LDO Regulator Bias Current Dynamics for Step Response
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Solution Overview
Problem
Low-dropout (LDO) regulators face conflicting objectives in optimizing quiescent current, power supply rejection ratio (PSRR), and step response, leading to suboptimal performance in battery-powered devices where low voltage operation and noise suppression are critical.
Innovation Solution
The proposed LDO voltage regulator incorporates a power transistor with a control electrode receiving a driver signal, a reference circuit, and a feedback network providing multiple feedback signals to an error amplifier, which adjusts the bias current based on output voltage and current gradients to minimize quiescent current while maintaining high PSRR and fast step response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the regulator is designed for fast step response, then the output voltage swing suppression is improved, but the quiescent current increases
Solution Approach 1:
The bias current of the error amplifier is made dynamically adjustable based on operating conditions. During transient events, the circuit detects voltage gradients and increases the bias current to accelerate the step response. During steady-state operation, the bias current is reduced to minimize quiescent current consumption, thus resolving the contradiction between fast response and low power consumption.
Solution Approach 2:
The patent changes the bias current parameter of the error amplifier based on the operating mode. By detecting the voltage gradient across the output capacitor, the circuit determines whether to operate in high-current (fast response) mode or low-current (low power) mode, thereby optimizing the trade-off between step response speed and quiescent current.
2Object-affected harmful factors
If the regulator is designed for high PSRR, then the noise suppression is improved, but the quiescent current increases
Solution Approach 1:
The error amplifier's bias current is dynamically adjusted based on the detected voltage gradient. During transient conditions requiring high PSRR, the bias current is increased to enhance noise suppression capability. During steady-state operation, the bias current is reduced to minimize power consumption, thus resolving the contradiction between high PSRR and low quiescent current.
3Use of energy by moving object
If the regulator is designed for low quiescent current, then the battery life is extended, but the step response becomes slow
Solution Approach 1:
The circuit continuously monitors the voltage gradient across the output capacitor in advance to detect transient conditions. When a transient is detected, the bias current is immediately increased to prepare for fast step response. This preliminary detection and rapid response mechanism allows the regulator to maintain low quiescent current during normal operation while ensuring fast step response when needed.
4Use of energy by moving object
If the regulator is designed for low voltage operation, then the portability is improved, but the breakdown voltage is reduced
Solution Approach 1:
The patent employs parameter changes in the transistor operating points and biasing conditions to enable low voltage operation while maintaining adequate breakdown margins. By carefully adjusting the bias currents and voltage drops across different components, the regulator achieves operation at low input voltages suitable for portable devices while preventing breakdown through proper parameter selection.
Data Source
AI summary
A low-dropout voltage regulator includes a power transistor configured to receive an input voltage and to provide a regulated output voltage at an output voltage node. The power transistor includes a control electrode configured to receive a driver signal. A reference circuit is configured to generate a reference voltage. A feedback network is coupled to the power transistor and is configured to provide a first feedback signal and a second feedback signal. The first feedback signal represents the output voltage and the second feedback signal represents an output voltage gradient. An error amplifier is configured to receive the reference voltage and the first feedback signal representing the output voltage. The error amplifier is configured to generate the driver signal dependent on the reference voltage and the first feedback signal. The error amplifier includes an output stage that is biased with a bias current responsive to the second feedback signal.