A method for increasing frame rate of an image sensor

Abstract

The application discloses a method for improving frame rate of an image sensor, and relates to the technical field of image sensors.The method comprises the following steps: obtaining information that a reset signal of a first flip-flop is triggered, and resetting output states of all latches; setting set signals of the first flip-flop to 1 to latch selected pixel row states, wherein the set signals comprise an exposure state set signal and a data reading state set signal, and the states of the selected pixel rows are transmitted 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, and setting output states of the first flip-flop to 1; repeatedly selecting multiple pixel rows, and controlling first transmission control signals and second transmission control signals of corresponding rows to act, and corresponding transmission signals start to act.The method can realize simultaneous selection of multiple pixel rows, can make different rows in different states at the same time, reduces the time for reading a frame of image, and improves the frame rate.

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] One problem with the Tx driver circuit is that when selecting pixel actions, it can only operate one row at a time. That is, the first row enters the exposure state, the first row enters the read state, the second row enters the exposure state, the second row enters the read state, and so on. This makes it very long to output one frame of image.

[0008] As the number of pixels increases and the structure becomes more complex, the time required to output a single frame of an image also increases, necessitating improvements in readout methods to increase the frame rate. For example... Figure 4 and Figure 5 The state shown is as follows. Traditionally, when selecting a row of pixels, the corresponding row's Pix_address signal must remain at 1. The Pix_address signal is generated by a digital module, and only one row can have Pix_address = 1 within a given time period. Therefore, the following approach is adopted... Figure 3 The circuit structure allows selection of actions one row at a time.

[0009] To select two or more rows of pixels simultaneously ( Figure 4 , Figure 5 In the case of a specific state, multiple sets of Pix_address signals are needed to ensure that Pix_addresses in different rows are simultaneously equal to 1 within the same time period. However, this increases the area of ​​the digital module and complicates its design. Summary of the Invention

[0010] The purpose of this invention is to provide a method for improving the frame rate of an image sensor, which enables the simultaneous selection of multiple pixel rows, allowing different rows to be in different states at the same time, reducing the time to read a frame of image, and also making the control of pixel rows more diverse, enabling more action modes.

[0011] This invention is achieved through the following technical solution:

[0012] This invention provides a method for improving the frame rate of an image sensor, comprising:

[0013] Obtain the information that the reset signal of the first flip-flop has been triggered, and reset the output state of all latches;

[0014] The set signals of the first trigger are all set to 1 to latch the state of the selected pixel row. The set signals include the exposure state set signal and the data reading state set signal, and the state of the selected pixel row is passed to the first trigger.

[0015] Set both the reset and set signals of the first flip-flop to 0, and the state of the first flip-flop will remain unchanged. Set the output state of the first flip-flop to 1.

[0016] By repeatedly selecting multiple rows of pixels, the action of the first and second transmission control signals for the corresponding rows is controlled, and the corresponding transmission signals begin to operate.

[0017] Furthermore, 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 their action time, and the action time of both the first transmission control signal and the second transmission control signal is after the action time of the setting signal.

[0018] Furthermore, after the steps of actuating the first and second transmission control signals corresponding to the row, the method further includes:

[0019] A second trigger is used to separate the set signal from the transmission control signal.

[0020] Furthermore, the step of using a second trigger to separate the set signal from the transmission control signal specifically includes:

[0021] When the first trigger is in the latching exposure state and the data reading state, the second trigger is in the off state, the transmission control signal is 1, the output signal of the second trigger is 0, so the transmission signal is 0.

[0022] Furthermore, it also includes: after the state of the pixel row to be selected is latched, the second trigger is in the open state, the transmission control signal is 0, the state of the output signal of the first trigger is transmitted to the output signal of the second trigger, and the set signal of the first trigger and the transmission control signal are set to operate in the same time period.

[0023] Furthermore, the method further includes: setting the action time of the transmission control signal after the action interval of the set signal; acting after the set signal latches the state of all selected rows to the first trigger; when the transmission control signal is 0, transmitting the state of the output signal of the first trigger to the output signal of the second trigger; when the output signal of the second trigger is 1, the transmission signal follows the transmission control signal.

[0024] Furthermore, the method also includes: changing the time of the selected action state.

[0025] Furthermore, the specific timing of changing the selected action state includes: using the first cycle to latch the state of the pixel row, not controlling the transmission signal action, and shifting the exposure state of the pixel row to the next cycle.

[0026] Furthermore, setting the set signal and transmission control signal of the first trigger to operate within the same time period includes: coinciding the action time of the exposure state set signal with the action time of the first transmission control signal, thereby shortening the exposure state time.

[0027] Furthermore, setting the set signal and transmission control signal of the first trigger to operate within the same time period includes: coinciding the action time of the data reading state set signal with the action time of the second transmission control signal, thereby shortening the data reading state time.

[0028] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[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. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0031] Figure 1 This is a schematic diagram of a 4-pixel structure in the prior art;

[0032] Figure 2 This is a circuit diagram of a traditional Tx signal driving circuit.

[0033] Figure 3 A schematic diagram illustrating the state switching of n rows of pixels for a traditional Tx signal driving circuit.

[0034] Figure 4 This is a schematic diagram illustrating the overlap of exposure and data reading states in different rows in existing technologies.

[0035] Figure 5 This is a schematic diagram illustrating how the exposure and data reading states of different rows overlap in existing technologies.

[0036] Figure 6 A circuit diagram of a driving circuit for a Tx signal provided in the first embodiment of the present invention;

[0037] Figure 7 A flowchart of a method for improving the frame rate of an image sensor, provided in another embodiment of the present invention;

[0038] Figure 8This is a comparison diagram of the timing control between the traditional Tx signal driving circuit and the Tx signal driving circuit of this embodiment of the invention;

[0039] Figure 9 This is a timing control diagram showing abnormal Tx signal behavior during signal overlap.

[0040] Figure 10 A circuit diagram of a driving circuit for a Tx signal provided in another embodiment of the present invention;

[0041] Figure 11 This invention provides a timing control diagram for improving the frame rate of an image sensor, as another embodiment of the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0043] like Figure 6 As shown in the figure, an embodiment of the present invention provides a driving circuit for a Tx signal, including a Tx signal control structure and a latch structure connected together. A latch structure is added to the conventional circuit. The latch structure is implemented using a first flip-flop, and R (reset signal), S1 (exposure state set signal), and S2 (readout state set signal) are introduced to control the flip-flop. Simultaneously, to enable the exposure state and data readout state to be realized at the same time, the original state control signal Pix_pulse is changed to an exposure state control signal Pix_pulse1 controlling the exposure state and a data readout state control signal Pix_pulse2 controlling the data readout state.

[0044] This invention provides a driving circuit for a Tx signal. By adding a first flip-flop to a traditional circuit, the structure is simple, the circuit area is small, and costs are saved. This circuit can simultaneously select multiple pixel rows, allowing different rows to be in different states at the same time, reducing the time to read a frame of image, and also making the control of pixel rows more diverse, enabling more action modes.

[0045] like Figure 7 As shown, another embodiment of the present invention provides a method for improving the frame rate of an image sensor, comprising:

[0046] Obtain the information that the reset signal of the first flip-flop has been triggered, and reset the output state of all latches;

[0047] The set signals of the first trigger are all set to 1 to latch the state of the selected pixel row. The set signals include the exposure state set signal and the data reading state set signal, and the state of the selected pixel row is passed to the first trigger.

[0048] Set both the reset and set signals of the first flip-flop to 0, and the state of the first flip-flop will remain unchanged. Set the output state of the first flip-flop to 1.

[0049] By repeatedly selecting multiple rows of pixels, the action of the first and second transmission control signals for the corresponding rows is controlled, and the corresponding transmission signals begin to operate.

[0050] like Figure 8 As shown, in the traditional structure, the transmission signal Tx will only act in accordance with the action of the status control signal Pix_pluse when the address control signal Pix_address=1.

[0051] The working principle of the modified Tx circuit:

[0052] 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.

[0053] 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.

[0054] 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.

[0055] To adapt to more application scenarios, such as high-speed and nighttime applications, larger pixel sizes and higher HDR readout modes are required. This inevitably leads to situations where multiple rows of pixels are selected simultaneously, lengthening the period of the set signal S and thus increasing the time of one cycle (exposure state & data readout state). To avoid this, the circuit structure was further modified... Figure 6 A signal transmission structure is added to the circuit structure shown to separate the set signal S and the transmission control signal Tx_pulse.

[0056] like Figure 10 As shown, another embodiment of the present invention provides a driving circuit for a Tx signal, in Figure 6 The circuit structure shown is further enhanced by adding a latch state transmission structure. The Tx signal control structure, latch state transmission structure, and latch structure are connected sequentially, with the latch state transmission structure implemented using a second flip-flop. When the first flip-flop is latching the exposure state and data read state, the second flip-flop is in the off state, i.e., its output signal q = 0, ensuring that the transmission signal Tx output by the Tx signal control structure remains 0. Once the state of the pixel row to be selected is latched, the second flip-flop is in the on state, and the signal is passed on; that is, the state of the first flip-flop's output signal Q is passed to the second flip-flop's output signal q. This allows the set signal S and the transmission control signal Tx_pulse to be set within the same time period, further reducing the time required.

[0057] This invention provides a driving circuit for a Tx signal. By adding a first flip-flop and a second flip-flop to a traditional circuit, the structure is simple, the circuit area is small, and costs are saved. This circuit can set the set signal and the transmission control signal in the same time period, reducing the time to output one frame of image, further reducing time and improving the frame rate of the image sensor.

[0058] like Figure 11 As shown, a second flip-flop is added to the driving circuit of the Tx signal. 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 change in the action 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.

[0059] The action time of the transmission control signal SW is set after the action interval of the set signal S. It operates after the set signal S stores the state of all selected rows in the first trigger. When the transmission control signal SW=0, the state of all selected rows is transmitted from the output signal Q of the first trigger to the output signal q of the second trigger, where q=1. Then, the transmission signal Tx follows the transmission control signal Tx_pulse. Simultaneously, the timing of the action state also changes. The first cycle is used for latching the pixel row state, and the pixel signal Tx is not activated. The exposure state of the first row is shifted to the next cycle for activation.

[0060] like Figure 11 As shown, the action times of the exposure state setting signal S1 and the first transmission control signal Tx_pulse1 can coincide, thus shortening the exposure state time by t1; the action times of the data readout state setting signal S2 and the second transmission control signal Tx_pulse2 can coincide, thus shortening the data readout time by t2. Therefore, it can be concluded that for a frame of image with n exposure states and data readout states, the time shortened is n*(t1+t2).

[0061] The present invention provides a method for improving the frame rate of an image sensor by coinciding the exposure time and data reading time of (n-1) rows, and coinciding the time of the set signals S1 and S2 and the transmission control signal Tx_pulse, thereby reducing the time to output one frame of image and thus improving the frame rate. The effect is more significant when there are many pixel rows.

[0062] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for increasing the frame rate of an image sensor, characterized in that, include: Obtain the information that the reset signal of the first flip-flop has been triggered, and reset the output state of all latches; The set signals of the first trigger are all set to 1 to latch the state of the selected pixel row. The set signals include the exposure state set signal and the data reading state set signal, and the state of the selected pixel row is passed to the first trigger. Set both the reset and set signals of the first flip-flop to 0, and the state of the first flip-flop will remain unchanged. Set the output state of the first flip-flop to 1. By repeatedly selecting multiple rows of pixels, the action of the first and second transmission control signals of the corresponding rows is controlled, and the corresponding transmission signals begin to operate. Following the steps of actuating the first and second transmission control signals of the corresponding row, the method further includes: A second trigger is used to separate the set signal from the transmission control signal; The step of using a second trigger to separate the set signal from the transmission control signal specifically includes: When the first trigger is in the latching exposure state and the data reading state, the second trigger is in the off state, the transmission control signal is 1, the output signal of the second trigger is 0, and the transmission signal is 0. It also includes: after the state of the pixel row to be selected is latched, the second trigger is in the open state, the transmission control signal is 0, the state of the output signal of the first trigger is transmitted to the output signal of the second trigger, and the set signal of the first trigger and the transmission control signal are set to act in the same time period.

2. The method for increasing the frame rate of an image sensor according to claim 1, characterized in that, The method further includes: setting the action time of the transmission control signal after the action interval of the set signal; acting after the set signal latches the state of all selected rows to the first trigger; when the transmission control signal is 0, transmitting the state of the output signal of the first trigger to the output signal of the second trigger; when the output signal of the second trigger is 1, the transmission signal follows the transmission control signal.

3. The method for increasing the frame rate of an image sensor according to claim 1, characterized in that, The method also includes: changing the time of the selected action state.

4. The method for increasing the frame rate of an image sensor according to claim 3, characterized in that, The specific timing for changing the selected action state includes: using the first cycle to latch the state of the pixel row, not controlling the transmission signal action, and shifting the exposure state of the pixel row to the next cycle.

5. The method for increasing the frame rate of an image sensor according to claim 1, characterized in that, The action of setting the first trigger's set signal and transmission control signal to operate within the same time period includes: coinciding the action time of the exposure state set signal with the action time of the first transmission control signal, thereby shortening the exposure state time.

6. The method for increasing the frame rate of an image sensor according to claim 1, characterized in that, The actions of the set signal and the transmission control signal of the first trigger being set to operate within the same time period include: coinciding the action time of the data reading state set signal with the action time of the second transmission control signal, thereby shortening the data reading state time.

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