Cascaded LDO Voltage Regulator Eliminates External Capacitors
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Solution Overview
Problem
Conventional voltage regulator circuits often require external capacitors to stabilize output voltage, which can complicate integration and increase circuit complexity, especially in integrated circuit (IC) implementations.
Innovation Solution
A cascaded two-stage voltage regulator design is introduced, where the first stage is capacitor-less and utilizes a PMOS source follower, and the second stage includes an operational amplifier and current mirror, both implemented with PMOS transistors, to provide a regulated output voltage without external capacitors, enhancing power supply rejection ratio (PSRR) and reducing circuit complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If external capacitors are used to stabilize output voltage in conventional voltage regulator circuits, then voltage stability is improved, but circuit complexity and integration difficulty increase
Solution Approach 1:
The patent extracts and eliminates the external capacitor component from the voltage regulator circuit by redesigning the compensation network to use only resistive elements (R1, R2, R3) and the operational amplifier. This removes the need for external capacitors while maintaining voltage stability through the op-amp's high gain and feedback mechanism.
Solution Approach 2:
The operational amplifier serves multiple functions simultaneously: it provides voltage amplification, implements feedback control for stability, and replaces the traditional capacitor-based compensation network. This multi-functionality eliminates the need for separate capacitor components while achieving the same stabilizing effect.
2Stability of the object's composition
If external capacitors are coupled to voltage regulator stages, then voltage stabilization is achieved, but integration ease deteriorates
Solution Approach 1:
The patent merges the compensation function traditionally performed by external capacitors into the integrated circuit itself by using the operational amplifier and resistive network. All stabilization components are combined within the IC, eliminating the need for external capacitor connections and simplifying the manufacturing and integration process.
Solution Approach 2:
By extracting the capacitor function from the external circuit and implementing it internally through the op-amp's feedback mechanism, the patent achieves voltage stabilization entirely within the integrated circuit, improving ease of manufacture and integration.
3Device complexity
If capacitor-less first stage with PMOS source follower is used, then circuit complexity is reduced, but power supply rejection ratio may be affected
Solution Approach 1:
The operational amplifier in the second stage implements a feedback mechanism that compensates for the reduced PSRR of the capacitor-less first stage. The high-gain feedback loop detects and corrects voltage variations, maintaining overall PSRR performance while keeping the first stage simple and capacitor-less.
Solution Approach 2:
The voltage regulator is divided into two functional stages: the first stage (PMOS source follower) handles basic voltage tracking with simple structure, while the second stage (op-amp with feedback) handles precision regulation and PSRR. This segmentation allows each stage to be optimized for its specific function.
Data Source
AI summary
A voltage regulator is disclosed. The voltage regulator is cascaded, including first and second stages. The first stage may be a capacitor-less first stage that includes a source follower implemented with a first PMOS transistor, with the first PMOS transistor receiving a first reference voltage on its respective gate terminal. The first stage is coupled to receive a first voltage from an external voltage supply, and to provide a second voltage to the second stage. The second stage may be directly and exclusively coupled to the first stage, with no capacitor or connection for one coupled to the first stage output. The second stage may provide an output voltage, on an output node, with the output voltage being less than the second voltage.