CN101064787B

CN101064787B - CMOS image sensor pixel

Info

Publication number: CN101064787B
Application number: CN2006100262438A
Authority: CN
Inventors: 赵立新; 李�杰; 董建民; 徐春花; 孟庆
Original assignee: Galaxycore Shanghai Ltd Corp
Current assignee: Galaxycore Shanghai Ltd Corp
Priority date: 2006-04-29
Filing date: 2006-04-29
Publication date: 2010-08-11
Anticipated expiration: 2026-04-29
Also published as: CN101064787A

Abstract

The invention discloses a CMOS imaging senor pixel, one or more pixels use one readout circuit, and a part or all circuits of readout circuit consist of transistor with parallel connection. In pixel designing, the invention applies several transistors, and improves the matching property of pixel, and reduces the noise.

Description

A kind of cmos image sensor pixel

Technical field

The present invention relates to a kind of CMOS (complementary metal oxide semiconductors (CMOS)) image sensor pixel.

Background technology

The design of cmos image sensor (CIS) pixel has a variety of structures, generally comprises n transistor, and each transistor is realized different functions.The cmos image sensor pixel is modal to be 3T and 4T structure.3T promptly has three transistors in pixel, be respectively reset transistor RST, source follower SF and row gating switch pipe SEL, as shown in Figure 1.And 4T has increased a transfer tube TX on the basis of 3T, as shown in Figure 2.In each pixel, a photodiode PD (as Fig. 1, shown in Figure 2) is all arranged, be used for light signal is changed into the signal of telecommunication, thereby reach the purpose of sensitization.In Fig. 1 and Fig. 2, VDD represents power supply.

Advantages such as cmos image sensor has the integrated level height for CCD (charge coupled device), low in energy consumption, and cost is low have obtained application more and more widely; But its noise is bigger, thereby CIS is with respect to CCD signal to noise ratio lower (based on the image sensing technical research and the progress of CMOS technology).And along with the raising of resolution and reducing of Pixel Dimensions, transistorized size is also more and more littler in the pixel, and its matching performance and noiseproof feature can further reduce.Therefore, people have found out various ways and have reduced noise, for example application of CDS (correlated-double-sampling) circuit etc.But these technology have just been eliminated partial noise, and not obvious for the do not match noise effects that causes of transistor in the pixel.

Summary of the invention

The technical problem to be solved in the present invention provides a kind of cmos image sensor pixel with many group transistors, and the matching that it has improved pixel has effectively reduced the noise of introducing thus.

For solving the problems of the technologies described above, the invention provides a kind of cmos image sensor pixel, wherein, and the shared reading circuit of one or more pixels, described reading circuit comprises the transistor of multiple realization difference in functionality; Described reading circuit comprises source follower, row gating switch pipe, reset transistor and transfer tube simultaneously; The source electrode of described source follower is received the drain electrode of capable gating switch pipe, and power supply is received in drain electrode, and grid is received floating diffusion amplifier; The source electrode of described reset transistor is received floating diffusion amplifier, and power supply is received in drain electrode, and grid is received the control signal wire of reset transistor; The source electrode of described transfer tube is received photodiode, and floating diffusion amplifier is received in drain electrode, and grid is received the control signal wire of transfer tube; The source electrode of described capable gating switch pipe is received the input of column decoding, and the source electrode of source follower is received in drain electrode, and grid is received the control signal wire of capable gating switch pipe; Described source follower is composed in parallel by many group transistors, and perhaps described capable gating switch pipe is composed in parallel by many group transistors, and perhaps described source follower and row gating switch pipe are composed in parallel by many group transistors simultaneously.

Each group transistor in described many group transistors is made up of single transistor, perhaps connected to form in mode in parallel or series connection by a plurality of transistors, and each group transistor in described many group transistors is realized identical functions.

The source of described single transistor, leakage the two poles of the earth all are made up of not divided active area separately.

The present invention has following beneficial effect: 1. improve the matching performance of cmos image sensor pixel, thereby reduced noise; 2. can not reduce activity coefficient, the transistor utilization of increase be position, space between pixel, do not reduce photosensitive area, so activity coefficient is maintained.

Description of drawings

Fig. 1 is the circuit diagram of prior art cmos image sensor 3T pixel;

Fig. 2 is the circuit diagram of prior art cmos image sensor 4T pixel;

Fig. 3 is the circuit diagram of the embodiment of cmos image sensor pixel of the present invention;

Fig. 4 is the domain of many group transistors among Fig. 3.

Embodiment

The invention will be further elaborated below in conjunction with drawings and Examples:

Be example with cmos image sensor 4T dot structure below, the application of the many group transistors of the present invention is described.

As shown in Figure 2, in the 4T structure, after sensitization after a while, at first reset transistor RST resets FD (floating diffusion amplifier), through source follower SF signal is amplified, and by row gating switch pipe SEL signal is read again; Then reset transistor RST is closed, transfer tube TX opens, the optical charge of storing among the photodiode PD is passed on the FD, and by source follower SF and row gating switch pipe SEL output.Twice signal subtraction promptly obtained photoelectricity and transformed the signal that produces.Open reset transistor RST and transfer tube TX at last simultaneously, PD resets with photodiode, closes transfer tube TX then, enters circulation next time.In this process, all transistors all might be introduced noise, if its size is less, thereby matching degree is not high, more is easy to generate noise.

In order to increase the transistor matching degree, valid approach is to increase its size.But in less pixel, if just simple its width and the length of strengthening certainly will reduce photosensitive area, i.e. activity coefficient, thus reduce signal to noise ratio.The present invention proposes, can utilize the gap between pixel, make several transistors more, some among their connected mode and function and the 4T or certain several transistor is identical, thereby can under the prerequisite that does not reduce activity coefficient, increase transistor size, improve the matching performance of pixel effectively.

As one embodiment of the present of invention, in the design of 4 shared cover reading circuits of pixel, source follower and row gating switch pipe can be made double transistor SF1, SF2 and SEL1, SEL2, its circuit diagram as shown in Figure 3, the domain of many group transistors part is as shown in Figure 4.As shown in Figure 3, in the design of this image element circuit, four photodiode PD1～PD4 are arranged, four transfer tube TX1～TX4, their shared cover reading circuits have 9 transistors, and on average each pixel has 2.25 transistors.As seen from Figure 4, the source follower SF1 of two-fold, SF2 and row gating switch pipe SEL1, SEL2 makes transistor length not have change, and width doubles.So not only make the electric capacity of source follower increase by one times, and speed and matching also be improved, thereby reduced noise.Simultaneously, the transistor utilization of increase be position, space between pixel, do not reduce photosensitive area, so activity coefficient is maintained.

Certainly, range of application of the present invention is not limited to cmos image sensor 4T dot structure, also can be applied to cmos image sensor 3T dot structure or other dot structure.

Many group transistors of the present invention, each group transistor has played identical functions and effect, is applied to source follower as many group transistors, promptly realizes and the source follower identical functions; Be applied to capable gating switch pipe as many group transistors, promptly realize and row gating switch pipe identical functions.Forked pipe in the picture layout design promptly is an example of many group transistors.Each group transistor in many group transistors can be electrically connected in mode in parallel or series connection by a plurality of transistors, for example: the transistor of two series connection can be formed a group transistor, can form a group transistor etc. after the transistor AND gate single transistor series connection of two parallel connections.

Certainly, range of application of the present invention is not limited to source follower and row gating switch pipe, also is not limited to the shared transistorized structure of pixel.

Claims

1. cmos image sensor pixel, wherein, the shared reading circuit of one or more pixels, described reading circuit comprises the transistor of multiple realization difference in functionality; Described reading circuit comprises source follower, row gating switch pipe, reset transistor and transfer tube simultaneously; The source electrode of described source follower is received the drain electrode of capable gating switch pipe, and power supply is received in drain electrode, and grid is received floating diffusion amplifier; The source electrode of described reset transistor is received floating diffusion amplifier, and power supply is received in drain electrode, and grid is received the control signal wire of reset transistor; The source electrode of described transfer tube is received photodiode, and floating diffusion amplifier is received in drain electrode, and grid is received the control signal wire of transfer tube; The source electrode of described capable gating switch pipe is received the input of column decoding, and the source electrode of source follower is received in drain electrode, and grid is received the control signal wire of capable gating switch pipe; It is characterized in that described source follower is composed in parallel by many group transistors, perhaps described capable gating switch pipe is composed in parallel by many group transistors, and perhaps described source follower and row gating switch pipe are composed in parallel by many group transistors simultaneously.

2. cmos image sensor pixel as claimed in claim 1, it is characterized in that, each group transistor in described many group transistors is made up of single transistor, perhaps connect to form in mode in parallel or series connection, and each group transistor in described many group transistors is realized identical functions by a plurality of transistors.

3. cmos image sensor pixel as claimed in claim 2 is characterized in that, the source of described single transistor, leakage the two poles of the earth all are made up of not divided active area separately.