Comparator Output Stage Gating for Low-Power High-Speed Switching
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Solution Overview
Problem
In electronic devices employing many slope (ramp) analog to digital converters, the power consumption by comparators is significant, posing a challenge to achieve both low power operation and high speed operation, especially in large pixel devices like CMOS imaging applications where a million pixel devices require a large number of comparators.
Innovation Solution
The implementation of a comparator with an input stage that produces both a near decision and a true decision, where the near decision is used to power up a switching output stage, allowing it to be powered only for a fraction of the ramp time of the reference voltage, reducing power consumption while maintaining high speed operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the output stage is powered up continuously to ensure high-speed operation, then the comparator can switch within one clock cycle, but power consumption becomes significant
Solution Approach 1:
The input stage generates a near decision signal in advance, before the true decision is needed, to trigger preliminary powering up of the output stage. This ensures the output stage is ready when the true decision occurs, maintaining high-speed operation while limiting power consumption to only the necessary time window
Solution Approach 2:
The output stage power state is changed from static (continuous powering) to dynamic (temporary powering based on near decision signal). The output stage is powered up only when the near decision indicates it will be needed, and powered down afterwards, creating a dynamic power management system that adapts to actual operational needs
2Use of energy by moving object
If the output stage is powered down to reduce power consumption, then energy efficiency improves, but the comparator cannot switch in time causing incorrect values to be latched
Solution Approach 1:
The near decision signal serves as an advance warning that triggers the output stage to power up before the true decision occurs. This preliminary action ensures the output stage is operational and ready to capture the correct value when the comparison completes, preventing incorrect values from being latched
Solution Approach 2:
The input stage continuously monitors the comparison progress and provides feedback through the near decision signal when the ramp voltage approaches the input voltage. This feedback mechanism ensures the output stage is powered up at the precise moment needed, maintaining reliability while enabling power savings
Data Source
AI summary
A comparator with an input stage that selectively powers up an output stage provides an electronic device with a comparator that operates at low power. In an embodiment, an input stage produces a near decision and a true decision, where the near decision is provided to power up an output stage for the comparator to provide an output representative of the true decision.