LDO Regulator Feed-Forward Amplifier Noise Cancellation
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Solution Overview
Problem
Low drop-out voltage regulators face challenges in providing a clean power supply due to power supply noise coupling through the error amplifier, leading to performance degradation and increased output voltage glitches and settling time, especially in systems-on-a-chip applications where analog and RF circuits are sensitive to noise.
Innovation Solution
A low drop-out voltage regulator circuit incorporating a fully differential first stage amplifier with common-mode feedback and a feed-forward amplifier stage, which eliminates the need for large on-chip capacitors, improves transient response, and reduces output voltage glitches and settling time by canceling power supply noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If Miller compensation capacitor is used to provide stability, then the LDO regulator becomes stable, but the output voltage glitches and settling time increase
Solution Approach 1:
The patent introduces a feed-forward amplifier as an intermediary component that processes the error signal before it reaches the main amplifier stage. This feed-forward path compensates for the slow response caused by Miller compensation by providing a direct, fast correction path for load changes, thereby reducing settling time while maintaining stability.
Solution Approach 2:
The error amplifier is segmented into multiple stages: a feed-forward amplifier stage and a main amplifier stage with Miller compensation. The feed-forward stage handles fast transient responses while the main stage provides stable DC regulation, allowing the system to achieve both fast settling and stability simultaneously.
2Stability of the object's composition
If Miller compensation capacitor is integrated on-chip, then the LDO regulator achieves stability, but the surface area and cost increase
Solution Approach 1:
The patent changes the compensation approach from using a large on-chip capacitor to using a feed-forward amplifier with smaller capacitors. By altering the compensation mechanism from capacitive dominance to active amplification, the required capacitor size is dramatically reduced, minimizing on-chip area while maintaining stability.
Solution Approach 2:
The feed-forward amplifier acts as an intermediary that provides stability compensation without requiring large capacitors. It uses active circuitry to achieve the compensation effect, replacing the passive capacitor-based Miller compensation with an active amplification-based approach that consumes less area.
3Measurement precision
If error amplifier provides high gain, then the regulation accuracy improves, but the power supply noise rejection degrades
Solution Approach 1:
The error amplifier is segmented into feed-forward and main stages with different functions. The feed-forward stage provides high gain for accurate regulation while the main stage with Miller compensation provides noise filtering. This segmentation allows each stage to be optimized for its specific function without compromising the other.
Solution Approach 2:
The patent employs dual feedback paths: a fast feed-forward feedback path for high-frequency noise rejection and a slower main feedback path for DC accuracy. This multi-rate feedback approach allows the system to reject power supply noise across a broad frequency range while maintaining high regulation accuracy.
Data Source
AI summary
A circuit and method for regulating an output voltage are provided. The circuit includes a fully differential first stage amplifier, a second stage amplifier, and a power output driver transistor. The first stage amplifier receives a reference voltage and feedback voltage relative to an output voltage of the power output driver transistor. A differential output of the first stage amplifier is received at differential inputs of the second stage amplifier. The second stage amplifier provides a voltage at a control terminal of the power transistor. The output voltage of the power transistor is based on the voltage at the control terminal and a supply voltage coupled to the power output driver transistor.