Clipping Circuit for CMOS Image Sensor Voltage Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The variation in threshold voltage among amplification transistors in pixels causes fluctuations in the reset level, necessitating a margin in the gate voltage of the clipping circuit and the dynamic range of the AD conversion circuit, hindering a reduction in the voltage of the AD conversion circuit.
Innovation Solution
A solid-state imaging device with a clipping circuit that includes a transistor to generate a predetermined voltage and a sample holding circuit to hold and input the reset level, allowing for voltage limitation of the vertical signal line, using capacitors and a voltage generation circuit to apply different voltages during reset and signal level readings, and a selector to control the voltage limitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gate voltage of the clipping circuit is set to include a margin to account for reset level fluctuations, then the reliability of sunspot correction is improved, but the voltage requirement of the AD conversion circuit increases
Solution Approach 1:
The patent applies dynamics by making the clipping circuit's gate voltage adaptive rather than fixed. The gate voltage is dynamically adjusted based on the actual reset level detected from each pixel, allowing the system to respond to variations in threshold voltage without requiring a predetermined margin. This dynamic adjustment eliminates the need to over-design the AD conversion circuit voltage headroom.
Solution Approach 2:
The patent implements feedback by using the detected reset level to control the gate voltage of the clipping circuit transistor. The reset level detection circuit measures the actual reset level, and this information is fed back to adjust the clipping threshold. This closed-loop feedback mechanism ensures reliable sunspot correction while optimizing the voltage requirements of subsequent circuit stages.
2Device complexity
If a fixed gate voltage is used in the clipping circuit to simplify design, then the device complexity is reduced, but the ability to handle reset level variations deteriorates
Solution Approach 1:
The patent applies preliminary action by detecting and measuring the reset level before using it to set the clipping threshold. The reset level detection circuit performs this measurement in advance, allowing the gate voltage to be pre-adjusted to the appropriate level. This preliminary detection enables the system to handle reset level variations without requiring complex real-time adjustment mechanisms.
Solution Approach 2:
The patent changes the parameter of gate voltage from a fixed value to a variable value that depends on the detected reset level. By making the gate voltage a function of the reset level, the circuit can adapt to different threshold voltage conditions while maintaining a relatively simple overall structure. This parameter change allows the same hardware to handle varying conditions effectively.
Data Source
AI summary
The present technology relates to a solid-state imaging device and an electronic device that enable a reduction in the voltage of an AD conversion circuit. A solid-state imaging device includes: a plurality of pixels; a vertical signal line configured to output a pixel signal of the pixel; and a clipping circuit configured to limit a voltage of the vertical signal line to a predetermined voltage. The clipping circuit includes a transistor configured to generate the predetermined voltage in accordance with a voltage of a gate, and a sample holding circuit configured to hold a reset level of the pixel that is output to the vertical signal line, and input the reset level to the gate of the transistor. The present technology can be applied to a CMOS image sensor, for example.