# US 11,310,454 B2 · Pixel circuit and image sensor having the same

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- Number: US 11,310,454 B2
- Document ID: US11310454B2
- Status: Granted
- Kind: B2
- Application number: 16/706,374
- Filed: 2019-12-06
- Published: 2020-05-21
- Granted: 2022-04-19
- Earliest claimed: 2018-11-20
- Assignees: Shenzhen Goodix Technology Co., Ltd.
- Applicants: Shenzhen Goodix Technology Co., Ltd.
- Inventors: Chien-Jian Tseng; Wei-Min Chao
- Web page: https://patentgrep.com/patent/US11310454B2

## CPC

- H04N 25/77: Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
- H04N 25/778: comprising amplifiers shared between a plurality of pixels, i.e. at least one part of the amplifier must be on the sensor array itself
- H10F 39/182: {Colour image sensors}
- H04N 25/78: Readout circuits for addressed sensors, e.g. output amplifiers or A/D converters
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION

## Abstract

Provided are a pixel circuit and an associated image sensor, including an inverting input circuit, an active load and a signal reading circuit. Each pixel circuit includes a light sensing component, a transmission switch, a reset switch and a unity gain buffer. The transmission switch is series-connected between the light sensing component and the transmission switch. The unity gain buffer is connected to a node of connection of the transmission switch and the reset switch. The signal read circuit reads a sensing signal of the light sensing component through the unity gain buffer. An output signal of the unity gain buffer varies with an input signal of the unity gain buffer, attaining a linear relationship between the output signal and the input signal. Therefore, the photoelectric conversion curve of each pixel circuit is linear.

## Claims

### Claim 1

A pixel circuit, characterized by comprising:
a light sensing component;
a reset switch connected to a first reference voltage;
a transmission switch series-connected between the light sensing component and the reset switch; and
a unity gain buffer comprising:
a non-inverting input circuit comprising a non-inverting input terminal connected to a node of connection of the transmission switch and the reset switch;
an inverting input circuit comprising an inverting input terminal; and
an active load comprising an output terminal connected to the inverting input terminal, the active load being connected to the non-inverting input circuit and the inverting input circuit.

### Claim 2 (depends on 1)

The pixel circuit of claim 1, wherein the unity gain buffer further comprises a current source for providing current to the unity gain buffer.

### Claim 3 (depends on 2)

The pixel circuit of claim 2, wherein the non-inverting input circuit comprises:
a first transistor with a gate connected to the non-inverting input terminal and a drain connected to the active load; and
a second transistor with a gate connected to a selection signal, a drain connected to a source of the first transistor, and a source connected to the current source.

### Claim 4 (depends on 3)

The pixel circuit of claim 3, wherein the inverting input circuit comprises:
a third transistor, wherein a gate and a drain of the third transistor are jointly connected to the inverting input terminal, wherein the third transistor and the first transistor have substantially identical ion implantation so as to generate substantially identical threshold voltage; and
a fourth transistor with a gate connected to the active load, a drain connected to a source of the third transistor, and a source connected to the current source, wherein the fourth transistor and the second transistor have substantially identical ion implantation so as to generate substantially identical threshold voltage.

### Claim 5 (depends on 4)

The pixel circuit of claim 4, wherein the active load comprises:
a fifth transistor; and
a sixth transistor;
wherein a gate of the fifth transistor is connected to a gate of the sixth transistor, sources of the fifth transistor and the sixth transistor are jointly connected to the gate of the fourth transistor of the inverting input circuit, a drain of the fifth transistor is connected to the output terminal, and a drain of the sixth transistor is connected to gate of the sixth transistor and connected to the drain of the first transistor of the non-inverting input circuit.

### Claim 6 (depends on 5)

The pixel circuit of claim 5, wherein the first through fourth transistors are NMOS transistors, whereas the fifth and sixth transistors are PMOS transistors, and the light sensing component in each of the pixel circuits is a photoelectric diode.

### Claim 7

An image sensor, comprising:
a plurality of pixel circuits each comprising:
a light sensing component;
a reset switch connected to a first reference voltage;
a transmission switch series-connected between the light sensing component and the reset switch; and
a non-inverting input circuit comprising a non-inverting input terminal connected to a node of connection of the transmission switch and the reset switch;
an inverting input circuit comprising an inverting input terminal; and
an active load comprising an output terminal connected to the inverting input terminal, the active load being connected to the inverting input circuit and the non-inverting input circuit of each of the pixel circuits, wherein the pixel circuits in each column share the inverting input circuit and the active load.

### Claim 8 (depends on 7)

The image sensor of claim 7, further comprising:
a signal reading circuit connected to an output terminal of the active load to read a sensing result of the light sensing component of each of the pixel circuits.

### Claim 9 (depends on 8)

The image sensor of claim 8, further comprising a pixel region guard ring for surrounding therein the pixel circuits and the inverting input circuit.

### Claim 10 (depends on 8)

The image sensor of claim 8, further comprising:
a current source connected to the inverting input circuit and the non-inverting input circuit of each of the pixel circuits, wherein, when the signal reading circuit selects one of the pixel circuits, the non-inverting input circuit of the selected pixel circuit, the inverting input circuit, the active load and the current source equivalently form a unity gain buffer.

### Claim 11 (depends on 10)

The image sensor of claim 10, wherein the non-inverting input circuit of each of the pixel circuits comprises:
a first transistor with a gate connected to the non-inverting input terminal and a drain connected to the active load; and
a second transistor with a gate connected to a selection signal, a drain connected to a source of the first transistor, and a source connected to the current source.

### Claim 12 (depends on 11)

The image sensor of claim 11, wherein the inverting input circuit comprises:
a third transistor, wherein a gate and a drain of the third transistor are jointly connected to the inverting input terminal, wherein the third transistor and the first transistor have substantially identical ion implantation so as to generate substantially identical threshold voltage; and
a fourth transistor with a gate connected to the active load, a drain connected to a source of the third transistor, and a source connected to the current source, wherein the fourth transistor and the second transistor have substantially identical ion implantation so as to generate substantially identical threshold voltage.

### Claim 13 (depends on 12)

The image sensor of claim 12, wherein the active load comprises:
a fifth transistor; and
a sixth transistor;
wherein a gate of the fifth transistor is connected to a gate of the sixth transistor, sources of the fifth transistor and the sixth transistor are jointly connected to the gate of the fourth transistor of the inverting input circuit, a drain of the fifth transistor is connected to the output terminal, and a drain of the sixth transistor is connected to a gate of the sixth transistor and connected to the drain of the first transistor of the non-inverting input circuit of each of the pixel circuit.

### Claim 14

An image sensor, comprising:
a plurality of pixel circuits each comprising:
a light sensing component;
a reset switch connected to a first reference voltage;
a transmission switch series-connected between the light sensing component and the reset switch;
a non-inverting input circuit comprising a non-inverting input terminal connected to a node of connection of the transmission switch and the reset switch; and
an inverting input circuit comprising an inverting input terminal; and
an active load comprising an output terminal connected to the inverting input terminal, the active load being connected to the inverting input circuit of each of the pixel circuits and the non-inverting input circuit of each of the pixel circuits, wherein the pixel circuits in each column share the active load.

### Claim 15 (depends on 14)

The image sensor of claim 14, further comprising:
a signal reading circuit connected to an output terminal of the active load to read a sensing result of the light sensing component of each of the pixel circuits.

### Claim 16 (depends on 15)

The image sensor of claim 15, further comprising a pixel region guard ring for surrounding therein the pixel circuits.

### Claim 17 (depends on 15)

The image sensor of claim 15, further comprising:
a current source connected to the inverting input circuit of each of the pixel circuits and the non-inverting input circuit of each of the pixel circuits, wherein, when the signal reading circuit selects one of the pixel circuits, the non-inverting input circuit of the selected pixel circuit, the inverting input circuit of the selected pixel circuit, the active load and the current source equivalently form a unity gain buffer.

### Claim 18 (depends on 17)

The image sensor of claim 17, wherein the non-inverting input circuit of each of the pixel circuits comprises:
a first transistor with a gate connected to the non-inverting input terminal and a drain connected to the active load; and
a second transistor with a gate connected to a selection signal, a drain connected to a source of the first transistor, and a source connected to the current source.

### Claim 19 (depends on 17)

The image sensor of claim 17, wherein the inverting input circuit of each of the pixel circuits comprises:
a third transistor, wherein a gate and a drain of the third transistor are jointly connected to the inverting input terminal, wherein the third transistor and the first transistor have substantially identical ion implantation so as to generate substantially identical threshold voltage; and
a fourth transistor with a gate connected to the active load, a drain connected to a source of the third transistor, and a source connected to the current source, wherein the fourth transistor and the second transistor have substantially identical ion implantation so as to generate substantially identical threshold voltage.

### Claim 20 (depends on 17)

The image sensor of claim 17, wherein the active load comprises:
a fifth transistor; and
a sixth transistor;
wherein a gate of the fifth transistor is connected to a gate of the sixth transistor, sources of the fifth transistor and the sixth transistor are jointly connected to the gate of the fourth transistor of the inverting input circuit of each of the pixel circuits, a drain of the fifth transistor is connected to the output terminal, and a drain of the sixth transistor is connected to a gate of the sixth transistor and connected to the drain of the first transistor of the non-inverting input circuit of each of the pixel circuit.