Auxiliary Amplifier LDO Regulator for PSRR and Stability
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Solution Overview
Problem
Conventional low dropout (LDO) voltage regulators face challenges in achieving stability and high power supply rejection ratio (PSRR) simultaneously, especially in battery-operated devices with large off-chip bypass capacitors, where traditional compensation methods require large capacitors that cannot be placed on the chip and provide no power supply rejection.
Innovation Solution
The introduction of an auxiliary amplifier before the compensation capacitor increases the effective gain of the compensation capacitor, allowing it to be significantly smaller while improving PSRR, and the addition of an active clamp provides short-circuit protection without engaging in normal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If traditional compensation methods are used in LDO voltage regulators, then stability can be achieved, but the compensation capacitor size becomes large and cannot be placed on the chip
Solution Approach 1:
An auxiliary amplifier is introduced as an intermediary component between the main amplifier and the compensation capacitor. This auxiliary amplifier boosts the signal before it reaches the compensation capacitor, allowing the capacitor to be much smaller while still achieving the required stability. The auxiliary amplifier acts as a mediator that enables the system to maintain stability with a reduced capacitor size that can be integrated on-chip.
2Stability of the object's composition
If traditional compensation methods are used in LDO voltage regulators, then stability can be achieved, but power supply rejection ratio (PSRR) remains low
Solution Approach 1:
The auxiliary amplifier serves as an intermediary that enhances the PSRR by providing additional gain before the compensation stage. This intermediate amplification stage improves the rejection of power supply variations and noise, while still maintaining the stability required for proper LDO operation.
3Object-affected harmful factors
If LDO voltage regulators are used in battery-operated devices with large off-chip bypass capacitors, then noise filtering is improved, but the device complexity and external component requirements increase
Solution Approach 1:
The noise filtering function is extracted from the external bypass capacitor and implemented within the LDO regulator itself through the auxiliary amplifier and reduced compensation capacitor. This internalization of the filtering function eliminates the need for large external capacitors, reducing device complexity and external component requirements while maintaining effective noise filtering.
Data Source
AI summary
Disclosed is a low dropout (LDO) voltage regulator that includes a differential amplifier configured to amplify a differential between a reference voltage and a regulated output voltage, a pass transistor coupled to the differential amplifier and driven by an output of the differential amplifier, a compensation capacitor coupled to an output node of the differential amplifier, and an auxiliary amplifier, wherein an output node of the auxiliary amplifier is coupled to the compensation capacitor, and wherein an input node of the auxiliary amplifier is coupled to the pass transistor.