Adaptive-Biased LDO Output Stage for Stable Clean Supply Voltage
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Solution Overview
Problem
Ultra-low-power low dropout (LDO) voltage regulators face stability issues and poor transient performance due to limited bandwidth and power supply rejection ratio (PSRR), and adaptive biasing worsens error amplifier parameters, especially in ultra-low-power applications where kickback on the reference voltage is a concern.
Innovation Solution
An LDO voltage regulator with an output stage that is adaptively biased without affecting the error amplifying circuit, using a bias transistor controlled by the error signal and a cascode amplifier for high bandwidth, along with a current source to ensure stability at zero load current, and an impedance circuit to manage loop gain at low output currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If adaptive biasing is applied to the error amplifier to reduce power consumption, then power consumption is reduced, but bandwidth and stability deteriorate
Solution Approach 1:
The biasing system is segmented into two independent parts: the error amplifier receives fixed biasing to maintain stability and bandwidth, while the output stage receives adaptive biasing to reduce power consumption. This segmentation allows each part to be optimized independently without compromising the other.
Solution Approach 2:
Adaptive biasing is applied locally only to the output stage where it is most beneficial for power reduction, while the error amplifier maintains fixed biasing to preserve its stability and performance characteristics. This local application of adaptive biasing avoids the stability issues that would affect the entire system.
2Speed
If adaptive biasing is applied to improve transient performance, then transient performance is improved, but error amplifier parameters such as DC-gain and PSRR worsen
Solution Approach 1:
The biasing control is segmented so that only the output stage receives adaptive biasing signals that respond to transient conditions, while the error amplifier maintains constant biasing to preserve its DC-gain and PSRR characteristics.
Solution Approach 2:
An intermediate biasing stage is introduced between the error amplifier and the output device. This intermediate stage receives adaptive biasing and transfers it to the output device, acting as a mediator that allows adaptive performance improvement without directly affecting the error amplifier's precision parameters.
3Use of energy by moving object
If ultra-low-power biasing is used, then power consumption is reduced, but bandwidth is limited resulting in stability issues
Solution Approach 1:
Ultra-low-power adaptive biasing is applied locally to the output stage where it provides sufficient performance improvement, while the error amplifier operates with fixed biasing that maintains adequate bandwidth and stability margins.
Data Source
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AI summary
A low dropout, LDO, voltage regulator (100; 200) comprising: an LDO input (102) configured to receive an input voltage signal; an LDO output (104) configured to output an output voltage signal; an error amplifying circuit (108), which is configured to receive a reference signal and a feedback signal associated with the output voltage signal, the error amplifying circuit (108) being further configured to output an error signal; an output stage (112), which is configured to receive the error signal and output a control signal; and an output device (106), which is connected to the LDO input (102) and configured to provide the output voltage signal and which is controlled by the control signal for regulating the output voltage signal; wherein the output stage (112) is connected to the input voltage for receiving an adaptive bias current.