Dual-Feedback LDO Amplifier for Wide Bandwidth and PSRR
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Solution Overview
Problem
Conventional low dropout regulators face challenges in increasing frequency bandwidth due to instability issues related to smaller phase margins, which affect their power supply rejection ratio (PSRR).
Innovation Solution
The proposed low dropout regulator incorporates a dual-stage amplifier circuit with specific feedback mechanisms, including a first feedback circuit with a capacitor and resistor providing positive feedback, and a second feedback circuit with a capacitor and resistor providing negative feedback, enhancing the frequency bandwidth and open-loop gain bandwidth to improve PSRR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the frequency bandwidth of the operation amplifier is increased, then the power supply rejection ratio is improved, but the phase margin becomes smaller causing instability
Solution Approach 1:
The operation amplifier is divided into two stages: a first stage amplifier circuit with positive and negative output ends, and a second stage amplifier circuit. This segmentation allows independent optimization of each stage's characteristics to achieve both wide bandwidth and sufficient phase margin.
Solution Approach 2:
A first feedback circuit is introduced, coupled between the negative output end of the first stage amplifier circuit and the output end of the second stage amplifier circuit. This feedback mechanism compensates for phase shift and stabilizes the amplifier while maintaining wide bandwidth operation.
Data Source
AI summary
A low dropout regulator includes an output circuit and an amplifier. The output circuit includes a signal input end configured to receive an input voltage and a signal output end configured to output an output voltage. The amplifier includes a first stage amplifier circuit, a second stage amplifier circuit, a first feedback circuit and a second feedback circuit. The first stage amplifier circuit includes a positive output end and a negative output end. The second stage amplifier circuit includes an input end and an output end, wherein the input end and the positive output end are coupled at a first node, and the output end is coupled to the output circuit. The first feedback circuit is coupled between the negative output end and the output end. The second feedback circuit is coupled between the first node and the output end.