CN112449125B - Image sensor reading circuit based on self-adaptive threshold adjustment - Google Patents
Image sensor reading circuit based on self-adaptive threshold adjustment Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/60—Noise processing, e.g. detecting, correcting, reducing or removing noise
- H04N25/65—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to reset noise, e.g. KTC noise related to CMOS structures by techniques other than CDS
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/50—Control of the SSIS exposure
- H04N25/57—Control of the dynamic range
- H04N25/58—Control of the dynamic range involving two or more exposures
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/70—SSIS architectures; Circuits associated therewith
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/70—SSIS architectures; Circuits associated therewith
- H04N25/71—Charge-coupled device [CCD] sensors; Charge-transfer registers specially adapted for CCD sensors
- H04N25/75—Circuitry for providing, modifying or processing image signals from the pixel array
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Abstract
An image sensor readout circuit based on adaptive threshold adjustment, comprising: the pixel array, the row addressing circuit, the related double sampling circuit, the column level amplifier, the comparator, the counter, the adaptive threshold value adjusting logic and the ramp generator; the key technology of the invention is that the real-time adjustment of the threshold value in the chip is realized by introducing a comparator, a slope generator, a counter and self-adaptive threshold value adjustment logic, and the dynamic range of the image sensor is improved. The circuit adopts a self-adaptive threshold value adjusting circuit, the threshold value is adjusted in real time according to the actual exposure, and the threshold value is quickly adjusted by using a digital logic circuit, so that the image details of high brightness and high darkness can be simultaneously acquired under a certain frame frequency, and the dynamic range of the image sensor is improved.
Description
Technical Field
The invention relates to a quantum image sensor, in particular to a readout circuit of a multi-carrier single-bit quantum image sensor, namely an image sensor readout circuit based on adaptive threshold adjustment.
Background
The quantum image sensor is a third generation solid-state image sensor which is provided under the condition that the pixel size is continuously reduced, the capacity of a full well is continuously reduced, and the digital processing capability is continuously improved. Compared with a traditional image sensor, a sub-diffraction limit size pixel in the quantum image sensor is sensitive to a single photon, photoelectrons collected in the pixel pass through a source follower, a related double sampling circuit and a column-level amplifier, and are finally compared and output through a comparator, when the pixel output is greater than a set threshold, the pixel output is 1, when the pixel output is less than the set threshold, the pixel output is 0, 0 represents that the number of photons incident on the pixel in the frame is less than the set photon threshold number, 1 represents that the number of photons incident on the pixel in the frame is greater than the set photon threshold number, and the comparator threshold of the quantum image sensor is usually set to be a fixed value.
Because the full-well capacity of the pixel of the multi-carrier single-bit quantum image sensor is small, when the exposure is large, the pixel output of the pixel array is 1 at a certain frame frequency, when highlight and darker details appear in a scene at the same time, due to the fact that the threshold value of the whole pixel array comparator is fixed, the picture with a high dynamic range cannot be obtained, the quality of an output image is poor, the threshold value of the comparator can be adjusted in a self-adaptive mode according to the size of the exposure, and the dynamic range of the quantum image sensor is improved. Furthermore, recent theoretical studies at present show that for different exposures, optimal comparator thresholds exist, so that the bit error rate of the quantum image sensor is minimized. Therefore, the reading scheme of the adaptive threshold adjustment has great significance, only theoretical research and discussion on the threshold adjustment are carried out at home and abroad at present, and more relevant reports are not provided for the specific adaptive threshold adjustment scheme.
Disclosure of Invention
Aiming at the problems in the prior art, the image sensor reading circuit based on the self-adaptive threshold adjustment adopts the self-adaptive threshold adjustment circuit, the threshold is adjusted in real time according to the actual exposure, and the threshold is quickly adjusted by using a digital logic circuit, so that the image details with high brightness and high darkness can be simultaneously obtained under a certain frame frequency, and the dynamic range of the image sensor is improved.
An image sensor readout circuit based on adaptive threshold adjustment, as shown in fig. 1, the main blocks include: the pixel array, the row addressing circuit, the correlated double sampling circuit, the column level amplifier, the comparator, the counter, the adaptive threshold adjusting logic and the ramp generator. The key technology of the invention is that the real-time adjustment of the threshold value in the chip is realized by introducing a comparator, a slope generator, a counter and self-adaptive threshold value adjustment logic, and the dynamic range of the image sensor is improved. The working principle of the adaptive threshold adjustment mode of the present invention will now be briefly described with reference to fig. 1: in a signal reading path of the image sensor, a pixel array carries out photoelectric conversion to generate a reset signal and a photoelectric signal; the row addressing circuit generates a control signal of the pixel array and selects a specific pixel to read out; eliminating reset noise through a correlated double sampling circuit; then the signal enters a column amplifier for signal amplification; the amplified signal is compared with a slope voltage with constant slope through a comparator, the slope voltage is generated through a slope generator, and meanwhile counting is carried out through a counter; the final counter records the number of pulses to reflect the size of the pixel output; the output of the counter is accessed into the self-adaptive threshold value adjusting logic, and the module is realized by a digital circuit and is used for comparing the output of the counter with the threshold value, setting the value of the counter corresponding to the threshold value voltage for the same slope voltage, and judging whether to adjust the threshold value or not by comparing the set value with the output value of the actual counter.
The image sensor reading circuit based on self-adaptive threshold adjustment has the advantages that the threshold in the chip is adjusted in real time, the threshold can be adjusted according to different bright and dark conditions in the same scene, meanwhile, the threshold can also be adjusted according to the bright and dark conditions in different time, the image sensor reading circuit is suitable for a binary image sensor, and the dynamic range of the image sensor can be effectively improved.
Drawings
FIG. 1 is an image sensor architecture diagram with adaptive threshold-based adjustment readout;
FIG. 2 is a schematic diagram of an implementation of adaptive threshold adjustment logic;
fig. 3 is a specific circuit diagram of a key circuit in the present invention.
Detailed Description
The invention is explained in detail below with reference to the figures and the specific embodiments.
As shown in fig. 2, the readout strategy of the adaptive threshold adjustment logic unit, the comparison of the output of the pixel with the ramp voltage outputs as the enable signal of the counter, and the output of the counter reflects the magnitude of the pixel output. In the adaptive threshold adjustment logic circuit, an initial threshold voltage is set by using the output of the counter for the same ramp voltage. After the image sensor starts to work, the output of the counter is compared with a set threshold, when the value of the counter is within 70% -130% of the set threshold, the next comparison is carried out, if the value of the counter is larger than the set threshold, the output is 1, and if the value of the counter is smaller than the set threshold, the output is 0; and when the value of the counter is not in the range of 70% -130% of the set threshold, comparing the value of the counter, if the value of the counter is greater than the set threshold, adjusting the threshold to be 70% of the output of the counter and simultaneously outputting the counter to be 1, and if the value of the counter is less than the set threshold, adjusting the threshold to be 130% of the output of the counter and simultaneously outputting the counter to be 0, wherein the threshold of the image sensor is changed.
As shown in fig. 3, the key circuit of the image sensor readout circuit of the present invention is that the comparator is a dynamic latch comparator, which has a fast speed and low power consumption, and has a positive input terminal connected to the ramp generator, a negative input terminal connected to the output of the pixel, an output terminal connected to the enable terminal of the counter for controlling the operation of the counter, and an output terminal connected to the adaptive threshold adjustment logic circuit for controlling the adjustment of the threshold.
Claims (1)
1. An image sensor readout circuit based on adaptive threshold adjustment, the threshold being a binary digital code value set in advance, the number of bits of the code value coinciding with the number of bits of the output code value of a counter, the predetermined code value being a counter threshold value, which is compared with the output code value of an actual counter to determine whether or not to perform threshold adjustment, characterized in that: the main module comprises: the pixel array, the row addressing circuit, the related double sampling circuit, the column-level amplifier, the comparator, the counter, the adaptive threshold adjusting logic and the ramp generator; by introducing a comparator, a slope generator, a counter and self-adaptive threshold value adjusting logic, the threshold value in the chip is adjusted in real time, and the dynamic range of the image sensor is improved; in a signal reading path of the image sensor, firstly, a pixel array carries out photoelectric conversion to generate a reset signal and a photoelectric signal; the row addressing circuit generates a control signal of the pixel array and selects a specific pixel to read out; eliminating reset noise through a correlated double sampling circuit; then the signal enters a column amplifier for signal amplification; the amplified signal is compared with a slope voltage with constant slope through a comparator, the slope voltage is generated through a slope generator, and meanwhile counting is carried out through a counter; the final counter records the number of pulses to reflect the size of the pixel output; the output of the counter is accessed into the self-adaptive threshold value adjusting logic, and the module is realized by a digital circuit and is used for comparing the output of the counter with the threshold value, setting the value of the counter corresponding to the threshold voltage for the same slope voltage, and judging whether to adjust the threshold value or not by comparing the set value with the output value of the actual counter.
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