Load-Dependent Miller Circuit in Capacitor-Less LDO Regulators
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Solution Overview
Problem
Capacitor-less low dropout (LDO) regulators face challenges in maintaining a high power supply rejection ratio (PSRR) due to varying load conditions, which affects their ability to effectively suppress output voltage ripples.
Innovation Solution
A load-dependent Miller circuit is introduced, allowing dynamic adjustment of capacitance in response to load conditions, shifting the dominant pole of the LDO regulator and improving PSRR by altering capacitance values based on signals from a sensing terminal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a capacitor-less LDO regulator is used to reduce area, then the area occupied by output capacitor is reduced, but the PSRR deteriorates under varying load conditions
Solution Approach 1:
The patent implements a dynamic capacitance adjustment mechanism where the Miller circuit capacitance is varied based on load conditions. The control circuit monitors the load current and dynamically adjusts the Miller circuit capacitance to maintain optimal PSRR across different operating conditions, transforming a static capacitor-less design into a dynamically adaptive system.
Solution Approach 2:
The patent changes the capacitance parameter of the Miller circuit dynamically based on load conditions. By adjusting the capacitance value according to the sensed load current, the system maintains high PSRR performance without requiring a large fixed output capacitor, thus resolving the contradiction between area reduction and PSRR maintenance.
2Device complexity
If a fixed capacitance Miller circuit is used, then the circuit structure is simplified, but the PSRR cannot be maintained under varying load conditions
Solution Approach 1:
The patent introduces a feedback mechanism where the control circuit continuously monitors the load current through the sensing terminal and adjusts the Miller circuit capacitance accordingly. This closed-loop feedback system ensures that the PSRR is maintained under varying load conditions while adding minimal complexity to the overall circuit structure.
Solution Approach 2:
The control circuit automatically adjusts the Miller circuit capacitance based on the sensed load conditions without requiring external intervention. The system serves itself by monitoring its own operating state and making real-time adjustments to maintain optimal performance.
Data Source
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AI summary
A low dropout regulator is provided. The low dropout regulator includes a first gain-stage, a second gain-stage, an output setting stage, and a Miller circuit. The first gain-stage generates a signal at a first gain-stage terminal based on a signal at a second gain-stage signal. The second gain-stage receives the signal at the first gain-stage terminal and generates a signal at a sensing terminal. The output setting stage outputs a load current to an output terminal. The signal at the sensing terminal is changed with the load current. The Miller circuit is electrically connected to the first gain-stage, the second gain-stage, and the output setting stage: The Miller circuit provides a capacitance related to a dominant pole of the low dropout regulator. The capacitance is changed with the signal at the sensing terminal.