Transmission Gate Voltage Regulation for Image Sensor Charge Transfer
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Solution Overview
Problem
Conventional image sensors face challenges in achieving high imaging accuracy due to inefficient charge transfer and charge injection issues, which are influenced by the gate voltage of the transmission gate in the pixel structure.
Innovation Solution
A circuit and method for regulating the gate voltage, comprising a storage module, comparison module, and voltage regulation module, which compares electrical signals under different gate voltages and adjusts the gate voltage to optimize charge transfer efficiency while minimizing charge injection, using a digital-to-analog conversion unit to output the optimal voltage for the transmission gate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the gate voltage is increased to improve charge transfer efficiency, then more charges are transferred to the floating diffusion node, but a larger number of charges remain in the transmission gate region, causing charge injection into the photodiode and reducing imaging accuracy
Solution Approach 1:
The patent applies dynamics by making the gate voltage adjustable rather than fixed. The control circuit dynamically changes the gate voltage according to different working conditions, allowing the system to optimize between charge transfer efficiency and charge injection prevention. The gate voltage can be switched between a first voltage (for high transfer efficiency) and a second voltage (for reducing charge injection), resolving the contradiction through temporal variation.
Solution Approach 2:
The patent directly applies parameter changes by modifying the gate voltage parameter to resolve the contradiction. By changing the gate voltage from a fixed value to an adjustable parameter with at least two different voltage levels, the system can switch between optimizing for charge transfer efficiency and minimizing charge injection, thus resolving the technical contradiction through parameter optimization.
2Measurement precision
If the gate voltage is decreased to reduce charge injection, then fewer charges remain in the transmission gate region, but the voltage difference between the transmission gate region and photodiode decreases, affecting charge transfer efficiency
Solution Approach 1:
The patent resolves this contradiction through dynamics by implementing time-varying gate voltage control. During the charge transfer phase, a higher first voltage is applied to maximize transfer efficiency. During the readout or idle phase, a lower second voltage is applied to minimize charge injection. This temporal separation of voltage levels allows both requirements to be satisfied at different times.
Solution Approach 2:
The patent applies periodic action through cyclic switching between different gate voltage levels. The control circuit periodically switches the gate voltage between the first voltage (for efficient charge transfer) and the second voltage (for reducing charge injection), creating a rhythmic pattern of high and low voltage states that balances both charge transfer efficiency and imaging accuracy requirements.
Data Source
AI summary
There are provided a circuit and a method for regulating a gate voltage, and a sensor applying the circuit. In the circuit, an input end of the storage module is connected to a first end of a signal storage unit, an output end thereof is connected to an input end of the comparison module, an output end of the comparison module is connected to an input end of the voltage regulation module, and an output end of the voltage regulation module is connected to a transmission gate. The storage module stores electrical signals outputted by the signal storage unit. The comparison module compares at least two of the electrical signals correspond to different gate voltages to obtain a comparison result. The voltage regulation module regulates, based on the comparison result, an output voltage according to a predetermined rule to change the gate voltage.