CN104270582A - Image sensor with a plurality of pixels - Google Patents

Abstract

An image sensor includes a sensing matrix and a plurality of shutter control lines. The sensing matrix is provided with a plurality of sensing units, each sensing unit is provided with an electronic shutter and a light detection element, and the electronic shutter controls the exposure time of the light detection element. Each shutter control line is coupled to the electronic shutters in the same row or the same column in the sensing matrix, so as to independently control the exposure time of the light detection elements in different rows or different columns, and the light detection elements coupled to the same shutter control line have the same exposure time.

Description

Image Sensor

The present invention is a divisional application, the filing date of the original application is March 3, 2011, the application number is 201110050503.6, and the invention name is: image sensor.

technical field

The invention relates to an image sensor, in particular to an image sensor with light source variation compensation function.

Background technique

Image sensors can convert light into electrical charges, and after processing the charges, output digital electrical signals that constitute images. The digital electrical signal can be stored on a storage medium, or output to an image display device to present an image formed by it on a display screen, so it is very convenient to use. Due to its convenience, image sensors have been used in many electronic devices, such as digital cameras, digital video cameras, mobile phones or mice, and so on.

A general image sensor includes a semiconductor device, which can be a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS). An image sensor is generally composed of pixels arranged in a matrix. When illuminated by light, a pixel generates an electrical charge, or voltage, that represents image information. Charges or voltages stored in the pixels can be sequentially output and processed through shift registers coupled to the pixels.

Image sensors can also be used in touch technology. FIG. 1 shows an optical touch system 1 . Referring to FIG. 1 , the optical touch system 1 includes two light guides 11 , a plurality of LEDs 12 , and an image sensor 13 . The light guide 11 is disposed on adjacent two sides of the sensing area 14 . A plurality of light emitting diodes 12 are adjacent to the end of the light guide 11 and projected to the light sensing region 14 through the light guide 11 . The image sensor 13 is disposed opposite to the light guide 11 .

FIG. 2 shows a brightness distribution diagram of a background light image captured by the image sensor 13 . Referring to FIG. 1 and FIG. 2 , in the optical touch system 1 , the brightness distribution of the background light projected on the image sensor 13 is not uniform. Inhomogeneous brightness distribution will cause the following disadvantages: pixels subject to strong light will accumulate charges quickly, which will easily cause pixel saturation, which will affect the recognition of objects; in areas with weaker brightness, due to the signal-to-noise ratio noise ratio; SNR) is low, so it is easy to generate a large calculation error of the center of gravity of the object image; and if the object image falls on a place with a large slope of the curve in Figure 2, the calculation of the center of gravity is not easy to be accurate.

It is a common method nowadays to normalize the luminance curve in Fig. 2 by means of software calculation to obtain a more uniform luminance distribution. Although this method can make the calculation of the center of gravity of the object image no longer affected by the uneven brightness distribution, it still cannot improve the problem of the center of gravity calculation error of the image generated by the object in a region with weaker brightness.

Contents of the invention

In view of the above problems, an object of the present invention is to provide an image sensor that can provide an image with uniform brightness distribution of the background light.

According to the above purpose, an embodiment of the present invention discloses an image sensor, which includes a sensing matrix and a plurality of shutter control lines. The sensing matrix has a plurality of sensing units, and each sensing unit has an electronic shutter and a light detection element, wherein the electronic shutter controls the exposure time of the light detection element. Each shutter control line is coupled to the electronic shutters in the same column or row in the sensing matrix, thereby independently controlling the exposure time of the photodetection elements in different columns or rows, and making the shutters coupled to the same line Said light detecting elements of the control line have the same exposure time.

Another embodiment of the present invention discloses an image sensor, which includes a plurality of sensing units in at least one column or row, a plurality of electronic shutters, and a storage device. Each sensing unit includes a light detection element. The multiple electronic shutters are respectively coupled to corresponding photodetection elements. The storage device stores a plurality of timing instructions corresponding to the electronic shutters, wherein the timing instructions correspond to generating shutter control signals for respectively controlling the electronic shutters.

Still another embodiment of the present invention discloses an image sensor, which includes a plurality of sensing units in at least one row or column, a plurality of electronic shutters, and an image processing unit. Each sensing unit includes a light detection element. The multiple electronic shutters are respectively coupled to corresponding photodetection elements. The image processing unit is electrically connected to the plurality of sensing units and obtains the output signals of the plurality of sensing units, and generates corresponding sensing signals, wherein the shutter opening times of the plurality of electronic shutters are according to the corresponding Sensing signals are controlled separately.

The technical features and advantages of the present disclosure have been briefly described above, so that the following detailed description of the present invention can be better understood. Other technical features and advantages forming the subject of the claims of the invention will be described hereinafter. Those skilled in the art of the present invention should understand that the concepts and specific embodiments disclosed below can be used as a basis to easily modify or design other structures or processes to achieve the same purpose of the present invention. Those skilled in the art to which the present invention belongs should also understand that such equivalent constructions cannot deviate from the spirit and scope of the present invention set forth in the claims.

The beneficial effect of the present invention is that the image sensor provided by the present invention can provide an image with uniform background light brightness distribution.

Description of drawings

FIG. 1 shows an optical touch system;

Figure 2 shows the brightness distribution diagram on the image sensor;

FIG. 3 shows a schematic functional block diagram of an image sensor according to an embodiment of the present invention;

FIG. 4 shows a schematic diagram of some sensing units and their control circuits in an image sensor according to an embodiment of the present invention;

FIG. 5 shows a timing diagram for operating the image sensor of FIG. 4;

Fig. 6 shows the luminance distribution diagrams on the image sensor before compensation and after compensation; and

FIG. 7 shows a partial circuit diagram of an image sensor according to another embodiment of the present invention.

Wherein, the reference signs are explained as follows:

1 Optical touch system

2 image sensor

3 image sensor

5 Curves

6 Curves

7 Predetermined brightness interval

11 light guide

12 LEDs

13 image sensor

14 sensing area

21 Sensing matrix

22 timing generator

23 storage device

24 image processing unit

211 sensing unit

212 electronic shutter

213 light detection element

214 transistors

215 transistors

216 constant current

217 transistors

218 transistors

219 line decoder

220 read circuit

221 Shutter control line

222 shutter control line

223 Shutter control line

224 shutter control line

225 timing control circuit

226 bit lines

T ₁ exposure time

_T2 exposure time

Detailed ways

FIG. 3 shows a functional block diagram of the image sensor 2 according to an embodiment of the present invention. FIG. 4 shows a schematic diagram of part of the sensing unit 211 and its control circuit in the image sensor 2 according to an embodiment of the present invention. Referring to FIG. 3 , the image sensor 2 includes a sensor matrix (sensor matrix) 21 , a timing generator 22 , a storage device 23 , a plurality of electronic shutters 212 , and an image processing unit 24 . The sensing matrix 21 includes a plurality of sensing units 211 arranged in a matrix in horizontal and vertical directions. Multiple electronic shutters 212 are set corresponding to multiple sensing units 211 . As shown in FIG. 4 , each sensing unit 211 includes a photodetector 213 , and the electronic shutter 212 is coupled to the corresponding photodetector 213 to regulate the exposure time of the photodetector 213 . In this embodiment, each electronic shutter 212 is included in a corresponding sensing unit 211 . As shown in FIG. 3 , the clock generator 22 provides clock signals required for extracting light images on the sensing unit 211 , including shutter control signals. The storage device 23 is coupled to the timing generator 22, the storage device 23 can store timing instructions, and the timing generator 22 generates a shutter control signal according to the timing instruction, wherein the timing instruction can be modified so that the shutter control signal can be adjusted, thereby controlling the corresponding electronic The opening time of the shutter 212. The image processing unit 24 is coupled to the sensing matrix 21 . The image processing unit 24 can be electrically connected to the plurality of sensing units 211 to obtain output signals of the plurality of sensing units 211 to generate corresponding sensing signals. The image sensor 2 can control the opening time of the electronic shutter 212 according to the intensity of the sensing signals corresponding to the plurality of sensing units 211, so that the plurality of sensing units 211 output an output with relatively consistent background brightness. Signal.

In another embodiment, the storage device 23 can be disposed in the timing generator 22 .

Referring to FIG. 4 , the sensing units 211 in the image sensor 2 may be arranged in a matrix. In each sensing unit 211 , the photodetection element 213 generates charges correspondingly according to the received brightness. The transistor 214 controls charge transfer from the photodetection element 213 to a floating diffusion (FD) output node. The transistor 215 and the constant current 216 constitute a source follower, and the source follower can amplify the photoelectric conversion voltage generated by the photodetection element 213 . Transistor 217 is used to output data to bit line 226 . When RST1 or RST2 and TG1 or TG2 are at high level, the transistor 218 and the transistor 214 can be turned on, so that the supply voltage VDDAY can reset the photo-detection element 213 to its photo-electric conversion initiation state. When transistor 214 is turned on, charge can be transferred from photodetection element 213 to the floating diffusion output region. When a high-level RST1 or RST2 signal is input, the floating diffusion output area can be reset by using the supply voltage VDDAY.

In another embodiment, each sensing unit 211 may include a plurality of light detection elements 213 and a plurality of corresponding electronic shutters 212 . The plurality of electronic shutters 212 respectively control the exposure time of each light detecting element 213 .

In another embodiment, the electronic shutter 212 is a transistor. The electronic shutter 212 is connected in series between the supply voltage VDDAY and the light detection element 213 . When the shutter control signal AB1 or AB2 is at a high level, the supply voltage VDDAY resets the light detection element 213 to maintain the photoelectric conversion initial state. When the light detecting element 213 starts to expose, the shutter control signal AB1 or AB2 drops to a low level, so that the light detecting element 213 starts to perform photoelectric conversion. By adjusting the opening or closing time of the electronic shutter 212 , the length of the exposure time of the light detection element 213 can be regulated.

The row decoder 219 provides reset signals (RST1˜RST2), signals TG1˜TG2, signals AB1˜AB2 and word-line readout control signals (word-line readout control signals) WL1˜WL2. The reading circuit 220 reads image data from each sensing unit 211 . The reading circuit 220 can be coupled to a decoder (not shown in the figure) to receive the column selection signal. The timing generator 22 provides timing signals required by the row decoder 219 and the reading circuit 220 .

In particular, the image sensor 2 includes a plurality of shutter control lines 221 and 222 . As shown in FIG. 4 , each shutter control line 221 or 222 is coupled to the electronic shutters 212 of the sensing units 211 arranged in the same horizontal direction (row direction) in the sensing matrix 21, so that the optical shutters 212 arranged in the same horizontal direction The detection elements 213 can be exposed with the same exposure time. Furthermore, the plurality of shutter control lines 221 and 222 can be independent of each other, so different shutter control signals can be provided on the plurality of shutter control lines 221 and 222, so that the light detection elements 213 connected to different control lines 221 and 222 Exposures can be performed at different exposure times.

FIG. 5 shows a timing chart for operating the image sensor 2 of FIG. 4 , which shows the synchronous signal Vsync, the word line read control signals WL˜WLn, and the shutter control signals AB1 ˜AB2 . Referring to FIG. 1, FIG. 4 and FIG. 5, the storage device 23 can store timing instructions corresponding to the shutter control lines 221 and 222, so that on different shutter control lines 221 or 222, different pulse widths (pulse width) are generated. The shutter control signal AB1 or AB2, as shown in the figure. In this embodiment, the exposure of all photodetection elements 213 starts at the same time and ends at the falling edge of a sync signal Vsync. Therefore, by adjusting the pulse width of the shutter control signal AB1 or AB2 , the light detecting elements 213 arranged in different horizontal directions can be exposed with different exposure times. In the embodiment of FIG. 5 , since the pulse width of the shutter control signal AB1 is smaller than the pulse width of the shutter control signal AB2 , the exposure time T ₁ It is longer than the exposure time T ₂ experienced by the light detection element 213 connected to the shutter control line 222 .

FIG. 6 shows a schematic diagram of the brightness distribution of the light detection element 213 before and after the exposure time adjustment according to an embodiment of the present invention. By using the circuit architecture disclosed in FIG. 4 , variations in the brightness distribution of the background light in the image captured by the image sensor 2 can be compensated. Referring to FIG. 4 and FIG. 6 , in a system, in the image captured by the image sensor 2 according to a predetermined exposure time, the brightness distribution of the background light is a curve 5 . The luminance distribution curve 5 represents the average luminance distribution along a direction transverse (or perpendicular) to the control lines 221 and 222, which is the column direction in this embodiment. Shorten the exposure time of the photodetection element 213 irradiated by stronger background light, that is, apply a shutter control signal with a wider pulse width to the control line 221 or 222 connected to the photodetection element 213 irradiated by stronger background light; The exposure time of the photodetection element 213 irradiated by the weaker background light, that is, the shutter control signal with a smaller pulse width is applied to the control line 221 or 222 connected to the photodetection element 213 irradiated by the weaker background light. By changing the aforementioned exposure time, an image with a relatively uniform background brightness distribution (as shown in curve 6) can be obtained, thereby achieving the effect of compensating for variations in the light source.

In another embodiment, the exposure time of the light detection element 213 connected to each control line 221 or 222 can be determined according to a predetermined brightness interval 7 . As shown in FIG. 6 , according to the original luminance value and the predetermined luminance interval 7 constituting the luminance distribution curve 5 , the image sensor 2 can calculate the exposure time of the light detection element 213 connected to each control line 221 or 222 . For example, the exposure time can be calculated proportionally by using the original brightness value obtained according to the original exposure time and a value (such as an intermediate value) within the predetermined brightness interval 7 . By using the calculated exposure time to expose, the image sensor 2 can obtain a background image whose luminance values are distributed within a predetermined luminance interval.

In one embodiment, as shown in FIG. 3 , the image processing unit 24 is electrically connected to the sensing unit 211 , so the output signal of the sensing unit 211 can be obtained. The image processing unit 24 can also process the output signal to generate a corresponding sensing signal. The sensing signal represents the brightness value sensed by the corresponding sensing unit 211 .

FIG. 7 shows a partial circuit diagram of an image sensor 3 according to another embodiment of the present invention. Referring to FIG. 7, the image sensor 3 is similar to the image sensor 2 disclosed in FIG. connect. In this way, the electronic shutters 212 of the sensing units 211 in the same row can be exposed at the same exposure time, while the electronic shutters 212 of the sensing units 211 in different columns can be exposed at different exposure times. The circuit design of the image sensor 3 can compensate the variation of the light source in the row direction of the sensing matrix 21, so that the brightness distribution value of the extracted image is uniform or within a predetermined brightness range. The shutter control lines 223 and 224 can be coupled to a timing control circuit 225 , through the timing control circuit 225 , the timing generator 22 can provide shutter control signals corresponding to each shutter control line 223 or 224 .

Connect the electronic shutters in the same row or column in the image sensor with the shutter control line, and then extract the background light brightness distribution in the image according to the image sensor, and apply different shutter control signals to different shutter control lines, so that the light under strong light The detection element is exposed for a short time; and the photodetection element subjected to weaker light is exposed for a longer time, so that it can solve the problem that the charge accumulation of the photodetection element subjected to strong light is relatively fast, which is easy to cause saturation, and in the Areas with weak brightness are prone to problems such as calculation errors of the center of gravity of the large object image, and avoid the part with a large slope on the brightness distribution curve, resulting in the problem that the calculation of the center of gravity is not easy to be accurate.

The technical content and technical features of the present invention have been disclosed above, but those skilled in the art may still make various substitutions and modifications based on the teaching and disclosure of the present invention without departing from the spirit of the present invention. Therefore, the protection scope of the present invention should not be limited to the disclosed embodiments, but should include various replacements and modifications that do not depart from the present invention, and are covered by the following claims.

Claims (10)

1. an imageing sensor, comprises:

One sensing matrix, have multiple sensing cell, each sensing cell has an electronic shutter and a photodetector, and wherein this electronic shutter controls the time for exposure of this photodetector;

Many shutter control lines, each shutter control line couples same row or the described electronic shutter with a line in this sensing matrix, control the time for exposure of the described photodetector of phase heterotaxy or different row whereby independently, and make the described photodetector of this shutter control line coupling same have the identical time for exposure; And

One clock generator, couples with described many shutter control lines, and wherein this clock generator makes the electronic shutter opening time of phase heterotaxy or different row different by described many shutter control lines.

2. imageing sensor according to claim 1, is characterized in that, this electronic shutter is a transistor, is arranged at corresponding between this photodetector and a supply voltage.

3. imageing sensor according to claim 1, is characterized in that, this clock generator produces the multiple shutter control signals corresponding with described many shutter control lines.

4. imageing sensor according to claim 3, is characterized in that, this imageing sensor also comprises a storage device, and this memory bank device stores multiple timing instructions, and wherein multiple shutter control signal produces according to described multiple timing instructions.

5. imageing sensor according to claim 3, it is characterized in that, this imageing sensor accepts a bias light, and when wherein this time for exposure of the described photodetector of each column or row increases, the brightness of this bias light that the described photodetector of each column or row accepts also can increase.

6. an imageing sensor, comprises:

One sensing matrix, have multiple sensing cell, each sensing cell has an electronic shutter and a photodetector, and wherein this electronic shutter controls the time for exposure of this photodetector; And

Many shutter control lines, each shutter control line couples same row or the described electronic shutter with a line in this sensing matrix, control the time for exposure of the described photodetector of phase heterotaxy or different row whereby independently, and make the described photodetector of this shutter control line coupling same have the identical time for exposure;

Described many shutter control lines are independent of one another, on described bar shutter control line, different shutter control signals is provided respectively, shortens the time for exposure of the photodetector by stronger background illumination, increase the time for exposure of the photodetector irradiated by more weak bias light.

7. imageing sensor according to claim 6, is characterized in that, this electronic shutter is a transistor, is arranged at corresponding between this photodetector and a supply voltage.

8. imageing sensor according to claim 6, is characterized in that, this imageing sensor also comprises a clock generator, couples with described many shutter control lines, and this clock generator produces the multiple shutter control signals corresponding with described many shutter control lines.

9. imageing sensor according to claim 8, is characterized in that, this imageing sensor also comprises a storage device, and this memory bank device stores multiple timing instructions, and wherein multiple shutter control signal produces according to described multiple timing instructions.

10. imageing sensor according to claim 8, it is characterized in that, this imageing sensor accepts a bias light, and when wherein this time for exposure of the described photodetector of each column or row increases, the brightness of this bias light that the described photodetector of each column or row accepts also can increase.