ADC Leakage Compensation for Image Sensor Charge Drift
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Solution Overview
Problem
Charge leakage in image sensors degrades the accuracy of light intensity measurement by causing drift in the input voltage, leading to measurement errors and reducing the dynamic range of image sensors, especially in low light conditions where the quantity of charge stored is small.
Innovation Solution
An analog-to-digital converter (ADC) circuit with a leakage compensation circuit that generates a leakage-compensated signal pair to compensate for charge leakage by introducing a time-varying offset or replenishing the charge, allowing the quantizer to perform accurate quantization and extend the dynamic range of image sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If charge is stored in the capacitor for extended measurement period, then measurement accuracy is improved, but charge leakage causes drift and reduces measurement accuracy
Solution Approach 1:
The patent applies preliminary action by performing auto-zeroing before the measurement period to pre-compensate for offset errors. The capacitor is charged to the input voltage level before measurement begins, and any charge leakage during the measurement period is compensated by continuously tracking the voltage drift and adjusting the reference signal accordingly.
Solution Approach 2:
The patent implements feedback through a leakage compensation circuit that continuously monitors the input voltage during the measurement period. The circuit tracks charge leakage by comparing the input voltage with a reference signal and dynamically adjusts the reference signal to compensate for drift, ensuring measurement accuracy is maintained throughout the extended measurement period.
2Measurement precision
If conventional ADC circuit is used, then device complexity is low, but measurement accuracy deteriorates due to charge leakage
Solution Approach 1:
The patent introduces an intermediary leakage compensation circuit between the capacitor and the quantizer. This circuit includes a reference capacitor and switching network that mediates the charge leakage effect by generating a compensated reference signal. The intermediary circuit isolates the quantizer from direct exposure to charge leakage while maintaining measurement accuracy.
3Adaptability or versatility
If measurement period is extended to improve dynamic range, then low light detection is improved, but charge leakage effects are amplified
Solution Approach 1:
The patent performs preliminary auto-zeroing to establish a baseline compensation for offset errors before the extended measurement period begins. This preliminary action ensures that the leakage compensation circuit starts with accurate calibration, enabling stable measurements throughout the extended period required for low light detection.
Solution Approach 2:
The leakage compensation circuit provides continuous feedback during the extended measurement period, dynamically adjusting the reference signal to counteract charge leakage effects. This feedback mechanism enables the system to maintain measurement precision throughout the extended time period required for detecting low light intensities.
Data Source
AI summary
Methods and systems for performing analog-to-digital conversion is provided. In one example, an analog-to-digital converter (ADC) circuit comprises a leakage compensation circuit and a quantizer. The leakage compensation circuit is configured to: receive an input signal, the input signal being susceptible to a drift due to a charge leakage; receive a reference signal; and generate a leakage-compensated signal pair to compensate for the charge leakage, wherein the leakage-compensated signal pair comprises one of: (a) a leakage-compensated version of the input signal and the reference signal, (b) the input signal and a leakage-compensated version of the reference signal, or (c) a leakage-compensated version of the input signal and a leakage-compensated version of the reference signal. The quantizer is configured to perform a leakage-compensated quantization of the input signal based on the leakage-compensated signal pair to generate a digital output representing the input signal.