Pixel reading device and pixel reading method
A pixel reading device, which includes a first capacitor, a second capacitor, a voltage generating circuit, and an analog front-end (AFE) circuit, is provided. A first terminal of the first capacitor is coupled to a fingerprint sensing pixel to receive a sensing voltage. A first terminal of the second capacitor is coupled to a second terminal of the first capacitor. The voltage generating circuit provide a compensation voltage to a second terminal of the second capacitor. During a sensing period of the fingerprint sensing pixel, the compensation voltage is at an initial level. During a level reading period of the fingerprint sensing pixel, the compensation voltage is pulled up from the initial level to a compensation level to compensate a common mode component of the sensing voltage. An input terminal of the AFE circuit is coupled to the second terminal of the first capacitor.
1. A pixel reading device, comprising:
a first capacitor, having a first terminal coupled to a fingerprint sensing pixel to receive a sensing voltage;
a second capacitor, having a first terminal coupled to a second terminal of the first capacitor;
a voltage generating circuit, coupled to a second terminal of the second capacitor to provide a compensation voltage, wherein the compensation voltage is at an initial level during a sensing period of the fingerprint sensing pixel, and the compensation voltage is pulled up from the initial level to a compensation level during a level reading period of the fingerprint sensing pixel to compensate a common mode component of the sensing voltage; and
an analog front-end circuit, having an input terminal coupled to the second terminal of the first capacitor.
2. The pixel reading device according to claim 1 , wherein
in a first phase of the level reading period, the sensing voltage of the fingerprint sensing pixel has not yet been reset, and the compensation voltage is pulled up to the compensation level;
in a second phase of the level reading period, the sensing voltage is reset, and the compensation voltage continues to be pulled up to the compensation level; and
in a third phase of the level reading period, the sensing voltage is continuously reset, and the compensation voltage is maintained at the compensation level.
3. The pixel reading device according to claim 1 , wherein the voltage generating circuit comprises:
a digital to analog converter, having an output terminal coupled to the second terminal of the second capacitor to provide the compensation voltage.
4. The pixel reading device according to claim 1 , wherein the voltage generating circuit comprises:
a switch circuit, having a common terminal coupled to the second terminal of the second capacitor to provide the compensation voltage, wherein a first selection terminal of the switch circuit receives a first voltage with the initial level, and a second selection terminal of the switch circuit receives a second voltage with the compensation level.
5. The pixel reading device according to claim 1 , wherein the voltage generating circuit comprises:
a switch circuit, having a first selection terminal receiving a first voltage having the initial level, wherein a second selection terminal of the switch circuit receives a second voltage with the compensation level;
a resistor, having a first terminal coupled to a common terminal of the switch circuit, wherein a second terminal of the resistor is coupled to the second terminal of the second capacitor to provide the compensation voltage; and
a third capacitor, having a first terminal coupled to the second terminal of the resistor, wherein a second terminal of the third capacitor is coupled to a reference voltage.
6. The pixel reading device according to claim 1 , wherein the analog front-end circuit comprises:
a first switch, having a first terminal coupled to the second terminal of the first capacitor;
an amplifier, having a first input terminal coupled to a second terminal of the first switch, wherein a second input terminal of the amplifier is coupled to a common mode voltage;
a third capacitor, having a first terminal coupled to the first input terminal of the amplifier, wherein a second terminal of the third capacitor is coupled to an output terminal of the amplifier; and
a second switch, having a first terminal coupled to the first input terminal of the amplifier, wherein a second terminal of the second switch is coupled to the output terminal of the amplifier.
7. The pixel reading device according to claim 1 , wherein the analog front-end circuit comprises:
an amplifier, having a first input terminal coupled to the second terminal of the first capacitor, wherein a second input terminal of the amplifier is coupled to a common mode voltage;
a third capacitor, having a first terminal coupled to the first input terminal of the amplifier, wherein a second terminal of the third capacitor is coupled to an output terminal of the amplifier; and
a switch, having a first terminal coupled to the first input terminal of the amplifier, wherein a second terminal of the switch is coupled to the output terminal of the amplifier.
8. The pixel reading device according to claim 1 , further comprising:
a current source, coupled to the fingerprint sensing pixel to provide a sensing current.
9. A pixel reading method, comprising:
receiving a sensing voltage of a fingerprint sensing pixel by an input terminal of an analog front-end circuit through a first capacitor; and
providing a compensation voltage to the input terminal of the analog front-end circuit by a voltage generating circuit through a second capacitor, wherein,
during a sensing period of the fingerprint sensing pixel, the compensation voltage is at an initial level; and
during a level reading period of the fingerprint sensing pixel, the compensation voltage is pulled up from the initial level to a compensation level to compensate a common mode component of the sensing voltage.
10. The pixel reading method according to claim 9 , wherein pulling up the compensation voltage from the initial level to the compensation level comprises:
raising the compensation voltage to the compensation level in a first phase of the level reading period, wherein the sensing voltage of the fingerprint sensing pixel has not yet been reset in the first phase;
continuing to pull up the compensation voltage to the compensation level in a second phase of the level reading period, wherein the sensing voltage is reset in the second phase; and
maintaining the compensation voltage at the compensation level in a third phase of the level reading period, wherein the sensing voltage is continuously reset in the third phase.