Analog front end circuit for use with fingerprint sensor, and device having the same

Patent metadata

Field	Value
Publication number	US-10146985-B2
Application number	US-201715438463-A
Country	US
Kind code	B2
Filing date	Feb 21, 2017
Priority date	Aug 2, 2016
Publication date	Dec 4, 2018
Grant date	Dec 4, 2018

Abstract

A sensing read-out circuit includes an amplifier circuit that converts a charge output from a sensing line of a sensor into a first voltage, another amplifier circuit that converts a charge output from another sensing line into a second voltage, another amplifier circuit that generates a first amplified voltage by amplifying a difference between the first voltage and the second voltage, an analog-to-digital converter that converts the first amplified voltage into a digital signal, a first mixer that generates a second mixed signal by mixing the first digital signal and an in-phase clock signal, a second mixer that generates a second mixed signal by mixing the first digital signal and a quadrature-phase clock signal, a first filter that generates an in-phase signal by performing low-pass filtering on the first mixed signal, and a second filter that generates a quadrature-phase signal by performing low-pass filtering on the second mixed signal.

First claim

What is claimed is:

1. A sensor read-out circuit, comprising:
a first amplifier circuit that converts a first charge output from a first sensing line of a sensor into a first voltage;
a second amplifier circuit that converts a second charge output from a second sensing line of the sensor into a second voltage;
a third amplifier circuit that generates a first amplified voltage by amplifing a difference between the first voltage and the second voltage;
a first analog-to-digital converter that converts the first amplified voltage into a first digital signal;
a first mixer that generates a first mixed signal by mixing the first digital signal and an in-phase clock signal;
a second mixer that generates a second mixed signal by mixing the first digital signal and a quadrature-phase clock signal;
a first filter that generates a first in-phase signal by performing low-pass filtering on the first mixed signal; and
a second filter that generates a first quadrature-phase signal by performing low-pass filtering on the second mixed signal.

2. The sensor read-out circuit of claim 1 , wherein the first amplifier circuit comprises:
a first charge amplifier that amplifies the first charge; and
a first band-pass filter connected to an output terminal of the first charge amplifier, wherein the first band-pass filter outputs the first voltage,
wherein the second amplifier circuit comprises:
a second charge amplifier that amplifies the second charge; and
a second band-pass filter connected to an output terminal of the second charge amplifier, wherein the second band-pass filter outputs the second voltage.

3. The sensor read-out circuit of claim 1 , wherein the third amplifier circuit comprises:
an amplifier that amplifies the difference between the first voltage and the second voltage; and
a band-pass filter connected to an output terminal of the amplifier, wherein the band-pass filter outputs the first amplified voltage.

4. The sensor read-out circuit of claim 1 , wherein the third amplifier circuit comprises:
a first amplifier that amplifies the difference between the first voltage and the second voltage;
a first band-pass filter connected to an output terminal of the first amplifier;
a second amplifier connected to an output terminal of the first band-pass filter; and
a second band-pass filter connected to an output terminal of the second amplifier, wherein the second band-pass filter outputs the first amplified voltage.

5. The sensor read-out circuit of claim 4 , wherein a level of a second common mode voltage of the second band-pass filter is lower than a level of a first common mode voltage of the first band-pass filter.

6. The sensor read-out circuit of claim 1 . further comprising:
a clock signal generator that generates the in-phase clock signal and the quadrature-phase clock signal; and
a driver that generates a drive pulse by buffering the in-phase clock signal, and supplies the drive pulse to a drive line of the sensor.

7. The sensor read-out circuit of claim 1 , wherein a sampling frequency of the first analog-to-digital converter is higher than a frequency of the in-phase clock signal.

8. The sensor read-out circuit of claim 1 , further comprising:
a digital signal processor that calculates a vector magnitude and a polarity based on the first in-phase signal and the first quadrature-phase signal.

9. The sensor read-out circuit of claim 1 , further comprising:
a fourth amplifier circuit that converts a third charge output from a third sensing line of the sensor into a third voltage;
a fifth amplifier circuit that generates a second amplified voltage by amplifying a difference between the second voltage and the third voltage; and
a switch circuit that transmits the first voltage and the second voltage to the third amplifier circuit or transmits the second voltage and the third voltage to the fifth amplifier circuit in response to a selection signal,
wherein the first sensing line, the second sensing line, and the third sensing line are sequentially arranged.

10. The sensor read-out circuit of claim 9 , further comprising:
a second analog-to-digital converter that converts the second amplified voltage into a second digital signal;
a third mixer that generates a third mixed signal by mixing the second digital signal and the in-phase clock signal;
a fourth mixer that generates a fourth mixed signal by mixing the second digital signal and the quadrature-phase clock signal;
a third filter that generates a second in-phase signal by performing low-pass filtering on the third mixed signal; and
a fourth filter that generates a second quadrature-phase signal by performing low-pass filtering on the fourth mixed signal.

11. A sensor read-out circuit, comprising:
an analog circuit that converts and amplifies a difference between a first mutual capacitance value of a first sensing line connected to a sensor and a second mutual capacitance value of a second sensing line connected to the sensor, and generates a band-pass filtered voltage by performing band-pass filtering on an amplified voltage;
an analog-to-digital converter that converts the band-pass filtered voltage into a digital signal;
a first mixer that generates a first mixed signal by mixing the digital signal and an in-phase clock signal;
a second mixer that generates a second mixed signal by mixing the digital signal and a quadrature-phase clock signal;
a first filter that generates an in-phase signal by performing low-pass filtering on the first mixed signal; and
a second filter that generates a quadrature-phase signal by performing low-pass filtering on the second mixed signal.

12. The sensor read-out circuit of claim 11 , wherein the analog circuit comprises:
a first amplifier circuit that converts a first charge corresponding to the first mutual capacitance value into a first voltage;
a second amplifier circuit that converts a second charge corresponding to the second mutual capacitance value into a second voltage;
a first amplifier that amplifies a difference between the first voltage and the second voltage; and
a first band-pass filter that generates the band-pass filtered voltage based on an output voltage of the first amplifier.

13. The sensor read-out circuit of claim 12 , further comprising:
a second band-pass filter; and
a second amplifier,
wherein the second band-pass filter and the second amplifier are connected in series between an output terminal of the first amplifier and an output terminal of the first band-pass filter.

14. The sensor read-out circuit of claim 13 , wherein a level of a common mode voltage of the first band-pass filter is lower than a level of a common mode voltage of the second band-pass filter.

15. The sensor read-out circuit of claim 11 , wherein a sampling frequency of the analog-to-digital converter is higher than a frequency of the in-phase clock signal.

16. A fingerprint sensing system, comprising:
a fingerprint sensor; and
a sensor read-out circuit that reads out output signals of the fingerprint sensor, wherein the fingerprint sensor comprises:
a first sensing element connected between a drive line and a first sensing line;
a second sensing element connected between the drive line and a second sensing line; and
a third sensing element connected between the drive line and a third sensing line, wherein the sensor read-out circuit comprises:
a first amplifier circuit that converts a first charge output from the first sensing line into a first voltage;
a second amplifier circuit that converts a second charge output from the second sensing line

Assignees

• Samsung Electronics Co Ltd

Inventors

• Chung Dae Young
• Park Jae Jin
• Hwang Hee Chang

Classifications

• G06K9/00046

  Physics · mapped topic

• G06K9/0002 Primary

  Physics · mapped topic

• G06K9/00013

  Physics · mapped topic

• G06V40/12 Primary

  Fingerprints or palmprints · CPC title

• G06V40/1306 Primary

  non-optical, e.g. ultrasonic or capacitive sensing · CPC title