Capacitance sensor with improved noise filtering characteristics, method for noise filtering of capacitance sensor and computer-readable recording medium

• US 9,535,530 B2
• Filed: 06/25/2012
• Issued: 01/03/2017
• Est. Priority Date: 06/24/2011
• Status: Active Grant

• Current Assignee: HiDeep Inc.
• Original Assignee: HiDeep Inc.
• Inventors: Cho, Youngho, Kim, Bonkee
• Primary Examiner(s): Le, Son
• Assistant Examiner(s): Andrews, Brent J
• Application Number:
  US13/531,879
• Publication Number:
  US 20120326734A1
• Time in Patent Office: 1,653 Days
• Field of Search: 324650-690, 345/173, 327100-333
• US Class Current: 1/1
• CPC Class Codes: G01D 3/032 affecting incoming signal, e.g. by averaging; gating undesired signals
• CPC Class Codes: G01D 5/24 by varying capacitance
• CPC Class Codes: G06F 3/0416 Control or interface arrangements specially adapted for digitisers
• 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: G11C 27/026 associated with an amplifier G11C27/028 takes precedence
• CPC Class Codes: H03H 19/004 Switched capacitor networks
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 2217/960705 Safety of capacitive touch and proximity switches, e.g. increasing reliability, fail-safe
• CPC Class Codes: H03K 2217/960725 Charge-transfer

Abstract

Disclosed is a capacitance sensor including: a capacitance-voltage/current converter which converts a capacitance value of a sense capacitor into a voltage signal or a current signal by using an input signal; a multiplier which applies a weight to an output signal of the capacitance-voltage/current converter and outputs the weighted output signal; and an accumulator which accumulates continuously the output signal of the multiplier.

Claims

1. A capacitance sensor comprising:

a capacitance-voltage/current converter which converts a capacitance value of a sense capacitor into a voltage signal or a current signal by using an input signal;

a multiplier which applies one of a plurality of weights, each weight being different from the other weights, to each of a plurality of output signals of the capacitance-voltage/current converter with respect to the sense capacitor and outputs a plurality of weighted samples; and

an accumulator which accumulates continuously the weighted samples of the multiplier;

wherein the capacitance-voltage/current converter and the multiplier comprises;

a first amplifier;

a first switch which controls the on/off of the connection between an input terminal to which the input signal is applied and one end of the sense capacitor;

a second switch which controls the on/off of the connection between the other end of the sense capacitor and a ground;

a third switch which controls the on/off of the connection between the one end of the sense capacitor and the ground;

a fourth switch which controls the on/off of the connection between the other end of the sense capacitor and a first input terminal of the first amplifier; and

a variable capacitor which is located between the first input terminal of the first amplifier and an output terminal of the first amplifier and is connected to the first input terminal of the first amplifier and the output terminal of the first amplifier, and which has a variable capacitance value,

wherein a second input terminal of the first amplifier is connected to the ground and wherein the output terminal of the first amplifier is an output terminal of the multiplier; and

wherein the accumulator comprises;

a sampling capacitor;

a second amplifier;

a sixth switch which controls the on/off of the connection between an output terminal of the multiplier and one end of the sampling capacitor;

a seventh switch which controls the on/off of the connection between the other end of the sampling capacitor and a ground;

an eighth switch which controls the on/off of the connection between the one end of the sampling capacitor and the ground;

a ninth switch which controls the on/off of the connection between the other end of the sampling capacitor and a first input terminal of the second amplifier; and

an accumulation capacitor which is located between and connected to the first input terminal of the second amplifier and an output terminal of the second amplifier,

wherein a second input terminal of the second amplifier is connected to the ground, and the output terminal of the second amplifier is an output terminal of the accumulator.

2. The capacitance sensor of claim 1, wherein the first switch and the second switch are synchronized and are in an ON or OFF state, and the third switch and the fourth switch are synchronized and are in an ON or OFF state, and wherein the third switch and fourth switch are in an OFF-state during an ON-state of the first switch and the second switch, and the first switch and the second switch are in an OFF-state during an ON-state of the third switch and fourth switch.

3. The capacitance sensor of claim 2, wherein the first switch and the second switch are in an ON-state during a time when a phase of a control signal is a first phase, wherein the third switch and fourth switch are in an ON-state during a time when the phase of the control signal is a second phase, and wherein the capacitance sensor functions as a filter.

4. The capacitance sensor of claim 2, further comprising a fifth switch which is synchronized with the first switch and the second switch and is in an ON or OFF state, and is located between and connected to both ends of the variable capacitor.

5. The capacitance sensor of claim 2, wherein an electric charge is charged in the sense capacitor by the input signal during an ON-state of the first switch and the second switch, and wherein the electric charge charged in the sense capacitor is transferred to the variable capacitor during an ON-state of the third switch and fourth switch.

6. The capacitance sensor of claim 1, wherein the sixth switch and the seventh switch are synchronized and are in an ON or OFF state, and the eighth switch and the ninth switch are synchronized and are in an ON or OFF state, and wherein the eighth switch and the ninth switch are in an OFF-state during an ON-state of the sixth switch and seventh switch, and the sixth switch and seventh switch are in an OFF-state during an ON-state of the eighth switch and the ninth switch.

7. The capacitance sensor of claim 6, wherein the eighth switch and the ninth switch are in an ON-state during a time when a phase of a control signal is a first phase, and wherein the sixth switch and seventh switch are in an ON-state during a time when the phase of the control signal is a second phase.

8. The capacitance sensor of claim 6, further comprising a tenth switch which is located between and connected to both ends of the accumulation capacitor, and is synchronized and is in an ON state during a time when a reset signal is applied.

9. The capacitance sensor of claim 6, wherein an electric charge is charged in the sampling capacitor by an output terminal voltage of the multiplier during an ON-state of the sixth switch and seventh switch, and wherein the electric charge charged in the sampling capacitor is accumulated in the accumulation capacitor during an ON-state of the eighth switch and the ninth switch.

10. A capacitance sensor comprising:

a capacitance-voltage/current converter which converts a capacitance value of a sense capacitor into a voltage signal or a current signal by using an input signal;

a plurality of multiplier-holders each of which applies one of a plurality of weights, each weight being different from the other weights, to one of a plurality of output signals of the capacitance-voltage/current converter with respect to the sense capacitor and outputs a weighted sample; and

an adder which adds up all of the weighted samples of the plurality of the multiplier-holders;

wherein the capacitance-voltage/current converter comprises a switch which controls the on/off of the connection between an input terminal to which the input signal is applied and one end of the sense capacitor, and wherein the other end of the sense capacitor is connected to a ground;

wherein each of the multiplier-holders comprises;

a sampling capacitor of which one end is connected to a ground;

a first amplifier of which a first input terminal is connected to the other end of the sampling capacitor and of which a second input terminal is connected to an output terminal; and

a switch which controls the on/off of the connection between an output terminal of the capacitance-voltage/current converter and the other end of the sampling capacitor,

wherein an output terminal of the first amplifier is an output terminal of each of the multiplier-holders; and

wherein the adder comprises;

pre-charge capacitors provided as many as the number of the multiplier-holders;

a second amplifier;

a first pre-charge switch which controls the on/off of the connection between each of output terminals of the multiplier-holders and one end of each of the pre-charge capacitors;

a second pre-charge switch which controls the on/off of the connection between the connection between the other end of each of the pre-charge capacitors and a ground;

a first sum switch which controls the on/off of the one end of each of the pre-charge capacitors and the ground;

a second sum switch which controls the on/off of the connection between the other end of each of the pre-charge capacitors and a first input terminal of the second amplifier; and

a sum capacitor which is located between and connected to the first input terminal of the second amplifier and an output terminal;

wherein a second input terminal of the second amplifier is connected to the ground, and an output terminal of the second amplifier is an output terminal of the adder.

11. The capacitance sensor of claim 10, wherein an electric charge is charged in the sense capacitor by the input signal during an ON-state of the switch.

12. The capacitance sensor of claim 10, wherein at least two sampling capacitors included in each of the multiplier-holders have mutually different capacitance values.

13. The capacitance sensor of claim 10, wherein the switches included in each of the multiplier-holders become in an ON-state at mutually different points of time.

14. The capacitance sensor of claim 10, wherein an electric charge is charged in the sampling capacitance by the voltage of the sense capacitor during an ON-state of the switch, and wherein a voltage value of both ends of the sampling capacitance is transferred to the output terminal of each of the multiplier-holders.

15. The capacitance sensor of claim 10, wherein at least two pre-charge capacitors have mutually different capacitance values.

16. The capacitance sensor of claim 10, wherein the first pre-charge switch and the second pre-charge switch are synchronized and are in an ON or OFF state, and the first sum switch and the second sum switch are synchronized and are in an ON or OFF state, and wherein the first sum switch and the second sum switch are in an OFF-state during an ON-state of the first pre-charge switch and the second pre-charge switch, and the first pre-charge switch and the second pre-charge switch are in an OFF-state during an ON-state of the first sum switch and the second sum switch.

17. The capacitance sensor of claim 16, wherein the first pre-charge switch and the second pre-charge switch are in an ON-state during a time when a phase of a control signal is a first phase, wherein the first sum switch and second sum switch are in an ON-state during a time when the phase of the control signal is a second phase.

18. The capacitance sensor of claim 16, further comprising a third pre-charge switch which is synchronized with the first pre-charge switch and the second pre-charge switch and is in an ON or OFF state, and is located between and connected to both ends of the sum capacitor.

19. The capacitance sensor of claim 16, wherein an electric charge is charged in each of the pre-charge capacitors by an output terminal voltage of each of a plurality of the multiplier-holders during an ON-state of the first pre-charge switch and the second pre-charge switch, and wherein the electric charge stored in each of the pre-charged capacitors are all transferred to the sum capacitor and summed during an ON-state of the first sum switch and the second sum switch.

20. A noise filtering method of a capacitance sensor, the method comprising:

converting a capacitance value of a sense capacitor into an electrical signal related to the capacitance value by using an input signal and a capacitance-voltage/current converter;

generating a plurality of weighted samples using a multiplier by performing a plurality of processes, each of which applies one of a plurality of weights, each weight being different from the other weights, to one of a plurality of output signals obtained from the electrical signal of the converting with respect to the sense capacitor and outputting; and

accumulating or adding up the plurality of the weighted samples using an accumulator;

wherein the capacitance-voltage/current converter and the multiplier comprises;

a first amplifier;

a first switch which controls the on/off of the connection between an input terminal to which the input signal is applied and one end of the sense capacitor;

a second switch which controls the on/off of the connection between the other end of the sense capacitor and a ground;

a third switch which controls the on/off of the connection between the one end of the sense capacitor and the ground;

a fourth switch which controls the on/off of the connection between the other end of the sense capacitor and a first input terminal of the first amplifier; and

a variable capacitor which is located between the first input terminal of the first amplifier and an output terminal of the first amplifier and is connected to the first input terminal of the first amplifier and the output terminal of the first amplifier, and which has a variable capacitance value,

wherein a second input terminal of the first amplifier is connected to the ground and wherein the output terminal of the first amplifier is an output terminal of the multiplier; and

wherein the accumulator comprises;

a sampling capacitor;

a second amplifier;

a sixth switch which controls the on/off of the connection between an output terminal of the multiplier and one end of the sampling capacitor;

a seventh switch which controls the on/off of the connection between the other end of the sampling capacitor and a ground;

an eighth switch which controls the on/off of the connection between the one end of the sampling capacitor and the ground;

a ninth switch which controls the on/off of the connection between the other end of the sampling capacitor and a first input terminal of the second amplifier; and

an accumulation capacitor which is located between and connected to the first input terminal of the second amplifier and an output terminal of the second amplifier,

wherein a second input terminal of the second amplifier is connected to the ground, and the output terminal of the second amplifier is an output terminal of the accumulator.

21. A non-transitory computer-readable recording medium for recording a computer program for performing the method of claim 20.