A driving method for an image sensor used for rolling exposure and an image sensor

Abstract

The present invention relates to a driving method for an image sensor used in rolling exposure, and an image sensor. During rolling exposure, the method identifies idle pixel rows in the image sensor's pixel array and then outputs a gate transfer control signal to the transfer transistors of the pixel cells in the idle pixel rows, thereby continuously turning on the transfer transistors. By continuously turning on the transfer transistors of the idle pixel rows in the pixel array, the present invention can address the blooming phenomenon caused by image charge generated in the photodiodes of idle pixel cells overflowing into pixel cells in adjacent rows undergoing normal charge reading operations when illuminated by strong light.

Description

Technical Field

[0001] The present invention relates to the technical field of image sensors, and in particular to a driving method for an image sensor used in rolling exposure and the image sensor. Background Art

[0002] CMOS image sensors are widely used in various technological fields, such as digital cameras, drones, video surveillance equipment, and autonomous driving. CMOS image sensor pixels can be categorized as 3T, 4T, or 5T types, depending on the number of transistors they contain. The more common 4T pixel consists of a photodiode (PD) and four transistors: a reset transistor, a source-follower transistor, a select transistor, and a transfer transistor.

[0003] Image sensor exposure methods can be categorized as rolling shutter and global shutter. Rolling shutter exposes different rows of the image sensor's pixel array at different times, and each row is read out according to a selected sequence. Because the readout sequence and other parameters can be specified based on the address, signal charge can be acquired from pixels at any location. Global shutter exposes all rows of pixels simultaneously for the same duration.

[0004] In rolling exposure mode, because each row of the pixel array has a different exposure time or time period, only one row is in the read state at any one time. To ensure correct timing, some rows of pixels are neither exposed nor read. However, since idle rows continue to receive light, and the photodiode (PD) has a limited charge storage capacity, once the amount of charge converted exceeds the full well capacity of the photodiode (PD), the excess charge overflows into adjacent pixels, causing overexposure and blooming (blooming or haloing). In other words, idle pixel rows can affect exposed rows, severely impacting image sensor image quality. Furthermore, existing image sensors typically feature high dynamic range (HDR) imaging, a highly desirable feature for applications such as automotive and machine vision. Blooming is exacerbated in HDR mode because of the long and short exposures between each row. Short rows, due to their shorter exposure times and longer idle periods, can easily overexpose the short rows, affecting charge accumulation in surrounding rows. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a driving method and an image sensor for rolling exposure, which can solve the blooming phenomenon caused by the image charge generated in the photodiode of the pixel unit in the idle state overflowing into the pixel unit in the adjacent row performing normal charge reading operation when the pixel unit is irradiated by strong light.

[0006] To achieve the above-mentioned objective, a first aspect of an embodiment of the present invention provides a method for driving an image sensor for rolling exposure. As one implementation manner, the method includes:

[0007] outputting a latch address signal based on the exposure row address signal, the read row address signal, the exposure row transfer signal, the read row transfer signal, and the latch enable signal;

[0008] outputting a gate transfer control signal based on the exposure row address signal, the read row address signal, the exposure row transfer signal, the read row transfer signal, and the latch address signal; and

[0009] When a pixel row in the image sensor pixel array is in an idle state, the gate transfer control signal is at a first level to continuously turn on the transfer transistors of the pixel units in the pixel row in the idle state.

[0010] In one embodiment, when a pixel row in the image sensor pixel array is in an idle state, the gate transfer control signal is at a first level to continuously turn on the transfer transistors of the pixel units in the pixel row in the idle state, further comprising:

[0011] determining rows of pixels in an image sensor pixel array that are in an idle state;

[0012] The step of determining the pixel rows in the image sensor pixel array that are in an idle state includes:

[0013] The pixel rows in the image sensor pixel array that are in an idle state are determined based on the exposure row address signal and the read row address signal. The exposure row address signal is used to indicate a row of pixels in the pixel array that are in a pre-charge state and ready to start exposure. The read row address signal is used to indicate a row of pixels in the pixel array that are in a read state.

[0014] In one embodiment, the step of determining a pixel row in an idle state in the image sensor pixel array according to the exposure row address signal and the read row address signal includes:

[0015] determining a pixel row in an exposure state with a row address between the exposure row address signal and the read row address signal;

[0016] A pixel row that is not in the pre-charge state, the exposure state, and the read state is a pixel row in the idle state.

[0017] As one embodiment, the method further includes:

[0018] A first pulse signal is output to the transfer transistors of the pixel units in the pixel row in the pre-charge state to turn on the transfer transistors.

[0019] As one implementation manner, the amplitude of the gate transmission control signal is smaller than the amplitude of the pulse signal.

[0020] As one embodiment, the method further includes:

[0021] The gate transfer control signal is continuously outputted to the transfer transistors of the pixel units in the pixel row in the pre-charge state to turn on the transfer transistors.

[0022] As one embodiment, the method further includes: when the pixel row in the image sensor pixel array is in an exposure state, the gate transfer control signal is a second level to continuously turn off the transfer transistor; when the pixel row in the image sensor pixel array is in a reading state, the gate transfer control signal is a second pulse signal to turn on the transfer transistor.

[0023] As one embodiment, the method further includes: outputting a reset control signal to the reset transistors of the pixel units in the pixel row in the idle state, so as to continuously turn on the reset transistors.

[0024] To achieve the above-mentioned purpose, a second aspect of an embodiment of the present invention provides an image sensor. As one implementation method thereof, the image sensor includes: a pixel array, a control unit, and a driving unit, wherein:

[0025] The pixel array includes a plurality of pixel units arranged in rows and columns, wherein each pixel unit includes:

[0026] a photodiode for accumulating image charge in response to incident light; and

[0027] a transfer transistor coupled between the photodiode and a floating diffusion node to selectively transfer the image charge accumulated in the photodiode to the floating diffusion node;

[0028] The control unit is coupled to the driving unit and is configured to determine a pixel row in the pixel array that is in an idle state during rolling exposure;

[0029] Wherein, the image sensor further includes a latch unit and a gate driver;

[0030] The latch unit outputs a latch address signal based on the exposure row address signal, the read row address signal, the exposure row transfer signal, the read row transfer signal, and the latch enable signal;

[0031] The gate driver outputs a gate transfer control signal based on the exposure row address signal, the read row address signal, the exposure row transfer signal, the read row transfer signal, and the latch address signal; when the pixel row in the image sensor pixel array is in an idle state, the gate transfer control signal is at a first level to continuously turn on the transfer transistor of the pixel unit in the pixel row in the idle state.

[0032] As one of the embodiments, the control unit determines a pixel row in an idle state in the pixel array based on the exposure row address signal and the read row address signal, the exposure row address signal is used to indicate a row of pixels in the pixel array that is in a pre-charge state and ready to start exposure, and the read row address signal is used to indicate a row of pixels in the pixel array that is in a read state.

[0033] As one of the embodiments, the control unit determines the pixel row in the exposure state using the row address between the exposure row address signal and the read row address signal, and the pixel row that is not in the pre-charge state, the exposure state, and the read state is the pixel row in the idle state.

[0034] As one implementation manner, the latch unit is provided in the control unit, the gate driver is provided in the driving unit, and each pixel row corresponds to a latch unit and a gate driver.

[0035] As one implementation manner, the latch unit and the gate driver are both provided in the driving unit, and each pixel row corresponds to a latch unit and a gate driver.

[0036] As one embodiment, the gate driver includes an exposure path, a read path and a latch path. The first ends of the exposure path, the read path and the latch path are all connected to a positive voltage to pull the gate transmission control signal to a high level. The second ends of the exposure path, the read path and the latch path are all connected to a negative voltage to pull the gate transmission control signal to a low level. The exposure path includes a first latch transistor, and the latch path includes a second latch transistor. The first latch transistor and the second latch transistor are used to receive the latch address signal to perform a logical operation with the exposure row address signal, the read row address signal, the exposure row transmission signal and the read row transmission signal to output the gate transmission control signal.

[0037] In one embodiment, the latch path includes a third latch transistor for receiving the latch address signal and performing a logic operation with the exposure row address signal and the reading row address signal to turn off the latch function of the image sensor.

[0038] As one embodiment, the control unit is further configured to control the driving unit to output a first pulse signal to the transfer transistors of the pixel units in the pixel row in the pre-charge state, so as to turn on the transfer transistors.

[0039] As one implementation manner, the amplitude of the gate transmission control signal is smaller than the amplitude of the pulse signal.

[0040] As one embodiment, when the pixel row in the image sensor pixel array is in an exposure state, the gate transfer control signal is a second level to continuously turn off the transfer transistor; when the pixel row in the image sensor pixel array is in a reading state, the gate transfer control signal is a second pulse signal to turn on the transfer transistor.

[0041] As one embodiment, each pixel unit further includes a reset transistor, and the control unit is further configured to control the driving unit to output a reset control signal to the reset transistor of the pixel unit in the pixel row in an idle state, so as to continuously turn on the reset transistor.

[0042] The present invention adopts the above technical solution, which has the following beneficial effects compared with the prior art:

[0043] The present invention provides an image sensor driving method and image sensor for rolling exposure. During rolling exposure, the method determines the idle pixel rows in the image sensor pixel array and then outputs a gate transfer control signal to the transfer transistors of the pixel cells in the idle pixel rows to continuously turn on the transfer transistors. This solves the blooming phenomenon caused by image charge generated in the photodiodes of idle pixel cells overflowing into pixel cells in adjacent rows undergoing normal charge reading operations when the idle pixel cells are exposed to strong light. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 The figure is a schematic structural diagram of a pixel unit of an image sensor in the prior art.

[0045] Figure 2 This is a flowchart of a method for driving an image sensor for rolling exposure provided by an embodiment of the present invention.

[0046] Figure 3 A partial structural block diagram of an image sensor provided by one embodiment of the present invention.

[0047] Figure 4 150th row of pixel array according to an embodiment of the present invention.

[0048] Figure 5 FIG. 1 is a timing diagram of the relationship between the associated signals of rows 149-151 in a pixel array according to an embodiment of the present invention.

[0049] Figure 6 A schematic structural diagram of an image sensor provided by an embodiment of the present invention.

[0050] Figure 7 A gate driver structure diagram provided by an embodiment of the present invention DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments, and are only used to explain the present invention, not to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. In this patent specification, "one embodiment" or "one implementation method" refers to the specific features, structures or characteristics described in the example included in at least one embodiment of the present invention. The specific features, structures or characteristics may be included in integrated circuits, electronic circuits, combinational logic circuits or other suitable components that provide the described functionality. In addition, this specification only describes the content related to the present invention, and those skilled in the art can understand other content in conjunction with the prior art.

[0052] First, in order to better understand the present invention, before describing the present invention in detail, the image sensor-related parts involved in the embodiments of the present invention and the inventive concept of the present invention are generally described.

[0053] The image sensor includes a pixel array having a plurality of pixel units arranged in rows and columns. In the pixel array, all pixels (pixel units) in each column are simultaneously selected by a column select line, and all pixels in each row are selectively output by a row select line. Each pixel has a row address and a column address. The column address of the pixel corresponds to the column select signal line driven by the column driver unit, and the row address of the pixel corresponds to the row select signal line driven by the row driver unit. The control unit controls the row driver unit and the column driver unit to selectively read the pixels corresponding to the appropriate rows and columns in the pixel array to output image signals.

[0054] Please refer to Figure 1 , Figure 1FIG. 1 is a schematic diagram of a pixel unit of an image sensor in the prior art. Figure 1 As shown, each pixel cell in the pixel array includes a photodiode 10, a transfer transistor 11, a reset transistor 12, a source follower (SF) transistor 13, and a row select transistor 14, which is coupled to the transfer transistor 11 and the photodiode 10. An amplifier transistor in a source follower configuration is an amplifier transistor in which a signal is input at the gate and output at the source. During operation, the photodiode 10 generates photogenerated electrons in response to incident light during exposure. The transfer transistor 11 is coupled to receive a transfer signal TX, causing the transfer transistor 11 to transfer the charge accumulated in the photodiode 10 to a floating diffusion (FD) node 15. The floating diffusion node 15 is effectively the drain of the transfer transistor 11, while the photodiode 10 is the source of the transfer transistor 11. In one embodiment, the transfer transistor 11 is a metal oxide semiconductor field effect transistor (MOSFET). The reset transistor 12 is coupled between the power supply VDD and the floating diffusion node 15 to reset the pixel (e.g., discharge or charge the floating diffusion node 15 and the photodiode 10 to a predetermined voltage) in response to a reset signal RST. Floating diffusion node 15 is coupled to control the gate of source-follower transistor 13. Source-follower transistor 13 is coupled between power supply VDD and row select transistor 14 to amplify the signal generated by the charge on floating diffusion node 15. Row select transistor 14 couples the output of the pixel circuit from source-follower transistor 13 to a read column or bit line 16 in response to row select signal RS. Photodiode 10 and floating diffusion node 15 are reset by temporarily asserting reset signal RST and transfer signal TX. An accumulation period or accumulation window (e.g., exposure period) begins when transfer signal TX is deasserted, allowing incident light to be converted into photogenerated electrons in photodiode 10. As photogenerated electrons accumulate in photodiode 10, their voltage decreases (electrons are negative charge carriers). The voltage or charge on photodiode 10 during exposure represents the intensity of light incident on photodiode 10. After the exposure period ends, reset signal RST is deasserted, turning off reset transistor 12 and isolating floating diffusion node 15 from power supply VDD. Transfer signal TX is asserted, coupling photodiode 10 to floating diffusion node 15. Photogenerated electrons are transferred from the photodiode 10 to the floating diffusion node 15 through the transfer transistor 11 , causing the voltage of the floating diffusion node 15 to drop by an amount proportional to the photogenerated electrons accumulated on the photodiode 10 during the exposure period.

[0055] From the above description, it can be seen that during the operation of the image sensor, the pixel unit generally includes three states: reset, exposure, and reading under the control of the control unit and the driving unit. For the rolling exposure mode, the state of each row of pixels generally includes an idle state, a precharge state, an exposure state, and a sampling state, wherein the precharge state and the sampling state can also be understood as the aforementioned reset and reading states. It is precisely because each row of pixels in the rolling exposure mode has the above-mentioned multiple states, the timing characteristics of the rolling exposure, and the long and short exposure characteristics in the HDR mode that the pixels of the idle state pixel row will be overexposed (the pixels of the idle state row will also receive light), and then the charge overflows to the pixels of the adjacent rows, seriously affecting the charge accumulation of the pixels of the adjacent rows in the normal exposure state. Therefore, the technical solution of the embodiment of the present application performs corresponding control on the pixels in the idle state to solve the influence of the pixels of the idle state pixel row on the pixels of the sampling state pixel row, and plays an anti-blooming role.

[0056] Based on the above description, the present invention provides a driving method for an image sensor for rolling exposure, including the following detailed description of the specific technical solutions of the embodiments of the present application in conjunction with the accompanying drawings. Figure 2 , Figure 2 Flowchart of a method for driving an image sensor for rolling exposure according to an embodiment of the present invention. Figure 2 As shown, the method includes:

[0057] S1: Outputting a latch address signal based on an exposure row address signal, a read row address signal, an exposure row transfer signal, a read row transfer signal, and a latch enable signal;

[0058] S2: outputting a gate transfer control signal based on the exposure row address signal, the read row address signal, the exposure row transfer signal, the read row transfer signal, and the latch address signal; and

[0059] S3: When a pixel row in the image sensor pixel array is in an idle state, the gate transfer control signal is at a first level to continuously turn on the transfer transistors of the pixel units in the pixel row in the idle state.

[0060] Specifically, during rolling exposure, the pixel rows in the image sensor pixel array that are in an idle state are determined. During rolling exposure, the pre-charge rows (i.e., the pixel rows in the pre-charge state) and the sampling rows (i.e., the pixel rows in the sampling state or the reading state) are performed row by row, i.e., the pre-charge rows and the sampling rows are both one row, while there can be multiple exposure rows, i.e., there are multiple rows in the exposure state at the same time. By determining the pixel rows in the pixel array that are in an idle state, anti-overflow timing control is performed on the pixels in the idle pixel rows to prevent the over-exposed charge from overflowing to the normally exposed pixels in the adjacent rows. That is, a control signal is transmitted to the transfer transistor of the pixel unit in the pixel row in the idle state through the output gate, so as to continuously turn on the transfer transistor during the idle state, transfer the charge accumulated in the photodiode to the floating diffusion node, and prevent the charge in the photodiode of the pixel unit in the idle state from overflowing to the pixel unit in the adjacent row in the normally exposed state. The first level can be, for example, a high-level signal.

[0061] In one embodiment, step S3: when a pixel row in the image sensor pixel array is in an idle state, the gate transfer control signal is at a first level to continuously turn on the transfer transistors of the pixel units in the pixel row in the idle state, further comprising:

[0062] determining rows of pixels in an image sensor pixel array that are in an idle state;

[0063] The step of determining the pixel rows in the image sensor pixel array that are in an idle state includes:

[0064] The pixel row in the image sensor pixel array that is in an idle state is determined based on the exposure row address signal and the read row address signal. The exposure row address signal is used to indicate a row of pixels in the pixel array that is in a pre-charge state and ready to start exposure. The read row address signal is used to indicate a row of pixels in the pixel array that is in a read state.

[0065] Specifically, the exposure row address signal is also the precharge row address, i.e., the address of the pixel row in the precharge state. During rolling exposure, the exposure row address signal and the read row address signal are determined. A typical image sensor includes a row selection decoder. Based on the control signal provided by the control unit, the row decoder generates an address signal indicating a row of pixels in the pixel array for which a shutter operation (precharge operation or reset operation) is to be performed, and an address signal indicating a row of pixels from which pixel signals are to be read (sampled). The row decoder then provides these two address signals to the row driver unit to drive the corresponding pixel rows. Therefore, the state of the current pixel row can be determined based on the address signal provided by the image sensor.

[0066] In one embodiment, the step of determining a pixel row in an idle state in the image sensor pixel array according to the exposure row address signal and the read row address signal includes:

[0067] Determine the pixel row in the exposure state with a row address between the exposure row address signal and the read row address signal;

[0068] A pixel row that is not in a pre-charge state, an exposure state, and a read state is a pixel row in an idle state.

[0069] Specifically, since the exposure row address signal and the read row address signal are fixed, they scroll row by row in the scrolling mode, and the exposure row is between the pre-charge row and the read row. Therefore, the pixel row that is not in the pre-charge state, exposure state and read state is the idle pixel row.

[0070] In one embodiment, the method further includes: outputting a reset control signal to the reset transistors of the pixel units in the pixel row in the idle state to continuously turn on the reset transistors.

[0071] Specifically, for pixels in a pixel row that is in an idle state, in addition to continuously turning on the transfer transistor in the pixel, the reset transistor is also continuously turned on through a reset control signal, which is equivalent to keeping the photodiode in a pre-charge state. This can ensure that the voltage of the photodiode in the idle pixel can be kept constant even when the pixel is exposed to strong light, thereby better solving the impact of the idle pixel on the pixel in the reading (sampling) state.

[0072] In one embodiment, the method further comprises:

[0073] A first pulse signal is output to the transfer transistors of the pixel units in the pixel row in the precharge state to turn on the transfer transistors.

[0074] Specifically, in the pixel array, the transfer transistors of the pixel units in the pixel row in the pre-charge state are turned on by a first pulse signal to implement a pre-charge operation. The first pulse signal and the gate transfer control signal may be the same or different, that is, the gate transfer control signal may be used to control the transfer transistor to be turned on in the pre-charge state. In one embodiment, the transfer transistor may be controlled by different transfer control signals in different states, for example, the amplitude of the gate transfer control signal is smaller than the amplitude of the pulse signal, so that the degree of conduction of the transfer transistor of the pixel unit in the idle state is smaller than the degree of conduction of the transfer transistor of the pixel unit in the pre-charge state, that is, the transfer transistor may be partially turned on in the idle state, thereby saving power consumption.

[0075] In order to better illustrate the technical solution of the present application, the following is an explanation by combining a timing diagram of a specific pixel row in a pixel array.

[0076] Please refer to Figure 3 , Figure 3 This is a partial structural block diagram of an image sensor provided by an embodiment of the present invention. Figure 3 As shown, the image sensor includes a latch unit 31 and a gate driver 32. The latch unit 31 outputs a latch address signal lat_addb to the gate driver 32 according to the exposure row address signal sp_add, the read row address signal rp_add, the exposure row transfer signal sp_tx, the read row transfer signal rp_tx and the latch enable signal lat_en, so as to control the gate driver 32 to output a gate transfer control signal to the transfer transistor of the pixel in the idle state. The latch unit 31 outputs a latch address signal lat_addb based on the exposure row address signal sp_add, the read row address signal rp_add, the exposure row transmission signal sp_tx, the read row transmission signal rp_tx, and the latch enable signal lat_en; the gate driver 31 outputs a gate transmission control signal TX based on the exposure row address signal sp_add, the read row address signal rp_add, the exposure row transmission signal sp_tx, the read row transmission signal rp_tx, and the latch address signal lat_addb; when the pixel row in the image sensor pixel array is in an idle state, the gate transmission control signal TX is a first level (e.g., a high level) to continuously turn on the transmission transistors of the pixel units in the pixel row in the idle state. Wherein, when the latch enable signal lat_en is invalid, Figure 4 The waveform of the medium signal TX is output according to the existing waveform, that is, the lat_tx function is closed.

[0077] Based on the above structure diagram, please refer to Figure 4 , Figure 4 150th row of pixel array in the embodiment of the present invention. Figure 4 As shown, from the overall perspective, Figure 4 The two addresses (sp_add and rp_add) correspond to two times respectively, not the same time. The time difference is the exposure time in the middle. One row has one time and corresponds to one state. sp_add corresponds to the precharge row, and rp_add corresponds to the sample row. Precharge and sampling are both in one row, and there are 49 rows exposed between the two. Figure 4Taking row 150 (precharge) as an example, the reset control signal (RST) is low during the sample period and high at other times; in one embodiment, the transmission control signal (TX) has a pulse during the precharge and sample periods to start executing the corresponding operation, or in one embodiment, the transmission control signal (TX) has a pulse only during the sample period to start executing the corresponding operation, and is high during both the idle and precharge periods and does not change. Specifically,

[0078] At time T0, rp_add@row150=0, sp_add@row150=0, lat_addb@150=0, TX@row150=1; that is, the pixels in row 150 are in an idle state, and the row driver unit outputs a valid signal ( Figure 4 The transfer transistor of the pixel in the 150th row is turned on, and the potential of the photodiode PD remains constant, and no charge accumulation occurs.

[0079] At time T1, sp_add@row150=1, and when sp_tx=1, lat_addb@150 changes from low level to high level, that is, the pixels in row 150 change from idle state to precharge state; after the sp_tx pulse ends, the control signal TX of the transmission transistor of the pixels in row 150 is in invalid state ( Figure 4 ), TX@row150 changes from 1 to 0, and the transfer transistors of the pixels in the 150th row are turned off.

[0080] At time T2, i.e. during the exposure state, lat_addb@150=1, i.e. maintaining a high level, so that the control signal TX of the transfer transistor loaded on the 150th row of pixels is in an invalid state ( Figure 4 ), so that the transfer transistors of the pixels in the 150th row are turned off.

[0081] At time T3, i.e., the reading phase (sampling or quantization phase), rp_add@row150=1, and when rp_tx=1, lat_addb@150 changes from high level to low level, TX@row150=1; after the rp_tx pulse ends, TX@row150=0.

[0082] At time T4, that is, the idle state, rp_add@row150=0, sp_add@row150=0, lat_addb@150=0, TX@row150=1, and the transfer transistors of the pixels in the 150th row are in the on state.

[0083] Furthermore, during the entire timing period, the row selection signal ROWsel@row150 is a valid level signal only in the read state, and the reset control signal RST@row150 is a negative level signal only in the read state.

[0084] It is worth mentioning that the latch address signal lat_addb is 0 when the pixel behavior is in the idle state and 1 in other states, or it can be 1 in the idle state and 0 in other states. As a signal control, it is not limited here. And, when the latch enable signal lat_en is invalid, Figure 4 The waveform of the medium signal TX is output according to the existing waveform, that is, the lat_tx function is closed.

[0085] exist Figure 4 Further references based on Figure 5 , Figure 5 149-151 rows of pixel array in an embodiment of the present invention. Detailed descriptions can be found in the above descriptions and will not be repeated here.

[0086] In summary, the present invention provides a driving method for an image sensor for rolling exposure. During rolling exposure, the method determines the idle pixel rows in the image sensor pixel array and then outputs a gate transfer control signal to the transfer transistors of the pixel cells in the idle pixel rows to continuously turn on the transfer transistors. This method can thus address the blooming phenomenon caused by image charge generated in the photodiodes of idle pixel cells overflowing into pixel cells in adjacent rows undergoing normal charge reading operations when the idle pixel cells are illuminated by strong light.

[0087] The embodiment of the present invention also provides an image sensor, please refer to Figure 6 , Figure 6 A schematic diagram of the structure of an image sensor provided by an embodiment of the present invention is shown in FIG. Figure 6 As shown, the image sensor includes: a pixel array 60, a control unit 61, a driving unit (a row driving unit 621 and a column driving unit 622), wherein:

[0088] The pixel array 60 includes a plurality of pixel cells arranged in rows and columns, wherein each pixel cell includes:

[0089] a photodiode, which responds to incident light to accumulate image charge;

[0090] a transfer transistor coupled between the photodiode and the floating diffusion node to selectively transfer image charges accumulated in the photodiode to the floating diffusion node;

[0091] The control unit 61 is coupled to the driving unit (row driving unit 621 and column driving unit 622) and is used to determine the pixel rows in the pixel array 60 that are in an idle state during rolling exposure, and control the row driving unit 621 to output a gate transfer control signal to the transfer transistor of the pixel unit in the pixel row that is in the idle state to continuously turn on the transfer transistor.

[0092] In one embodiment, the control unit 61 determines a pixel row in an idle state in the pixel array 60 based on an exposure row address signal and a read row address signal. The exposure row address signal is used to indicate a row of pixels in the pixel array that is in a pre-charge state and is ready to start exposure. The read row address signal is used to indicate a row of pixels in the pixel array 60 that is in a read state.

[0093] In one embodiment, the control unit 61 determines the pixel rows in the exposure state using the row address between the exposure row address signal and the read row address signal, and the pixel rows that are not in the pre-charge state, exposure state, and read state are the pixel rows in the idle state.

[0094] In one embodiment, the control unit 61 includes a latch unit (ie Figure 3 31), the latch unit is used to output a latch signal based on the exposure row address signal and the read row address signal to control the driving unit to output a gate transfer control signal to the transfer transistor of the pixel unit in the pixel row in the idle state, so as to continuously turn on the transfer transistor. In one embodiment, the latch unit 31 is provided in the control unit 61, the gate driver 32 is provided in the row driving unit 621, and each pixel row corresponds to a latch unit and a gate driver. In another embodiment, the latch unit 31 and the gate driver 32 are both provided in the row driving unit 621, and each pixel row corresponds to a latch unit and a gate driver.

[0095] Specifically, in combination with the above description, the latch unit 31 outputs the latch address signal lat_addb (that is, the latch signal mentioned above, which is 0 when the pixel row is in the idle state and 1 in other states, or can also be 1 in the idle state and 0 in other states, which is not limited this time) to the row driving unit according to the exposure row address signal sp_add, the read row address signal rp_add, the exposure row transmission signal sp_tx, the read row transmission signal rp_tx and the latch enable signal lat_en, so as to control the row driving unit to output the gate transmission control signal to the transmission transistor of the pixel in the idle state.

[0096] Accordingly, the structure of the gate driver in the row driving unit 621 in the driving unit can refer to Figure 7 , Figure 7 This is a structural diagram of a gate driver provided by an embodiment of the present invention. Figure 7 As shown, the gate driver includes an exposure path 110, a read path 120, and a latch path 130. The first ends of the exposure path 110, the read path 120, and the latch path 130 are all connected to a positive voltage AVDD to pull the gate transmission control signal TX to a high level. The second ends of the exposure path 110, the read path 120, and the latch path 130 are all connected to a negative voltage NVDD to pull the gate transmission control signal TX to a low level. The exposure path 110 includes a first latch transistor, and the latch path 130 includes a second latch transistor. The storage transistor and the second latch transistor are used to receive the latch address signal lat_addb, perform a logical operation with the exposure row address signal sp_add, the read row address signal rp_add, the exposure row transmission signal sp_tx, and the read row transmission signal rp_tx (where sp_add and sp_addb are inverted signals, rp_add and rp_add are inverted signals, sp_tx and sp_txb are inverted signals, rp_tx and rp_txb are inverted signals, and so on), and then output the gate transmission control signal TX. In one embodiment, the latch path 130 includes a third latch transistor for receiving the latch address signal lat_addb and performing a logical operation with the exposure row address signal sp_add and the read row address signal rp_add to disable the latch function of the image sensor.

[0097] Specifically, Figure 7 The method is to add a latch transistor to the exposure path and a latch path 130 for outputting a gate transmission control signal according to the latch signal output by the latch unit 31 on the basis of the existing row driving unit (including the exposure path 110 and the reading path 120). That is, the latch path 130 outputs a transmission control signal of a corresponding level to the transmission transistor of the pixel row according to the latch address signal lat_addb, the exposure row address signal sp_add and the reading row address signal rp_add. For example, Figure 7 The upper two transistors of the middle latch path 130 (first type transistors such as PMOS transistors) output high level AVDD to the transfer transistor of the pixel row according to the input signal (latch address signal lat_addb and read row address signal rp_add), and the lower three transistors (second type transistors such as NMOS transistors) output low level NVDD to the transfer transistor of the pixel row according to the input signal (latch address signal lat_addb and the opposite level signal rp_addb of the read row address signal, and the opposite level signal sp_addb of the exposure row address signal). The other two columns of transistors (110 and 120) are existing sub-units for controlling pre-charging operations and reading operations, respectively, and will not be repeated here.

[0098] In one embodiment, the control unit 61 is further configured to control the driving unit to output a pulse signal to the transfer transistors of the pixel units in the pixel row in the pre-charge state, so as to turn on the transfer transistors.

[0099] In one embodiment, the amplitude of the gate transfer control signal is smaller than the amplitude of the pulse signal.

[0100] In one embodiment, when a pixel row in the image sensor pixel array is in an exposure state, the gate transfer control signal TX is at a second level (e.g., a low level) to continuously turn off the transfer transistor; when a pixel row in the image sensor pixel array is in a reading state, the gate transfer control signal TX is a second pulse signal to turn on the transfer transistor.

[0101] In one embodiment, each pixel unit further includes a reset transistor, and the control unit 61 is further configured to control the driving unit to output a reset control signal to the reset transistors of the pixel units in the pixel row in an idle state, so as to continuously turn on the reset transistors.

[0102] For the specific principle of the image sensor, please refer to the detailed description of the aforementioned embodiment, which will not be repeated here.

[0103] In summary, the image sensor provided by the present invention determines the idle pixel rows in the image sensor pixel array during rolling exposure, and then outputs a gate transfer control signal to the transfer transistors of the pixel cells in the idle pixel rows to continuously turn on the transfer transistors. This solves the blooming phenomenon caused by the image charge generated in the photodiodes of idle pixel cells overflowing into the pixel cells in adjacent rows undergoing normal charge reading operations when illuminated by strong light.

[0104] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of the technical contents disclosed above without departing from the scope of the technical solution of the invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the invention without departing from the content of the technical solution of the invention are still within the scope of the technical solution of the present invention.

Claims

1. A driving method for an image sensor used in rolling exposure, characterized in that: include: outputting a latch address signal based on the exposure row address signal, the read row address signal, the exposure row transfer signal, the read row transfer signal, and the latch enable signal; outputting a gate transfer control signal based on the exposure row address signal, the read row address signal, the exposure row transfer signal, the read row transfer signal, and the latch address signal; as well as When a pixel row in the pixel array of the image sensor is in an idle state, the gate transfer control signal is at a first level to continuously turn on the transfer transistor of the pixel unit in the pixel row in the idle state, and a reset control signal is output to the reset transistor of the pixel unit in the pixel row in the idle state to continuously turn on the reset transistor so that the voltage of the photodiode of the pixel unit is in a constant state; A first pulse signal is output to the transfer transistor of the pixel unit in the pixel row in the precharge state to turn on the transfer transistor, wherein the amplitude of the first level of the gate transfer control signal is smaller than the amplitude of the first pulse signal.

2. The method for driving an image sensor for rolling exposure according to claim 1, wherein: When a pixel row in the image sensor pixel array is in an idle state, the gate transfer control signal is at a first level to continuously turn on the transfer transistors of the pixel units in the pixel row in the idle state, further comprising: determining rows of pixels in an image sensor pixel array that are in an idle state; The step of determining the pixel rows in the image sensor pixel array that are in an idle state includes: The pixel rows in the image sensor pixel array that are in an idle state are determined based on the exposure row address signal and the read row address signal. The exposure row address signal is used to indicate a row of pixels in the pixel array that are in a pre-charge state and ready to start exposure. The read row address signal is used to indicate a row of pixels in the pixel array that are in a read state.

3. The method for driving an image sensor for rolling exposure according to claim 2, wherein: The step of determining a pixel row in an idle state in the image sensor pixel array according to the exposure row address signal and the read row address signal comprises: determining a pixel row in an exposure state with a row address between the exposure row address signal and the read row address signal; A pixel row that is not in the pre-charge state, the exposure state, and the read state is a pixel row in the idle state.

4. The method for driving an image sensor for rolling exposure according to claim 1, wherein: The method further comprises: The gate transfer control signal is continuously outputted to the transfer transistors of the pixel units in the pixel row in the pre-charge state to turn on the transfer transistors.

5. The method for driving an image sensor for rolling exposure according to claim 1, wherein: The method further includes: when the pixel row in the image sensor pixel array is in an exposure state, the gate transfer control signal is a second level to continuously turn off the transfer transistor; when the pixel row in the image sensor pixel array is in a reading state, the gate transfer control signal is a second pulse signal to turn on the transfer transistor.

6. An image sensor, characterized in that: include: Pixel array, control unit, driving unit, wherein, The pixel array includes a plurality of pixel units arranged in rows and columns, wherein each pixel unit includes: Reset transistor; a photodiode for accumulating image charge in response to incident light; and a transfer transistor coupled between the photodiode and a floating diffusion node to selectively transfer the image charge accumulated in the photodiode to the floating diffusion node; The control unit is coupled to the driving unit and is configured to determine a pixel row in the pixel array that is in an idle state during rolling exposure; Wherein, the image sensor further includes a latch unit and a gate driver; The latch unit outputs a latch address signal based on the exposure row address signal, the read row address signal, the exposure row transfer signal, the read row transfer signal, and the latch enable signal; The gate driver outputs a gate transfer control signal based on the exposure row address signal, the read row address signal, the exposure row transfer signal, the read row transfer signal, and the latch address signal; when a pixel row in the image sensor pixel array is in an idle state, the gate transfer control signal is at a first level to continuously turn on the transfer transistors of the pixel units in the pixel row in the idle state; The control unit is further configured to control the driving unit to output a reset control signal to the reset transistor of the pixel unit in the pixel row in an idle state, so as to continuously turn on the reset transistor so that the voltage of the photodiode of the pixel unit is in a constant state; The control unit is also used to control the driving unit to output a first pulse signal to the transfer transistor of the pixel unit in the pixel row in the pre-charge state to turn on the transfer transistor, and the amplitude of the first level of the gate transmission control signal is less than the amplitude of the first pulse signal.

7. The image sensor according to claim 6, wherein: The control unit determines a pixel row in an idle state in the pixel array based on the exposure row address signal and the read row address signal. The exposure row address signal is used to indicate a row of pixels in the pixel array that is in a pre-charge state and is ready to start exposure. The read row address signal is used to indicate a row of pixels in the pixel array that is in a read state.

8. The image sensor according to claim 7, wherein: The control unit determines the pixel rows in the exposure state using the row address between the exposure row address signal and the read row address signal, and the pixel rows that are not in the pre-charge state, the exposure state, and the read state are the pixel rows in the idle state.

9. The image sensor according to claim 6, wherein: The latch unit is arranged in the control unit, the gate driver is arranged in the driving unit, and each pixel row corresponds to a latch unit and a gate driver.

10. The image sensor according to claim 6, wherein: The latch unit and the gate driver are both arranged in the driving unit, and each pixel row corresponds to a latch unit and a gate driver.

11. The image sensor according to claim 6, wherein The gate driver includes an exposure path, a read path, and a latch path. The first ends of the exposure path, the read path, and the latch path are all connected to a positive voltage to pull the gate transmission control signal to a high level. The second ends of the exposure path, the read path, and the latch path are all connected to a negative voltage to pull the gate transmission control signal to a low level. The exposure path includes a first latch transistor, and the latch path includes a second latch transistor. The first latch transistor and the second latch transistor are used to receive the latch address signal to perform a logical operation with the exposure row address signal, the read row address signal, the exposure row transmission signal, and the read row transmission signal to output the gate transmission control signal.

12. The image sensor according to claim 11, wherein: The latch path includes a third latch transistor for receiving the latch address signal and performing a logic operation with the exposure row address signal and the reading row address signal to turn off the latch function of the image sensor.

13. The image sensor according to claim 6, wherein: When the pixel row in the image sensor pixel array is in an exposure state, the gate transfer control signal is at a second level to continuously turn off the transfer transistor; when the pixel row in the image sensor pixel array is in a reading state, the gate transfer control signal is a second pulse signal to turn on the transfer transistor.

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