CMOS Image Sensor ADC Noise Isolation via Dedicated Reference Lines
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Solution Overview
Problem
In single-slope-integrating analog-to-digital converters, noise generated in voltage comparators is transmitted through common wiring, affecting the operation of other comparators and degrading the AD conversion process.
Innovation Solution
The implementation of a reference signal supply interface unit that provides the reference signal to multiple comparators via different signal lines, isolating noise and preventing its transmission between comparators, and using a counter to count the comparison time and hold the count value for each comparator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If common wiring is used to supply reference signals to multiple comparators, then device complexity is reduced, but noise interference between comparators increases
Solution Approach 1:
The patent divides the common reference signal wiring into separate dedicated signal lines for each comparator. Instead of using a single shared wiring path, each comparator receives the reference signal through its own isolated signal line, thereby segmenting the noise transmission paths and preventing cross-interference between comparators.
Solution Approach 2:
The patent applies different wiring configurations to different parts of the system: comparators that are susceptible to noise interference receive reference signals through dedicated isolated lines, while other parts of the circuit can continue to use common wiring where noise isolation is not critical. This localized application of noise isolation measures optimizes the balance between complexity and performance.
2Object-affected harmful factors
If dedicated signal lines are used for each comparator, then noise interference is reduced, but device complexity increases
Solution Approach 1:
The patent employs switching mechanisms that dynamically connect comparators to appropriate signal lines based on operational requirements. The switching circuitry can reconfigure the signal path topology, connecting multiple comparators to shared reference signal sources when noise isolation is not critical, and switching to dedicated isolated lines when high precision is required, thereby adapting the wiring complexity to the actual operational needs.
3Measurement precision
If noise isolation measures are implemented, then AD conversion accuracy is improved, but processing time increases
Solution Approach 1:
The patent implements preliminary noise isolation measures by providing dedicated reference signal lines to comparators before the AD conversion process begins. By pre-establishing isolated signal paths, the system prevents noise interference from affecting the comparison process, thereby ensuring high conversion accuracy without requiring additional time-consuming noise filtering or correction operations during the actual conversion.
Data Source
AI summary
An electronic apparatus includes a CMOS image sensor and a signal processor operable to process an output signal from the CMOS image sensor. The CMOS image sensor includes the following elements: an imaging region; a reference signal generator operable to generate a reference signal; a comparator operable to compare the reference signal generated by the reference signal generator with a signal transmitted from the imaging region; a counter operable to count, in parallel with comparison performed by the comparator, a predetermined count clock and to hold a count value at the time of completion of comparison performed by the comparator; and a reference signal supply interface unit operable to supply the reference signal generated by the reference signal generator to a plurality of comparators via different signal lines, respectively.