Multi-Stage Operational Amplifier Common-Mode Feedback Stability
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Solution Overview
Problem
Designing a high-gain and high-bandwidth operational amplifier at low operating voltage is challenging due to stability issues in multi-stage common-mode feedback loops, especially with increasing poles.
Innovation Solution
A multi-stage operational amplifier design with N stages and M common-mode feedback circuits, where N≥3 and N≥M>1, splits the amplifiers into M combinations, each with a corresponding feedback circuit to stabilize the common-mode output voltage, simplifying the circuit structure and enhancing stability and settling speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the quantity of stages of the operational amplifier is increased to achieve high-gain and high-bandwidth performance at low operating voltage, then the performance is improved, but the stability of the common-mode feedback loop deteriorates due to an increase in the number of poles
Solution Approach 1:
The patent divides the multi-stage operational amplifier into multiple groups, with each group having its own common-mode feedback circuit. This segmentation reduces the number of poles in each individual common-mode feedback loop, thereby improving stability while maintaining the overall multi-stage architecture needed for high-gain and high-bandwidth performance.
Solution Approach 2:
The patent implements common-mode feedback circuits that detect common-mode output voltages and regulate electrical parameters of amplifier stages to stabilize the common-mode output. This feedback mechanism compensates for the stability issues introduced by multiple poles in the multi-stage configuration.
2Reliability
If the quantity of stages of the operational amplifier is increased to achieve high-gain and high-bandwidth performance, then the gain and bandwidth are improved, but the settling speed deteriorates
Solution Approach 1:
By dividing the multi-stage amplifier into groups with separate common-mode feedback circuits, each group can settle independently and more quickly, improving the overall settling speed while maintaining the high-gain and high-bandwidth characteristics of the multi-stage configuration.
Solution Approach 2:
The common-mode feedback circuits provide rapid regulation of electrical parameters in response to common-mode voltage changes, accelerating the settling process while preserving the gain and bandwidth benefits of multiple amplifier stages.
3Reliability
If the quantity of common-mode feedback circuits is increased to match the number of amplifier stages, then the stability control is improved, but the circuit structure becomes overly complex
Solution Approach 1:
The patent segments the amplifier stages into groups and assigns one common-mode feedback circuit per group rather than per stage. This reduces the total number of feedback circuits needed, simplifying the overall circuit structure while maintaining adequate stability control through the segmented approach.
Data Source
AI summary
This application provides an operational amplifier that increases the stability and settling speed of a common-mode feedback circuit. The operational amplifier includes N stages of amplifiers connected in series and M common-mode feedback circuits, where N and M are integers, N≥3, and N≥M>1. An ith common-mode feedback circuit in the M common-mode feedback circuits is configured to: detect a common-mode output voltage of a (j+b)th stage of amplifier, and regulate an electrical parameter of at least one of the jth stage of amplifier to the (j+b)th stage of amplifier, to stabilize the common-mode output voltage of the (j+b)th stage of amplifier. An Mth common-mode feedback circuit is configured to detect and stabilize a common-mode output voltage of an Nth stage of amplifier. Herein i, j, and b are integers, M≥i≥1, N≥j≥1, i≥j, j+b≤N, and b≥0.