection operation of the detection circuit with a second threshold;

a second counter configured to count an output from the second comparator,

wherein the determiner is configured to output the determination signal when detecting an output of the first counter and an output of the second counter.

2. The capacitance sensor according to claim 1, wherein

the first charging voltage detector includes a detection circuit configured to detect the voltage loaded into the first capacitor, and the second charging voltage detector includes a detection circuit configured to detect the charge in voltage loaded into the second capacitor, wherein

a first detection operation configured to detect the charge in voltage loaded into the first capacitor, and a second detection operation configured to detect the charge in voltage loaded into the second capacitor, are carried out in a time division manner by a shared detection circuit.

3. The capacitance sensor according to claim 2, wherein

the shared detection circuit includes:

an operational amplifier having an output terminal and an input terminal coupled one of the first capacitor and second capacitor selectively; and

a first switch coupled between the input terminal and the output terminal,

wherein

when the first switch becomes conductive, a low potential side reference voltage is supplied to the first and second capacitors, when the first switch becomes non-conductive, a high potential side reference voltage is supplied to the first and second capacitors.

4. The capacitance sensor according to claim 3, further comprising:

a generation circuit configured to generate a control signal which open/close-controls each of the first to fourth switches and, after rendering the third switch non-conductive, renders the first switch conductive, then renders the fourth switch conductive.

5. The capacitance sensor according to claim 3, further comprising:

a switch configured to couple a plurality of third capacitors between a plurality of third electrodes to the operational amplifier.

6. The capacitance sensor according to claim 3, further comprising:

a switch configured to, when the first switch conducts, supply a reference voltage to be input into the operational amplifier to the output terminal of the operational amplifier.

7. The capacitance sensor according to claim 3, wherein

the reference voltage is supplied to the input terminal of the operational amplifier through a switch which becomes conductive concurrently with the first switch, and becomes non-conductive prior to the first switch becoming non-conductive.

8. The capacitance sensor according to claim 3, wherein

the determiner is a microcomputer which A/D converts the detection voltages transmitted from the first and second charging voltage detectors into digital signals and, based on the digital signals, generates the determination signal.

9. The capacitance sensor according to claim 3, wherein

the shared detection circuit further includes:

a feedback capacitor provided between the input terminal and the output terminal;

a second switch configured to select one of the first capacitor and second capacitor to be coupled to the input terminal of the operational amplifier;

a third switch configured to, when conducting, supply the low potential side reference voltage to the first capacitor and the second capacitor; and

a fourth switch configured to, when conducting, supply the high potential side reference voltage to the first capacitor and the second capacitor,

wherein the signal output from the operational amplifier is reset when the first switch becomes conductive.

10. The capacitance sensor according to claim 1, wherein the first comparator, when the first detection voltage exceeds the first threshold, transmits an output signal having a first level;

and

the first counter configured to transmit a first detection flag based on a count value,

the second comparator, when the second detection voltage exceeds the second threshold, to transmit an output signal having a first level; and

the second counter configured to transmit a second detection flag based on a count value, and

wherein the determiner generates the determination signal based on the first and second detection flags.

11. The capacitance sensor according to claim 10, wherein the second threshold is set at a voltage higher than the first threshold.

12. The capacitance sensor according to claim 1, wherein the second electrode is connected to a third capacitor connected between the second electrode and the ground terminal.

13. The capacitance sensor according to claim 1,

wherein the first electrode and the second electrode are disposed under a touch surface.

14. The capacitance sensor according to claim 1, wherein the capacitance sensor is a touch sensor.

15. A capacitance sensor comprising:

a first charging voltage detector configured to detect a change in a voltage loaded into a first capacitor between a first electrode and a ground terminal;

a second charging voltage detector configured to detect a change in a voltage loaded into a second capacitor between the first electrode and a second electrode; and

a determiner configured to generate a determination signal based on a detection voltage transmitted from each of the first charging voltage detector and second charging voltage detector,

wherein the first charging voltage detector includes a detection circuit configured to detect the voltage loaded into the first capacitor, and the second charging voltage detector includes a detection circuit configured to detect the charge in voltage loaded into the second capacitor,

wherein a first detection operation configured to detect the charge in voltage loaded into the first capacitor, and a second detection operation configured to detect the charge in voltage loaded into the second capacitor, are carried out in a time division manner by a shared detection circuit,

wherein the shared detection circuit includes;

an operational amplifier having an output terminal and an input terminal coupled one of the first capacitor and second capacitor selectively; and

a first switch coupled between the input terminal and the output terminal,

wherein, when the first switch becomes conductive, a low potential side reference voltage is supplied to the first and second capacitors and, when the first switch becomes non-conductive, a high potential side reference voltage is supplied to the first and second capacitors.

16. The capacitance sensor according to claim 15, wherein

the shared detection circuit further includes:

a feedback capacitor provided between the input terminal and the output terminal;

a second switch configured to select one of the first capacitor and second capacitor to be coupled to the input terminal of the operational amplifier;

a third switch configured to, when conducting, supply the low potential side reference voltage to the first capacitor and the second capacitor; and

a fourth switch configured to, when conducting, supply the high potential side reference voltage to the first capacitor and the second capacitor,

wherein the signal output from the operational amplifier is reset when the first switch becomes conductive.