Method for measuring minimum exposure driving pulse width of image sensor chip

Abstract

The invention relates to a pulse width measuring system and method, in particular to a method for measuring the minimum exposure driving pulse width of an image sensor chip. In order to overcome the defect that the deviation between the theoretical minimum exposure driving pulse width and the actual minimum exposure driving pulse width of the image sensor chip is difficult to measure in the prior art, the method for measuring the minimum exposure driving pulse width of the image sensor chip comprises the following steps of: transmitting pulsed light and a light synchronizing signal; the light synchronization signal is output as two paths of initial synchronization trigger signals, one path of trigger signal and initial delay of the pulsed light are detected, the other path of trigger signal is used for controlling exposure starting of the image sensor to be detected, the other path of trigger signal is used for controlling the pulsed light generation moment to be gradually delayed from the-texp position of the initial exposure time, and the image sensor to be detected is obtained. And finding out a pulse light generation moment and an effective exposure starting alignment moment, and reducing the exposure time by taking the minimum exposure driving clock period of the to-be-detected image sensor as a step to obtain the minimum exposure driving pulse width of the to-be-detected image sensor.

Description

Technical Field

[0001] This invention relates to a pulse width measurement system and method, specifically to a method for measuring the minimum exposure driven pulse width of an image sensor chip. Background Technology

[0002] High temporal resolution imaging modules are widely used in experimental research on high-speed transient physical processes. By obtaining high temporal resolution images, they can reflect changes in ultrafast physical processes, explain ultrafast physical mechanisms, and have important application value in fields such as high-speed collision experiments and plasma physics research.

[0003] The core component of a high temporal resolution imaging module is the image sensor chip. The minimum exposure time of the image sensor chip directly affects its ability to capture transient motion or events, thus determining its temporal resolution capability. The minimum exposure time of the image sensor chip is the effective exposure time under the minimum exposure drive pulse width. Therefore, to obtain the minimum exposure time of the image sensor chip, it is necessary to first obtain its minimum exposure drive pulse width. However, in practical design, there is a certain deviation between the theoretical minimum exposure drive pulse width and the actual minimum exposure drive pulse width of the image sensor chip, and this deviation is often difficult to measure. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies where the deviation between the theoretical minimum exposure drive pulse width and the actual minimum exposure drive pulse width of image sensor chips is difficult to measure, and to provide a method for measuring the minimum exposure drive pulse width of image sensor chips.

[0005] To achieve the above objectives, the technical solution provided by this invention is as follows: A method for measuring the minimum exposure driving pulse width of an image sensor chip, characterized by the following steps: S1, obtain the minimum exposure drive clock cycle T, the initial exposure time texp for normal imaging, and the maximum effective gray value V of the image sensor chip under test; S2, emit pulsed light and optical synchronization signal, convert the pulsed light into an electrical signal, and convert the optical synchronization signal into a first trigger signal and a second trigger signal for synchronization, detect the initial delay between the first trigger signal and the electrical signal, that is, obtain the initial delay t0 between the first trigger signal and the generation of pulsed light; the second trigger signal is used to control the exposure of the image sensor chip under test to realize the imaging of pulsed light; The pulse width of the pulsed light is less than the minimum exposure drive clock period T; S3, adjust the intensity of the pulsed light to obtain the light intensity E when the image grayscale value is between 1 / 2 and 1 / 3 of the maximum effective grayscale value V of the image sensor under test. Fix the light intensity E, and the image sensor chip under test continuously acquires multiple images, calculating the average grayscale value u of the multiple images. a and standard deviation σ; S4, adjust the delay time t2=t0+texp of the second trigger signal to control the pulse light generation time t1 to be located at -texp of the exposure start time; S5, Set the light intensity E of the pulsed light. At the current moment when the pulsed light is generated, the image sensor chip under test performs imaging, continuously acquires multiple images, and calculates the average gray value u of the images. b ; S6, determine u b -u a Does the difference satisfy u? b -u a >±3σ; If so, the pulse light generation time is moved to the next time step by the minimum delay time Δt0, and S5 is returned; otherwise, the current pulse light generation time t3 is recorded and the process proceeds to step S7; the minimum delay time Δt0 is less than the minimum exposure drive clock period T. S7, set the pulse light intensity E and the pulse light generation time t3, and gradually decrease the exposure time in steps of the minimum exposure drive clock period T to control the image sensor chip under test to perform imaging at each exposure time until the imaging is abnormal. Based on the current step number K of the minimum exposure drive clock period T and the minimum exposure drive clock period T, calculate the minimum exposure drive pulse width texp. min .

[0006] Further, in step S6, the pulse light generation time t3 is calculated using the following formula: t3 = t0 + m × Δt0; Where m is the current number of steps with the minimum delay unit Δt0 as the step size, and m ≥ 0 and is an integer.

[0007] Furthermore, in step S6, the shift range of the pulse light generation time is [-texp, 2texp].

[0008] Furthermore, step S7 specifically includes: S7.1. Set the light intensity E of the pulsed light, the pulsed light generation time t3, and the initial exposure time texp; S7.2. Control the image sensor chip under test to perform imaging, and calculate the average gray value u of the image obtained at the current exposure time. c ; S7.3. Determine u c -ua Does the difference satisfy u? c -u a >±3σ; If not, then reduce the exposure time in steps of minimum exposure drive clock period T, and return to step S7.2; If so, the minimum exposure drive pulse width of the sensor of the image under test is calculated according to the following formula: texp min =texp-(K-1)×T.

[0009] Furthermore, in step S1, the maximum light intensity of the pulsed light is greater than the light intensity corresponding to the maximum effective gray value V of the image sensor under test; Maximum effective grayscale value V=2 n , where n is the maximum effective data bit width of the image sensor under test; In step S3, the number of multiple images is at least two.

[0010] Furthermore, in step S2, the pulsed light is an ultrashort pulsed light; In step S3, the number of images is 20.

[0011] The beneficial effects of this invention are: 1. The present invention has a simple process, synchronously emitting pulsed light and an optical synchronization signal, converting the pulsed light into an electrical signal, and outputting the optical synchronization signal as a synchronized first trigger signal and a second trigger signal. The initial delay between the first trigger signal and the electrical signal is detected, thereby obtaining the initial delay between the first trigger signal and the pulsed light. The second trigger signal is used to control the exposure to start, thus accurately determining the initial time difference between the exposure to start and the pulsed light. This solves the problem that when the exposure to start is directly triggered by the optical synchronization signal, the initial time difference between the exposure to start and the pulsed light cannot be accurately determined, thus improving the testing accuracy.

[0012] 2. The present invention uses an ultrashort pulse laser, which can scan the effective exposure start time position more precisely, thereby further improving the testing accuracy. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the measurement system structure in an embodiment of the present invention; Figure 2 This is a schematic diagram of exposure activation, pulsed light, and minimum exposure pulse width in an embodiment of the present invention.

[0014] Explanation of reference numerals in the attached figures: 1-Dark box, 2-Light inlet, 3-Pulsed laser, 4-Photodiode, 5-Pulse signal source, 6-Oscilloscope, 7-Imaging module, 8-Moving module, 9-Data processing module. Detailed Implementation

[0015] This invention relates to a method for measuring the minimum exposure driving pulse width of an image sensor chip, based on a system for measuring the minimum exposure driving pulse width of an image sensor chip, such as... Figure 1 As shown, it includes a dark box 1, a pulsed laser 3, a photodiode 4, a pulse signal source 5, an oscilloscope 6, an imaging module 7, a moving module 8, and a data processing module 9, with the data processing module 9 configured as a computer.

[0016] The dark box 1 is equipped with a light inlet 2, which provides a bright and dark light field environment for the image sensor chip under test, ensuring that the image sensor chip under test only receives pulsed light illumination during illumination, avoiding the influence of other light sources.

[0017] The pulsed laser 3 has a pulsed light output port, an external trigger input port, and an optical synchronization signal output port. The external trigger input port of the pulsed laser 3 is used to receive an external trigger signal to generate pulsed light and an optical synchronization signal. The optical synchronization signal output by the pulsed laser 3 is generated earlier than the pulsed light generation time, with an initial delay between them. The pulsed laser 3 can delay the pulsed light generation time in units of a minimum delay time Δt0. The pulsed light output port of the pulsed laser 3 is correspondingly set to the light inlet 2 of the dark chamber 1. The pulsed light is emitted to the light inlet 2 of the dark chamber 1 through the pulsed light output port of the pulsed laser 3. The pulsed laser 3 uses an ultrashort pulse laser.

[0018] The photodiode 4 is placed between the pulsed light output port of the pulsed laser 3 and the light inlet 2 of the dark box 1 to convert the pulsed light output by the pulsed laser 3 into an electrical signal output.

[0019] The external trigger input port of the pulse signal source 5 is connected to the optical synchronization signal output port of the pulse laser 3. The optical synchronization signal of the pulse laser 3 is output to the pulse signal source 5, and the pulse signal source 5 outputs it as two trigger signals, which are respectively denoted as the first trigger signal and the second trigger signal.

[0020] The oscilloscope 6 is connected to the electrical signal of the photodiode 4 and the first trigger signal generated by the pulse signal source 5, respectively, to detect the delay between the electrical signal and the first trigger signal, thereby obtaining the initial delay between the first trigger signal and the pulse light.

[0021] The imaging module 7 includes a test image sensor chip and an FPGA chip, which serve as the main functional chips. The test image sensor chip is located inside the dark chamber 1 and opposite the light inlet 2, and is used to image pulsed light to obtain corresponding image data. The FPGA chip serves as a control component, used to control the exposure time of the test image sensor chip, as well as to receive, store, and transmit the image data acquired by the test image sensor chip. The FPGA chip is also connected to a second trigger signal generated by the pulse signal source 3, and triggers the exposure of the test image sensor chip upon receiving the second trigger signal.

[0022] The movable module 8 is located at the bottom of the dark box 1 and connected to the imaging module 7. It is used to adjust the position of the imaging module 7. The imaging module 7 is fixed to the movable module 8 by a clamp. Adjusting the movable module 8 controls the test position of the imaging module 7 so that the pulse light generated by the pulse laser 3 is aligned with the image sensor chip under test, ensuring that the image sensor chip under test receives the pulse light.

[0023] Computer 9 is connected to the FPGA chip to receive and process image data sent by the FPGA chip.

[0024] Based on the above system, the minimum exposure driving pulse width measurement method for image sensor chips of the present invention specifically includes the following steps: Step 1: Obtain the minimum exposure drive clock cycle T, the initial exposure time texp for normal imaging, and the maximum effective grayscale value V of the image sensor chip under test, where V=2 n , where n is the maximum effective data bit width of the image sensor chip under test; Step 2: Control the pulsed laser 3 to generate pulsed light and optical synchronization signal. There is an initial delay between the pulsed light and the optical synchronization signal. The oscilloscope 6 detects the delay between the electrical signal of the photodiode 4 and the first trigger signal generated by the pulse signal source 5, thereby obtaining the initial delay t0 between the first trigger signal and the generation of pulsed light.

[0025] At this time, the first trigger signal and the second trigger signal are synchronous trigger signals. The imaging module receives the second trigger signal generated by the pulse signal source 5 and turns on the image sensor chip under test for exposure, that is, the exposure start time is earlier than the pulse light generation time t0.

[0026] In this invention, the maximum light intensity of the pulsed light is greater than the light intensity corresponding to the maximum effective gray value V of the image sensor under test.

[0027] Step 3: Adjust the intensity of the pulsed light. Use the initial exposure time texp to obtain the light intensity E when the image grayscale value is between 1 / 2 and 1 / 3 of the maximum effective grayscale value V of the image sensor under test. Fix the light intensity E and continuously acquire 20 images. The computer receives and calculates the average grayscale value u of the 20 images. a and standard deviation σ; In other embodiments of the present invention, the number of images acquired is adjusted according to the calculation accuracy, and is usually set to a minimum of 2 images.

[0028] Step 4: Determine the initial generation time t1 of the pulse light; Adjust the delay time t2 = t0 + texp of the second trigger signal of pulse signal source 5 to control the initial generation time t1 of the pulse light to be located at -texp of the exposure start time, such as... Figure 2 ① in the middle.

[0029] Step 5: Set the pulse light intensity E. At the current pulse light generation time, the image sensor chip under test performs imaging, continuously acquiring multiple images and calculating their average gray value u. b .

[0030] Step 6: Adjust the pulse light generation time, i.e., adjust its delay time with the optical synchronization signal. Repeat step 5, based on the u obtained after each adjustment. b -u a The difference is used to find the time t3 when the pulse generation time aligns with the effective exposure start time. The effective exposure start time is the earliest image formation position within the exposure range where the pulse generation location is located. Due to chip delays and other factors, the set exposure start time may not be the true exposure start time. Therefore, this step helps find the true exposure start time, i.e., the effective exposure start time. Specifically: According to u b -u a Determine whether the pulse light is generated at the effective exposure start time, i.e., u b -u a Does the difference satisfy u? b -u a >±3σ; If so, the pulse light is generated in the non-effective exposure area. Figure 2 In step ②, the image acquired at this time is abnormal. Using the smallest delay unit Δt0 as the step, the generation time of the pulse light is increased, and it is moved to the next moment. Then, return to step 5. The range of the generation time of the pulse light is [-texp, 2texp]. If not, i.e., u b -u a If ≤±3σ, then the pulse light generation time is aligned with the effective exposure start time, such as... Figure 2In step ③, the image obtained at this time is normal. Calculate and save the pulse light generation time t3=t0+m×Δt0, where m is the number of steps with the minimum delay unit Δt0 as the step, m≥0 and is an integer; proceed to step 7.

[0031] In a normal distribution, 3σ indicates that approximately 99.73% of the values ​​in the data will fall within the range of mean ± 3 times the standard deviation. In this invention, if the difference in the average gray values ​​of two images is less than ± 3σ, it means that the difference in the mean between the two datasets is within the normal fluctuation range. Therefore, this step uses this method to determine whether the location where the pulse light is generated is the effective exposure start time. The determination of the effective exposure start time is: the distribution characteristics of the image obtained at the effective exposure start time are similar to those of the image obtained at normal exposure.

[0032] Step 7: Set the light intensity E, the pulse generation time t3, and the exposure time; perform imaging; continuously acquire multiple images; calculate the average gray value u of the image obtained at the current exposure time. c ; The initial value for the exposure time is the initial exposure time texp, such as... Figure 2 [0-④] in the image can be imaged normally; Step 8, according to u c -u a The magnitude of the difference determines the minimum exposure drive pulse width texp min Specifically: Determine u c -u a Does the difference satisfy u? c -u a >±3σ; If not, normal imaging is possible. The exposure time is reduced by stepping the minimum exposure driving clock period T, and the process returns to step 7. If so, the imaging is abnormal, such as Figure 2 [0-⑥] in the code retrieves the current exposure time texp. K =texp-K×T, where K is the number of steps driven by the minimum exposure clock cycle T, K≥1 and is an integer; The minimum exposure drive pulse width of the sensor for the image under test is calculated using the following formula: texp min =texp-(K-1)×T; Minimum exposure drive pulse width as Figure 2 As shown in [0-⑤].

[0033] The system described above has a simple structure, with readily available components and low cost. It requires only common, easy-to-operate laboratory instruments and an FPGA chip to effectively test the minimum exposure drive pulse width of an image sensor chip. The measurement process of this invention is simple, achieving high-precision measurement using an ultrashort pulse laser and a high-precision pulse signal source.

[0034] The pulse width of the pulsed light and the minimum delay Δt0 of the pulsed light generation time are both much smaller than the minimum exposure drive clock period T. In this invention, using ultrashort pulsed light allows for the determination of the effective exposure start time position by scanning within the normal imaging exposure time. In other embodiments of this invention, other pulsed lights can also be used, but their pulse width must be smaller than the minimum exposure drive clock period T. The specific reason is: assuming the pulse width of the pulsed light is greater than the minimum exposure drive clock period T, and the actual effective exposure start time position of the chip is at (1 / 2)T, then when the pulsed light generation position is at time 0, an image can still be measured, which will lead to an incorrect measurement of the effective exposure position. Meanwhile, assuming the minimum delay Δt0 of the pulse light generation time is greater than the minimum exposure drive clock period T, when the actual minimum exposure drive pulse width of the image sensor chip under test is T, and the effective exposure start time is (1 / 2)T, in the process of moving the pulse light generation position with the minimum delay Δt0 to determine the pulse light position at the effective exposure start time, it is possible to determine the effective exposure start time position after the minimum exposure drive clock period T (assuming it is at 2T). Therefore, in the process of reducing the exposure time in steps of the minimum exposure drive clock period T, when the exposure time is reduced to the minimum exposure drive pulse width T, the pulse light position is outside the exposure area, resulting in an imaging error. This leads to the mistaken assumption that the actual minimum exposure drive pulse width of the chip is greater than T, causing a test error. Therefore, the smaller the pulse width of the pulse light and the minimum delay Δt0 of the pulse light generation time, the more accurate the measured minimum exposure drive pulse width.

Claims

1. A method for measuring the minimum exposure driving pulse width of an image sensor chip, characterized in that, The method comprises the following steps: S1, obtaining a minimum exposure driving clock period T of a to-be-tested image sensor chip, an initial exposure time texp at which the to-be-tested image sensor chip can normally image, and a maximum effective gray value V; S2, emitting pulsed light and a light synchronization signal, converting the pulsed light into an electric signal, converting the light synchronization signal into a first trigger signal and a second trigger signal, detecting an initial delay of the first trigger signal from the electric signal, i.e., obtaining an initial delay t0 between the first trigger signal and the pulsed light, and using the second trigger signal to control exposure opening of the to-be-tested image sensor chip to realize imaging of the pulsed light; A pulse width of the pulsed light is less than the minimum exposure driving clock period T; S3, adjusting the light intensity of the pulsed light, obtaining the light intensity E when the image gray value is between 1 / 2-1 / 3 of the maximum effective gray value V of the to-be-measured image sensor, fixing the light intensity as E, and the to-be-measured image sensor chip continuously collects multiple images, and calculates the average gray value u of the multiple images a and the standard deviation σ; S4, adjusting a delay time t2 of the second trigger signal as t2=t0+texp, and controlling a pulsed light generation time t1 to be located at -texp of the exposure opening time; S5, set the light intensity E of the pulse light, at the current pulse light generation moment, the image sensor chip to be measured performs imaging, a plurality of images are continuously acquired and the average gray value u of the images is calculated b ; S6, judge whether the difference of u b - u a whether the difference of u b - u a > ± 3σ; If yes, moving the pulsed light generation time to a next time by a minimum delay time Δt0 as a step, and returning to S5; if no, recording a current pulsed light generation time t3, and entering step S7; the minimum delay time Δt0 is less than the minimum exposure driving clock period T. S7, set the light intensity E of the pulse light, the pulse light generation time t3, gradually reduce the exposure time with the minimum exposure driving clock period T as a step, control the image sensor chip to be tested to image under each exposure time until the imaging is not normal, and calculate the minimum exposure driving pulse width texp according to the step number K of the current step with the minimum exposure driving clock period T and the minimum exposure driving clock period T min .

2. The method according to claim 1, wherein: In step S6, the pulsed light generation time t3 is calculated by the following formula: t3=t0+m×Δt0; wherein m is a step number of stepping by the minimum delay unit Δt0, m≥0 and is an integer.

3. The method according to claim 2, wherein: In step S6, a moving range of the pulsed light generation time is [-texp, 2texp].

4. The method for measuring the minimum exposure drive pulse width of an image sensor chip according to any one of claims 1-3, characterized in that, Step S7 is specifically: S7.

1. setting a light intensity E of the pulsed light, the pulsed light generation time t3, and the initial exposure time texp; S7.

2. Control the image sensor chip under test to perform imaging, calculate the average gray value u of the image obtained under the current exposure time c ; S7.

3. Determine u c - u a if the difference of u c - u a > ± 3σ; If no, stepping by the minimum exposure driving clock period T to reduce the exposure time, and returning to step S7.2; If yes, calculating the minimum exposure driving pulse width of the to-be-tested image sensor according to the following formula: texp min = texp - (K - 1) x T.

5. The method according to claim 4, wherein: In step S1, a maximum light intensity of the pulsed light is greater than a light intensity corresponding to the maximum effective gray value V of the to-be-tested image sensor; Maximum effective gray value V = 2 n wherein n is the maximum effective data bit width of the image sensor to be measured. In step S3, a number of the multiple images is at least 2.

6. The method according to claim 5, wherein: In step S2, the pulsed light is ultra-short pulsed light; In step S3, the number of the multiple images is 20.

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