Image Sensor Readout Circuitry Reducing Sampling Kickback
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Solution Overview
Problem
Image sensors in electronic devices experience signal sampling kickback due to the sampling process, leading to additional phase delay and increased current requirements, which is undesirable in certain applications.
Innovation Solution
The implementation of readout circuitry with a programmable gain amplifier and a voltage follower configuration, along with interposed source follower stages, to reduce signal sampling kickback by performing coarse and final sampling operations, thereby minimizing kickback noise and delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional sampling process is used, then signal can be read out, but kickback noise is generated causing phase delay
Solution Approach 1:
A buffer stage is introduced as an intermediary component between the sampling capacitor and the signal path. This buffer stage isolates the sampling operation from the main signal path, preventing kickback noise from propagating and causing phase delay while maintaining signal readout capability.
Solution Approach 2:
The readout circuit is segmented into distinct stages: a sampling stage with capacitor, a buffer stage, and a signal output stage. This segmentation allows the sampling operation to be performed independently without directly affecting the signal path timing, thus reducing phase delay caused by kickback.
2Loss of time
If additional current is provided to improve line settling, then settling time is reduced, but current requirements increase
Solution Approach 1:
The buffer stage acts as an intermediary that provides isolation between the sampling capacitor and the signal line. This isolation allows the signal line to settle naturally without requiring additional current, as the buffer prevents kickback noise from disrupting the settling process.
Solution Approach 2:
The circuit is designed to settle naturally using its own inherent characteristics without requiring external current assistance. The buffer stage enables the signal line to self-settle by preventing kickback interference, eliminating the need for additional current to improve settling time.
Data Source
AI summary
An image sensor may include an array of image pixels. The image pixel pixels may be arranged in columns and rows. Each column of image pixels may be coupled to column readout circuitry via respective column lines. The column readout circuitry may include amplifier circuitry, a first source follower stage, and a second source follower stage. The first and second source follower stages may be interposed between the amplifier circuitry and a sampling capacitor. A switch may be interposed between the first and second source follower stages. The second source follower transistor may be configured to provide an intermediate sampling voltage to the sampling capacitor. The first source follower transistor may be configured to provide a final sampling voltage to the sampling capacitor. In such a manner, kickback from sampling signals using readout circuitry may be reduced.