CN106470321B - Image sensor and reading method of image sensor - Google Patents
Image sensor and reading method of image sensor Download PDFInfo
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- CN106470321B CN106470321B CN201510515490.3A CN201510515490A CN106470321B CN 106470321 B CN106470321 B CN 106470321B CN 201510515490 A CN201510515490 A CN 201510515490A CN 106470321 B CN106470321 B CN 106470321B
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Abstract
The invention discloses an image sensor and a reading method thereof, wherein the image sensor comprises a pixel array formed by a plurality of pixel units, each pixel unit comprises a photodiode and a floating diffusion node, and the method comprises the following steps: s1: acquiring preset pseudo reading times; s2: in each reading period, performing a normal reading operation on the pixel array to cause the sample-and-hold circuit to read the charge derived from the photodiode to the floating diffusion node; s3: after the normal read operation is completed, a dummy read operation is performed to lead out residual charges in the photodiode to the floating diffusion node until the number of times of performing the dummy read operation reaches a preset dummy read number. Therefore, by performing additional pseudo-reading for a plurality of times in the idle time of each reading period, the image smear phenomenon can be eliminated, the image quality can be improved, the basic structure of the relevant image sensor does not need to be modified, and the frame rate of image output is not influenced.
Description
Technical Field
The present invention relates to the field of image sensor technologies, and in particular, to a method for reading an image sensor and an image sensor.
Background
A typical structure of a CMOS (Complementary Metal-Oxide Semiconductor) image sensor in the related art may be as shown in fig. 5. The image sensor may include a photodiode 21, a floating diffusion 22, a transfer gate 30, a source follower gate 40, a reset gate 50, and a row select gate 60, wherein the photodiode 21 is configured to convert light energy into electrical energy; the transfer gate 30 is used to control the charge of the photodiode 21 to be conducted to the floating diffusion 22; the gate of the source follower gate 40 is connected to the floating diffusion node 22; the reset gate 50 is used to reset the potential of the floating diffusion 22 to a set potential, and the row select gate 60 is used to output a signal to an external processing circuit.
In the related art, a typical reset timing of the CMOS image sensor is shown in fig. 6, and when a read operation is performed, the row selection signal PEN is changed to a high level to turn on the row selection gate 60, and the reset signal RST is also changed to a high level to turn on the reset gate 50, so that the potential of the floating diffusion node 22 is reset to the set value Vrst, and at this time, the SHR signal in the sample-and-hold circuit generates a pulse, and the sample-and-hold circuit collects and stores the set value Vrst. The TX signal is then changed to a high level to open the transfer gate 30 and conduct the charge in the photodiode 21 to the floating diffusion 22, and then changed to a low level while the SHS signal in the sample and hold circuit generates a pulse, at which time the sample and hold circuit collects and holds the pixel signal Vphoto in the photodiode 21. The row select signal PEN signal is changed to low after the read process is completed to cause the row select gate 60 to close.
As described above, the related art performs the read operation only once in each read cycle.
Disclosure of Invention
The present application is based on the discovery and recognition by the inventors of the following problems and facts:
with the image sensor of the related art described above, as shown in fig. 7, there is a potential barrier 70 between the photodiode 21 and the floating diffusion 22, and since the existence of this potential barrier causes the transfer gate 30 to be opened, the reading operation of the related art is not enough to completely conduct the charge in the photodiode 21 to the floating diffusion 22, and a part of the charge remains in the photodiode 21, and the part of the charge is conducted to the sample-and-hold circuit in the next reading cycle.
Specifically, as shown in fig. 8a, in a bright environment where the photodiode 21 starts integrating, the transfer gate 30 is in an off state, as the charge in the photodiode 21 is accumulated, the charge 41 is accumulated in the photodiode 21, when the transfer gate 30 is opened to transfer a part of the charge 43 of the charge 41 to the floating diffusion 22, as shown in fig. 8b, the potential of the floating diffusion 22 is reduced, and the height of the potential barrier 70 is increased, which causes a part of the charge 42 to remain in the photodiode 21 and cannot be derived, as shown in fig. 8c, as the charge 43 in the floating diffusion 22 is read out to the sample hold circuit, the potential of the floating diffusion 22 becomes higher, and the height of the potential barrier 70 is restored to the level just before integrating.
Thus, since the charge 42 in the photodiode is left in the photodiode 21, if the scene is cut to a dark environment at this time, the charge 42 in the photodiode is read out to the sample hold circuit in the next reading period, which affects the next frame of image, and thus an image tailing phenomenon is formed, which affects the image quality.
Therefore, an object of the present invention is to solve the technical problems in the related art at least to some extent, and to provide a reading method of an image sensor, which can eliminate an image smear phenomenon and improve image quality by performing additional pseudo-reading for a plurality of times.
Another object of the present invention is to propose an image sensor.
To achieve the above object, an embodiment of an aspect of the present invention provides a reading method of an image sensor, the image sensor including a pixel array constituted by a plurality of pixel units, each of the pixel units including a photodiode and a floating diffusion node, the method including: s1: acquiring preset pseudo reading times; s2: performing a normal read operation on the pixel array to cause a sample and hold circuit to read the charge drawn from the photodiode to the floating diffusion node in each read cycle; s3: after the normal reading operation is completed, performing a dummy reading operation to lead out residual charges in the photodiode to the floating diffusion node until the number of times of performing the dummy reading operation reaches the preset dummy reading number.
According to the reading method of the image sensor provided by the embodiment of the invention, the image smear phenomenon can be eliminated and the image quality can be improved by carrying out additional pseudo reading for multiple times in the idle time of each reading period, the realization algorithm of the method is simple, the basic structure of the related image sensor is not required to be modified, the method can be realized by only adding a corresponding logic control circuit, and the pseudo reading operation is carried out in the idle period, so that the frame rate of image output can not be influenced by reasonably arranging the pseudo reading time.
In order to achieve the above object, an embodiment of another aspect of the present invention provides an image sensor, including: a pixel array constituted by a plurality of pixel units, wherein each of the pixel units includes a photodiode and a floating diffusion node; a controller configured to obtain a preset number of dummy read operations, perform a normal read operation on the pixel array in each read cycle to enable the sample-and-hold circuit to read charges led from the photodiode to the floating diffusion node, and perform the dummy read operation to lead residual charges in the photodiode to the floating diffusion node after the normal read operation is completed until the number of dummy read operations reaches the preset number of dummy read operations.
According to the image sensor provided by the embodiment of the invention, the controller performs additional pseudo reading for multiple times in the idle time of each reading period, the image smear phenomenon can be eliminated, the image quality is improved, the implementation mode of the image sensor is simple, the basic structure of the related image sensor is not required to be modified, the image sensor can be implemented by only adding a corresponding logic control circuit, and the pseudo reading operation is performed in the idle period, so that the frame rate of image output can not be influenced by reasonably arranging the pseudo reading time.
Drawings
Fig. 1 is a flowchart of a reading method of an image sensor according to an embodiment of the present invention;
fig. 2 is a timing diagram of a reading method of an image sensor according to an embodiment of the present invention;
FIG. 3 is a flow chart of a method of reading an image sensor according to one embodiment of the invention;
FIG. 4 is a block schematic diagram of an image sensor according to an embodiment of the invention;
fig. 5 is a schematic view of a principle of an image sensor in the related art;
fig. 6 is a timing diagram of a reading method of an image sensor in the related art;
fig. 7 is a schematic diagram of a potential barrier between a photodiode and a floating diffusion node 22 in the related art; and
fig. 8a to 8c are schematic diagrams showing changes in potential barriers in the related art.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
An image sensor and a reading method of the image sensor proposed by an embodiment of the present invention are described below with reference to the drawings, in which the image sensor is used to convert an optical image into a digital signal.
Fig. 1 is a flowchart of a reading method of an image sensor according to an embodiment of the present invention. The image sensor includes a pixel array composed of a plurality of pixel units, each pixel unit including a photodiode and a floating diffusion node, and the pixel unit may further include a reset gate, a transfer gate, a source follower gate, and a row select gate. It should be understood that the specific structure and operation principle of the image sensor are well known in the art, and are not described herein for the purpose of brevity. Among them, according to an embodiment of the present invention, the structure of the image sensor may be preferably the example of fig. 5.
As shown in fig. 1, the reading method of the image sensor includes the steps of:
s1: and acquiring preset pseudo reading times.
S2: in each read cycle, a normal read operation is performed on the pixel array to cause the sample and hold circuit to read the charge that is directed from the photodiode to the floating diffusion.
S3: after the normal read operation is completed, a dummy read operation is performed to lead out residual charges in the photodiode to the floating diffusion node until the number of times of performing the dummy read operation reaches a preset dummy read number.
Specifically, according to an embodiment of the present invention, performing a dummy read operation to induce residual charges in the photodiode to a floating diffusion node specifically includes: controlling the reset gate to be conducted so as to reset the potential of the floating diffusion node to a preset voltage; controlling the reset gate to be closed and controlling the transfer gate to be opened to lead out residual charges in the photodiode to the floating diffusion node; the transmission door is controlled to be closed.
Also, in step S3, after the normal read operation is completed, the row select gate is also turned off so that the sample and hold circuit cannot read the residual charge that is derived from the photodiode to the floating diffusion node at the time of the dummy read operation. That is, the row select gate is controlled to turn off when the positive read operation is completed, and the sample-and-hold circuit cannot read the residual charge derived from the photodiode to the floating diffusion node while the row select gate is controlled to turn off.
That is, as shown in fig. 2, in the current read cycle, a normal read operation may be performed first, such as the control timing of part a in fig. 2, that is, the row select gate is controlled to be opened, during the opening of the row select gate, the reset gate is controlled to be opened to reset the potential of the floating diffusion node to a preset voltage, the transfer gate is controlled to be opened to conduct the charge in the photodiode to the floating diffusion node, and then the sample-and-hold circuit may read the charge conducted from the photodiode to the floating diffusion node. After completing a normal reading operation, a dummy reading operation can be performed according to a preset dummy reading number, for example, the control timing of part B in fig. 2 is to control the row selection gate to be closed, and during the closing of the row selection gate, the reset gate and the transfer gate are repeatedly controlled according to the normal reading operation timing to repeatedly lead out the charges in the photodiode to the floating diffusion node as much as possible.
Specifically, for each pixel cell in the pixel array, a normal read operation is performed on the photodiode of each pixel cell first in each read period, and the sample-and-hold circuit reads the electric charge derived from the photodiode to the floating diffusion node. And then, before the normal reading is finished and the next reading is started, performing multiple times of pseudo reading operation on each photodiode, namely controlling the row selection gate to be closed, repeatedly leading out the residual charge in each photodiode to a corresponding floating diffusion node through multiple times of pseudo reading operation, but enabling the row selection gate to be closed to enable the sampling and holding circuit not to read the residual charge led out from the photodiode to the floating diffusion node, and accordingly clearing the residual charge in the photodiode which cannot be led out to the floating diffusion node due to a potential barrier, and enabling the pixel array to be reset more thoroughly.
Therefore, the image sensor reading method provided by the embodiment of the invention can eliminate the image smear phenomenon and improve the image quality by performing additional pseudo reading for multiple times in the idle time of each reading period, has simple realization algorithm, can be realized by only adding a corresponding logic control circuit without modifying the basic structure of the related image sensor, and can not influence the frame rate of image output by reasonably arranging the pseudo reading time due to the fact that the pseudo reading operation is performed in the idle period.
It should be noted that the dummy read time points may be set according to a preset number of dummy reads, and the dummy read operation may be performed once at each set dummy read time point. Specifically, as shown in fig. 2, during the period from the completion of the normal read operation to the start of the next read cycle, a plurality of dummy read time points, for example, Tp1, Tp2, Tp3, Tp4, and Tp5 are set, the dummy read operation is performed on the photodiode once at each dummy read time point, and the charge in the photodiode is repeatedly led out to the floating diffusion node as much as possible in accordance with the control timing of the reset gate and the transfer gate in fig. 2.
The following describes a reading method of an image sensor according to an embodiment of the present invention in detail with reference to fig. 2 and 3.
S101: the row select signal PEN is controlled to go high, at which time the row select gate is in a conducting state.
S102: when the row selection signal PEN is changed to a high level and the control reset signal RST is also changed to a high level, the reset gate is turned on, and the potential of the floating diffusion node is reset to a predetermined voltage.
S103: the reset signal RST is controlled to be low, and the reset gate is turned off.
S104: the SHR signal in the sample-and-hold circuit generates a pulse that latches a predetermined voltage.
S105: the control sampling signal TX goes high, at which time the transfer gate opens, and the charge in the photodiode is conducted out to the floating diffusion node.
S106: the sampling signal TX is then controlled to go low, at which time the transmission gate is turned off.
S107: the SHS signal in the sample and hold circuit generates a pulse that latches the charge information.
S108: the normal read operation is completed and the row select signal PEN is controlled to go low, at which time the row select gate is in an off state.
S109: and repeating the step S102 and the step S103, controlling the reset gate to be turned on, and then controlling the reset gate to be turned off.
S110: and repeating the step S105 and the step S106, controlling the transmission gate to be turned on, and then controlling the transmission gate to be turned off.
S111: and adding 1 to the repetition times, and judging whether the repetition times reach the set pseudo-reading times. If yes, go to step S112; if not, return to step S109.
S112: the recorded number of repetitions is set as the number of pseudo-reads.
In addition, according to an embodiment of the present invention, the preset number of times of the pseudo read may be determined by a process and a pixel structure of the image sensor. That is, image sensors employing the same process and pixel structure have the same number of pseudo-reads.
Specifically, the number of times of pseudo-reading of the image sensor of any specific process and pixel structure can be tested by the following method: before the normal reading operation is completed and the next reading period begins, performing 1 additional pseudo reading on the pixel array, namely leading out residual charges in the photodiode onto the floating diffusion node but turning off the row selection gate, not outputting the residual charges led out to the floating diffusion node into the sample and hold circuit, cleaning charges which cannot be led out to the floating diffusion node due to potential barriers in the photodiode, enabling the pixel array to be reset more thoroughly, reading out the remaining residual charges into the sample and hold circuit in the next reading period, testing corresponding charge residual values, increasing the number of pseudo reading times until the tested charge residual values are lower than a set threshold value, and setting the number of pseudo reading times at the moment as a preset number of pseudo reading times.
For example, for an image sensor of a specific process and pixel structure, when the pseudo read number is set to 1, if the charge residue is 1% (> 0.05%), then 1 is added to the pseudo read number, and the charge residue continues to be tested; when the number of pseudo-reads is set to 2, if the charge retention is 0.4% (> 0.05%), then 1 is added to the number of pseudo-reads again, and the charge retention continues to be tested; when the number of pseudo read times is set to 3 times, if the charge residue value is 0.2% (> 0.05%), then 1 is added to the number of pseudo read times, and the charge residue value continues to be tested; when the number of pseudo read times is set to 4 times, if the charge retention is 0.1% (> 0.05%), then 1 is added to the number of pseudo read times and the charge retention continues to be tested; when the number of pseudo-reads is set to 5, if the charge retention value is 0.04%, the charge retention value is lower than the preset threshold value of 0.05% at this time, and thus the number of pseudo-reads of the image sensor is preset to 5.
Thus, for the image sensor adopting the process and the pixel structure, after 5 times of pseudo-reading operation in each reading period, the residual charge in the photodiode is less, the possible influence on the next frame image is eliminated, and the problem of image quality reduction is solved.
Therefore, according to the reading method of the image sensor provided by the embodiment of the invention, the image smear phenomenon can be eliminated and the image quality can be improved by performing additional pseudo reading for multiple times in the idle time of each reading period, the realization algorithm of the method is simple, the basic structure of the related image sensor is not required to be modified, the method can be realized by only adding a corresponding logic control circuit, and the pseudo reading operation is performed in the idle period, so that the frame rate of image output can not be influenced by reasonably arranging the pseudo reading time.
Based on the reading method of the image sensor, the embodiment of the invention also provides the image sensor.
FIG. 4 is a block schematic diagram of an image sensor according to an embodiment of the invention. As shown in fig. 4, the image sensor includes: a pixel array 10 and a controller 20.
Wherein the pixel array 10 is composed of a plurality of pixel units, wherein each pixel unit 100 includes a photodiode 11 and a floating diffusion node 12; the controller 20 is configured to obtain a preset number of dummy read operations, perform a normal read operation on the pixel array 10 in each read cycle to cause the sample and hold circuit to read the charges led from the photodiode 11 to the floating diffusion 12, and perform the dummy read operation to lead the residual charges in the photodiode 11 to the floating diffusion 12 after the normal read operation is completed until the number of dummy read operations reaches the preset number of dummy read operations.
Specifically, according to one embodiment of the present invention, when performing a dummy read operation to conduct out residual charge in the photodiode 11 to the floating diffusion 12, the controller 20 is specifically configured to: controlling the reset gate to be turned on to reset the potential of the floating diffusion node 12 to a preset voltage; controlling the reset gate to be closed and controlling the transfer gate to be opened to lead out the residual charge in the photodiode 11 to the floating diffusion 12; the transmission door is controlled to be closed.
Also, after the normal read operation is completed, the controller 20 also controls the row select gate to be turned off so that the sample-and-hold circuit cannot read the residual charge derived from the photodiode 11 to the floating diffusion 12 at the time of the dummy read operation. That is, the row select gate is controlled to turn off when the positive read operation is completed, and the sample-and-hold circuit cannot read the residual charge derived from the photodiode to the floating diffusion node while the row select gate is controlled to turn off.
That is, as shown in fig. 2 and 5, in the current reading period, a normal reading operation may be performed, for example, the control timing of the portion a in fig. 2 is that the controller 20 controls the row selection gate to be opened, during the opening of the row selection gate, the controller 20 controls the reset gate to be opened to reset the potential of the floating diffusion 12 to a preset voltage, controls the transfer gate to be opened to lead out the charge in the photodiode 11 to the floating diffusion 12, and then the sample-and-hold circuit may read the charge led out from the photodiode to the floating diffusion. After completing one normal reading operation, the dummy reading operation may be performed according to a preset dummy reading number, such as the control timing of part B in fig. 2, that is, the controller 20 controls the row selection gate to be closed, and during the closing of the row selection gate, the controller 20 repeatedly controls the reset gate and the transfer gate according to the normal reading operation timing to repeatedly lead out the charge in the photodiode 11 to the floating diffusion 12 as much as possible, at which time, the charge in the floating diffusion 12 cannot be output to the sample-and-hold circuit because the row selection gate is closed, so that the charge will not be read out to the sample-and-hold circuit by resetting the potential of the floating diffusion to a preset voltage in the next reading period, thereby eliminating the tailing phenomenon.
Specifically, for each pixel cell in the pixel array, in each reading period, a normal reading operation is performed on the photodiode 11 of each pixel cell first, and the sample-and-hold circuit reads the electric charge derived from the photodiode 11 to the floating diffusion 12. After that, before the normal reading is completed and the next reading is started, the controller 20 performs a plurality of dummy reading operations on each photodiode, that is, the controller 20 controls the row selection gate to close, so that the residual charge in each photodiode is repeatedly led out to the corresponding floating diffusion node 12 through the plurality of dummy reading operations, but the row selection gate closes, so that the sample-and-hold circuit cannot read the residual charge led out from the photodiode to the floating diffusion node, and therefore the residual charge in the photodiode, which cannot be led out to the floating diffusion node due to the potential barrier, is cleared, and the pixel array is reset more thoroughly.
Therefore, the image sensor provided by the embodiment of the invention can eliminate the image smear phenomenon and improve the image quality by carrying out additional pseudo reading for multiple times in the idle time of each reading period, and the method has simple realization algorithm, does not need to modify the basic structure of the related image sensor, can be realized by only adding a corresponding logic control circuit, and can not influence the frame rate of image output by reasonably arranging the pseudo reading time because of carrying out the pseudo reading operation in the idle time.
It should be noted that the controller 20 may set the dummy read time points according to a preset number of dummy reads, and perform the dummy read operation once at each set dummy read time point. Specifically, as shown in fig. 2, during the period from the completion of the normal read operation to the start of the next read cycle, the controller 20 may set a plurality of dummy read time points, for example, Tp1, Tp2, Tp3, Tp4, Tp5, perform a dummy read operation on the photodiode 11 at each dummy read time point, and repeatedly lead as much charge in the photodiode 11 as possible to the floating diffusion 12 in accordance with the control timings of the reset gate and the transfer gate in fig. 2.
As described above, as shown in fig. 2, the image sensor of the embodiment of the present invention may perform the following operations at each reading cycle:
the controller 20 outputs a high-level row selection signal PEN to the row selection gate to turn on the row selection gate;
during the on period of the row selection gate, the controller 20 firstly outputs a high-level reset signal RST to the reset gate to enable the reset gate to be turned on, the electric potential of the floating diffusion node 12 is reset to a preset voltage, after a first preset time, the controller 20 outputs a low-level reset signal RST to the reset gate to enable the reset gate to be turned off, and then an SHR signal in the sample-and-hold circuit generates a pulse to latch the preset voltage;
then, the controller 20 outputs a high-level sampling signal TX to the transmission gate to open the transmission gate, and guides the charge in the photodiode 11 to the floating diffusion node 12, and after a preset time, the controller 20 outputs a low-level sampling signal TX to the transmission gate to close the transmission gate, and then the SHS signal in the sample-and-hold circuit generates a pulse to latch the charge information;
the controller 20 outputs a low-level row selection signal PEN to the row selection gate to turn off the row selection gate, so that the normal read operation is completed through the above control;
after the normal reading operation is completed, the controller 20 controls the reset gate to be turned on and off according to the control timing sequence of the normal reading operation, and then controls the transmission gate to be turned on and off according to the control timing sequence of the normal reading operation, so that one pseudo reading operation is completed, the controller 20 judges whether the number of times of performing the pseudo reading operation reaches a preset pseudo reading number, if so, the pseudo reading operation is finished, and if not, the pseudo reading operation is continued.
In addition, according to an embodiment of the present invention, the preset number of times of the pseudo read may be determined by a process and a pixel structure of the image sensor. That is, image sensors employing the same process and pixel structure have the same number of pseudo-reads.
Specifically, the number of times of pseudo-reading of the image sensor of any specific process and pixel structure can be tested by the following method: before the normal reading operation is completed to the beginning of the next reading period, performing 1 additional pseudo reading on the pixel array 10, namely, exporting the residual charge in the photodiode 11 to the floating diffusion node 12 but turning off the row selection gate, not outputting the residual charge exported to the floating diffusion node 12 to the sample hold circuit, cleaning the charge in the photodiode 11 which cannot be exported to the floating diffusion node 12 due to the potential barrier, so that the pixel array 10 is reset more thoroughly, and the remaining residual charge is read out to the sample hold circuit in the next reading period, testing the corresponding residual charge value, and if the residual charge value is higher than a set threshold (for example, 0.05%), increasing the number of pseudo reading until the tested residual charge value is lower than the set threshold, and setting the number of pseudo reading at this time as the preset number of pseudo reading.
For example, for an image sensor of a specific process and pixel structure, when the pseudo read number is set to 1, if the charge residue is 1% (> 0.05%), then 1 is added to the pseudo read number, and the charge residue continues to be tested; when the number of pseudo-reads is set to 2, if the charge retention is 0.4% (> 0.05%), then 1 is added to the number of pseudo-reads again, and the charge retention continues to be tested; when the number of pseudo read times is set to 3 times, if the charge residue value is 0.2% (> 0.05%), then 1 is added to the number of pseudo read times, and the charge residue value continues to be tested; when the number of pseudo read times is set to 4 times, if the charge retention is 0.1% (> 0.05%), then 1 is added to the number of pseudo read times and the charge retention continues to be tested; when the number of pseudo-reads is set to 5, if the charge retention value is 0.04%, the charge retention value is lower than the preset threshold value of 0.05% at this time, and thus the number of pseudo-reads of the image sensor is preset to 5.
Thus, for the image sensor adopting the process and the pixel structure, after 5 times of pseudo-reading operations in each reading period, the residual charge in the photodiode 11 is little, the possible influence on the next frame image is eliminated, and the problem of image quality degradation is solved.
Therefore, according to the image sensor provided by the embodiment of the invention, the image smear phenomenon can be eliminated and the image quality can be improved by carrying out additional pseudo reading for multiple times in the idle time of each reading period, the implementation algorithm of the method is simple, the basic structure of the related image sensor is not required to be modified, the method can be realized by only adding a corresponding logic control circuit, and the pseudo reading operation is carried out in the idle period, so that the frame rate of image output can not be influenced by reasonably arranging the pseudo reading time.
In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the invention and to simplify the description, and are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and are therefore not to be considered limiting of the invention.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (4)
1. A reading method of an image sensor including a pixel array constituted by a plurality of pixel units each including a photodiode and a floating diffusion node, the method comprising the steps of:
s1: acquiring preset pseudo reading times;
s2: performing a normal read operation on the pixel array to cause a sample and hold circuit to read the charge drawn from the photodiode to the floating diffusion node in each read cycle;
s3: after the normal reading operation is finished, performing a dummy reading operation to lead out residual charges in the photodiode to the floating diffusion node until the number of times of performing the dummy reading operation reaches the preset dummy reading number;
wherein, in step S3, after the normal read operation is completed, the row select gate is also turned off so that the sample and hold circuit cannot read the residual charge derived from the photodiode to the floating diffusion node in the dummy read operation;
wherein performing a dummy read operation to derive residual charge in the photodiode to the floating diffusion node specifically comprises:
controlling a reset gate to be conducted so that the potential of the floating diffusion node is reset to a preset voltage;
controlling the reset gate to be closed and controlling a transfer gate to be opened to conduct out residual charges in the photodiode to the floating diffusion node;
controlling the transmission door to be closed.
2. The reading method of the image sensor according to claim 1, wherein the preset number of pseudo-readings is determined by a process and a pixel structure of the image sensor.
3. An image sensor, comprising:
a pixel array constituted by a plurality of pixel units, wherein each of the pixel units includes a photodiode and a floating diffusion node; and
a controller configured to obtain a preset number of dummy read operations, perform a normal read operation on the pixel array in each read cycle to enable a sample-and-hold circuit to read charges led from the photodiode to the floating diffusion node, and perform the dummy read operation to lead residual charges in the photodiode to the floating diffusion node after the normal read operation is completed until the number of dummy read operations reaches the preset number of dummy read operations;
wherein the controller further controls a row select gate to be turned off after the normal read operation is completed, so that the sample and hold circuit cannot read residual charges derived from the photodiode to the floating diffusion node in the dummy read operation;
wherein, in performing a dummy read operation to direct residual charge in the photodiode to the floating diffusion node, the controller is specifically to:
controlling a reset gate to be conducted so that the potential of the floating diffusion node is reset to a preset voltage;
controlling the reset gate to be closed and controlling a transfer gate to be opened to conduct out residual charges in the photodiode to the floating diffusion node;
controlling the transmission door to be closed.
4. The image sensor of claim 3, wherein the preset number of pseudo-reads is determined by a process and a pixel structure of the image sensor.
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| CN110012246B (en) * | 2019-03-26 | 2020-06-02 | 电子科技大学 | Method for realizing high-speed window function of focal plane array reading circuit |
| CN113395468A (en) * | 2020-03-11 | 2021-09-14 | 格科微电子（上海）有限公司 | Method for sampling and amplifying image sensor signal |
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