Multistage Amplifier Feedback Topology for Wider 3-dB Bandwidth
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Solution Overview
Problem
Conventional two-staged amplifier circuits face a trade-off between phase improvement and gain bandwidth, where Miller compensation decreases the 3-dB bandwidth.
Innovation Solution
The proposed amplifier circuit incorporates a multistage amplifier configuration with both negative and positive feedback circuits, utilizing multiple feedback loops with compensating resistors and capacitors to enhance 3-dB bandwidth without affecting unity gain frequency, and increase gain through a cascaded structure of first-staged, middle-staged, and last-staged differential amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Miller compensation is used to separate poles and improve phase, then phase margin is improved, but 3-dB bandwidth decreases
Solution Approach 1:
The patent divides the feedback path into multiple segments: a main feedback loop from output to input, and additional feedback paths from intermediate stages to the input. This segmentation allows independent control of different frequency responses, enabling phase improvement without sacrificing bandwidth. The first feedback circuit connects output to input while the second feedback circuit connects intermediate stage to input, creating separate control paths.
Solution Approach 2:
The patent transitions from conventional single-loop Miller compensation to a multi-dimensional feedback architecture by adding feedback paths from multiple stages (first stage, second stage, and output) to the input. This dimensional expansion in feedback topology allows simultaneous optimization of phase margin and bandwidth that cannot be achieved with single-loop compensation.
2Reliability
If conventional two-staged amplifier with Miller compensation is used, then phase is improved, but gain bandwidth product decreases
Solution Approach 1:
The patent employs multiple feedback circuits with different time constants and gain characteristics. The first feedback circuit provides overall loop feedback while the second feedback circuit provides intermediate stage feedback. This multi-feedback approach allows the system to achieve improved phase margin through selective frequency-dependent feedback without reducing the gain bandwidth product, as each feedback path operates effectively in different frequency ranges.
Data Source
AI summary
An amplifier circuit includes a multistage amplifier, a first feedback circuit and a second feedback circuit. The multistage amplifier includes a first-staged amplifier, a last-staged amplifier and at least one middle-staged amplifier cascaded between the first-staged amplifier and the last-staged amplifier. The first feedback circuit is configured to couple a positive output end of the last-staged amplifier to a positive input end of the at least one middle-staged amplifier, or is configured to couple a negative output end of the last-staged amplifier to a negative input end of the at least one middle-staged amplifier. The second feedback circuit is configured to couple the positive output end of the last-staged amplifier to a positive input end of the last-staged amplifier, or is configured to couple the negative output end of the last-staged amplifier to a negative input end of the last-staged amplifier.