CN104796635A - Global reset release control method used for oversized-area-array CMOS (complementary metal-oxide-semiconductor transistor) image sensor - Google Patents

Abstract

The invention belongs to the field of CMOS (complementary metal-oxide-semiconductor transistor) image sensors and particularly relates to a global reset release control method used for an oversized-area-array CMOS image sensor. The global reset release control method includes the steps of firstly, controlling rows of pixels in a pixel photosensitive area to reset row by row; after resetting operation in the rows is over, controlling the pixels in an integral area array to enter into and exit from an exposure status, and reading exposure data row by row after exposure is over. The global reset release control method has the advantages that by means of controlling the area array to enter into and exit from the exposure status, distortion of the oversized-area-array CMOS image sensor capturing a moving object can be eliminated, the problem of inconformity of dark current of large-area-array pixels in a traditional global exposure control condition can be solved, and the global reset release control method is easy to implement, high in expansibility and wide in application range.

Description

A kind of Global reset releasing control method for super large face array CMOS image sensor

Technical field

The invention belongs to cmos image sensor field, be specifically related to a kind of Global reset releasing control method for super large face array CMOS image sensor.

Background technology

Cmos image sensor, due to the advantage of its low-power consumption, low cost, high integration capability, has more and more wider application in business, medical treatment and military field.And along with the progress of technology, cmos image sensor is also constantly expanding scale, from mega pixel level to ten million Pixel-level, hundreds of millions even higher Pixel-level stride forward, the various problems of ultra-large area array sensor are also arisen at the historic moment thereupon, the inconsistent image quality decrease etc. caused of dark current that the roll exposure mode as conventional is introduced for super large face battle array for the fuzzy and traditional overall Exposure mode that moving object catches.These problems make ultra-large sensor chip introduce some in the application and extra trim circuit overhead, are very important so address these problems in sensor chip inside.

Current 4T APS is a kind of conventional pixel structure, and as shown in Figure 1, this kind of pixel structure comprises photodiode PD, transfer tube TX, source follower M, reset transistor RST and line EAC SEL.The conventional Exposure mode of this kind of 4T pixel structure is roll exposure, and feature is line by line to photosensitive area with float that diffusion point resets, pixel array enters exposure status line by line and exit exposure status line by line, complete the reading of light signal line by line.Be applied to the general overall Exposure mode of 4T pixel structure as shown in Figure 2, for the transducer of super large pixel face battle array, this overall Exposure mode also exists following defect: because all pixel cells in the battle array of pixel face complete reset simultaneously, integration operation, read photosignal line by line, this just means for the capable pixel array of a N, the first row carry out the pixel that reads its integration terminate to the time interval between reading be 0, and its integration of pixel that the second row carries out reading terminate to the time interval between reading be the duration of a line period, the time interval of the third line is the duration of two line periods, by that analogy, its integration of pixel that last column carries out reading terminate to the time interval between reading be the duration of N number of line period.And during this period of time, dark current is also in accumulation, and each horizontal reset anomalous integral reads the time difference between waiting for, causes the inconsistency of every a line dark current, finally can cause output image noise in the row direction, greatly reduce picture quality.

Summary of the invention

The object of the invention is to the defect for prior art existence and deficiency, a kind of Global reset releasing control method for super large face array CMOS image sensor is provided, the moving object that exists in effective solution prior art catches problem of dtmf distortion DTMF, and the inconsistency of dark current and the image quality issues introduced in the face battle array that causes of traditional overall Exposure mode.

The moving object that the roll exposure mode solving existing super large face battle array scale cmos image sensor is introduced catches distortion

For achieving the above object, the present invention is by the following technical solutions: comprise the following steps:

Step 1) reset of pixel photosensitive region: according to the pixel line number participating in imaging, control each row pixel and carry out reset operation line by line;

Step 2) pixel array integration: after reset operation completes line by line, whole photosurface battle array enters exposure status simultaneously, starts to accept illumination, produces photogenerated charge, to end exposure;

Step 3) exposure data reading: after end exposure, read exposure data line by line; For each row pixel cell, after the exposure data of previous frame has read, to enter before the exposure of next frame reset operation line by line; Read exposure data to last frame last column pixel cell to terminate.

Further, described step 1) concrete operations are: for each imaging, according to the pixel line number participating in imaging, control each row pixel to reset line by line: the reset transistor and the transfer tube that first control the first row pixel are opened, reset operation is carried out to photodiode, after the pixel of the first row completes reset, the reset transistor of the first row pixel and transfer tube reset transistor and transfer tube are closed, the pixel reset transistor of the second row and transfer tube are opened simultaneously again, reset operation is carried out to the photodiode of the second row, the rest may be inferred, and the reset operation to last column pixel completes.

Further, described step 1) every a line pixel reset operation is when completing, and judges whether this row is footline, if so, then enters step 2), if not, then return to reset addressing register to row, enter next line pixel reset operation.

Further, it is characterized in that, described step 3) concrete operations are: after the set time of integration, by the first row pixel, control pixel line by line carries out resetting to the secondary of FD point, resetting voltage sampling, transfer tube is opened afterwards, and optical charge reads photosignal value to the transfer of FD point, reading circuit.

Further, it is characterized in that, described step 3) after every a line pixel reads photosignal value by reading circuit, determine whether frame end, if so, then frame end; If not, then return to reading addressing register to row, enter next line pixel and read exposure data.

Further, it is characterized in that, for the pixel cell having the capable physics combinatorial construction of adjacent M, under nonjoinder pattern, after the exposure data that the capable pixel of M all completes previous frame reads, then reset operation line by line before the exposure entering next frame, namely interFrameGap is M line period; Under merging patterns, the exposure data that the capable pixel of M carries out previous frame simultaneously reads, then interFrameGap is 1 line period.

Further, the frame frequency of the Exposure mode of Global reset releasing control method is:

$\mathrm{frame}\_\mathrm{rate}=\frac{1}{(N+M*\mathrm{binning})\×\mathrm{period}+\mathrm{INTE}}$

Wherein N is that line number, INTE that pixel array comprises are integration duration, M is combinatorial construction on pixel cell is expert at, binning is 0 under merging application, is 1, period is line period under unconsolidated application.

Compared with prior art, the present invention has following useful technique effect: first this method controls each row pixel of pixel photosensitive region and reset line by line, the all pixels controlling whole battle array at reset operation line by line after terminating enter simultaneously, exit exposure status, after end exposure, read exposure data line by line.Enter simultaneously by all pixels controlling whole battle array, exit exposure status, realize the undistorted seizure to moving object.Concerning every a line photosensitive area of pixel face battle array, reset mode and be on all four to the time interval between photosignal reads before exiting integration, namely for all pixel cells in the battle array of face, the time of their accumulation dark current is on all four, and such operation effectively eliminates the inconsistent noise in the ranks caused due to face battle array dark current.This method effectively to solve in prior art moving object and catches distortion, and the inconsistency of dark current and the image quality issues introduced in the face battle array that causes of traditional overall Exposure mode.Simultaneously this method has and is easy to realize, and autgmentability is strong, the advantage of applied range.

Accompanying drawing explanation

Fig. 1 is 4T pixel unit circuit figure;

Fig. 2 is traditional overall Exposure mode workflow schematic diagram;

Fig. 3 is the workflow schematic diagram that the invention provides method;

Fig. 4 is the time diagram that the invention provides the Global reset release type Exposure mode that method is taken continuously.

Embodiment

Below in conjunction with accompanying drawing, the present invention is described in further detail.

See Fig. 3, method of the present invention controls whole all pixel of battle array and enters simultaneously, exits exposure status, realizes the undistorted seizure to moving object; Before exposure starts, control pixel array reset line by line, make the time consistency of often row pixel accumulation dark current; Comprise the following steps:

Step 1), pixel photosensitive region resets: according to the pixel line number participating in imaging, control each row pixel and carry out reset operation line by line;

Concrete operations are: for each imaging, according to the pixel line number participating in imaging, control each row pixel to reset line by line: the reset transistor and the transfer tube that first control the first row pixel are opened, reset operation is carried out to photodiode, after the pixel of the first row completes reset, the reset transistor of the first row pixel and transfer tube reset transistor and transfer tube are closed, the pixel reset transistor of the second row and transfer tube are opened simultaneously again, reset operation is carried out to the photodiode of the second row, the rest may be inferred, in the end the photodiode of a line completes reset operation, i.e. after reset operation completes line by line of pixel array photosensitive area, whole photosurface battle array enters exposure status simultaneously again.

And when often a line pixel reset operation completes, judge whether this row is footline, if so, then enters step 2), if not, then return to reset addressing register to row, enter next line pixel reset operation.

Step 2) pixel array integration: after reset operation completes line by line, whole photosurface battle array enters exposure status simultaneously, starts to accept illumination, produces photogenerated charge, to end exposure;

Step 3) exposure data reading: through the set time of integration, after end exposure, read exposure data line by line; For each row pixel cell, after the exposure data of previous frame has read, to enter before the exposure of next frame reset operation line by line; Read exposure data to last frame last column pixel cell to terminate;

Concrete operations are: after the set time of integration, and by the first row pixel, control pixel line by line carries out resetting to the secondary of FD point, resetting voltage sampling, and transfer tube is opened afterwards, and optical charge is to the transfer of FD point, reading circuit reading photosignal value.

After every a line pixel reads photosignal value by reading circuit, determine whether frame end, if so, then frame end; If not, then return to reading addressing register to row, enter next line pixel and read exposure data.For a two field picture, this frame last column pixel reads after exposure data completes and namely terminates; For multiframe consecutive image, last frame last column pixel reads after exposure data completes and namely terminates whole control flow.

See Fig. 4, this method realizes carrying out in the process read at the image of previous frame, just can to start to carry out before the integration of next frame reset operation line by line.Concrete operations are: for the imaging process of a two field picture, be divided into reset before integration line by line, both full-pixel array integration, line by line light signal read this three parts.Wherein K frame the reading of light signal line by line part can with the integration line by line of K+1 frame before reset to partially overlap and carry out.Both for any a line in array, after the light signal having completed its K frame when this row reads, this row can enter reset operation before the integration of K+1 frame.Be illustrated in figure 4 the successive frame sequential signal that comprises three row pixel arrays, after the light signal completing the first frame at the first row pixel reads, both entered reset operation before the integration of the second frame, the light signal that the second row pixel carries out the first frame simultaneously reads, by that analogy, successive frame shooting is realized.

M line period is spaced apart between frame and frame, M value depends in pixel cell the physics combinatorial construction whether had on line direction: as pixel cell adopts the physics combinatorial construction of 2 × 1, then M=2, then, under nonjoinder mode of operation, be spaced apart 2 line periods between frame and frame.The frame frequency of Global reset release type Exposure mode is:

$\mathrm{frame}\_\mathrm{rate}=\frac{1}{(N+M*\mathrm{binning})\×\mathrm{period}+\mathrm{INTE}}$

Wherein N is that line number, INTE that pixel array comprises are integration duration, M is combinatorial construction on pixel cell is expert at, binning is 0 under merging application, is 1, period is line period under unconsolidated application;

Namely frame frequency is 1/ (line number * (line period+merging line number)+exposure time) under the application of nonjoinder, is 1/ (line number * line period+exposure time) under the application merged.

For the pixel cell having the capable physics combinatorial construction of adjacent M, under nonjoinder pattern, after the exposure data that the capable pixel of M all completes previous frame reads, then reset operation line by line before the exposure entering next frame, namely interFrameGap is M line period; Under merging patterns, the exposure data that the capable pixel of M carries out previous frame simultaneously reads, then interFrameGap is 1 line period.For whole battle array, between each row, reset is accomplished to the time interval reading exposure data is (effective line number+exposure time), namely the dark current of each row is consistent for integration time, and such method eliminates the inconsistent noise in the ranks caused due to face battle array dark current to a great extent.

Claims (7)

1., for a Global reset releasing control method for super large face array CMOS image sensor, it is characterized in that, comprise the following steps:

Step 1) reset of pixel photosensitive region: according to the pixel line number participating in imaging, control each row pixel and carry out reset operation line by line;

Step 2) pixel array integration: after reset operation completes line by line, whole photosurface battle array enters exposure status simultaneously, starts to accept illumination, produces photogenerated charge, to end exposure;

Step 3) exposure data reading: after end exposure, read exposure data line by line; For each row pixel cell, after the exposure data of previous frame has read, to enter before the exposure of next frame reset operation line by line; Read exposure data to last frame last column pixel cell to terminate.

2. a kind of Global reset releasing control method for super large face array CMOS image sensor according to claim 1, is characterized in that,

Described step 1) concrete operations are: for each imaging, according to the pixel line number participating in imaging, control each row pixel to reset line by line: the reset transistor and the transfer tube that first control the first row pixel are opened, reset operation is carried out to photodiode, after the pixel of the first row completes reset, the reset transistor of the first row pixel and transfer tube reset transistor and transfer tube are closed, the pixel reset transistor of the second row and transfer tube are opened simultaneously again, reset operation is carried out to the photodiode of the second row, the rest may be inferred, and the reset operation to last column pixel completes.

3. a kind of Global reset releasing control method for super large face array CMOS image sensor according to claim 1 and 2, it is characterized in that, described step 1) every a line pixel reset operation is when completing, judge whether this row is footline, if so, then step 2 is entered), if not, then return to reset addressing register to row, enter next line pixel reset operation.

4. a kind of Global reset releasing control method for super large face array CMOS image sensor according to claim 1, it is characterized in that, described step 3) concrete operations are: after the set time of integration, by the first row pixel, control pixel line by line carries out resetting to the secondary of FD point, resetting voltage sampling, transfer tube is opened afterwards, and optical charge reads photosignal value to the transfer of FD point, reading circuit.

5. a kind of Global reset releasing control method for super large face array CMOS image sensor according to claim 1 or 4, it is characterized in that, described step 3) after every a line pixel reads photosignal value by reading circuit, determine whether frame end, if so, then frame end; If not, then return to reading addressing register to row, enter next line pixel and read exposure data.

6. a kind of Global reset releasing control method for super large face array CMOS image sensor according to claim 1 or 4, it is characterized in that, for the pixel cell having the capable physics combinatorial construction of adjacent M, under nonjoinder pattern, after the capable pixel of M all completes the exposure data reading of previous frame, to enter before the exposure of next frame reset operation line by line again, namely interFrameGap is M line period; Under merging patterns, the exposure data that the capable pixel of M carries out previous frame simultaneously reads, then interFrameGap is 1 line period.

7. a kind of Global reset releasing control method for super large face array CMOS image sensor according to claim 6, it is characterized in that, the frame frequency of the Exposure mode of Global reset releasing control method is:

$\mathrm{frame}\_\mathrm{rate}+\frac{1}{(N+M*\mathrm{binning})\×\mathrm{period}+\mathrm{INTE}}$

Wherein N is that line number, INTE that pixel array comprises are integration duration, M is combinatorial construction on pixel cell is expert at, binning is 0 under merging application, is 1, period is line period under unconsolidated application.