Column-Parallel ADC Reference Signal Voltage Stabilization
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Solution Overview
Problem
Existing column-parallel analog-to-digital converters in image sensors face challenges in accurately converting pixel signals due to variations in reference signal voltages, leading to inaccuracies in digital value measurement.
Innovation Solution
The proposed imaging device incorporates a sampling circuit, a reference signal generation circuit that adjusts voltage, and a comparator to measure the length of time until the pixel signal matches the reference signal, with a voltage adjustment circuit to fine-tune the reference signal voltage, ensuring accurate AD conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reference signal generation circuit uses a predetermined analog voltage to generate a reference signal, then the AD conversion process can be completed, but variations in reference signal voltages cause inaccuracies in digital value measurement
Solution Approach 1:
The voltage adjustment circuit performs preliminary adjustment of the reference signal voltage before the reference signal is used for comparison. By adjusting the analog voltage in advance (before the first timing of the first period), the circuit ensures that the reference signal voltage is stable and accurate when needed for AD conversion, preventing measurement inaccuracies before they occur.
Solution Approach 2:
The voltage adjustment circuit monitors the analog voltage and performs adjustments based on detected variations. The circuit compares the first voltage with the second voltage and makes corrections to maintain voltage stability, creating a feedback mechanism that continuously ensures reference signal accuracy throughout operation.
2Area of moving object
If column-parallel ADCs are used to reduce image sensor area, then the sensor size decreases, but voltage variations in the reference signal still cause conversion inaccuracies
Solution Approach 1:
The voltage adjustment circuit is specifically applied to the reference signal generation path in the column-parallel ADC structure. Rather than adjusting all voltages in the sensor, the circuit locally adjusts only the reference signal voltage where it is critical for accurate conversion, maintaining precision in the compact column-parallel architecture.
Solution Approach 2:
The circuit dynamically changes the analog voltage parameter to maintain stability. By adjusting the voltage level based on detected variations (comparing first and second voltages), the system maintains conversion accuracy despite the compact column-parallel structure that is more sensitive to voltage variations.
Data Source
AI summary
An imaging device includes pixels, a sampling circuit, a reference signal generation circuit, a comparator, a measurement circuit, and a voltage adjustment circuit. The sampling circuit is configured to sample an analog signal. The comparator is configured to compare a voltage of the analog signal with a voltage of the reference signal. The reference signal generation circuit is configured to generate the reference signal that has a first voltage in a first period and has a second voltage in a second period. The measurement circuit is configured to measure the length of a period until the voltage of the analog signal and the voltage of the reference signal match each other. The voltage adjustment circuit is configured to adjust an analog voltage provided to the reference signal generation circuit such that a value of the first voltage nears a value of the second voltage.