Method for improving frame rate of image sensor

Abstract

The invention discloses a method for improving the frame rate of an image sensor, and relates to the technical field of image sensors, and the method comprises the steps: obtaining the triggered information of a reset signal of a first trigger, and resetting the output states of all latches; setting the setting signals of the first trigger as 1 to latch a selected pixel row state, the setting signals including an exposure state setting signal and a data reading state setting signal, and transmitting the state of the selected pixel row to the first trigger; setting a reset signal and a set signal of the first trigger to be 0, keeping the state of the first trigger all the time, and setting the output state of the first trigger to be 1; and repeatedly selecting multiple rows of pixels, controlling the first transmission control signal and the second transmission control signal of the corresponding row to act, and starting the corresponding transmission signal to act. According to the method, multiple pixel rows can be selected at the same time, different rows can be in different states at the same time, the time for reading one frame of image is shortened, and the frame rate is improved.

Description

Technical Field

[0001] This invention relates to the field of image sensor technology, and more specifically to a method for improving the frame rate of an image sensor. Background Technology

[0002] As people's demands for image quality increase, the number of rows and columns of pixels is also increasing. With a larger number of rows and columns, the pixel readout time also increases accordingly, leading to low frame rates. Traditional methods to improve frame rates include increasing the number of column ADCs, but this results in a significant increase in the image sensor area, which is difficult to implement when chip area is a constraint.

[0003] like Figure 1 As shown, this is a 4-transistor structure for a single pixel. The Tx signal controls the charge transfer from the photodiode (PD) to the FD. The Rx signal controls the charge reset of the FD. The MOSFET at Dx and the MOSFET controlled by the Sx signal form a source follower. The switching on and off of the MOSFET connected to Sx directly affects the signal output. When the MOSFET controlled by the Rx signal is off, the MOSFET controlled by the Sx signal is on, and the MOSFET controlled by the Tx signal is also on, the change in voltage at FD is transferred to V_pix.

[0004] The Tx signal controls the transfer of accumulated charge in the photodiode, making its control crucial. The following section introduces the traditional driving circuit for the Tx signal.

[0005] like Figure 2 As shown, the traditional Tx signal driving circuit structure consists of a NAND gate and an inverter. Its working principle is as follows: when the first row of pixels needs to be selected, Pix_address1=1, and the output state of Tx1 is determined by Tx_pulse. We can control Tx by controlling the state of Tx_pulse. Pix_address and Tx have a one-to-one correspondence, and at any given time, only one Pix_address is 1; for example, Pix_address1=1, and all other Pix_addresses=0.

[0006] like Figure 3 As shown, the traditional Tx signal driving circuit reads the time of n rows of pixels. Only one row of pixels can be selected at any given time, and the exposure state and data reading state of each row of pixels are completely separated.

[0007] The problem of the Tx driving circuit is that when selecting the pixel action, it can only act on one row at a time, that is, the first row enters the exposure state, the first row enters the reading state, the second row enters the exposure state, the second row enters the reading state, and so on. The time required to output a frame of image is very long.

[0008] With the increase in the number of pixels and the complexity of the structure, the time required to output a frame of image is also increasing, so it is necessary to improve the readout mode to improve the frame rate. For example Figure 4 and Figure 5 When selecting a certain row of pixels, the corresponding row of Pix_address signals must always be maintained as 1. The Pix_address signal is generated by a digital module, and only one row of Pix_address=1 can be maintained in a time period. Therefore, the circuit structure of Figure 3 can only act on one row at a time.

[0009] When two or more rows of pixels are selected at the same time Figure 4 , Figure 5 , the digital module needs to provide multiple sets of Pix_address signals so that the Pix_address signals of different rows can be 1 at the same time. However, this will increase the area of the digital module and complicate the design of the digital module. SUMMARY

[0010] The purpose of the present application is to provide a method for improving the frame rate of an image sensor, which can select multiple rows of pixels at the same time, can make different rows in different states at the same time, can reduce the time required to read a frame of image, and can also make the control of the pixel row more diversified and can realize more action modes.

[0011] The present application is realized by the following technical solutions: The method for improving the frame rate of an image sensor provided by the embodiment of the present application comprises: obtaining information that the reset signal of the first flip-flop is triggered, and resetting the output state of all the latches; setting the set signal of the first flip-flop to 1 to latch the selected pixel row state, the set signal including an exposure state set signal and a data reading state set signal, and transmitting the state of the selected pixel row into the first flip-flop; setting the reset signal and the set signal of the first flip-flop to 0, keeping the state of the first flip-flop, and setting the output state of the first flip-flop to 1; repeating the selection of multiple rows of pixels multiple times, controlling the action of the first transmission control signal and the second transmission control signal of the corresponding row, and starting the action of the corresponding transmission signal.

[0012] Further, the first transmission control signal and the exposure state setting signal, and the second transmission control signal and the data reading state setting signal do not overlap in action time, and the first transmission control signal and the second transmission control signal are both after the setting signal in action time.

[0013] Further, the method further comprises, after the step of controlling the first transmission control signal and the second transmission control signal of the corresponding row to act: The second flip-flop separates the setting signal and the transmission control signal.

[0014] Further, the second flip-flop separates the setting signal and the transmission control signal specifically comprises: When the first flip-flop is in the latch exposure state and the data reading state, the second flip-flop is in the closed state, the transfer control signal is 1, the output signal of the second flip-flop is 0, and the transmission signal is 0.

[0015] Further, it further comprises: after the selected pixel row state is latched, the second flip-flop is in the open state, the transfer control signal is 0, the state of the first flip-flop output signal is transmitted to the output signal of the second flip-flop, and the setting signal and the transmission control signal of the first flip-flop are set to act at the same time.

[0016] Further, the method further comprises: the action time of the transfer control signal is set after the action interval of the setting signal, and the transfer control signal is 0 after the setting signal latches the state of all selected rows to the first flip-flop. When the output signal of the first flip-flop is transmitted to the output signal of the second flip-flop, the output signal of the second flip-flop is 1, and the transmission signal follows the transmission control signal to act.

[0017] Further, the method further comprises: changing the time of the selected action state.

[0018] Further, the method further comprises: changing the time of the selected action state.

[0019] Further, the first flip-flop setting signal and the transmission control signal are set to act at the same time, which comprises: the action time of the exposure state setting signal coincides with the action time of the first transmission control signal, and the exposure state time is shortened.

[0020] Further, the first flip-flop setting signal and the transmission control signal are set to act at the same time, which comprises: the action time of the data reading state setting signal coincides with the action time of the second transmission control signal, and the data reading state time is shortened.

[0021] Compared with the prior art, the present application has the following advantages and beneficial effects: The method for improving the frame rate of an image sensor provided by the embodiment of the present application can realize simultaneous selection of multiple pixel rows, can make different rows simultaneously in different states, reduces the time for reading a frame of image, improves the frame rate, and makes the control of pixel rows more diversified and can realize more action modes. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be considered as a limitation to the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor. In the drawings: Figure 1 It is a schematic diagram of the pixel 4 tube structure in the prior art; Figure 2 It is a circuit diagram of the driving circuit of the traditional Tx signal; Figure 3 It is a state switching schematic diagram of reading n rows of pixels of the driving circuit of the traditional Tx signal; Figure 4 It is a schematic diagram of the exposure state and the data reading state of different rows in the prior art; Figure 5 It is a schematic diagram of the exposure state and the data reading state of different rows in the prior art; Figure 6 It is a circuit diagram of the driving circuit of the Tx signal provided by the first embodiment of the present application; Figure 7 It is a flowchart of the method for improving the frame rate of an image sensor provided by another embodiment of the present application; Figure 8 It is a timing control comparison diagram between the driving circuit of the traditional Tx signal and the driving circuit of the Tx signal of the embodiment of the present application; Figure 9 It is a timing control diagram of the abnormal action of the Tx signal when the signals overlap; Figure 10 It is a circuit diagram of the driving circuit of the Tx signal provided by another embodiment of the present application; Figure 11 It is a timing control diagram of the method for improving the frame rate of an image sensor provided by another embodiment of the present application. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below with reference to the embodiments and drawings, the illustrative embodiments of the present application and the description thereof are only used to explain the present application, and do not limit the present application.

[0024] As shown in Figure 6 The Tx signal driving circuit provided by the embodiment of the present application comprises a Tx signal control structure and a latch structure connected with each other. The latch structure is realized by a first flip-flop, and R (reset signal), S1 (exposure state setting signal) and S2 (data reading state setting signal) are introduced to control the flip-flop. In order to realize the exposure state and the data reading state at the same time, the original state control signal Pix_pulse is changed into the exposure state control signal Pix_pulse1 and the data reading state control signal Pix_pulse2.

[0025] The Tx signal driving circuit provided by the embodiment of the present application adds the first flip-flop to the traditional circuit, and has simple structure, small circuit area and low cost. The circuit can realize the simultaneous selection of multiple pixel rows, and can make different rows in different states at the same time, thereby reducing the time for reading a frame of image and making the control of the pixel rows more diversified and realizing more action modes.

[0026] As shown in Figure 7 The method for improving the frame rate of the image sensor provided by another embodiment of the present application comprises the following steps. The information that the reset signal of the first flip-flop is triggered is acquired, and the output states of all the latches are reset. The setting signals of the first flip-flop are all set to 1 to latch the selected pixel row state, and the setting signals comprise the exposure state setting signal and the data reading state setting signal. The state of the selected pixel row is transmitted into the first flip-flop. The reset signal and the setting signal of the first flip-flop are both set to 0, and the state of the first flip-flop is always kept. The output states of the first flip-flop are all set to 1. The selected pixel rows are repeated multiple times, and the first transmission control signal and the second transmission control signal of the corresponding row are controlled to act, and the corresponding transmission signal starts to act.

[0027] As shown in Figure 8 In the traditional structure, when the address control signal Pix_address=1, the transmission signal Tx will act following the action of the state control signal Pix_pluse.

[0028] Working principle of the modified Tx circuit: On the far left of the waveform, the R signal of the first flip-flop is triggered first, resetting the states of all latches so that Q1=Q2=……=Q(n)=0 (state cleared). Then, the address control signals Pix_address of the pixel rows to be selected are sequentially set to 1. During the time Pix_address=1, the S signal only needs to be set to 1 to transmit the pixel row selection state to the first flip-flop. Then, R=S=0 is set, and the state inside the first flip-flop remains unchanged. Repeating this process multiple times allows multiple rows of pixels to be selected in a short time, i.e., Q1=Q2=……=Q(n=1). After the pixel rows are selected, the exposure state control signal Pix_pulse1 and the data read state control signal Pix_pulse2 are activated, thus starting the transmission signal Tx for the corresponding pixel rows. If the data read state of each row coincides with the exposure state of the next row, the exposure state time for (n-1) rows can be saved.

[0029] This invention provides a method for improving the frame rate of an image sensor. By using a trigger as a latching structure to latch the state of selected row pixels, the exposure state and data reading state of row pixels in different rows can be latched simultaneously. This allows multiple pixel rows to be selected at the same time, enabling different rows to be in different states simultaneously. This reduces the time to read a frame of image, improves the frame rate, and also makes the control of pixel rows more diverse, enabling more action modes.

[0030] The first trigger first sets the address control signal Pix_address of the pixel row to be selected to 1, latching the state of the selected pixel row. The trigger controlled by the exposure state set signal S1 latches the exposure state, and the trigger controlled by the data read state set signal S2 latches the data read state. After the state of the pixel row to be controlled is selected, the first transmission control signal Tx_Pulse1 and the second transmission control signal Tx_pulse2 are activated. However, the exposure state set signal S1 and the first transmission control signal Tx_pulse1, data read state set signal S2 and the second transmission control signal Tx_pulse2 must not overlap in time. The action of the transmission control signal Tx_pulse should be after the set signal S. This is because the state of the selected pixel row can only be transmitted to the latch after the set signal S is activated. If the above signals overlap, the following will occur: Figure 9 The shortened duration of the Tx signal (1) causes electrons in the photodiode (PD) of the nth row to not be fully transferred to the floating diffusion region (FD), resulting in image quality defects. Therefore, by separating the action time intervals of the set signal and the transmission control signal Tx_pulse, the exposure state and data readout state times are extended. The absence of temporal overlap between the set signal and the transmission control signal ensures the quality of the transmitted image.

[0031] To adapt to more application scenarios, such as high speed, night and other more extreme application scenarios, a larger pixel size and a higher readout mode of HDR are required, and then the situation of multiple rows of pixels being selected together will occur, the action period of the set signal S will be longer, and the time of one cycle (exposure state & data read state) will be longer. In order to avoid the occurrence of the above situation, the circuit structure is continuously modified, and a signal transmission structure is added to the circuit structure as shown in the figure to separate the set signal S and the transmission control signal Tx_pulse. Figure 6

[0032] As shown in the figure, another embodiment of the present application provides a Tx signal driving circuit, and a latch state transmission structure is added to the circuit structure as shown in the figure. Figure 10 Figure 6 When the first flip-flop is latching the exposure state and the data read state, the second flip-flop is in a closed state, that is, the output signal q of the second flip-flop is 0, so that the transmission signal Tx output by the Tx signal control structure is always 0; when the selected pixel row state is latched, the second flip-flop is in an open state, and the signal is transmitted backward, that is, the state of the output signal Q of the first flip-flop is transmitted to the output signal q of the second flip-flop. In this way, the set signal S and the transmission control signal Tx_pulse can be set in the same time period, and the time is further reduced.

[0033] The Tx signal driving circuit provided by the embodiment of the present application adds a first flip-flop and a second flip-flop to the traditional circuit, and has the advantages of simple structure, small circuit area and cost saving. The circuit can set the set signal and the transmission control signal in the same time period, reduce the time of outputting one frame of image, further reduce the time, and improve the frame rate of the image sensor.

[0034] As shown in the figure, a second flip-flop is added to the Tx signal driving circuit, and the transmission control signal of the second flip-flop is SW. When the transmission control signal SW=1, the signal is not transmitted, and the action change of the output signal Q of the first flip-flop will not affect the output signal q of the second flip-flop; when the transmission control signal SW=0, the state of the output signal Q of the first flip-flop is transmitted to the output signal q of the second flip-flop. Figure 11

[0035] ​​​The action time of the transfer control signal SW is set after the action interval of the set signal S, and the set signal S stores the state of all selected rows in the first flip-flop after the action, when the transfer control signal SW=0, the state of all selected rows is transferred from the output signal Q of the first flip-flop to the output signal q of the second flip-flop, q=1, and then the transmission signal Tx follows the action of the transmission control signal Tx_pulse. At the same time, the time of the action state also changes, the first cycle is used for the latch of the pixel row state, and the action of the pixel signal Tx is not performed, and the exposure state of the first row is moved to the next cycle for action.

[0036] As shown in Figure 11 The action time of the exposure state set signal S1 and the first transmission control signal Tx_pulse1 can be overlapped, and the exposure state can be shortened by t1; the action time of the data reading state set signal S2 and the second transmission control signal Tx_pulse2 can be overlapped, and the data reading state can be shortened by t2. Therefore, the time that can be shortened by n times of exposure state and data reading state of one frame of image is n*(t1+t2).

[0037] The method for improving the frame rate of the image sensor provided by the embodiment of the present application can overlap the exposure time and the data reading time of (n-1) rows, overlap the set signals S1 and S2 and the transmission control signal Tx_pulse, reduce the time for outputting one frame of image, and further improve the frame rate, and the effect is more significant in the case of more pixel rows.

[0038] The above-described specific embodiments further explain the purpose, technical solutions and beneficial effects of the present application, and it should be understood that the above-described specific embodiments are only specific embodiments of the present application, and are not used to limit the protection scope of the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method of increasing frame rate of an image sensor, the method comprising: The method comprises: acquiring information that a reset signal of a first flip-flop is triggered, and resetting output states of all latches; setting all set signals of the first flip-flop to 1 to latch selected pixel row states, the set signals comprising an exposure state set signal and a data reading state set signal, and transmitting the states of the selected pixel rows into the first flip-flop; setting the reset signal and the set signal of the first flip-flop to 0, and keeping the state of the first flip-flop unchanged, and setting all output states of the first flip-flop to 1; repeating the selection of multiple pixel rows, and controlling the first transfer control signal and the second transfer control signal of the corresponding row to act, and the corresponding transfer signal starts to act.

2. The method of increasing frame rate of an image sensor of claim 1, wherein, The first transfer control signal and the exposure state set signal, the second transfer control signal and the data reading state set signal do not overlap in the action time, and the action time of the first transfer control signal and the second transfer control signal is after the action time of the set signal.

3. The method of increasing the frame rate of an image sensor according to claim 1 or 2, wherein, The method further comprises: using a second flip-flop to separate the set signal and the transfer control signal.

4. The method of increasing the frame rate of an image sensor of claim 3, wherein, The method of using the second flip-flop to separate the set signal and the transfer control signal specifically comprises: when the first flip-flop is latching the exposure state and the data reading state, the second flip-flop is in a closed state, the transmission control signal is 1, the output signal of the second flip-flop is 0, and the transfer signal is 0.

5. The method of increasing the frame rate of an image sensor of claim 4, wherein, The method further comprises: after the state of the selected pixel row is latched, the second flip-flop is in an open state, the transmission control signal is 0, the state of the output signal of the first flip-flop is transmitted to the output signal of the second flip-flop, and the set signal and the transfer control signal of the first flip-flop are set to act at the same time.

6. The method of increasing the frame rate of an image sensor of claim 5, wherein, The method further comprises: setting the action time of the transmission control signal after the action interval of the set signal, and the transmission control signal acts after the set signal latches the states of all selected rows to the first flip-flop, when the transmission control signal is 0, the state of the output signal of the first flip-flop is transmitted to the output signal of the second flip-flop, and when the output signal of the second flip-flop is 1, the transfer signal follows the transfer control signal to act.

7. The method of increasing the frame rate of an image sensor of claim 6, wherein, The method further comprises: changing the time of the selected action state.

8. The method of increasing the frame rate of an image sensor of claim 7, wherein, The method of changing the time of the selected action state specifically comprises: using the first period to latch the state of the pixel row, and not controlling the transfer signal to act, and moving the exposure state of the pixel row to the next period.

9. The method of increasing the frame rate of an image sensor of claim 5, wherein, The method of setting the set signal and the transfer control signal of the first flip-flop to act at the same time specifically comprises: coinciding the action time of the exposure state set signal with the action time of the first transfer control signal, and shortening the exposure state time.

10. The method of increasing the frame rate of an image sensor of claim 5, wherein, The method of setting the set signal and the transfer control signal of the first flip-flop to act at the same time specifically comprises: coinciding the action time of the data reading state set signal with the action time of the second transfer control signal, and shortening the data reading state time.

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