CAPACITANCE SENSOR

• US 20090224775A1
• Filed: 03/10/2009
• Published: 09/10/2009
• Est. Priority Date: 03/10/2008
• Status: Active Grant

• Current Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Original Assignee: Fujitsu Microelectronics Limited (Fujitsu Limited)
• Inventors: Nishizono, Kazunori
• Granted Patent: US 8,283,934 B2
• Time in Patent Office: Days
• 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 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.

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 voltage loaded into the second capacitor, wherein

a first detection operation configured to detect the voltage loaded into the first capacitor, and a second detection operation configured to detect the 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 first charging voltage detector includes:

a first comparator configured to compare a detection voltage obtained from the first detection operation of the detection circuit with a first threshold and, when the detection voltage exceeds the first threshold, transmits output signals of an H level; and

a first counter configured to transmit a first detection flag based on a count value in which the output signals of the H level from the first comparator are counted,

the second charging voltage detector includes;

a second comparator configured to compare a detection voltage obtained from the second detection operation of the detection circuit with a second threshold and, when the detection voltage exceeds the second threshold, to transmit output signals of the H level; and

a second counter configured to transmit a second detection flag based on a count value in which the output signals of the H level from the second comparator are counted, and

the first and second charging voltage detectors further include a determiner configured to generate the determination signal based on the first and second detection flags.

4. The capacitance sensor according to claim 3, wherein

the second threshold is set at a voltage higher than the first threshold.

5. The capacitance sensor according to claim 2, wherein

the detection circuit includes:

an operational amplifier including a feedback capacitor provided between an input terminal and an output terminal of the operational amplifier;

a first switch coupled in parallel to the feedback capacitor;

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 a low potential side reference voltage to the first capacitor and the second capacitor; and

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

when rendering the first switch conductive, and resetting the signals output from the operational amplifier, the low potential side reference voltage is supplied to the first and second capacitors by the third switch while, when rendering the first switch non-conductive, the high potential side reference voltage is supplied to the first and second capacitors by the fourth switch.

6. The capacitance sensor according to claim 5, 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.

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

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

8. The capacitance sensor according to claim 5, 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.

9. The capacitance sensor according to claim 5, 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.

10. The capacitance sensor according to claim 5, 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.