# US 11,910,111 B2 · Pixel cell and method for operating a pixel cell

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- Number: US 11,910,111 B2
- Document ID: US11910111B2
- Status: Granted
- Kind: B2
- Application number: 17/264,668
- Filed: 2019-07-17
- Published: 2021-07-29
- Granted: 2024-02-20
- Earliest claimed: 2018-08-03
- Assignees: ams Sensors Belgium BVBA
- Applicants: ams Sensors Belgium BVBA
- Inventors: Guy Meynants
- Web page: https://patentgrep.com/patent/US11910111B2

## CPC

- H04N 25/531: by controlling rolling shutters in CMOS SSIS
- H10F 39/813: {Electronic components shared by multiple pixels, e.g. one amplifier shared by two pixels}
- H04N 25/532: by controlling global shutters in CMOS SSIS
- H04N 25/616: involving a correlated sampling function, e.g. correlated double sampling [CDS] or triple sampling
- H04N 25/771: comprising storage means other than floating diffusion
- H04N 25/78: Readout circuits for addressed sensors, e.g. output amplifiers or A/D converters
- H04N 25/79: Arrangements of circuitry being divided between different or multiple substrates, chips or circuit boards, e.g. stacked image sensors
- 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 39/199: {Back-illuminated image sensors}
- H10F 39/8053: {Colour filters}
- H10F 39/806: {Optical elements or arrangements associated with the image sensors}
- H10F 39/809: {of hybrid image sensors}
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION

## Abstract

A pixel cell includes a pixel set with a plurality of pixels, with each pixel of the pixel set being configured to capture optical information incident upon the respective pixel and generate electrical information representative of the optical information. The pixel cell further includes a readout circuit which is configured to manage collection and output of the electrical information from each pixel of the pixel set and to operate the pixel set in a global shutter mode and in a rolling shutter mode of operation. In the global shutter mode, the electrical information from each pixel is combined for generating a global shutter output signal, while in the rolling shutter mode, the electrical information from each pixel is used to generate individual rolling shutter output signals.

## Claims

### Claim 1

A pixel cell comprising:
a pixel set with a plurality of pixels, with each pixel comprising a photodiode and a transfer gate coupled to the photodiode; and
a readout circuit comprising
a floating diffusion with an adjustable capacitance coupled to all of the transfer gates;
a column output line;
a sample-and-hold stage (SHS) coupled to the floating diffusion, the sample-and-hold-stage comprising a first storage stage and a second storage stage arranged in series or in parallel, each of the first and second storage stages comprising a switch and a capacitor that is coupled between the switch and a fixed potential;
a first switch coupling the sample-and-hold-stage to the column output line; and
a second switch coupling the floating diffusion to the column output line or to a further column output line,
wherein
the readout circuit is configured to:
in a global shutter mode of operation, control the plurality of pixels such that corresponding charges generated by the photodiode of each of the plurality of pixels in response to incident radiation are simultaneously transferred to the floating diffusion in accordance with transfer control signals simultaneously transmitted to the transfer gates;
in a rolling shutter mode of operation, control the plurality of pixels such that corresponding charges generated by the photodiode of each of the plurality of pixels in response to incident radiation are sequentially transferred to the floating diffusion in accordance with transfer control signals sequentially transmitted to the transfer gates; and
adjust the capacitance of the floating diffusion such that the capacitance of the floating diffusion in the global shutter mode is larger than the capacitance of the floating diffusion in the rolling shutter mode;
wherein the pixel set is operated
in the global shutter mode for charges generated by the photodiode of each of the plurality of pixels based on incident radiation in a first wavelength range, wherein the first wavelength range is a near-infrared range; and
in the rolling shutter mode for charges generated by the photodiode of each of the plurality of pixels based on incident radiation in a second wavelength range;
wherein the capacitance of the floating diffusion in the global shutter mode is larger than the capacitance of the floating diffusion in the rolling shutter mode by a factor that is equal to the number of pixels in the pixel cell.

### Claim 2 (depends on 1)

The pixel cell according to claim 1, wherein the readout circuit is further configured, in the global shutter mode of operation, to
generate a global shutter output signal depending on the corresponding charges from the photodiode of each of the plurality of pixels, in particular depending on a sum or an average of said corresponding charges from the photodiode (PD1-PD4) of each of the plurality of pixels; and
transfer the global shutter output signal to the column output line in accordance with a global shutter control signal transmitted to the first switch; and
is configured, in the rolling shutter mode of operation, to
generate individual rolling shutter output signals, with each rolling shutter output signal depending on the corresponding charges from the photodiode of one of the plurality of pixels; and
transfer the individual rolling shutter output signal to the column output line or to the further column output line in accordance with a rolling shutter control signal transmitted to the second switch.

### Claim 3 (depends on 1)

The pixel cell according to claim 1, wherein the pixel set is exclusively operated,
in the global shutter mode for charges generated by the photodiode of each of the plurality of pixels based on incident radiation in a near-infrared range including 940 nm; and
in the rolling shutter mode for charges generated by the photodiode of each of the plurality of pixels based on incident radiation in a visible range.

### Claim 4 (depends on 1)

The pixel cell according to claim 1, further comprising the further column output line, wherein the further column output line is configured as a rolling shutter column output line and the column line is configured as a global shutter column output line.

### Claim 5 (depends on 1)

The pixel cell according to claim 1, further comprising a color filter arrangement of filters, wherein
each filter acts as a bandpass filter for a distinct wavelength range such that each of or a majority of pixels of the pixel set comprises a distinct color filter; and
the filters act as bandpass filters for a further wavelength range.

### Claim 6 (depends on 1)

The pixel cell according to claim 1, wherein the pixel set comprises
three pixels; or
four pixels.

### Claim 7 (depends on 1)

The pixel cell according to claim 1, wherein each of the plurality of pixels is equal in size and has a footprint smaller than 2 μm×2 μm.

### Claim 8 (depends on 1)

The pixel cell according to claim 1, wherein the capacitance of the floating diffusion is adjustable by means of a switch.

### Claim 9 (depends on 1)

An image sensor comprising a plurality of pixel cells according to claim 1, in particular a CMOS image sensor.

### Claim 10 (depends on 9)

The image sensor according to claim 9, wherein the image sensor is configured to operate in a global shutter mode of operation for three dimensional imaging of an object or a scene.

### Claim 11 (depends on 9)

An electronic device with a camera system comprising an image sensor according to claim 9.

### Claim 12 (depends on 1)

A method for operating the pixel cell according to claim 1, wherein each of the plurality of pixels is configured to capture optical information incident upon the respective pixel and generate electrical information representative of the optical information, the method comprising:
collecting and outputting the electrical information from each of the plurality of pixels; and
operating the pixel set in the global shutter mode and in the rolling shutter mode; wherein
in the global shutter mode of operation the electrical information from each of the plurality of pixels is combined, in particular as a sum or average, for generating a global shutter output signal; and
in the rolling shutter mode of operation the electrical information from each of the plurality of pixels is used to generate individual rolling shutter output signals.

### Claim 13 (depends on 1)

The pixel cell according to claim 1, further comprising a color filter arrangement of filters, wherein
each filter acts as a bandpass filter for a distinct wavelength range of red, green or blue light, such that each of or a majority of pixels of the pixel set comprises a distinct color filter; and
the filters act as bandpass filters for a further wavelength range of infrared light.

### Claim 14 (depends on 1)

The pixel cell according to claim 1, wherein each of the plurality of pixels is equal in size and has a footprint equal to or smaller than 1.4 μm×1.4 μm.

### Claim 15 (depends on 1)

The pixel cell according to claim 1, wherein the fixed potential is the same for both the first and second storage stages.

### Claim 16

An imaging system, comprising:
An infrared light source; and
an image sensor comprising a plurality of pixel cells, wherein the light source is configured to operate in combination with the image sensor, each pixel cell comprising:
a pixel set with a plurality of pixels, with each pixel comprising a photodiode and a transfer gate coupled to the photodiode, and with each pixel being sensitive to a near-infrared wavelength range including 940 nm and to at least part of a visible wavelength range; and
a readout circuit comprising:
a floating diffusion with an adjustable capacitance coupled to all of the transfer gates;
a column output line;
a sample-and-hold stage (SHS) coupled to the floating diffusion, the sample-and-hold-stage comprising a first storage stage and a second storage stage arranged in series or in parallel, each of the first and second storage stages comprising a switch and a capacitor that is coupled between the switch and a fixed potential;
a first switch coupling the sample-and-hold-stage to the column output line; and
a second switch coupling the floating diffusion to the column output line or to a further column output line, wherein the readout circuit is configured to:
in a global shutter mode of operation,
control the plurality of pixels such that corresponding charges generated by the photodiode of each of the plurality of pixels in response to incident radiation are simultaneously transferred to the floating diffusion in accordance with transfer control signals simultaneously transmitted to the transfer gates;
generate a global shutter output signal depending on the corresponding charges from the photodiode of each of the plurality of pixels; and
transfer the global shutter output signal to the column output line in accordance with a global shutter control signal transmitted to the first switch;
in a rolling shutter mode of operation,
control the plurality of pixels such that corresponding charges generated by the photodiode of each of the plurality of pixels in response to incident radiation are sequentially transferred to the floating diffusion in accordance with transfer control signals sequentially transmitted to the transfer gates;
generate individual rolling shutter output signals, with each rolling shutter output signal depending on the corresponding charges from the photodiode of one of the plurality of pixels;
transfer the individual rolling shutter output signal to the column output line or to the further column output line in accordance with a rolling shutter control signal transmitted to the second switch; and
adjust the capacitance of the floating diffusion such that the capacitance of the floating diffusion in the global shutter mode is larger than the capacitance of the floating diffusion in the rolling shutter mode:
wherein the image sensor is operated:
in the global shutter mode for charges generated by the photodiode of each of the plurality of pixels based on incident radiation in a near-infrared wavelength range, wherein the infrared light source is employed for projecting a pattern onto an object or a scene; and
in the rolling shutter mode for charges generated by the photodiode of each of the plurality of pixels based on incident radiation in the visible wavelength range;
wherein the capacitance of the floating diffusion in the global shutter mode is larger than the capacitance of the floating diffusion in the rolling shutter mode by a factor that is equal to the number of pixels in the pixel cell.