CN105516699B - Image sensor, imaging method thereof, imaging device and electronic device - Google Patents

Abstract

The invention discloses an image sensor, an imaging method, an imaging device and an electronic device thereof, wherein the image sensor comprises: a pixel cell array including a plurality of pixel cells, each pixel cell comprising: the anode electrodes of the N photosensitive devices are all grounded; one end electrode of the transmission tube is connected to the cathode electrodes of the N photosensitive devices; a source follower, the grid of which is connected to the other end electrode of the transmission tube; the conversion gain adjustment module comprises a plurality of capacitors connected with the grid electrode of the source electrode follower, and is used for adjusting the number of the capacitors connected with the grid electrode of the source electrode follower; the filter is arranged above the pixel unit array and comprises a filter unit array with a plurality of filter units, and each filter unit correspondingly covers one pixel unit. The image sensor prevents saturation of image highlights and increases pixel sensitivity in dim light environments.

Description

Image sensor and imaging method thereof, imaging device and electronic device

technical field

The invention relates to the field of imaging technology, in particular to an image sensor, an imaging method thereof, an imaging device and an electronic device.

Background technique

With the increasing number of pixels of mobile phone image sensors, the ability to restore image details is getting stronger and stronger, but at the same time, because the total area of image sensors has not actually increased, increasing the number of pixels is at the expense of the size of a single photosensitive pixel, resulting in Mobile phones have limited ability to shoot in low light.

In low light or fast exposure conditions, the performance of image sensor sensitivity plays a leading role. Therefore, in appropriate scenarios, the image resolution can be reduced in exchange for the photosensitive performance of the image sensor.

In this regard, pixel merging is adopted in related technologies. For example, 4 adjacent pixels of the same filter color in a 16MP image sensor are combined into 1 pixel. The advantage of this technology can improve the signal-to-noise ratio of the image sensor. The disadvantage is that In the case of sufficient ambient light, it is easy to overexpose, resulting in saturation of the highlights.

Contents of the invention

The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

For this reason, the present invention needs to provide an image sensor, which prevents the saturation of the bright part of the image and increases the sensitivity of the pixels in the dark environment.

The second object of the present invention is to provide an imaging method for an image sensor.

A third object of the present invention is to provide an imaging device.

A fourth objective of the present invention is to provide an electronic device.

In order to achieve the above object, the image sensor in the embodiment of the first aspect of the present invention includes: a pixel unit array, the pixel unit array includes a plurality of pixel units, and each pixel unit includes: N photosensitive devices, the N The anode electrodes of the photosensitive devices are all grounded; the transfer tube, one end electrode of the transfer tube is connected to the cathode electrodes of the N photosensitive devices; the source follower, the gate of the source follower is connected to the transfer tube The other end electrode of the tube; a conversion gain adjustment module, the conversion gain adjustment module includes a plurality of capacitors connected to the gate of the source follower, and the conversion gain adjustment module is used to adjust the connection with the source follower The number of capacitors connected to the gate; the filter set above the pixel unit array, the filter includes a filter unit array with a plurality of filter units, each filter unit correspondingly covers one of the pixel unit.

According to the image sensor of the embodiment of the present invention, the conversion gain of the pixel unit is changed by adjusting the number of capacitors connected to the source follower through the conversion gain adjustment module, thereby changing the sensitivity of the pixel unit to meet the exposure of different scenes, which can prevent The saturation of the bright part of the image caused by overexposure can also increase the pixel sensitivity in dark light environments, thereby improving the shooting effect in dark light.

In one embodiment of the present invention, the conversion gain adjustment module includes: a plurality of conversion gain units, each of which includes a switch and a capacitor connected in series with the switch, and one end of the switch is connected to the The other end electrode of the transmission tube, the other end of the switch is connected to one end of the capacitor, and the other end of the capacitor is grounded.

In an embodiment of the present invention, the four filter units arranged adjacently include one red filter unit, two green filter units and one blue filter unit.

In one embodiment of the present invention, it further includes: a lens array disposed above the filter unit array, and the lens array is used for converging light onto the photosensitive device below the filter unit array.

In one embodiment of the present invention, the lens array includes a plurality of microlenses, and each microlens is arranged corresponding to one of the photosensitive devices.

In one embodiment of the present invention, the photosensitive device is a photodiode.

In an embodiment of the present invention, N=4.

In order to solve the above technical problems, based on the image sensor of the embodiment of the first aspect of the present invention, the imaging method of the image sensor of the embodiment of the second aspect of the present invention includes the following steps: acquiring the current ambient brightness of the image sensor; according to the Control the conversion gain of the pixel unit of the image sensor according to the ambient brightness to adjust the sensitivity of the image sensor; read the output of the image sensor to generate an image.

According to the imaging method of the image sensor in the embodiment of the present invention, the sensitivity of the pixel unit of the image sensor is adjusted according to the difference in ambient brightness, which can prevent high-brightness image saturation and increase the pixel sensitivity in a dark environment, thereby obtaining Better signal-to-noise ratio improves image quality, which in turn improves user experience.

In an embodiment of the present invention, the controlling the conversion gain of the pixel unit of the image sensor according to the ambient brightness specifically includes: judging the level of ambient brightness where the image sensor is currently located; The preset relationship between the level and the conversion gain adjusts the conversion gain of the pixel unit of the image sensor to a corresponding value, wherein the preset relationship between the level of the ambient brightness and the conversion gain is an inverse proportional relationship.

In an embodiment of the present invention, it further includes: synchronously adjusting conversion gains of all pixel units in the image sensor.

In an embodiment of the present invention, it further includes: adjusting the conversion gains of the pixel units covered by the filter units of different colors in the image sensor respectively.

In an embodiment of the present invention, the controlling the conversion gain of the pixel unit of the image sensor according to the ambient brightness includes: controlling the capacitance value of the capacitance connected to the gate of the source follower to control the The conversion gain of the image sensor pixel unit.

In order to achieve the above object, the imaging device of the embodiment of the third aspect of the present invention includes the image sensor of the embodiment of the first aspect of the present invention; a control module connected to the image sensor, and the control module is used to acquire the current ambient brightness, and control the conversion gain of the pixel unit of the image sensor according to the ambient brightness to adjust the sensitivity of the image sensor; and an image processing module connected to the image sensor, the image processing module uses for reading the output of the image sensor to generate an image.

According to the imaging device of the embodiment of the present invention, the control module adjusts the sensitivity of the pixel unit of the image sensor according to the difference in ambient brightness, which can not only prevent high-brightness image saturation, but also increase the pixel sensitivity in a dark environment, thereby obtaining better The best signal-to-noise ratio improves the image quality, which in turn enhances the user experience.

In an embodiment of the present invention, the control module is specifically configured to: determine the level of ambient brightness where the image sensor is currently located, and convert the The conversion gain of the pixel unit of the image sensor is adjusted to a corresponding value, wherein the preset relationship between the ambient brightness level and the conversion gain is an inverse proportional relationship.

In an embodiment of the present invention, the control module is further configured to: adjust the conversion gains of all pixel units in the image sensor synchronously.

In an embodiment of the present invention, the control module is further configured to: separately adjust conversion gains of pixel units in the image sensor that are covered by filter units of different colors.

In one embodiment of the present invention, the control module controls the conversion gain of the pixel unit of the image sensor by adjusting the capacitance of the capacitor connected to the gate of the source follower.

In order to achieve the above purpose, the electronic device of the embodiment of the fourth aspect of the present invention includes the imaging device of the embodiment of the third aspect of the present invention.

According to the electronic device of the embodiment of the present invention, since it has the imaging device, it can not only prevent high-brightness image saturation when taking pictures, but also increase the pixel sensitivity in a dark environment, thereby obtaining a better signal-to-noise ratio and improving image quality, thereby enhancing the user experience.

In one embodiment of the present invention, the electronic device is a mobile phone or a tablet computer.

Description of drawings

FIG. 1 is a schematic block diagram of an image sensor according to an embodiment of the present invention;

Fig. 2 is the schematic diagram of the optical filter according to one embodiment of the present invention;

3 is a schematic circuit diagram of a pixel unit according to an embodiment of the present invention;

4 is a schematic structural diagram of an image sensor according to an embodiment of the present invention;

5 is a flowchart of an imaging method of an image sensor according to an embodiment of the present invention;

FIG. 6 is a schematic block diagram of an imaging device according to an embodiment of the present invention.

detailed description

Embodiments of the present invention are described in detail below, examples of which are shown in the drawings, wherein the same or similar reference numerals designate the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the figures are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

An image sensor, an imaging method for an image sensor, an imaging device, and an electronic device according to embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic block diagram of an image sensor according to one embodiment of the present invention. As shown in FIG. 1 , an image sensor 10 according to an embodiment of the present invention includes: a pixel unit array 11 and a filter 12 arranged above the pixel unit array 11 .

The pixel unit array 11 includes a plurality of pixel units 111 , and each pixel unit 111 includes: N photosensitive devices 14 , transmission tubes 15 , source followers 16 and conversion gain adjustment modules 17 .

The anode electrodes of the N photosensitive devices 14 are all grounded; one end electrode of the transfer tube 15 is connected to the cathode electrodes of the N photosensitive devices 14; the grid of the source follower 16 is connected to the other end electrode of the transfer tube 15; conversion gain adjustment module 17 includes a plurality of capacitors 1711 connected to the gate of the source follower 16 , and the conversion gain adjustment module 17 is used to adjust the number of capacitors 1711 connected to the gate of the source follower 16 .

In one embodiment of the present invention, the photosensitive device 14 is a photodiode.

The filter 12 includes a filter unit array 121 having a plurality of filter units 1211 , and each filter unit 1211 covers one pixel unit 111 correspondingly.

The following will describe in detail with reference to accompanying drawings 2 and 3, taking N=4 as an example.

Please refer to FIG. 2 . FIG. 2 is a schematic diagram of the filter unit array 121 , one filter unit 1211 covers one pixel unit 111 , that is, one filter unit 1211 covers four photosensitive devices 14 in one pixel unit 111 . In FIG. 2 , Gr, R, B, and Gb are used to identify the colors of the filter unit 1211 respectively, and numbers 1, 2, 3, and 4 are used to identify the positions of the four photosensitive devices 14 covered under the filter unit 1211 . Specifically, R is used to identify the red filter unit 1211 , B is used to identify the blue filter unit 1211 , and Gr and Gb are used to identify the green filter unit 1211 .

In an embodiment of the present invention, the four filter units 1211 adjacently arranged include one red filter unit 1211 , two green filter units 1211 and one blue filter unit 1211 . That is to say, four filter units 1211 arranged adjacently together form a set of filter structures 1212 .

It should be noted that the filter unit 1211 covering the four photosensitive devices 14 can be constructed as a whole, or can be assembled and connected by four independent filters. Preferably, in the embodiment of the present invention, the filter unit 1211 is integrally constructed.

Please refer to Fig. 3, Fig. 3 takes the pixel unit 111 covered by the red filter unit 1211 as an example, the cathode electrodes of the four photosensitive devices 14 are connected together and then connected to one end electrode of the transmission tube 15, and the other end of the transmission tube 15 The electrode is connected to the gate electrode of the source follower 16 . The conversion gain adjustment module 17 is respectively connected to the other end electrode of the transmission tube 15 and the gate electrode of the source follower 16 .

Taking a 16M image sensor as an example, the image sensor of the embodiment of the present invention combines four adjacent pixels of the same color into one pixel, which is equivalent to increasing the size of the pixel and improving the sensitivity of the pixel. The image sensor also adds multi-level CG to the logic circuit of a pixel unit after merging, and obtains different conversion gain values by controlling the switch of CG, so as to obtain different sensitivities, and then meet the exposure of different scenes, which can prevent The saturation of the bright part of the image caused by overexposure can also increase the pixel sensitivity in dark light environments, thereby improving the shooting effect in dark light.

In one embodiment of the present invention, the conversion gain adjustment module 17 includes: a plurality of conversion gain units 171, each conversion gain unit 171 includes a switch 1710 (S) and a capacitor 1711 (CG) connected in series with the switch 1710, the switch 1710 One end of the switch 1710 is connected to the other end electrode of the transmission tube 15, the other end of the switch 1710 is connected to one end of the capacitor 1711, and the other end of the capacitor 1711 is grounded.

Specifically, the capacitance value of the capacitor connected to the gate of the source follower 16 is adjusted by adjusting the number of switches 1710 closed, so that the conversion gain of the pixel unit 111 can be adjusted.

More specifically, the current ambient brightness of the image sensor can be divided into several levels, and different levels of brightness correspond to different pixel sensitivities. For example, when the ambient brightness is higher, the number of switches 1710 closed is also more, the capacitance value of the capacitor connected to the gate of the source follower 16 is larger, and the conversion gain is smaller, thereby reducing the sensitivity of the pixel unit 111 , to prevent the saturation of the bright part of the image caused by overexposure. For another example, when the ambient brightness is lower, the number of switches 1710 closed is also less, and the capacitance value of the capacitor connected to the gate of the source follower 16 is smaller, and the conversion gain is larger, thereby improving the pixel unit 111. Sensitivity to improve the shooting effect in low light.

In one embodiment of the present invention, please refer to FIG. 4 , the image sensor 10 further includes: a lens array 19 arranged above the filter unit array 121 , and the lens array 19 is used to converge light to the light-sensitive sensor below the filter unit array 121 device 14 to increase the intensity of light received by the photosensitive device 14, thereby improving image quality. Wherein, the lens array 19 includes a plurality of microlenses 191 , and each microlens 191 is arranged corresponding to one photosensitive device 14 .

In the image sensor of the embodiment of the present invention, the conversion gain of the pixel unit is changed by adjusting the number of capacitors connected to the source follower through the conversion gain adjustment module, so as to change the sensitivity of the pixel unit to meet the exposure of different scenes and prevent excessive exposure. The saturation of the bright part of the image caused by exposure can also increase the pixel sensitivity in the dark light environment, thereby improving the shooting effect in the dark light.

Based on the image sensor of the above embodiments, the present invention proposes an imaging method of the image sensor.

FIG. 5 is a flowchart of an imaging method of an image sensor according to an embodiment of the present invention. As shown in FIG. 5, the imaging method of the image sensor of the embodiment of the present invention includes the following steps:

S1. Obtain the brightness of the environment where the image sensor is currently located.

That is, the brightness of the current shooting scene of the image sensor is acquired.

S2. Control the conversion gain of the pixel unit of the image sensor according to the ambient brightness, so as to adjust the sensitivity of the image sensor.

Specifically, when the ambient brightness is high, the image obtained by the image sensor is prone to the problems of overexposure and saturation of the bright part. Therefore, it is necessary to lower the sensitivity of the image sensor to prevent the occurrence of this problem; When the brightness is low, the imaging capability of the image sensor is limited, so the sensitivity needs to be increased to improve the image quality.

In one embodiment of the present invention, controlling the conversion gain of the pixel unit of the image sensor according to the ambient brightness specifically includes: judging the level of the ambient brightness where the image sensor is currently located; The conversion gain of the sensor pixel unit is adjusted to a corresponding value, wherein the preset relationship between the ambient brightness level and the conversion gain is an inverse proportional relationship.

Specifically, the current ambient brightness of the image sensor is divided into several levels, and each level corresponds to a different conversion gain, that is, different ambient brightness levels correspond to different pixel sensitivities. Wherein, the preset relationship between the level of ambient brightness and the conversion gain is: the higher the level of ambient brightness, the smaller the corresponding conversion gain, that is, the lower the sensitivity of the corresponding image sensor.

In one embodiment of the present invention, controlling the conversion gain of the pixel unit of the image sensor according to the ambient brightness includes: controlling the conversion gain of the pixel unit of the image sensor by adjusting the capacitance of a capacitor connected to the gate of the source follower.

For example, when the ambient brightness is higher, the number of switches closed is more, the capacitance value of the capacitor connected to the gate of the source follower is larger, and the conversion gain is smaller, thereby reducing the sensitivity of the pixel unit to prevent Saturated highlights of images caused by overexposure. For another example, when the ambient brightness is lower, the number of switches closed is also smaller, the capacitance value of the capacitor connected to the gate of the source follower is smaller, and the conversion gain is larger, thereby improving the sensitivity of the pixel unit, and Improve the shooting effect in low light.

In an embodiment of the present invention, it further includes: synchronously adjusting the conversion gains of all pixel units in the image sensor.

Specifically, the conversion gains of all pixel units in the image sensor are adjusted synchronously, that is, under the same ambient brightness level, the conversion gains of the pixel units covered by different color filter units are the same, that is, closed The number of switches is the same.

In another embodiment of the present invention, it further includes: separately adjusting the conversion gains of the pixel units covered by the filter units of different colors in the image sensor.

Specifically, since the pixel units are covered by filter units of different colors, the conversion gain of the pixel units can be adjusted according to the differences in colors, thereby better improving the image quality.

The pixel unit covered by the green filter unit is called the green pixel unit. Since the green pixel unit is more likely to be saturated, when adjusting the conversion gain of the green pixel unit, its conversion gain can be adjusted to be higher than that of other colors. Pixel units are lower. For example, under the same ambient brightness, two switches in the red pixel unit are closed, and three switches in the green pixel unit are closed, that is, the sensitivity of the green pixel unit is adjusted to be lower than that of the red pixel unit.

S3, reading the output of the image sensor to generate an image.

Specifically, dynamically adjusting the sensitivity of the image sensor according to the ambient brightness can prevent high-brightness image saturation, and can also increase pixel sensitivity in dark-light environments, thereby obtaining a better signal-to-noise ratio and improving image quality.

The imaging method of the image sensor in the embodiment of the present invention adjusts the sensitivity of the pixel unit of the image sensor according to the difference in ambient brightness, which can not only prevent high-brightness image saturation, but also increase the pixel sensitivity in a dark environment, so as to obtain better The best signal-to-noise ratio improves the image quality, which in turn enhances the user experience.

In order to realize the above embodiments, the present invention also proposes an imaging device.

FIG. 6 is a schematic block diagram of an imaging device according to an embodiment of the present invention. As shown in FIG. 6 , the imaging device 100 of the embodiment of the present invention includes: an image sensor 10 , a control module 20 connected to the image sensor 10 , and an image processing module 30 connected to the image sensor 10 .

The control module 20 is used to obtain the current ambient brightness of the image sensor 10, and control the conversion gain of the pixel unit of the image sensor 10 according to the ambient brightness, so as to adjust the sensitivity of the image sensor.

The image processing module 30 is used to read the output of the image sensor 10 to generate an image.

In one embodiment of the present invention, the control module 20 is specifically configured to: judge the level of the ambient brightness where the image sensor 10 is currently located, and convert the pixel unit of the image sensor 10 according to the preset relationship between the level of the ambient brightness and the conversion gain. The gain is adjusted to a corresponding value, wherein the preset relationship between the ambient brightness level and the conversion gain is an inverse proportional relationship.

Specifically, when the ambient brightness is high, the image obtained by the image sensor 10 is likely to be overexposed and the bright part is saturated. Therefore, it is necessary to lower the sensitivity of the image sensor 10 to prevent the occurrence of this problem; and When the ambient brightness is low, the imaging capability of the image sensor 10 is limited, so the sensitivity needs to be increased to improve the image quality.

More specifically, the current ambient brightness of the image sensor 10 is divided into several levels, and each level corresponds to a different conversion gain, that is, different ambient brightness levels correspond to different pixel sensitivities. Wherein, the preset relationship between the level of ambient brightness and the conversion gain is: the higher the level of ambient brightness, the smaller the corresponding conversion gain, that is, the lower the sensitivity of the corresponding image sensor 10 .

In one embodiment of the present invention, the control module 20 controls the conversion gain of the pixel unit of the image sensor 10 by adjusting the capacitance of the capacitor connected to the gate of the source follower.

For example, when the ambient brightness is higher, the number of closed switches 1710 controlled by the control module 20 is also larger, and the capacitance value of the capacitor connected to the gate of the source follower is larger, and the conversion gain is smaller, thereby reducing the pixel unit. Sensitivity of 111 to prevent saturation of bright parts of the image caused by overexposure. For another example, when the ambient brightness is lower, the number of closed switches 1710 controlled by the control module 20 is also smaller, and the capacitance value of the capacitor connected to the gate of the source follower 16 is smaller, and the conversion gain is larger, thereby improving The sensitivity of the pixel unit 111 is used to improve the shooting effect in low light.

In an embodiment of the present invention, the control module 20 is also used for: synchronously adjusting the conversion gains of all pixel units in the image sensor 10 .

Specifically, the control module 20 adjusts the conversion gains of all pixel units in the image sensor 10 synchronously, that is, at the same ambient brightness level, the conversion gains of the pixel units covered by filter units of different colors are the same. , that is, the number of closed switches is the same.

In another embodiment of the present invention, the control module 20 is further configured to: separately adjust the conversion gains of the pixel units in the image sensor 10 that are covered by filter units of different colors.

Specifically, since the pixel units are covered by filter units of different colors, the control module 20 can adjust the conversion gain of the pixel units according to the differences in colors, so as to better improve the image quality.

The pixel unit covered by the green filter unit is called a green pixel unit. Since the green pixel unit is more likely to be saturated, the control module 20 can adjust its conversion gain to the ratio when adjusting the conversion gain of the green pixel unit. Pixel units of other colors are lower. For example, under the same ambient brightness, two switches in the red pixel unit are closed, and three switches in the green pixel unit are closed, that is, the sensitivity of the green pixel unit is adjusted to be lower than that of the red pixel unit.

In the imaging device of the embodiment of the present invention, the control module adjusts the sensitivity of the pixel unit of the image sensor according to the brightness of the environment, which can not only prevent saturation of high-brightness images, but also increase the sensitivity of pixels in dark light environments, thereby obtaining better performance. The signal-to-noise ratio improves image quality, which in turn improves user experience.

Based on the imaging device 100 in the above embodiment, the present invention also proposes an electronic device 200, which includes the imaging device 100 in the embodiment of the present invention.

In one embodiment of the present invention, the electronic device 200 is a mobile phone or a tablet computer.

The electronic device of the embodiment of the present invention, with the imaging device, can not only prevent high-brightness image saturation when taking pictures, but also increase pixel sensitivity in dark light environments, thereby obtaining a better signal-to-noise ratio and improving image quality, thereby enhancing the user experience.

In the description of the present invention, it should be understood that the terms "first" and "second" are used for description purposes only, and cannot be interpreted as indicating or implying relative importance or implicitly indicating the quantity of indicated technical features. Thus, the features defined as "first" and "second" may explicitly or implicitly include at least one of these features. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

In the description of this specification, descriptions referring to the terms "one embodiment", "some embodiments", "example", "specific examples", or "some examples" mean that specific features described in connection with the embodiment or example , structure, material or characteristic is included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the described specific features, structures, materials or characteristics may be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples and features of different embodiments or examples described in this specification without conflicting with each other.

Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and those skilled in the art can make the above-mentioned The embodiments are subject to changes, modifications, substitutions and variations.

Claims (18)

1. An image sensor, characterized in that, comprising: A pixel unit array, the pixel unit array includes a plurality of pixel units, and each pixel unit includes: N photosensitive devices, the anode electrodes of the N photosensitive devices are all grounded; a transmission tube, one end electrode of the transmission tube is connected to the cathode electrodes of the N photosensitive devices; a source follower, the gate of the source follower is connected to the other end electrode of the transmission tube; A conversion gain adjustment module, the conversion gain adjustment module includes a plurality of capacitors connected to the gate of the source follower, and the conversion gain adjustment module is used to adjust the capacitance connected to the gate of the source follower number of which, The cathode electrodes of the N photosensitive devices are connected together and then connected to one end electrode of the transmission tube, and the conversion gain adjustment module is respectively connected to the other end electrode of the transmission tube and the gate electrode of the source follower connected; The conversion gain adjustment module includes: a plurality of conversion gain units, each of which includes a switch and a capacitor connected in series with the switch, one end of the switch is connected to the other end electrode of the transmission tube, the The other end of the switch is connected to one end of the capacitor, and the other end of the capacitor is grounded, wherein the ambient brightness is divided into multiple levels, and different levels of ambient brightness correspond to different pixel sensitivities; the higher the level of ambient brightness, The more the number of switches closed, the larger the capacitance of the capacitor connected to the gate of the source follower, the smaller the conversion gain, so as to reduce the sensitivity of the pixel unit; the lower the level of ambient brightness, the lower the number of closed switches. The smaller the number, the smaller the capacitance value of the capacitor connected to the gate of the source follower, and the larger the conversion gain, so as to improve the sensitivity of the pixel unit; and A filter arranged above the pixel unit array, the filter comprises a filter unit array with a plurality of filter units, each filter unit correspondingly covers one of the pixel units. 2 . The image sensor according to claim 1 , wherein the four adjacently arranged filter units comprise one red filter unit, two green filter units and one blue filter unit. 3. The image sensor according to claim 1, further comprising: a lens array arranged above the filter unit array, the lens array is used for converging light to the underside of the filter unit array on the photosensitive device. 4 . The image sensor according to claim 3 , wherein the lens array comprises a plurality of microlenses, and each microlens is corresponding to one of the photosensitive devices. 5. The image sensor according to claim 1, wherein the photosensitive device is a photodiode. 6. The image sensor according to claim 1, wherein N=4. 7. An imaging method of the image sensor according to any one of claims 1-6, comprising the following steps: Obtain the brightness of the environment where the image sensor is currently located; controlling the conversion gain of the pixel unit of the image sensor according to the ambient brightness to adjust the sensitivity of the image sensor; and The output of the image sensor is read to generate an image. 8. The imaging method of the image sensor according to claim 7, wherein the controlling the conversion gain of the pixel unit of the image sensor according to the ambient brightness comprises: Judging the brightness level of the environment where the image sensor is currently located; The conversion gain of the pixel unit of the image sensor is adjusted to a corresponding value according to a preset relationship between the ambient brightness level and the conversion gain, wherein the preset relationship between the ambient brightness level and the conversion gain is an inverse proportional relationship. 9. The imaging method of the image sensor according to claim 8, further comprising: The conversion gains of all pixel units in the image sensor are adjusted synchronously. 10. The imaging method of the image sensor according to claim 8, further comprising: The conversion gains of the pixel units covered by the filter units of different colors in the image sensor are adjusted respectively. 11. The imaging method of an image sensor according to any one of claims 7-10, wherein the controlling the conversion gain of the pixel unit of the image sensor according to the ambient brightness comprises: The conversion gain of the pixel unit of the image sensor is controlled by adjusting the capacitance value of the capacitor connected to the gate of the source follower. 12. An imaging device, characterized in that, comprising: The image sensor according to any one of claims 1-6; A control module connected to the image sensor, the control module is used to obtain the current ambient brightness of the image sensor, and control the conversion gain of the pixel unit of the image sensor according to the ambient brightness to adjust the image the sensitivity of the sensor; and An image processing module connected to the image sensor, the image processing module is used to read the output of the image sensor to generate an image. 13. The imaging device according to claim 12, wherein the control module is specifically used for: judging the level of ambient brightness where the image sensor is currently located, and adjusting the conversion gain of the pixel unit of the image sensor to a corresponding value according to a preset relationship between the level of the ambient brightness and the conversion gain, wherein the ambient brightness The default relationship between the level of the conversion gain and the conversion gain is an inverse proportional relationship. 14. The imaging device according to claim 13, wherein the control module is further configured to: The conversion gains of all pixel units in the image sensor are adjusted synchronously. 15. The imaging device according to claim 13, wherein the control module is further configured to: The conversion gains of the pixel units covered by the filter units of different colors in the image sensor are adjusted respectively. 16. The imaging device according to any one of claims 12-15, wherein the control module controls the image sensor by adjusting the capacitance value of the capacitor connected to the gate of the source follower The conversion gain of the pixel unit. 17. An electronic device, comprising the imaging device according to any one of claims 12-16. 18. The electronic device according to claim 17, wherein the electronic device is a mobile phone or a tablet computer.