ADC Switch Timing for RTS Noise Reduction in Image Sensors
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Solution Overview
Problem
Analog-to-digital converters in image sensors suffer from random telegraph signal (RTS) noise due to defects in the oxide layer of metal oxide semiconductor (MOS) transistors, which degrades the performance of the image sensor by varying the current flowing through the channel.
Innovation Solution
An analog-to-digital converter design that includes a comparator, a switch, and a counter circuit, where the switch is opened during the transient period of the analog signal application to disconnect the signal from the comparator, and closed after the signal stabilizes, and the comparator generates a comparison signal based on the analog and reference signals to produce a digital signal, maintaining the second transistor in an on state throughout the process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the switch is closed continuously to provide the analog signal to the comparator, then the analog signal can be continuously compared, but RTS noise occurs due to voltage transients affecting the comparator
Solution Approach 1:
The switch is opened before the analog signal is applied to the first signal line, preemptively preventing voltage transients from reaching the comparator and causing RTS noise, while still allowing the comparison process to proceed after the signal stabilizes
Solution Approach 2:
The switch timing is designed to counteract the harmful effect of voltage transients by being open during the transient period, thereby preventing the transients from affecting the comparator and generating noise
2Object-affected harmful factors
If the switch is opened during the transient period to prevent RTS noise, then noise is reduced, but the signal comparison is interrupted
Solution Approach 1:
The switch operates periodically, being open during transient periods when voltage changes occur and closed during stable periods when accurate comparison is needed, creating a rhythmic on-off pattern that eliminates noise while maintaining comparison functionality
Solution Approach 2:
The switch state is dynamically adjusted based on the signal conditions - open when voltage transients are present and closed when the signal is stable - allowing the system to adapt to changing conditions and optimize both noise reduction and comparison accuracy
Data Source
AI summary
An analog-to-digital converter includes a comparator, a switch, and a counter circuit. The comparator is configured to generate a comparison signal by comparing an analog signal received through a first signal line and a reference signal received through a second signal line. The switch is coupled between the first signal line and the comparator. The switch is open before the analog signal is applied to the first signal line to disconnect the first signal line from the comparator, and is closed after the analog signal is applied to the first signal line to provide the analog signal to the comparator. The counter circuit is configured to generate a digital signal corresponding to the analog signal by performing a count operation in synchronization with a count clock signal based on the comparison signal.