Multistage Comparator Structure for Offset Cancellation and Bandwidth
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Solution Overview
Problem
Comparator circuits face limitations in achieving high-speed and high-resolution performance due to offset voltage and charge injection noise, which restrict their ability to accurately measure small signal differences and require additional costly circuitry and large silicon area.
Innovation Solution
A multistage comparator circuit with latch offset cancellation and coupling capacitor sharing techniques, where offset voltages are stored on capacitors and used to compensate during comparison phases, and switches are operated to minimize charge injection noise, allowing for reduced capacitive loading and increased bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If switching capacitor circuits are used to compensate for offset voltage, then resolution is improved, but bandwidth is limited due to capacitive loading
Solution Approach 1:
The patent combines offset cancellation and capacitive coupling functions into a single shared capacitor structure. The coupling capacitor that normally connects amplifier stages is also used to store offset voltage, eliminating the need for separate switching capacitor circuits and reducing total capacitive loading on the signal path.
Solution Approach 2:
The coupling capacitor serves multiple functions: it couples signal between stages, stores offset voltage for cancellation, and reduces capacitive loading. This multi-functional use of the capacitor improves resolution through offset cancellation while maintaining bandwidth by minimizing additional capacitive elements in the signal path.
2Measurement precision
If switching capacitor circuits are used for offset compensation, then resolution is improved, but circuit complexity and silicon area increase
Solution Approach 1:
The patent merges the offset cancellation circuitry with the existing coupling capacitor structure between amplifier stages. By using the same capacitor for both signal coupling and offset storage, the design eliminates additional switching capacitor circuits, reducing overall circuit complexity and silicon area while maintaining offset compensation functionality.
3Speed
If bandwidth is increased in single-stage comparator, then speed is improved, but resolution decreases
Solution Approach 1:
The patent performs offset cancellation during a calibration phase before the actual comparison operation. By storing offset voltage on coupling capacitors in advance and then using it to compensate during the comparison phase, the system achieves high resolution without requiring additional capacitive loading that would limit bandwidth during the critical comparison operation.
Data Source
AI summary
Methods and circuits for performing high-speed, high-resolution signal comparisons using offset cancellation, reduction of charge injection noise, and sharing of coupling capacitors between circuit stages. A multistage comparator circuit includes first and second preamplifiers electrically coupled to each other through series connections including coupling capacitors. A latch for storing the comparison output signal is electrically coupled to the output of the second preamplifier. The multistage comparator operates such that the offset voltages of the first preamplifier and of the second preamplifier and latch are stored on the coupling capacitors before performing comparisons.