LDO Regulator Gm-Booster Circuit for Low IQ and Fast Transients
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Solution Overview
Problem
It is challenging to achieve both low quiescent current (IQ) and fast transient operation in a single linear voltage regulator, particularly in portable and IoT devices where battery life is a concern, due to the tradeoff between these performance metrics in existing LDO regulator designs.
Innovation Solution
A power supply circuit with a multi-stage error amplifier and a transconductance (gm)-booster circuit is implemented, using cascoded transistors and Miller compensation, to enhance the effective transconductance of the cascoded transistors, allowing for fast transient operation while maintaining low IQ.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a conventional LDO regulator design is used, then the quiescent current is reduced, but the transient response speed deteriorates
Solution Approach 1:
The error amplifier is divided into two separate amplifiers: a first amplifier that drives the gate of the pass transistor and a second amplifier that biases the gate of the cascode transistor. This segmentation allows each amplifier to be optimized independently, with the second amplifier providing fast transient response while the first amplifier maintains low quiescent current operation.
Solution Approach 2:
A cascode transistor is introduced as an intermediary element between the error amplifier output and the pass transistor gate. The cascode transistor, biased by the second amplifier, acts as a buffer that provides fast transient response while allowing the first amplifier to operate at low current, thus resolving the contradiction between low quiescent current and fast transient response.
2Speed
If a fast transient response is achieved, then the transient operation performance is improved, but the quiescent current increases
Solution Approach 1:
The error amplifier is divided into two separate amplifiers: a first amplifier that drives the gate of the pass transistor and a second amplifier that biases the gate of the cascode transistor. This segmentation allows each amplifier to be optimized independently, with the second amplifier providing fast transient response while the first amplifier maintains low quiescent current operation.
Solution Approach 2:
The circuit dynamically switches between different operational modes: during transient conditions, the second amplifier provides high-speed response by rapidly adjusting the cascode transistor gate voltage, while during steady-state operation, the system operates with low quiescent current. This dynamic behavior allows the circuit to achieve fast transient response without continuously consuming high current.
Data Source
AI summary
Apparatus and methods for voltage regulation. One example circuit generally includes a first transistor having a source coupled to a Vin node and having a drain coupled to a Vout node; a second transistor having a drain coupled to a gate of the first transistor; a third transistor having a drain coupled to a source of the second transistor and having a source coupled to a reference potential node of the power supply circuit; a first amplifier having a first input coupled to a reference voltage node and having an output coupled to a gate of the third transistor, with feedback between the Vout node and a second input of the first amplifier; and a second amplifier having a first input coupled to a bias node, having a second input coupled to the source of the second transistor, and having an output coupled to a gate of the second transistor.