Capacitive touch circuit

• US 8,330,735 B2
• Filed: 10/08/2009
• Issued: 12/11/2012
• Est. Priority Date: 07/14/2009
• Status: Active Grant

• Current Assignee: Sonix Technology Company Limited
• Original Assignee: Sonix Technology Company Limited
• Inventors: Lin, Chien-Liang, Chiu, Chun-Yen
• Primary Examiner(s): Lao, Lun-Yi
• Assistant Examiner(s): Siddiqui, Saiful A
• Application Number:
  US12/575,830
• Publication Number:
  US 20110011717A1
• Time in Patent Office: 1,160 Days
• Field of Search: 345174-178, 178/18.06, 178/18.07, 463 37- 38, 324/658, 324/686, 200/600, 200/5.R, 341/33
• US Class Current: 345/173
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 2217/94026 Automatic threshold calibration; e.g. threshold automatically adapts to ambient conditions or follows variation of input

Abstract

A capacitive touch circuit includes a single comparator, a reference voltage control unit, a resistance adjusting unit, a delay unit, and a relaxation oscillation control unit. The comparator has a first input terminal, a second input terminal, and an output terminal. The reference voltage control unit is electrically connected to the second input terminal and includes a high level voltage source, a low level voltage source, and a voltage switching controller. The voltage switching controller electrically connects either the high level voltage source or the low level voltage source to the second input terminal of the single comparator according to an output signal of the single comparator. The relaxation oscillation control unit is electrically connected to the resistance adjusting unit, the delay unit, and the reference voltage control unit. The relaxation oscillation control unit outputs a relaxation oscillation signal, and the frequency of the relaxation oscillation signal varies according to the resistance set by the resistance adjusting unit.

Claims

1. A capacitive touch circuit, comprising:

a single comparator having a first input terminal, a second input terminal, and an output terminal;

a reference voltage control unit electrically connected to the second input terminal, wherein the reference voltage control unit comprises;

a high level voltage source;

a low level voltage source; and

a voltage switching controller electrically connecting either the high level voltage source or the low level voltage source to the second input terminal of the single comparator according to an output signal of the single comparator;

a resistance adjusting unit electrically connected to the first input terminal of the single comparator;

a delay unit electrically connected to the output terminal of the single comparator for filtering out the transition of the output signal, wherein the delay unit comprises;

a delay time selector for deciding a delay time length according to the duration of the transition of the output signal of the single comparator; and

a delay time adjuster for delaying the start of the transition of the output signal of the single comparator according to the delay time length; and

a relaxation oscillation control unit electrically connected to the resistance adjusting unit, the delay unit, and the reference voltage control unit, wherein the relaxation oscillation control unit outputs a relaxation oscillation signal, the relaxation oscillation signal is fed into the first input terminal of the single comparator, and the frequency of the relaxation oscillation signal varies according to the resistance set by the resistance adjusting unit.

2. The capacitive touch circuit as claimed in claim 1, wherein the resistance adjusting unit comprises:

an adjustable resistor, the adjustable resistor together with an external capacitance sensor constituting an RC circuit; and

a resistance selector for setting the resistance of the adjustable resistor.

3. The capacitive touch circuit as claimed in claim 2, wherein the resistance selector has an N-bit (N is a positive integer) architecture to allow the adjustable resistor to have 2^N adjusting levels.

4. The capacitive touch circuit as claimed in claim 2, wherein the resistance selector is a read only memory (ROM), a random access memory (RAM), or a register.

5. The capacitive touch circuit as claimed in claim 2, wherein the relaxation oscillation control unit either charges the RC circuit or enables the RC circuit to discharge according to the output signal of the single comparator.

6. The capacitive touch circuit as claimed in claim 5, wherein the relaxation oscillation control unit outputs a logic-high voltage to charge the RC circuit when the output signal of the single comparator is in a logic-high level, and the relaxation oscillation control unit outputs a logic-low voltage to enable the RC circuit to discharge when the output signal of the single comparator is in a logic-low level.

7. The capacitive touch circuit as claimed in claim 5, wherein the output voltage of the high level voltage source is equal to an upper threshold voltage for charging the RC circuit, and the output voltage of the low level voltage source is equal to a lower threshold voltage for discharging the RC circuit.

8. The capacitive touch circuit as claimed in claim 7, wherein the voltage switching controller electrically connects the low level voltage source to the second input terminal of the single comparator at the instant when the voltage at the first input terminal increases to larger than the voltage at the second input terminal, and the voltage switching controller electrically connects the high level voltage source to the second input terminal of the single comparator at the instant when the voltage at the first input terminal decreases to smaller than the voltage at the second input terminal.

9. The capacitive touch circuit as claimed in claim 1 wherein the delay unit is a read only memory (ROM), a random access memory (RAM), or a register.

10. A capacitive touch circuit, comprising:

a single comparator having a first input terminal, a second input terminal, and an output terminal;

a reference voltage control unit electrically connected to the second input terminal, wherein the reference voltage control unit comprises;

a high level voltage source group for providing multiple different high reference voltages;

a high level voltage selector for selecting one of the high reference voltages and feeding the selected high reference voltage into the second input terminal of the single comparator;

a low level voltage source group for providing multiple different low reference voltages;

a low level voltage selector for selecting one of the low reference voltages and feeding the selected low reference voltage into the second input terminal of the single comparator; and

a voltage source group switching controller electrically connecting either the high level voltage source group or the low level voltage source group to the second input terminal of the single comparator according to an output signal of the single comparator;

a delay unit electrically connected to the output terminal of the single comparator for filtering out the transition of the output signal, wherein the delay unit comprises;

a delay time selector for deciding a delay time length according to the duration of the transition of the output signal of the single comparator; and

a delay time adjuster for delaying the start of the transition of the output signal of the single comparator according to the delay time length; and

a relaxation oscillation control unit electrically connected to the delay unit and the reference voltage control unit, wherein the relaxation oscillation control unit outputs a relaxation oscillation signal that is fed into the first input terminal of the single comparator, and the frequency and the amplitude of the relaxation oscillation signal vary according to a high reference voltage and a low reference voltage that are selected by the reference voltage control unit and fed into the second input terminal of the single comparator.

11. The capacitive touch circuit as claimed in claim 10, wherein the reference voltage control unit further comprises a command source that determines a high reference voltage and a low reference voltage needed by the capacitive touch circuit, and the command source orders the high level voltage selector to select the high reference voltage and the low level voltage selector to select the low reference voltage.

12. The capacitive touch circuit as claimed in claim 11, wherein the command source is implemented by firmware, software, or a microprocessor.

13. The capacitive touch circuit as claimed in claim 10, wherein both of the high level voltage selector and the low level voltage selector have a decoding circuit.

14. The capacitive touch circuit as claimed in claim 10, wherein the relaxation oscillation control unit either charges a capacitance sensor or enables the capacitance sensor to discharge according to the output signal of the single comparator.

15. The capacitive touch circuit as claimed in claim 14, wherein the relaxation oscillation control unit outputs a logic-high voltage to charge the capacitance sensor when the output signal of the single comparator is in a logic-high level, and the relaxation oscillation control unit outputs a logic-low voltage to enable the capacitance sensor to discharge when the output signal of the single comparator is in a logic-low level.

16. The capacitive touch circuit as claimed in claim 14, wherein the high reference voltage is equal to an upper threshold voltage for charging the capacitance sensor, and the low reference voltage is equal to a lower threshold voltage for discharging the capacitance sensor.

17. The capacitive touch circuit as claimed in claim 16, wherein the voltage source group switching controller electrically connects the low level voltage source group to the second input terminal of the single comparator at the instant when the voltage at the first input terminal increases to larger than the voltage at the second input terminal, and the voltage source group switching controller electrically connects the high level voltage source group to the second input terminal of the single comparator at the instant when the voltage at the first input terminal decreases to smaller than the voltage at the second input terminal.

18. The capacitive touch circuit as claimed in claim 10, wherein the delay unit is a read only memory (ROM), a random access memory (RAM), or a register.