Current Stabilization Circuit for CMOS Image Sensor Amplifiers
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Solution Overview
Problem
CMOS image sensors experience performance degradation due to power fluctuation caused by dynamic current flowing through amplifiers in the comparing circuit, which affects the accuracy of correlated double sampling operations.
Innovation Solution
Incorporating a current stabilization circuit within the second amplifier of the comparing circuit to supply constant current during correlated double sampling operations, independent of the output signal from the first amplifier, thereby preventing dynamic current generation and reducing power fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If dynamic current flows through the amplifier in the comparing circuit, then the amplifier can operate during correlated double sampling, but power fluctuation occurs causing performance degradation
Solution Approach 1:
A current stabilization circuit is introduced as an intermediary component between the power supply and the amplifier. This circuit includes a current stabilization transistor that receives a stabilization signal and adjusts the current flow to the amplifier, preventing direct dynamic current fluctuations from reaching the amplifier while maintaining its operational capability during CDS operations.
2Reliability
If separate ground terminals are used for first and second amplifiers to prevent dynamic current, then power fluctuation is reduced, but the number of ground pads and wires increases
Solution Approach 1:
The ground terminals of the first amplifier and the current stabilization circuit are merged into a single common ground terminal. This consolidation reduces the number of ground pads and wire connections required, while the current stabilization circuit ensures that power fluctuation is still prevented through controlled current supply, thus maintaining reliability while reducing complexity.
3Reliability
If current stabilization circuit is added to the second amplifier, then power fluctuation is reduced, but device complexity increases
Solution Approach 1:
The current stabilization circuit is applied locally only to the second amplifier where it is most needed, rather than to the entire comparing circuit or both amplifiers. This targeted approach provides the necessary power stability at the critical point while minimizing the overall increase in device complexity. The stabilization signal is generated and applied specifically where required.
Data Source
AI summary
A comparing circuit may include a first amplifier and a second amplifier. The first amplifier performs a correlated double sampling operation in response to a pixel signal and a ramp signal, and the second amplifier amplifies an output signal of the first amplifier. The second amplifier includes a current stabilization circuit that supplies current to the second amplifier during the correlated double sampling operation irrespective of the output signal of the first amplifier.