Dual-Loop LDO Regulator for PSRR and Feedback Stability
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Solution Overview
Problem
Low dropout (LDO) voltage regulators face instability and gain errors due to high bandwidth and low gain, leading to excessive phase shifting and regenerative feedback loops, which affect power supply rejection ratio (PSRR) and noise rejection.
Innovation Solution
A dual feedback loop system is implemented, where the first feedback loop has low gain and high bandwidth for fast transient response, and the second feedback loop has high gain and low bandwidth to correct gain errors by adjusting the bias voltage and resistance of pass elements, thereby stabilizing the feedback loop and reducing gain errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a single feedback loop with high bandwidth is used in LDO voltage regulator, then transient response speed is improved, but phase shifting increases causing instability and regenerative feedback
Solution Approach 1:
The single feedback loop is segmented into two separate feedback loops: a first feedback loop with high bandwidth for fast transient response and a second feedback loop with low bandwidth for stability. This segmentation allows each loop to operate in its optimal frequency range without causing phase shifting instability.
Solution Approach 2:
The system dynamically switches between different feedback loops based on operating conditions. The first feedback loop is enabled during transient conditions for fast response, while the second feedback loop operates during steady-state for stability, creating a dynamic adaptation mechanism.
2Measurement precision
If amplifier gain is increased to reduce gain errors, then measurement precision is improved, but bandwidth decreases causing slower response
Solution Approach 1:
The amplification function is segmented into two amplifiers with different gain characteristics. The first amplifier provides high bandwidth with moderate gain for fast response, while the second amplifier provides high gain for accuracy in steady-state conditions, eliminating the need to compromise between gain and bandwidth in a single amplifier.
Solution Approach 2:
The second feedback loop acts as an intermediary that corrects gain errors introduced by the first amplifier. It compensates for inaccuracies without requiring the first amplifier to have excessively high gain, thus preserving bandwidth while achieving overall precision.
3Object-affected harmful factors
If power supply rejection ratio is improved to reduce noise, then noise rejection is improved, but circuit complexity increases
Solution Approach 1:
The noise rejection function is segmented between two feedback loops operating at different frequencies. The first loop handles high-frequency transient noise while the second loop handles low-frequency steady-state noise, achieving comprehensive noise rejection through frequency-domain segmentation rather than requiring a single complex filtering system.
Data Source
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AI summary
In certain aspects, a method for voltage regulation includes adjusting, using a feedback circuit, a resistance of a first pass element in a direction that reduces a difference between a reference voltage and a feedback voltage, wherein the first pass element is coupled between an input and an output of a voltage regulator, and the feedback voltage is equal to or proportional to a voltage at the output of the voltage regulator. The method also includes adjusting a bias voltage of the feedback circuit in a direction that reduces the difference between the reference voltage and the feedback voltage.