US-12621585-B2 - Time delay integration sensor with in-pixel time delay integration

Abstract

The present disclosure provides a time delay integration (TDI) sensor to move with respect to a scene in an along-track direction. A pixel array of the TDI sensor includes multiple pixel columns each including multiple pixels arranged in the along-track direction. Each pixel column includes a first pixel and a second pixel adjacent to each other. The second pixel includes an extra transfer transistor connected between a photodiode of the second pixel and a floating diffusion node of the first pixel.

Inventors

• Ren-Chieh Liu
• Yi-Che Yen

Assignees

• PIXART IMAGING INC.
• Taiwan Space Agency

Dates

Publication Date

20260505

Application Date

20240624

Claims (19)

1. 1 . A time delay integration (TDI) image sensor, configured to move with respect to a scene in an along-track direction, the image sensor comprising: a pixel array, comprising multiple pixel columns, each of the multiple pixel columns comprising multiple pixels arranged in the along-track direction, and the multiple pixel columns respectively comprising a first pixel and a second pixel adjacent to each other, the first pixel comprising: a first photodiode; a first floating diffusion node; and a first transfer transistor, connected between the first photodiode and the first floating diffusion node; and the second pixel comprising: a second photodiode; a second floating diffusion node; a second transfer transistor, connected between the second photodiode and the second floating diffusion node; and a second extra transfer transistor, connected between the second photodiode and the first floating diffusion node, wherein a first pixel data of the second photodiode obtained in a first exposure interval is accumulated in the first floating diffusion node in a first transfer interval, a second pixel data of the first photodiode obtained in a second exposure interval is accumulated in the first floating diffusion node in a second transfer interval, and the first transfer interval is behind the first exposure interval, the second exposure interval is behind the first transfer interval, and the second transfer interval is behind the second exposure interval.
2. 2 . The image sensor as claimed in claim 1 , wherein the second transfer transistor and the second extra transfer transistor are not conducted within the same image frame.
3. 3 . The image sensor as claimed in claim 1 , wherein the first pixel further comprises a first extra transfer transistor connected between the first photodiode and a floating diffusion node of another pixel adjacent to the first pixel.
4. 4 . The image sensor as claimed in claim 1 , wherein there is no readout interval between the first transfer interval and the second transfer interval.
5. 5 . The image sensor as claimed in claim 1 , further comprising a third pixel and a fourth pixel adjacent to each other and in the same pixel column as the first pixel and the second pixel, wherein a first readout interval of the first and second pixels is different from a second readout interval of the third and fourth pixels.
6. 6 . The image sensor as claimed in claim 5 , wherein the first readout interval and the second readout interval are arranged alternatively.
7. 7 . The image sensor as claimed in claim 1 , wherein two adjacent pixels of each of the multiple pixel columns have a separation space to compensate a line time difference of using a rolling shutter.
8. 8 . The image sensor as claimed in claim 7 , wherein the separation space is a multiplication of a pixel height in the along-track direction by a time ratio of the line time difference of the rolling shutter and a frame period of capturing an image frame.
9. 9 . The image sensor as claimed in claim 7 , the separation space is a summation of a pixel height in the along-track direction and a multiplication of the pixel height by a time ratio of the line time difference of the rolling shutter and a frame period of capturing an image frame.
10. 10 . The image sensor as claimed in claim 1 , wherein two adjacent pixel groups of the multiple pixels have a separation space therebetween to compensate a line time difference of using a rolling shutter, and each of the pixel groups comprises the first pixel and the second pixel.
11. 11 . An operating method of a TDI image sensor, the TDI image sensor moving with respect to a scene in an along-track direction and comprising a first pixel row and a second pixel row, the operating method comprising: exposing the first pixel row and the second pixel row in a first exposure interval; transferring a first pixel data of the second pixel row to a floating diffusion node of each pixel of the first pixel row in a first transfer interval; exposing the first pixel row and the second pixel row in a second exposure interval; and transferring a second pixel data of the first pixel row to the floating diffusion node of the each pixel of the first pixel row in a second transfer interval, wherein the first pixel data and the second pixel data are pixel data corresponding to a same position of the scene.
12. 12 . The operating method as claimed in claim 11 , wherein there is no readout interval between the first transfer interval and the second transfer interval of the first and second pixel rows.
13. 13 . The operating method as claimed in claim 11 , further comprising: reading the first pixel data and the second pixel data accumulated in the floating diffusion node in a first readout interval.
14. 14 . The operating method as claimed in claim 13 , wherein the image sensor further comprises a third pixel row and a fourth pixel row arranged in the along-track direction with the first pixel row and the second pixel row, and the operating method further comprises: exposing the third pixel row and the fourth pixel row in the first exposure interval; transferring a third pixel data of the third pixel row to a floating diffusion node of each pixel of the third pixel row in the first transfer interval; exposing the third pixel row and the fourth pixel row in a third exposure interval; and transferring a fourth pixel data of the fourth pixel row to the floating diffusion node of the each pixel of the third pixel row in a third transfer interval, wherein the third pixel data and the fourth pixel data are pixel data corresponding to another same position of the scene, and accumulated pixel data in the floating diffusion node of the each pixel of the third pixel row is not readout in a third readout interval.
15. 15 . The operating method as claimed in claim 14 , further comprising: reading the accumulated pixel data in the floating diffusion node of the each pixel of the third pixel row in a second readout interval.
16. 16 . The operating method as claimed in claim 15 , wherein the first readout interval and the second readout interval are arranged alternatively.
17. 17 . The operating method as claimed in claim 15 , wherein the image sensor further comprises a readout circuit, and the operating method further comprising: accumulating pixel data readout in the first readout interval by the readout circuit to a first accumulator; and accumulating pixel data readout in the second readout interval by the readout circuit to a second accumulator.
18. 18 . The operating method as claimed in claim 11 , wherein two adjacent pixels of each pixel column of the image sensor have a separation space to compensate a line time difference of using a rolling shutter.
19. 19 . The operating method as claimed in claim 18 , wherein the separation space is a multiplication of a pixel height in the along-track direction by a time ratio of the line time difference of the rolling shutter and a frame period of capturing an image frame, or a summation of a pixel height in the along-track direction and a multiplication of the pixel height by a time ratio of the line time difference of the rolling shutter and a frame period of capturing an image frame.

Description

BACKGROUND 1. Field of the Disclosure This disclosure generally relates to a time delay integration (TDI) sensor and, more particularly, to a TDI Complementary Metal-Oxide-Semiconductor (CMOS) image sensor that uses in-pixel TDI to reduce a time interval to read pixel data. 2. Description of the Related Art The time delay integration (TDI) sensor uses an area array image sensor to capture images from an imaging platform that is moving relative to the imaged object or scene at a constant speed. The TDI sensor is conceptually considered as the stack of linear arrays, wherein each linear array moves across a same point of the scene at a time period that the image sensor moves a distance of one pixel. Conventionally, the charge-coupled device (CCD) technology has been used for TDI applications because CCDs intrinsically operate by shifting charge from pixel to pixel across the image sensor to allow charges between pixels to integrate when the image sensor moves across a same point of the imaged scene. However, CCD technology is relatively expensive to fabricate and CCD imaging devices consume relatively high power. Although using a CMOS circuit can achieve lower power, higher degree of integration and higher speed, the existing designs suffer from higher noises. Although a 4-transistor (4T) structure can be used to minimize noises, the 4T pixels are clocked using a rolling shutter technique. Using the rolling shutter clocking can cause artifacts in the captured image since not all pixels are integrated over the same time period. Therefore, U.S. Pat. No. 9,148,601 provides a CMOS image sensor for TDI imaging. Please refer to FIG. 1, the CMOS image sensor includes multiple pixel columns 112, and each pixel column is arranged to be parallel to an along-track direction Da_t. For compensating the integration interval of the rolling shutter of the CMOS image sensor, a physical offset 150 is further arranged between two adjacent pixels of each pixel column 112, wherein if the pixel column 112 has N rows, each physical offset 150 is equal to a pixel height divided by N. Accordingly, the present disclosure further provides a TDI CMOS image sensor that implements the rolling shutter operation by spatial compensation. SUMMARY The present disclosure provides a TDI CMOS image sensor with a separation space determined according to the pixel height, the line time difference of a rolling shutter and the frame period. The present disclosure further provides a TDI CMOS image sensor that changes the line time difference corresponding to different conditions with a fixed separation space. The present disclosure further provides a TDI image sensor that performs in-pixel TDI to reduce reading time of pixel data. The present disclosure provides a TDI image sensor to move with respect to a scene in an along-track direction. The image sensor includes a pixel array having multiple pixel columns. Each of the multiple pixel columns includes multiple pixels arranged in the along-track direction. The multiple pixel columns respectively include a first pixel and a second pixel adjacent to each other. The first pixel includes a first photodiode, a first floating diffusion node and a first transfer transistor connected between the first photodiode and the first floating diffusion node. The second pixel includes a second photodiode, a second floating diffusion node, a second transfer transistor connected between the second photodiode and the second floating diffusion node, and a second extra transfer transistor connected between the second photodiode and the first floating diffusion node. The present disclosure further provides an operating method of a TDI image sensor that moves with respect to a scene in an along-track direction and includes a first pixel row and a second pixel column arranged in the along-track direction. The operating method includes the steps of: exposing the first pixel row and the second pixel row in a first exposure interval; transferring a first pixel data of the second pixel row to a floating diffusion node of each pixel of the first pixel row in a first transfer interval; exposing the first pixel row and the second pixel row in a second exposure interval; and transferring a second pixel data of the first pixel row to the floating diffusion node of the each pixel of the first pixel row in a second transfer interval, wherein the first pixel data and the second pixel data are pixel data corresponding to a same position of the scene. In the present disclosure, the separation space is not directly related to a size of the pixel array (i.e. a number of pixels), and the separation space can be determined as long as the frame period and the line time difference have been determined. BRIEF DESCRIPTION OF THE DRAWINGS Other objects, advantages, and novel features of the present disclosure will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. FIG. 1 is a sche