Segmented Ramp Signal Generator for Image Sensor Linearity
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Solution Overview
Problem
The non-linear decrease of ramp signals in image sensors increases the probability of errors in correlated double sampling circuits, necessitating improved ramp signal linearity.
Innovation Solution
A ramp signal generator with a first and second unit current source, each comprising multiple sub-unit current sources, controlled by distinct sub-ramp signals to adjust current magnitudes, ensuring linear voltage changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional ramp signal generator is used, then the device complexity is low, but the ramp signal linearity deteriorates causing errors in CDS circuit operations
Solution Approach 1:
The ramp signal generator is divided into multiple unit current sources (first, second, third, fourth unit current sources), each comprising multiple sub-unit current sources. Each unit current source is controlled by dedicated control signals (first, second, third, fourth control signals), enabling independent adjustment of current contributions to achieve linear ramp signal generation through segmented control.
2Measurement precision
If the ramp signal linearity is improved using multiple unit current sources, then the measurement precision of the CDS circuit is improved, but the device complexity increases
Solution Approach 1:
Each unit current source is designed with specific sub-unit current sources tailored to its functional requirements. The first unit current source has sub-unit sources controlled by first control signals, the second by second control signals, and so on. This local differentiation allows each segment to contribute optimally to the overall ramp signal linearity, improving CDS circuit accuracy through localized optimization.
Data Source
AI summary
Disclosed is a ramp signal generator. The ramp signal generator includes: a first unit current source including first sub-unit current sources, and configured to output a first unit current during a first time period; and a second unit current source including second sub-unit current sources, and configured to output a second unit current during a second time period. The first sub-unit current sources are configured to operate according to first sub-ramp control signals, respectively. The second sub-unit current sources are configured to operate according to second sub-ramp control signals, respectively. n first sub-ramp control signals among the first sub-ramp control signals are activated, and m sub-ramp control signals among the second sub-ramp control signals are activated, n and m being different natural numbers.