Pixel array reading method and image sensor

Abstract

The invention provides a pixel array reading method and an image sensor. The pixel array reading method is realized based on a plurality of pixel units arranged in an array. Wherein each pixel unit at least comprises a photoelectric conversion module, a floating storage module and a reading module; the pixel array reading method comprises the following steps: resetting the floating storage module, exposing the photoelectric conversion module, and keeping the floating storage module on so as to output a charge signal to the floating storage module; reading an image signal of the floating storage module, then resetting the floating storage module and reading a reset signal of the floating storage module; and obtaining a real signal of the floating storage module based on the image signal and the reset signal so as to reduce noise introduced when the photoelectric conversion module outputs the charge signal to the floating storage module. According to the invention, the reset signal and the image signal corresponding to the switching tube connected with the photodiode are quantized and read firstly, so that signal noise introduced by operating the switching tube is effectively avoided.

Description

Technical Field

[0001] The present invention relates to the field of image sensing, and in particular to a pixel array reading method and an image sensor. Background Art

[0002] With the development of chip integration, CMOS sensors are evolving towards smaller size and lower power consumption, and are increasingly used in monitoring, vehicle-mounted, and artificial intelligence fields. At the same time, the requirements for certain performance of CMOS image sensors in different application scenarios are also getting higher and higher. For the field of vehicle-mounted monitoring, some image sensors need to monitor scenes outside the car, which involves traffic lights. Usually, traffic lights are a kind of stroboscopic LED, and the chip needs to have a long enough exposure time to cover the LED stroboscopic cycle to capture the image information of the LED "bright". However, at the same time, the scene outside the car will contain some high-brightness signals, such as the bright light at the exit of the tunnel, the sun in the sky, the headlights of nearby cars, and the bright light when the license plate reflects. Therefore, the sensor needs to have a relatively large full well capacity in order to cover the LED stroboscopic cycle in the long exposure and capture the information of the strong light area during the long exposure time without overexposure.

[0003] The existing pixel exposure conversion storage signal area requires at least a photodiode, a switch tube, and a storage area. The charge signal is input and output by turning the switch tube on and off, which is convenient for subsequent quantitative reading. However, the existing pixel array reading method often keeps the switch tube connected to the photodiode closed during exposure and turns it on during readout. On the one hand, it will introduce some noise. On the other hand, due to the opening action of the switch tube, some voltage changes will be coupled to the storage area, and additional timing logic design or subsequent signal processing is required to compensate for the charge signal changes caused by coupling; in addition, the method of completely transferring the charge in the photodiode to the storage area during quantization will also waste part of the photodiode's capacity.

[0004] Based on this, the present invention provides a new pixel array reading method, a pixel array, and an image sensor to solve the problems of noise introduced by the existing pixel array reading method, complex timing design, and inability to better utilize the diode capacity.

[0005] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present application and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because they are described in the background technology section of the present application. Summary of the invention

[0006] In view of the shortcomings of the prior art described above, an object of the present invention is to provide a pixel array reading method, a pixel array, and an image sensor comprising the pixel array, so as to solve the problems of noise introduced by the pixel array reading method in the prior art, complex timing design, and inability to better utilize the diode capacity.

[0007] To achieve the above-mentioned purpose and other related purposes, the present invention provides a pixel array reading method; the pixel array includes a plurality of pixel units arranged in an array; wherein each pixel unit includes at least a photoelectric conversion module, a floating storage module and a reading module; the photoelectric conversion module receives a light signal and converts it into a charge signal; the floating storage module receives and stores the charge signal; the reading module is used to read out the charge signal stored in the floating storage module;

[0008] The pixel array reading method comprises:

[0009] Reset the floating storage module and expose the photoelectric conversion module, keep the floating storage module turned on to output the charge signal to the floating storage module or store the charge signal in the photoelectric conversion module; first read out the image signal of the floating storage module, then reset the floating storage module and read out the reset signal of the floating storage module, and obtain the real signal of the floating storage module based on the image signal and the reset signal; based on the exposure readout, reduce the noise introduced when the photoelectric conversion module outputs the charge signal to the floating storage module.

[0010] Optionally, when the floating storage module includes a first charge storage area, a second charge storage area, and a first gain switch tube is arranged between the first charge storage area and the second charge storage area; the first charge storage area is used to receive and store the charge signal overflowed from the photoelectric conversion module; when the second charge storage area receives the charge signal overflowed from the photoelectric conversion module when the first gain switch tube is turned on, the pixel array reading method includes an exposure step and / or a readout step, wherein:

[0011] The exposure step comprises:

[0012] exposing the photoelectric conversion module when the first gain switch tube is turned on, so as to input the converted charge signal into the first charge storage area and the second charge storage area or store the converted charge signal in the photoelectric conversion module;

[0013] The reading step comprises:

[0014] Keeping the first gain switch on and reading the first image signal and the first reset signal of the first charge storage area and the second charge storage area, performing a difference calculation based on the first image signal and the first reset signal to obtain the real signal of the first charge storage area and the second charge storage area; and

[0015] The first gain switch tube is turned off and the second image signal and the second reset signal of the first charge storage area are read, and a real signal of the first charge storage area is obtained by performing a difference calculation based on the second image signal and the second reset signal.

[0016] Optionally, when the floating storage module includes a first charge storage area, a second charge storage area, a third charge storage area, a first gain switch tube is provided between the first charge storage area and the second charge storage area, and a second gain switch tube is provided between the second charge storage area and the third charge storage area; the first charge storage area is used to receive and store the charge signal overflowed from the photoelectric conversion module; the second charge storage area receives the charge signal overflowed from the photoelectric conversion module when the first gain switch tube is turned on; and the third charge storage area receives the charge signal overflowed from the photoelectric conversion module when the second gain switch tube is turned on, the pixel array reading method includes an exposure step and / or a readout step, wherein:

[0017] The exposure step comprises:

[0018] exposing the photoelectric conversion module when the first gain switch tube and the second gain switch tube are both turned on, so as to input the converted charge signal into the first charge storage area, the second charge storage area and the third charge storage area or store the converted charge signal in the photoelectric conversion module;

[0019] The reading step comprises:

[0020] Keeping the first gain switch tube and the second gain switch turned on and reading the third image signal and the third reset signal of the first charge storage area, the second charge storage area and the third charge storage area, performing a difference calculation based on the third image signal and the third reset signal to obtain the real signals of the first charge storage area, the second charge storage area and the third charge storage area; and

[0021] Turn off the second gain switch tube and read the fourth image signal and the fourth reset signal of the first charge storage area and the second charge storage area, and obtain the real signal of the first charge storage area and the second charge storage area by performing a difference calculation based on the fourth image signal and the fourth reset signal; and

[0022] A fifth image signal and a fifth reset signal of the first charge storage area are read, and a real signal of the first charge storage area is obtained by performing a difference calculation based on the fifth image signal and the fifth reset signal.

[0023] Optionally, a readout order of the fourth image signal, the fourth reset signal, the fifth image signal and the fifth reset signal includes:

[0024] A fourth reset signal of reading the first charge storage area and the second charge storage area based on the first gain switch tube being turned on;

[0025] Reading a fifth reset signal of the first charge storage area and a fifth image signal of the first charge storage area based on closing the first gain switch tube;

[0026] A fourth image signal is read based on the first gain switch being turned on and the first charge storage region and the second charge storage region.

[0027] Optionally, the pixel unit also includes a reset tube for resetting at least one of the first charge storage area, the second charge storage area and the third charge storage area; wherein, during the process of reading the fourth reset signal, the fourth image signal, the fifth reset signal and the fifth image signal, the reset tube is continuously turned on.

[0028] Optionally, the pixel array reading method further comprises setting the photoelectric conversion module to be partially turned on after resetting the floating storage module and when exposing the photoelectric conversion module, so as to output the charge signal to the floating storage module.

[0029] Optionally, the method of setting the photoelectric conversion module to be partially turned on includes: before resetting the floating storage module to turn off the corresponding reset tube, lowering the transmission tube of the photoelectric conversion module from the first level to the second level to turn off the transmission tube, and after resetting the floating storage module to turn off the corresponding reset tube, raising the transmission tube from the second level to a third level less than the first level.

[0030] To achieve the above-mentioned purpose and other related purposes, the present invention provides a pixel array for implementing the above-mentioned pixel array reading method, wherein the pixel array includes a plurality of pixel units arranged in an array; each pixel unit includes at least a photoelectric conversion module, a floating storage module and a reading module; the photoelectric conversion module receives a light signal and converts it into a charge signal; the floating storage module receives and stores the charge signal; and the reading module is used to read out the signal stored in the floating storage module.

[0031] To achieve the above-mentioned purpose and other related purposes, the present invention provides an image sensor, including a pixel array, wherein the pixel array is used to implement any of the pixel array reading methods described above, and the pixel array includes a plurality of pixel units arranged in an array; wherein each pixel unit includes at least a photoelectric conversion module, a floating storage module and a reading module; the photoelectric conversion module receives a light signal and converts it into a charge signal; the floating storage module receives and stores the charge signal; and the reading module is used to read out the signal stored in the floating storage module.

[0032] Optionally, the photoelectric conversion module includes a photodiode and a transmission tube, wherein:

[0033] The control end of the transmission tube is connected to the first switch control signal, and the photodiode is connected to the floating storage module via the transmission tube, for receiving the optical signal and transferring the converted charge signal to the floating storage module;

[0034] Optionally, the reading module includes an output tube and / or a selection tube, wherein:

[0035] The first end of the output tube is connected to the floating storage module, the second end is connected to the power supply voltage, and the third end is connected to the first end of the selection tube, so as to amplify the output signal of the floating storage module;

[0036] The control end of the selection tube is connected to the read switch signal, and the second end is used as the output end of the readout module. The selection tube is turned on based on the read switch signal to output the output signal of the output tube;

[0037] Optionally, the floating storage module includes a first charge storage area, a second charge storage area, and a first gain switch tube arranged between the first charge storage area and the second charge storage area, wherein:

[0038] The first charge storage area is used to receive and store the charge signal output by the photoelectric conversion module.

[0039] The control end of the first gain switch tube is connected to a second switch control signal, and the first gain switch tube is turned on or off based on the second switch control signal.

[0040] The second charge storage area receives the charge signal output by the first charge storage area when the first gain switch tube is turned on.

[0041] Optionally, the first charge storage region is set to a first floating diffusion node; the second charge storage region includes a second floating diffusion node and a first capacitor; the first plate of the first capacitor is grounded, and the second plate is connected to the second floating diffusion node; the second floating diffusion node is connected to the first floating diffusion node via the first gain switch tube.

[0042] Optionally, the floating storage module further includes a third charge storage area and a second gain switch tube arranged between the second charge storage area and the third charge storage area;

[0043] The control end of the second gain switch tube is connected to a third switch control signal, and the second gain switch tube is turned on or off based on the third switch control signal;

[0044] The third charge storage area receives the charge signal output by the second charge storage area when the second gain switch tube is turned on.

[0045] Optionally, the third charge storage region includes a second capacitor, a first plate of which is grounded, and a second plate of which is connected to the second charge storage region via the second gain switch tube.

[0046] Optionally, each pixel unit further includes a reset tube having a control terminal connected to a reset switch signal, a first terminal connected to a power supply voltage, and a second terminal connected to the floating storage module.

[0047] Optionally, when the floating storage module includes a first charge storage area, a second charge storage area, and a first gain switch tube arranged between the first charge storage area and the second charge storage area, the first end of the reset tube is connected to the power supply voltage, and the second end is connected to the second charge storage area;

[0048] When the floating storage module includes a first charge storage area, a second charge storage area, a third charge storage area, a first gain switch tube is arranged between the first charge storage area and the second charge storage area, and a second gain switch tube is arranged between the second charge storage area and the third charge storage area,

[0049] The first end of the reset tube is connected to the supply voltage, and the second end is connected to the third charge storage area or the second end is connected to the connection node between the second charge storage area and the third charge storage area.

[0050] Optionally, when the floating storage module includes a first charge storage area, a second charge storage area, a third charge storage area, a first gain switch tube is provided between the first charge storage area and the second charge storage area, and a second gain switch tube is provided between the second charge storage area and the third charge storage area, a first end of the reset tube is connected to a power supply voltage, and a second end is connected to a connection node between the second charge storage area and the third charge storage area, and the pixel unit further includes an additional reset tube;

[0051] The control end of the additional reset tube receives an additional reset signal, the first end is connected to the supply voltage, the second end is connected to the third charge storage area, and when the third charge storage area includes a second capacitor, the second end is connected to the second capacitor plate.

[0052] As described above, the pixel array reading method and pixel array of the present invention have the following beneficial effects: The pixel array reading method of the present invention first quantifies and reads the reset signal and image signal corresponding to the switch tube connected to the photodiode, thereby effectively avoiding the signal noise in the final read signal caused by operating the switch tube connected to the photodiode. The pixel array reading method of the present invention ensures that the switch tube can effectively leak the charge signal converted by the photodiode PD and transfer it to the storage area by setting the switch tube maintained in the subthreshold state, thereby effectively utilizing the storage space of each storage device. The pixel array reading method of the present invention is simple and the pixel array structure of the present invention is simple, and can be well applied to the field of image sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 Shown is a schematic structural diagram of a first pixel unit of the present invention.

[0054] Figure 2 Display as Figure 1 Timing diagram of the pixel unit reading method.

[0055] Figure 3 to Figure 7 Display as Figure 1 Schematic diagram of charge signal transfer of pixel unit in small signal mode.

[0056] Figure 8 to Figure 14 Display as Figure 1 Schematic diagram of charge signal transfer of a pixel unit in large signal mode.

[0057] Fig.15 It is a schematic structural diagram of a second pixel unit of the present invention.

[0058] Fig.16 FIG. 4 is a schematic diagram showing another example of the structure of the second pixel unit of the present invention.

[0059] Fig.17 It is a schematic structural diagram of the third pixel unit of the present invention.

[0060] Fig.18 Display as Fig.17 Timing diagram of the pixel unit reading method.

[0061] Fig.19 Display as Fig.17 Timing diagram of the pixel unit reading method.

[0062] Component number description

[0063] 1 pixel unit

[0064] 11 Photoelectric conversion module

[0065] 12 Floating Storage Modules

[0066] 13 Read module

[0067] 2 pixel unit

[0068] 21 Floating Storage Module

[0069] 22 Floating Storage Modules DETAILED DESCRIPTION

[0070] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0071] See also Figures 1 to 19 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0072] Embodiment 1

[0073] like Figure 1 As shown, this embodiment provides a pixel array reading method, which is implemented based on the pixel array provided as described below. The pixel array provided in this embodiment includes:

[0074] like Figure 1As shown, the pixel array includes a plurality of pixel units 1 arranged in an array; wherein each pixel unit 1 includes at least a photoelectric conversion module 11, a floating storage module 12 and a reading module 13; the photoelectric conversion module 11 receives a light signal and converts it into a charge signal; the floating storage module 12 receives and stores the charge signal; the reading module 13 is used to read out the charge signal stored in the floating storage module 12.

[0075] Specifically, the photoelectric conversion module 11 includes a photodiode PD and a transmission tube TX; the control end of the transmission tube TX is connected to the first switch control signal; the photodiode PD is connected to the floating storage module 12 via the transmission tube TX, and is used to receive the light signal and convert it into a charge signal, and when the transmission tube TX is turned on, the converted charge signal is output to the floating storage module 12. In this embodiment, the transmission tubes and the photodiodes are set in a one-to-one correspondence, and other examples can also be shared. In addition, the number of photodiodes can be based on actual needs. A pixel unit can include at least two photodiodes, and at least two photodiodes share pixel transistors in the pixel unit, such as an output tube, a reset tube, etc.

[0076] Specifically, the floating storage module 12 includes a first charge storage area, a second charge storage area, and a first gain switch tube SWT1 arranged between the first charge storage area and the second charge storage area; the first charge storage area is used to receive and store the charge signal output by the photoelectric conversion module 11; the control end of the first gain switch tube SWT1 is connected to the second switch control signal, and the first gain switch tube SWT1 is turned on or off based on the second switch control signal; the second charge storage area receives the charge signal output by the first charge storage area when the first gain switch tube is turned on.

[0077] As an example, Figure 1As shown, the first charge storage area is set to the first floating diffusion node FD1; the second charge storage area includes the second floating diffusion node FD2 and the first capacitor MIM1; the first plate of the first capacitor MIM1 is grounded, and the second plate is connected to the second floating diffusion node FD2; the second floating diffusion node FD2 is connected to the first floating diffusion node FD1 via the first gain switch tube SWT1. In this example, when the first gain switch tube SWT1 is turned on, the charge signal overflowed from the photoelectric conversion module 11 flows to the first floating diffusion node FD1, the second floating diffusion node FD2 and the first capacitor and is stored. The first capacitor MIM1 with a certain charge storage capacity can ensure that when the pixel unit 1 has a large signal (strong light signal), more charge signals can still be effectively stored by the first capacitor MIM1. Of course, when the signal is small (the light signal is weak), the charge signal converted by photoelectric conversion can be stored in the photoelectric conversion module.

[0078] It should be noted that in order to ensure that enough charge signals can be stored, in this embodiment, the capacitor is set to a MIM capacitor (Metal-Insulator-Metal, MIM), and can also be set to a MOM capacitor (Metal-Oxide-Metal, MOM) or any other type of capacitor, and is not limited to this embodiment.

[0079] Specifically, each pixel unit 1 further includes a reset tube RST whose control end is connected to a reset switch signal; a first end of the reset tube RST is connected to the power supply voltage VDD, and a second end is connected to the second charge storage area (in this embodiment, the second floating diffusion node FD2, that is, the second end is connected between the second floating diffusion node FD2 and the first capacitor MIM1). The voltage of the power supply voltage VDD is introduced to the corresponding position through the reset tube RST, thereby achieving reset.

[0080] Specifically, the reading module 13 includes an output tube SF and a selection tube Row_SEL; the first end of the output tube SF is connected to the floating storage module 12, the second end is connected to the power supply voltage VDD, and the third end is connected to the first end of the selection tube Row_SEL, so as to output the output signal of the floating storage module 12, such as a source follower transistor; the control end of the selection tube Row_SEL is connected to the reading switch signal, and the second end serves as the output end of the readout module 12, and the selection tube Row_SEL is turned on based on the reading switch signal to output the output signal of the output tube SF.

[0081] It should be noted that the pixel array reading method provided in this embodiment is not limited to the pixel array provided above, and all pixel arrays composed of pixel units including the photoelectric conversion module 11, the floating storage module 12 and the reading module 13 are within the protection scope of this embodiment.

[0082] This embodiment provides a pixel array reading method, including:

[0083] The floating storage module 12 is reset and the photoelectric conversion module 11 is exposed, and the charge signal generated by the photoelectric conversion module 11 is output to the floating storage module 12 while the floating storage module 12 is turned on. It can be understood that when the corresponding light intensity is weak, the charge signal generated by the photoelectric conversion module 11 can also be stored in the photoelectric conversion element of the photoelectric conversion module 11; during the above reset and exposure period, the image signal of the floating storage module 12 is directly read out first, and then the floating storage module 12 is reset and the reset signal of the floating storage module 12 is read out; the real signal of the floating storage module 12 is obtained based on the image signal and the reset signal. Through the above exposure and readout method, the noise introduced when the photoelectric conversion module 11 outputs the charge signal to the floating storage module 12 can be reduced. In addition, it can avoid that a part of the voltage change caused by the opening action of the connection switch is coupled to the first storage area and the second storage area, avoiding the need to compensate for the influence of the signal change caused by the coupling in the timing and subsequent signal processing.

[0084] Specifically, in this embodiment, when the floating storage module 12 includes a first charge storage area, a second charge storage area, and a first gain switch tube SWT1 is provided between the first charge storage area and the second charge storage area, the pixel array reading method at least includes an exposure step or a readout step:

[0085] As an example, the exposure step of this example includes: exposing the photoelectric conversion module 11 when the first gain switch tube SWT1 is turned on, so as to input the converted charge signal into the first charge storage area (in this embodiment, the first floating diffusion node FD1) and the second charge storage area (in this embodiment, the second floating diffusion node FD2 and the first capacitor MIM1); that is, the overflowed charge can be distributed in the storage node corresponding to the first storage area and the storage node corresponding to the second storage area. In one embodiment, the overflowed charge signal of the photoelectric conversion module is distributed according to the capacitance ratio of the storage nodes in each storage area, and the capacitance of the storage nodes in each storage area can be set according to actual needs and process conditions. Of course, it should also be noted that when the corresponding light intensity is weak, the charge signal converted by the photoelectric conversion module can also be directly stored in the photodiode; in this embodiment, the beginning of exposing the photoelectric conversion module 11 refers to turning on the transmission tube TX and then disconnecting it, so that the light signal is converted in the photodiode PD.

[0086] In this embodiment, the photoelectric conversion module is set to be partially turned on. When the transmission tube TX is turned on after being turned off, the gate voltage of the transmission tube TX is set to change from a low voltage to a positive voltage, and the transmission tube TX is turned on at a subthreshold, ensuring that the channel of the transmission tube TX has sufficient leakage energy so that the photons in the photoelectric conversion module 11 overflow and are transferred to at least the first floating diffusion point FD1.

[0087] As an example, the method of setting the photoelectric conversion module 11 to be partially turned on includes: before resetting the floating storage module 12 to turn off the corresponding reset tube RST, the transmission tube TX of the photoelectric conversion module 11 is reduced from the first level to the second level to turn off the transmission tube TX, and after resetting the floating storage module to turn off the corresponding reset tube RST, the transmission tube TX is raised from the second level (completely turned off state) to a third level (such as a subthreshold state) less than the first level. The turn-off of the transmission tube TX to the second level is set before the reset tube RST is turned off, and the influence of the noise caused by the turn-off of the transmission tube TX can be eliminated based on the reset state of the reset tube RST; in addition, after the reset tube RST is turned off, the transmission tube TX is further set to rise from the second level to the third level to offset the noise of the complete turn-off of the transmission tube TX before the start of reading.

[0088] As an example, the readout step of this example includes: reading the first image signal Overflow_SIG and the first reset signal Overflow_RST of the first charge storage area and the second charge storage area, and obtaining the real signals of the first charge storage area and the second charge storage area based on the difference between the first image signal Overflow_SIG and the first reset signal Overflow_RST; and reading the second image signal CDS_SIG of the first charge storage area (the charge signal is transferred to the first charge storage area by the photodiode after the transmission tube is turned on) and the second reset signal CDS_RST, and obtaining the real signal of the first charge storage area based on the difference between the second image signal CDS_SIG and the second reset signal CDS_RST.

[0089] Combine the following Figure 2 The pixel array reading method provided in this embodiment includes:

[0090] Reset exposure step: turn on the transmission tube TX (at time t11 in this embodiment) and then turn it off (at time t12 in this embodiment) to allow the photodiode PD to start exposure accumulation, wherein the reset is performed under the premise that the first gain switch tube SWT1 is turned on, so that the first charge storage area, the second charge storage area and the photoelectric conversion module are reset at the same time (in this embodiment, the reset tube RST is turned on at time t13 to achieve reset).

[0091] It should be noted that the reset exposure step also includes a charge overflow step: partially turning on the transmission tube TX (maintaining the level state in a subthreshold state) so that the charge signal can overflow through the transmission tube TX, so as to facilitate subsequent signal reading, and completely turning off the partially turned-on transmission tube TX before reading out the signal. In this process, through the control of the transistor, the overflowed charge signal can be simultaneously distributed to the nodes corresponding to the first storage area and the second storage area.

[0092] The steps of reading out the image signal and reset signal of the overflow charge: after resetting the first charge storage area and the second charge storage area, keep the first gain switch tube SWT1 turned on and control the transmission tube TX to be completely turned off when reading starts, wherein the control read switch signal is valid (at time t15 in this embodiment) to read the first image signal Overflow_SIG of the first charge storage area and the second charge storage area, and then reset the first charge storage area and the second charge storage area (from time t17 to time t18) to read the first reset signal Overflow_RST of the first charge storage area and the second charge storage area.

[0093] The steps of reading the image signal and reset signal under the correlated double sampling are as follows: the read switch signal is controlled to be effective, and after the first gain switch tube SWT1 is turned off (at time t19 in this embodiment), the reset signal of the first charge storage area is collected as the second reset signal CDS_RST. The transmission tube TX is controlled to be turned on (at time t110 to time t111) so that the exposed charge signal is transferred to the first charge storage area and the image signal of the first charge storage area is quantized and read as the second image signal CDS_SIG. In the above reading method, the charge is read in batches, which can avoid the waste of the capacity of the photodiode compared with the complete transfer method.

[0094] Combine the following Figure 2 to Figure 7 Analysis shows that the working mechanism of the pixel array reading method of this embodiment in the small signal mode is as follows:

[0095] like Figure 3 As shown, the first gain switch tube SWT1 is turned on, and the transmission tube TX is partially turned on in the small signal mode ( Figure 2 During the time period t14 to t16 , due to the small amount of charge, the charge signal is not transferred to the floating storage module 12 (in this embodiment, the first floating diffusion point FD1 to the first capacitor MIM1 ), but is stored in the photoelectric conversion module 11 .

[0096] like Figure 4 As shown, the control read switch signal is valid ( Figure 2 At time t15), the charge signal is not transferred to the floating storage module 12 (in the present embodiment, the first floating diffusion point FD1 to the first capacitor MIM1), and only the charge signal previously stored in the floating storage module 12 is read (if a reset operation has been performed before, the charge signal of the floating storage module 12 in the present embodiment is zero), that is, the first image signal Overflow_SIG stored in the first charge storage area and the second charge storage area is read out.

[0097] like Figure 5 As shown, the reset signal is valid ( Figure 2 From time t17 to time t18, the first reset signal Overflow_RST stored in the first charge storage area and the second charge storage area is read out.

[0098] like Figure 6 As shown, the first gain switch SWT1 is turned off ( Figure 2 At time t19, the space of the floating storage module 12 is divided into two parts. In this embodiment, only the second reset signal CDS_RST stored in the first charge storage area (the first floating diffusion point FD1) is read.

[0099] like Figure 7 As shown, the transmission tube TX is turned on ( Figure 2At time t110 , the charge signal in the photoelectric conversion module 11 is transferred to the first charge storage area (first floating diffusion point FD1 ) and is read out.

[0100] Combine the following Figure 8 to Figure 13 Analysis shows that the working mechanism of the pixel array reading method of this embodiment in the large signal mode is as follows:

[0101] like Figure 8 As shown, the first gain switch tube SWT1 is turned on, and the transmission tube TX is partially turned on in the large signal mode ( Figure 2 During the time period t14 to t16), the amount of charge is relatively large, and the charge signal will overflow and be transferred to the floating storage module 12 (in the present embodiment, from the first floating diffusion point FD1 to the first capacitor MIM1, and the charge is distributed at the nodes corresponding to each storage area), and part of the charge signal is stored in the photodiode PD, and part is stored in the floating storage module 12 at this time.

[0102] like Fig. 9 As shown, the control read switch signal is valid ( Figure 2 At time t15) and at the same time, the transmission tube TX is completely turned off to ensure that the charges of the two parts will not migrate to the floating storage module 12 again, and the charge signals in the first charge storage area and the second charge storage area are read as the first image signal Overflow_SIG.

[0103] like Fig.10 and Fig.11 As shown, the reset signal is disconnected after it is valid ( Figure 2 At time t17 and time t18, the signals in the first charge storage area and the second charge storage area are reset, and the signals in the first charge storage area and the second charge storage area are read as the first reset signal Overflow_RST.

[0104] like Fig.12 As shown, the first gain switch tube SWT1 is disconnected ( Figure 2 At time t19, the space of the floating storage module 12 is divided into two parts. In this embodiment, only the second reset signal CDS_RST stored in the first charge storage area (first floating diffusion point FD1) is read.

[0105] like Fig.13 and Fig.14 As shown, the transmission tube TX is turned on and then turned off, the charge is transferred to the first charge storage area, and only the second image signal CDS_SIG stored in the first charge storage area (first floating diffusion point FD1) is read.

[0106] Through the above steps, the accuracy of the collected signal can be effectively guaranteed, and the pixel array reading method of this embodiment can be applied to both the small signal mode and the large signal mode. That is, there are two situations for the final signal in this application, one is that the charge in the photodiode PD overflows, and the other is that the charge in the photodiode PD does not overflow, corresponding to the large signal and the small signal in the above description, and the digital algorithm module can be used to judge and fuse them later to realize the splicing of the two signals and improve the overall dynamic range.

[0107] Embodiment 2

[0108] In order to further improve the dynamic range of the pixel unit, this embodiment provides a pixel array reading method based on the following Fig.15 The pixel array reading of several pixel units 2 shown in the figure is different from the pixel unit provided in the first embodiment in that the floating storage module 21 is different and the floating storage module of the present embodiment further includes a third charge storage area and a second gain switch tube SWT2.

[0109] Specifically, Fig.15 The floating storage module 21 shown also includes a third charge storage area and a second gain switch tube SWT2 arranged between the second charge storage area and the third charge storage area; the control end of the second gain switch tube SWT2 is connected to the third switch control signal, and the second gain switch tube is turned on or off based on the third switch control signal; the third charge storage area receives the charge signal overflowed from the photoelectric conversion module when the second gain switch tube SWT2 is turned on.

[0110] As an example, Fig.15 As shown, the third charge storage area includes a second capacitor MIM2; the first plate of the second capacitor MIM2 is grounded, and the second plate is connected to the second charge storage area via the second gain switch tube SWT2. In this example, the second plate is connected to the second floating diffusion node FD2 via the second gain switch tube SWT2.

[0111] In this example, when the first gain switch tube SWT1 is turned on, the charge signal overflowed from the photoelectric conversion module 11 flows to the first floating diffusion node FD1, the second floating diffusion node FD2 and the first capacitor MIM1 and is stored; and when the first gain switch tube SWT1 and the second gain switch tube SWT2 are turned on at the same time, the charge signal overflowed from the photoelectric conversion module 11 flows to the first floating diffusion node FD1, the second floating diffusion node FD2, the first capacitor MIM1 and the second capacitor MIM2 and is stored. At this time, the overflowed charge can be distributed among the storage nodes corresponding to the first storage area, the second storage area and the third storage area. In one embodiment, the charge signal overflowed from the photoelectric conversion module is distributed according to the capacitance ratio of the storage nodes in each storage area, and the capacitance of the storage nodes in each storage area can be set according to actual needs and process conditions. Of course, it should also be noted that when the corresponding light intensity is weak, the charge signal converted and generated by the photoelectric conversion module can also be directly stored in the photodiode. Compared with the pixel unit of the first embodiment, a charge storage area is set, which can effectively improve the dynamic range.

[0112] As an example, the pixel unit 2 of this embodiment further includes a reset tube, and a control end of the reset tube is connected to a reset switch signal.

[0113] In the first example, if Fig.15 As shown, the first end of the reset tube RST in the pixel unit 2 is connected to the power supply voltage VDD, and the second end is connected to the connection node between the second charge storage area and the third charge storage area (the second floating diffusion point FD2 in this embodiment). The reset switch signal is controlled to introduce the power supply voltage VDD into the second charge storage area to reset the corresponding storage area, and when the second gain switch tube SWT2 is turned on, the third charge storage area is reset.

[0114] In a further example, Fig.16 As shown, the pixel unit also includes an additional reset tube RST_C, the control end of the additional reset tube RST_C receives an additional reset signal, the first end is connected to the power supply voltage VDD, and the second end is connected to the third charge storage area. When the third charge storage area includes a second capacitor MIM2, the second end is connected to one plate of the second capacitor MIM2. At this time, the other plate of the second capacitor MIM2 can be grounded. The above-mentioned additional reset tube RST_C is conducive to realizing rapid node reset.

[0115] In the second example, if Fig.17As shown, the first end of the reset tube RST in the pixel unit 2 is connected to the power supply voltage VDD, and the second end is connected to the third charge storage area. In this embodiment, the second end is connected to the node between the second gain switch tube SWT2 and the second capacitor MIM2, and the reset switch signal is controlled to introduce the power supply voltage VDD into the third charge storage area to reset the corresponding storage area, and reset the second charge storage area when the second gain switch tube SWT2 is turned on.

[0116] It should be noted that the photoelectric conversion module 11 and the reading module 13 of this embodiment are substantially the same as those of the first embodiment, and will not be described in detail herein.

[0117] The pixel array reading method of this embodiment is implemented based on a plurality of pixel units 2 provided in this embodiment, and the pixel array reading method of this embodiment is basically the same as that of embodiment 1, except that the pixel array reading method of this embodiment needs to read the signal in the floating storage module 21 including the third charge storage area.

[0118] Specifically, the exposure step of this embodiment includes: exposing the photoelectric conversion module 11 when the first gain switch tube SWT1 and the second gain switch tube SWT2 are both turned on, so as to input the converted charge signal into the first charge storage area, the second charge storage area and the third charge storage area; in this process, through the control of the transistor, the overflowed charge signal can be simultaneously distributed at the nodes corresponding to the first storage area and the second storage area.

[0119] Specifically, the readout step of this example includes: keeping the first gain switch tube and the second gain switch tube turned on after reset exposure, continuously reading the third image signal nonCDS_SIG and the third reset signal nonCDS_RST of the first charge storage area, the second charge storage area and the third charge storage area, and obtaining the real signals of the first charge storage area, the second charge storage area and the third charge storage area based on the difference between the third image signal nonCDS_SIG and the third reset signal nonCDS_RST; and, reading the fourth reset signal CDS_LCG_RST and the fourth image signal CDS_LCG_SIG of the first charge storage area and the second charge storage area, and obtaining the real signals of the first charge storage area and the second charge storage area based on the difference between the fourth image signal CDS_LCG_SIG and the fourth reset signal CDS_LCG_RST; and, reading the fifth reset signal CDS_HCG_RST and the fifth image signal CDS_HCG_SIG of the first charge storage area, and obtaining the real signal of the first charge storage area based on the difference between the fifth image signal CDS_HCG_SIG and the fifth reset signal CDS_HCG_RST. Similarly, based on controlling the first gain switch tube SWT1 and the second gain switch tube SWT2 , the charge storage area corresponding to the read charge is controlled.

[0120] Combination Fig.18 The pixel array reading provided by this embodiment is described, wherein the exposure step (t21 to t26) is basically the same as that of the first embodiment, wherein the first gain switch tube SWT1 and the second gain switch tube SWT2 are both kept turned on during the exposure process. The main difference between this embodiment and the first embodiment is that: at the beginning of the reading step, the second gain switch tube SWT2 and the first gain switch tube SWT1 are kept turned on, and the third image signal nonCDS_SIG and the third reset signal nonCDS_RST are sampled by controlling the reset tube RST to turn on and off (at t27 and t28, respectively). Then, the second gain switch tube SWT2 (t29) and the first gain switch tube SWT1 (t210) are turned off in sequence, and the fourth reset signal CDS_LCG_RST (between t29 and t210) and the fifth reset signal CDS_HCG_RST (between t210 and t211) are read out in sequence. Turn on the transmission tube TX (t211 to t212) to read the fifth image signal CDS_HCG_SIG; turn on the first gain switch SWT1 (t213) and turn on the transmission tube TX again (t214 to t215) to read the fourth image signal CDS_LCG_SIG. Fig.17The settings can still be applied to large-signal and small-signal scenarios corresponding to the pixel arrays, while ensuring the effectiveness and accuracy of the reading.

[0121] In this embodiment, the pixel array reading method further includes applying Fig.19 The reset and hold step of the pixel unit shown in FIG. 1 is as follows: during the process of quantizing and reading the fourth reset signal CDS_LCG_RST, the fifth reset signal CDS_HCG_RST, the fifth image signal CDS_HCG_SIG and the fourth image signal CDS_LCG_SIG, the reset tube RST is continuously turned on, such as Fig.19 The reset state is maintained continuously from the time t216' shown. In this embodiment, the reset tube RST is designed to be turned on and kept on after the third reset signal nonCDS_RST is read out, and the second gain switch tube SWT2 is turned off after the reset tube RST is turned on. At this time, the first gain switch tube SWT1 is in the on state. The above design can, on the one hand, improve the influence of charge movement on the potential of the corresponding storage node during the shutdown process of the reset tube RST based on the working voltage VDD, and on the other hand, it can also improve the influence of capacitive coupling caused by voltage changes during the operation of the reset tube RST on the potential of the corresponding storage node, for example, the coupling capacitance generated by the wiring of the reset tube RST and the second capacitor MIM2 during the voltage change of the reset tube RST. Further, it can be beneficial to improve the potential of the first floating diffusion node FD1, thereby facilitating the transmission of charges in the photoelectric conversion module.

[0122] In summary, the present invention provides a pixel array reading method and a pixel array, which are implemented based on a number of pixel units arranged in an array; wherein each pixel unit at least includes a photoelectric conversion module, a floating storage module and a reading module; the pixel array reading method includes: resetting the floating storage module and exposing the photoelectric conversion module to output the charge signal to the floating storage module; first reading out the image signal of the floating storage module, then resetting the floating storage module and reading out the reset signal of the floating storage module; obtaining the real signal of the floating storage module based on the image signal and the reset signal to reduce the noise introduced when the photoelectric conversion module outputs the charge signal to the floating storage module. The present invention effectively avoids the signal noise introduced by operating the switch tube by first quantizing and reading the reset signal and image signal of the switch tube connected to the photodiode. Therefore, the present invention effectively overcomes the various shortcomings in the prior art and has a high industrial utilization value.

[0123] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for reading a pixel array, wherein the pixel array comprises a plurality of pixel units arranged in an array; wherein: Each pixel unit at least includes a photoelectric conversion module, a floating storage module and a reading module; the photoelectric conversion module receives a light signal and converts it into a charge signal; the floating storage module receives and stores the charge signal; the reading module is used to read out the charge signal stored in the floating storage module; the pixel array reading method includes: Reset the floating storage module and expose the photoelectric conversion module, keep the floating storage module turned on to output the charge signal to the floating storage module or store the charge signal in the photoelectric conversion module; first read out the image signal of the floating storage module, then reset the floating storage module and read out the reset signal of the floating storage module, and obtain the real signal of the floating storage module based on the image signal and the reset signal; reduce the noise introduced when the photoelectric conversion module outputs the charge signal to the floating storage module based on the exposure readout.

2. The pixel array reading method according to claim 1, characterized in that: When the floating storage module includes a first charge storage area, a second charge storage area, and a first gain switch tube is arranged between the first charge storage area and the second charge storage area; the first charge storage area is used to receive and store the charge signal overflowed from the photoelectric conversion module; When the second charge storage area receives the charge signal overflowed from the photoelectric conversion module when the first gain switch tube is turned on, the pixel array reading method includes an exposure step and / or a readout step, wherein: The exposure step comprises: exposing the photoelectric conversion module when the first gain switch tube is turned on, so as to input the converted charge signal into the first charge storage area and the second charge storage area or store the converted charge signal in the photoelectric conversion module; The reading step comprises: Keeping the first gain switch on and reading the first image signal and the first reset signal of the first charge storage area and the second charge storage area, performing a difference calculation based on the first image signal and the first reset signal to obtain the real signal of the first charge storage area and the second charge storage area; and The first gain switch tube is turned off and the second image signal and the second reset signal of the first charge storage area are read, and a real signal of the first charge storage area is obtained by performing a difference calculation based on the second image signal and the second reset signal.

3. The pixel array reading method according to claim 2, characterized in that: When the floating storage module includes a first charge storage area, a second charge storage area, and a third charge storage area, a first gain switch tube is provided between the first charge storage area and the second charge storage area, and a second gain switch tube is provided between the second charge storage area and the third charge storage area; the first charge storage area is used to receive and store the charge signal overflowed from the photoelectric conversion module; the second charge storage area receives the charge signal overflowed from the photoelectric conversion module when the first gain switch tube is turned on; When the third charge storage area receives the charge signal overflowed from the photoelectric conversion module when the second gain switch tube is turned on, the pixel array reading method includes an exposure step and / or a readout step, wherein: The exposure step comprises: exposing the photoelectric conversion module when the first gain switch tube and the second gain switch tube are both turned on, so as to input the converted charge signal into the first charge storage area, the second charge storage area and the third charge storage area or store the converted charge signal in the photoelectric conversion module; The reading step comprises: Keeping the first gain switch tube and the second gain switch turned on and reading the third image signal and the third reset signal of the first charge storage area, the second charge storage area and the third charge storage area, performing a difference calculation based on the third image signal and the third reset signal to obtain the real signals of the first charge storage area, the second charge storage area and the third charge storage area; and Turn off the second gain switch tube and read the fourth image signal and the fourth reset signal of the first charge storage area and the second charge storage area, and obtain the real signal of the first charge storage area and the second charge storage area by performing a difference calculation based on the fourth image signal and the fourth reset signal; and A fifth image signal and a fifth reset signal of the first charge storage area are read, and a real signal of the first charge storage area is obtained by performing a difference calculation based on the fifth image signal and the fifth reset signal.

4. The pixel array reading method according to claim 3, characterized in that: The readout order of the fourth image signal, the fourth reset signal, the fifth image signal and the fifth reset signal includes: A fourth reset signal of reading the first charge storage area and the second charge storage area based on the first gain switch tube being turned on; Reading a fifth reset signal of the first charge storage area and a fifth image signal of the first charge storage area based on closing the first gain switch tube; A fourth image signal is read based on the first gain switch being turned on and the first charge storage region and the second charge storage region.

5. The pixel array reading method according to claim 4, characterized in that: The pixel unit also includes a reset tube for resetting at least one of the first charge storage area, the second charge storage area, and the third charge storage area; wherein, during the process of reading the fourth reset signal, the fourth image signal, the fifth reset signal, and the fifth image signal, the reset tube is continuously turned on.

6. The pixel array reading method according to claims 1 to 5, characterized in that: The pixel array reading method further includes setting the photoelectric conversion module to be partially turned on after resetting the floating storage module and when exposing the photoelectric conversion module, so as to output the charge signal to the floating storage module.

7. The pixel array reading method according to claim 6, characterized in that: The method of setting the photoelectric conversion module to be partially turned on includes: before resetting the floating storage module to turn off the corresponding reset tube, lowering the transmission tube of the photoelectric conversion module from the first level to the second level to turn off the transmission tube, and after resetting the floating storage module to turn off the corresponding reset tube, raising the transmission tube from the second level to a third level less than the first level.

8. An image sensor, comprising a pixel array, wherein the pixel array is used to implement the pixel array reading method according to any one of claims 1 to 7, characterized in that: The pixel array includes a plurality of pixel units arranged in an array; Among them, each pixel unit at least includes a photoelectric conversion module, a floating storage module and a reading module; the photoelectric conversion module receives the light signal and converts it into a charge signal; the floating storage module receives and stores the charge signal; the reading module is used to read out the signal stored in the floating storage module.

9. The image sensor according to claim 8, characterized in that: The photoelectric conversion module includes a photodiode and a transmission tube, wherein: The control end of the transmission tube is connected to the first switch control signal, and the photodiode is connected to the floating storage module via the transmission tube, for receiving the optical signal and transferring the converted charge signal to the floating storage module; And or, the reading module includes an output tube and / or a selection tube, wherein: The first end of the output tube is connected to the floating storage module, the second end is connected to the power supply voltage, and the third end is connected to the first end of the selection tube, so as to amplify the output signal of the floating storage module; The control end of the selection tube is connected to the read switch signal, and the second end is used as the output end of the readout module. The selection tube is turned on based on the read switch signal to output the output signal of the output tube; And / or, the floating storage module includes a first charge storage area, a second charge storage area, and a first gain switch tube arranged between the first charge storage area and the second charge storage area, wherein: The first charge storage area is used to receive and store the charge signal output by the photoelectric conversion module. The control end of the first gain switch tube is connected to a second switch control signal, and the first gain switch tube is turned on or off based on the second switch control signal. The second charge storage area receives the charge signal output by the first charge storage area when the first gain switch tube is turned on.

10. The image sensor according to claim 9, characterized in that: The first charge storage area is set as a first floating diffusion node; the second charge storage area includes a second floating diffusion node and a first capacitor; the first plate of the first capacitor is grounded, and the second plate is connected to the second floating diffusion node; the second floating diffusion node is connected to the first floating diffusion node via the first gain switch tube.

11. The image sensor according to claim 9, characterized in that: The floating storage module further includes a third charge storage area and a second gain switch tube arranged between the second charge storage area and the third charge storage area; The control end of the second gain switch tube is connected to a third switch control signal, and the second gain switch tube is turned on or off based on the third switch control signal; The third charge storage area receives the charge signal output by the second charge storage area when the second gain switch tube is turned on.

12. The image sensor according to claim 11, characterized in that: The third charge storage region includes a second capacitor, a first plate of which is grounded, and a second plate of which is connected to the second charge storage region via the second gain switch tube.

13. The image sensor according to any one of claims 8 to 12, characterized in that: Each pixel unit also includes a reset tube whose control end is connected to a reset switch signal, a first end is connected to a power supply voltage, and a second end is connected to the floating storage module.

14. The image sensor according to claim 13, characterized in that: When the floating storage module includes a first charge storage area, a second charge storage area, and a first gain switch tube arranged between the first charge storage area and the second charge storage area, the first end of the reset tube is connected to the power supply voltage, and the second end is connected to the second charge storage area; When the floating storage module includes a first charge storage area, a second charge storage area, a third charge storage area, a first gain switch tube is arranged between the first charge storage area and the second charge storage area, and a second gain switch tube is arranged between the second charge storage area and the third charge storage area, The first end of the reset tube is connected to the supply voltage, and the second end is connected to the third charge storage area or the second end is connected to the connection node between the second charge storage area and the third charge storage area.

15. The image sensor according to claim 14, characterized in that: When the floating storage module includes a first charge storage area, a second charge storage area, a third charge storage area, a first gain switch tube is arranged between the first charge storage area and the second charge storage area, and a second gain switch tube is arranged between the second charge storage area and the third charge storage area, a first end of the reset tube is connected to a power supply voltage, and a second end is connected to a connection node between the second charge storage area and the third charge storage area, and the pixel unit further includes an additional reset tube; The control end of the additional reset tube receives an additional reset signal, the first end is connected to the supply voltage, the second end is connected to the third charge storage area, and when the third charge storage area includes a second capacitor, the second end is connected to the second capacitor plate.

Images