Split Feedback LDO Amplifier for Stable Load Regulation
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Solution Overview
Problem
Amplifiers face challenges in load regulation due to variations in equivalent series resistance (ESR) of external capacitors, which affect stability and make compensation difficult, and the addition of intentional internal resistance to mitigate this degrades load regulation and is temperature-sensitive.
Innovation Solution
A split feedback technique is employed, where an intentionally added impedance is included in the amplifier output, and the feedback resistance and capacitance are connected to opposite ends of this impedance, with the junction point connected to the negative input of the amplifier, allowing for independent choice of feedback resistor values and supporting external feedback for noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If intentional internal resistance is added to reduce ESR variation impact, then stability is improved, but load regulation degrades
Solution Approach 1:
The feedback path is segmented into two separate paths: one through the capacitor Cf for AC stability and another through the resistor Rf for DC load regulation. This segmentation allows each path to independently optimize its function without interfering with the other, resolving the contradiction between stability and load regulation.
Solution Approach 2:
The intentional resistance Resr acts as an intermediary element placed in series with the feedback capacitor Cf. This intermediary allows the capacitor to provide AC stability while the resistor Rf provides DC load regulation, mediating between the conflicting requirements of stability and load regulation.
2Reliability
If intentional resistance value is increased to compensate for low temperature variation, then stability is maintained, but load regulation degrades even more at high temperatures
Solution Approach 1:
The feedback function is segmented into AC coupling (through Cf and Resr) for temperature stability and DC regulation (through Rf) for load regulation. This allows independent optimization of each function, resolving the temperature vs. load regulation contradiction.
Solution Approach 2:
Different parts of the feedback circuit have different qualities optimized for different functions: the capacitor Cf and resistor Resr provide AC coupling with temperature compensation, while the resistor Rf provides DC load regulation. Each component is optimized for its specific local function.
3Manufacturing precision
If feedback resistor values are fixed to optimize load regulation, then load regulation is improved, but adaptability to different applications is reduced
Solution Approach 1:
The split feedback circuit provides universal functionality by separating AC and DC feedback paths. The same circuit topology can be used across different applications with varying resistor values to optimize for different requirements, making the design universally applicable while maintaining both stability and load regulation.
Data Source
AI summary
A circuit arrangement and method for improving load regulation in an amplifier (e.g., LDO amplifier) uses a feedback circuit including a parallely connected feedback resistance Rf and a noise reduction feedback capacitance Cf, wherein an external capacitance has equivalent series resistance (ESR). The circuit arrangement includes a resistance Resr in the amplifier output, a junction point of the feedback resistance Rf and the feedback capacitor Cf being connected to a negative input of the LDO amplifier. Additionally, the circuit arrangement might include a resistance Rintentional in between Cf and Rf. The circuit arrangement provides good load regulation and better stability without increase in power/area. The arrangement supports external feedback mode providing design flexibility without compromising amplifier-stability, which provides high output current drive capability or enables driving heavy output capacitance. In a preferred form the invention includes split feedback including AC feedback and DC feedback.