Capacitor-Free LDO Regulator Using Internal RC Compensation
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Solution Overview
Problem
Low drop out (LDO) regulators face challenges in maintaining stable voltage regulation and handling loads greater than 100 milliamps without external capacitors, which are often required for high performance and stability, and can occupy significant space on circuit boards.
Innovation Solution
A novel LDO regulator design featuring an error amplifier with NMOS and PMOS differential pairs, a startup circuit, reference filter, quiescent current control, and pulse generator, along with internal RC networks for phase compensation, allowing operation without external capacitors and providing stable voltage regulation across varying load currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external capacitors are used at input and output interfaces, then regulator stability and performance are improved, but circuit board space requirement increases
Solution Approach 1:
The patent merges the functions of external input and output capacitors into internal compensation circuits within the regulator. The error amplifier includes integrated compensation capacitors and resistors that perform the stability function previously requiring external components, thereby eliminating the need for external capacitors and reducing circuit board space while maintaining regulator stability.
Solution Approach 2:
The compensation circuits are nested within the error amplifier structure of the regulator. The internal capacitors and resistors are integrated into the existing regulator architecture, with the compensation network embedded within the error amplifier block, allowing the regulator to achieve stability without external capacitors.
2Reliability
If external capacitors with low ESR are specified, then regulator stability is improved, but component selection constraints increase
Solution Approach 1:
The patent extracts the stability-critical capacitor function from external components and places it internally within the regulator. By integrating the compensation capacitor within the error amplifier, the regulator no longer depends on external capacitor ESR characteristics, thereby eliminating component selection constraints while maintaining stability.
Solution Approach 2:
The regulator performs its own compensation function through internal circuits rather than relying on external components. The error amplifier includes built-in capacitors and resistors that automatically provide the necessary phase compensation and stability, making the regulator self-sufficient and independent of external capacitor specifications.
3Area of stationary object
If capacitor-free design is implemented, then circuit board space is reduced, but ability to handle loads greater than 100 milliamps deteriorates
Solution Approach 1:
The patent implements dynamic compensation within the error amplifier that adapts to varying load conditions. The internal compensation circuits are designed to maintain stability and performance across a wide load range, enabling the regulator to handle loads greater than 100 milliamps effectively without external capacitors. The dynamic response is optimized through carefully selected internal RC time constants.
4Reliability
If external capacitors are used, then voltage regulation stability is improved, but equivalent series resistance effects adversely affect performance
Solution Approach 1:
The regulator uses internal compensation circuits that eliminate dependence on external capacitor ESR. The error amplifier includes built-in capacitors and resistors that provide the necessary phase compensation without being affected by external component characteristics, thereby removing ESR-related performance degradation while maintaining voltage regulation stability.
Data Source
AI summary
A low drop out (LDO) regulator that includes a novel error amplifier, which is arranged with a first stage that employs both NMOS and PMOS devices that are similarly doped in differential pairs and a second stage that operates with NMOS and PMOS devices in a push-pull arrangement. In addition to the error amplifier, the LDO regulator can also include a startup circuit coupled to an enable voltage, a reference filter circuit coupled to a reference voltage, an output circuit, a quiescent current control circuit, and a pulse generator circuit. Also, an internal RC network is provided to compensate for phase shift. The integrated operation of the components of the regulator enables stable and fast operation of an LDO regulator with no external capacitors connected to the input or output terminals.