Fingerprint detection circuit and method, electronic device

• US 10,248,829 B2
• Filed: 01/05/2016
• Issued: 04/02/2019
• Est. Priority Date: 02/13/2015
• Status: Active Grant

• Current Assignee: BYD Company Limited
• Original Assignee: BYD Company Limited
• Inventors: Li, Zhengang, Xu, Kunping, Yang, Yun
• Primary Examiner(s): Wong, K.
• Application Number:
  US15/549,896
• Publication Number:
  US 20180025198A1
• Time in Patent Office: 1,183 Days
• Field of Search: None
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing

Abstract

The present disclosure provides a fingerprint detection circuit and method. The circuit includes a fingerprint collecting module and a processing module. The fingerprint collecting module includes a plurality of collecting units, and each collecting unit has a regulation voltage and is configured to output a first voltage or a second voltage according to a capacitance value of one of ridge capacitors, a capacitance value of one of ridge capacitors and the regulation voltage. The processing module is configured to amplify the first and second voltages by a predetermined factor, to calculate a difference between the amplified first and second voltages, and to determine whether the difference is greater than or equal to the predetermined threshold. If no, the processing module adjusts at least one parameter, and configures the fingerprint detection circuit using at least one adjusted parameter.

Claims

1. A fingerprint detection circuit, configured to apply an excitation signal to a finger so as to generate ridge capacitors and valley capacitors, and comprising:

a fingerprint collecting module comprising a plurality of collecting units, wherein each of the plurality of collecting units has a regulation voltage, and is configured to output a first voltage or a second voltage according to a capacitance value of one of the ridge capacitors, a capacitance value of one of the ridge capacitors, and the regulation voltage; and

a processing module connected with the fingerprint collecting module, and configured to amplify the first voltage and the second voltage by a predetermined factor, to calculate a difference between an amplified first voltage and an amplified second voltage, and to determine whether the difference is greater than or equal to a predetermined threshold;

wherein;

when the difference is greater than or equal to the predetermined threshold, the processing module is further configured to calculate the capacitance value of one of the ridge capacitors according to the first voltage, and to calculate the capacitance value of one of the valley capacitors according to the second voltage; and

when the difference is less than the predetermined threshold, the processing module is further configured to adjust an excitation voltage of the excitation signal according to the predetermined threshold and the difference, wherein the excitation voltage is a voltage magnitude of the excitation signal.

2. The fingerprint detection circuit according to claim 1, wherein

when the excitation voltage is adjusted, the collecting unit is further configured to output a first adjusted voltage or a second adjusted voltage according to the capacitance value of one of the valley capacitors and the capacitance value of one of the ridge capacitors, and the processing module is further configured to amplify the first adjusted voltage and the second adjusted voltage by the predetermined factor, to calculate the adjusted difference between the amplified value of the first adjusted voltage and the amplified value of the second adjusted voltage, and to determine whether the adjusted difference is greater than or equal to the predetermined threshold.

3. The fingerprint detection circuit according to claim 1, wherein the first voltage has a non-linear relationship with the capacitance value of one of the ridge capacitors, and the second voltage has a non-linear relationship with the capacitance value of one of the valley capacitors.

4. The fingerprint detection circuit according to claim 1, wherein each collecting unit comprises a signal amplifier, a capacitor and a switch unit;

the signal amplifier has a negative input terminal connected with one of the ridge capacitors or one of the valley capacitors, a positive input terminal connected with a voltage reference terminal, and an output terminal configured to output the first voltage or the second voltage; and

the switch unit is connected with the negative input terminal and the output terminal of the signal amplifier respectively, and is configured to control the capacitor connected between the negative input terminal and the output terminal of the signal amplifier.

5. The fingerprint detection circuit according to claim 4, further comprising a first power supply connected with the capacitor via the switch unit,

wherein the switch unit is configured to control the first power supply to charge the capacitor or to control the capacitor to disconnect from the first power supply;

and

wherein a voltage between two terminals of the capacitor is configured to be the regulation voltage.

6. The fingerprint detection circuit according to claim 4, wherein the reference voltage terminal is a ground terminal.

7. The fingerprint detection circuit according to claim 4, wherein the switch unit comprises a first switch and a second switch;

the first switch has a first selecting terminal, a first power terminal and a first connecting terminal, the first selecting terminal is connected with a first terminal of the capacitor, the first power terminal is connected with a first electrode of the first power supply, and the first connecting terminal is connected with the negative input terminal of the signal amplifier;

the second switch has a second selecting terminal, a second power terminal and a second connecting terminal, the second selecting terminal is connected with a second terminal of the capacitor, the second power terminal is connected with a second electrode of the first power supply, and the second connecting terminal is connected with the output terminal of the signal amplifier; and

the first selecting terminal is configured to be connected with the first connecting terminal or the first power terminal, and the second selecting terminal is configured to be connected with the second connecting terminal or the second power terminal.

8. The fingerprint detection circuit according to claim 4, further comprising a second power supply, wherein:

the reference voltage terminal is an output terminal of the second power supply, the switch unit is connected to the capacitor in parallel, and the voltage of the second power supply is configured to be the regulation voltage;

when the switch unit is turned off, the capacitor is communicated with the negative input terminal of the signal amplifier and the output terminal of the signal amplifier respectively; and

when the switch unit is turned on, the capacitor is disconnected between the negative input terminal and the output terminal of the signal amplifier.

9. The fingerprint detection circuit according to claim 7, wherein, when the first selecting terminal is connected with the first connecting terminal and disconnected from the first power terminal, and the second selecting terminal is connected with the second connecting terminal and disconnected from the second power terminal, the capacitor is connected between the negative input terminal and the output terminal of the signal amplifier, and disconnected from the first power supply.

10. The fingerprint detection circuit according to claim 7, wherein, when the first selecting terminal is connected with the first power terminal and disconnected from the first connecting terminal, and the second selecting terminal is connected with the second power terminal and disconnected from the second connecting terminal, the first power supply is configured to charge the capacitor.

11. The fingerprint detection circuit according to claim 5, wherein the capacitance value of one of the ridge capacitors or the capacitance value of one of the valley capacitors is determined according to a formula of

Vo=(Vs−

Vt*Cx/Ci),

wherein Vo is the first voltage or the second voltage, Vt is the excitation voltage, Cx is the capacitance value of one of the ridge capacitors or the capacitance value of one of the valley capacitors, Ci is the capacitance value of the capacitor, and Vs is the regulation voltage.

12. The fingerprint detection circuit according to claim 1, wherein:

each collecting unit comprises a signal amplifier, a capacitor, a rheostat and a switch unit;

the signal amplifier has a negative input terminal connected with one of the ridge capacitors or one of the valley capacitors, a positive input terminal connected with a voltage reference terminal, and an output terminal configured to output the first voltage or the second voltage;

the capacitor is connected between the negative input terminal of the signal amplifier and the output terminal of the signal amplifier; and

the switch unit is connected with the rheostat in series and is configured to control the rheostat to be connected with the capacitor in parallel.

13. The fingerprint detection circuit according to claim 12, wherein the capacitance value of one of the ridge capacitors or the capacitance value of one of the valley capacitors is determined according to formulas of

Vo=(Vs−

Vt*Cx/Ci)

Vs=Vt*Cx*Ts/(Ci*Ci*Rs),

wherein Vo is the first voltage or the second voltage, Vt is the excitation voltage, Cx is the capacitance value of one of the ridge capacitors or the capacitance value of one of the valley capacitors, Ci is the capacitance value of the capacitor, Vs is the regulation voltage, Rs is a resistance value of the rheostat, and Ts is a detecting period.

14. The fingerprint detection circuit according to claim 1, wherein the processing module further comprises a sampling hold circuit and an analog-to-digital converter, and the sampling hold circuit is connected between the output terminal of the signal amplifier and the analog-to-digital converter.

15. The fingerprint detection circuit according to claim 1, wherein the excitation signal is transmitted to the finger via an emission electrode to generate the ridge capacitors and the valley capacitors.

16. An electronic device, comprising a fingerprint detection circuit configured to apply an excitation signal to a finger so as to generate ridge capacitors and valley capacitors, wherein the fingerprint detection circuit further comprises:

a fingerprint collecting module comprising a plurality of collecting units, wherein each of the plurality of collecting units has a regulation voltage, and is configured to output a first voltage or a second voltage according to a capacitance value of one of the ridge capacitors, a capacitance value of one of the ridge capacitors, and the regulation voltage; and

a processing module connected with the fingerprint collecting module, and configured to amplify the first voltage and the second voltage by a predetermined factor, to calculate a difference between an amplified first voltage and an amplified second voltage, and to determine whether the difference is greater than or equal to a predetermined threshold;

wherein;

when the difference is greater than or equal to the predetermined threshold, the processing module is further configured to calculate the capacitance value of one of the ridge capacitors according to the first voltage, and to calculate the capacitance value of one of the valley capacitors according to the second voltage; and

when the difference is less than the predetermined threshold, the processing module is further configured to adjust an excitation voltage of the excitation signal according to the predetermined threshold and the difference, wherein the excitation voltage is a voltage magnitude of the excitation signal.

17. The electronic device according to claim 16, wherein:

when the excitation voltage is adjusted, the collecting unit is further configured to output a first adjusted voltage or a second adjusted voltage according to the capacitance value of one of the valley capacitors and the capacitance value of one of the ridge capacitors, and the processing module is further configured to amplify the first adjusted voltage and the second adjusted voltage by the predetermined factor, to calculate the adjusted difference between the amplified value of the first adjusted voltage and the amplified value of the second adjusted voltage, and to determine whether the adjusted difference is greater than or equal to the predetermined threshold.

18. The electronic device according to claim 16, wherein the first voltage has a non-linear relationship with the capacitance value of one of the ridge capacitors, and the second voltage has a non-linear relationship with the capacitance value of one of the valley capacitors.

19. A fingerprint detection method, comprising:

applying an excitation signal to a finger so as to generate ridge capacitors and valley capacitors;

generating a first voltage or a second voltage by a collecting unit according to a regulation voltage, a capacitance value of one of the ridge capacitors and a capacitance value of one of the valley capacitors;

amplifying the first voltage and the second voltage with a predetermined factor by a processing module;

calculating a difference between an amplified first voltage and an amplified second voltage by the processing module;

determining whether the difference is greater than or equal to a predetermined threshold by the processing module;

when the difference is greater than or equal to the predetermined threshold, calculating the capacitance value of one of the ridge capacitors according to the first voltage and calculating the capacitance value of one of the valley capacitors according to the second voltage by the processing module; and

when the difference is less than the predetermined threshold, adjusting an excitation voltage of the excitation signal according to the predetermined threshold and the difference by the processing module, wherein the excitation voltage is a voltage magnitude of the excitation signal.