Imaging Sensor Amplifier Gain Control for AD Conversion
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Solution Overview
Problem
Existing imaging sensors face challenges in reducing circuit area while implementing a combination of successive approximation analog-to-digital (AD) converters and amplifiers, particularly in determining the appropriate circuit configuration for effective AD conversion and gain adjustment based on signal thresholds.
Innovation Solution
The proposed imaging sensor incorporates a successive approximation AD converter and an amplifier, where the amplifier adjusts gain based on the comparison between the pixel signal and a threshold, using a comparator and digital-to-analog converter to determine if the amplification signal is within a predetermined range, thereby reducing circuit area and ensuring accurate AD conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the amplifier and AD converter are integrated in the same chip, then device complexity is reduced, but it becomes difficult to determine appropriate gain settings for accurate AD conversion
Solution Approach 1:
The imaging sensor is divided into two separate chips: a first chip containing pixels and an amplifier, and a second chip containing an AD converter. This segmentation allows independent optimization of gain adjustment on the first chip and AD conversion on the second chip, resolving the contradiction between device simplicity and conversion accuracy.
Solution Approach 2:
A signal range determination circuit is introduced as an intermediary between the amplifier and AD converter. This circuit detects whether the amplification signal is within a predetermined range and provides feedback to adjust the amplifier gain, ensuring accurate AD conversion while maintaining a simplified two-chip architecture.
2Productivity
If the amplifier gain is increased to expand dynamic range, then signal detection capability is improved, but circuit area increases
Solution Approach 1:
The amplifier gain is made dynamically adjustable based on signal conditions. The signal range determination circuit monitors the amplification signal and adjusts the amplifier gain accordingly, allowing the system to achieve wide dynamic range without permanently increasing circuit area through fixed high-gain amplification.
Solution Approach 2:
The amplifier gain parameter is changed based on the detected signal range. When the amplification signal is within the predetermined range, a first gain is applied; when outside the range, a second gain is applied. This parameter adjustment enables dynamic range expansion without requiring additional circuit area for fixed high-gain stages.
3Measurement precision
If multiple gain stages are added to achieve wide dynamic range, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The signal range determination circuit performs preliminary detection of the amplification signal range before AD conversion. Based on this preliminary detection, the amplifier gain is adjusted in advance to ensure the signal is within the optimal conversion range, achieving precise signal detection without requiring multiple complex gain stages.
Solution Approach 2:
A feedback mechanism is implemented where the signal range determination circuit monitors the amplification signal and provides feedback to adjust the amplifier gain. This closed-loop control achieves precise signal detection across wide dynamic range using a single amplifier with adjustable gain, avoiding the complexity of multiple fixed gain stages.
Data Source
AI summary
An imaging sensor includes a pixel, an amplifier, and a successive approximation analog-to-digital (AD) converter. The pixel is configured to output a pixel signal. The amplifier is configured to output an amplification signal obtained by amplifying the pixel signal. The successive approximation AD converter detects whether or not the amplification signal is within a predetermined signal range.