Multi-Stage Amplifier Bias Loop for Fast Stable Output Regulation
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Solution Overview
Problem
Conventional multi-stage amplifier circuits face issues with low quiescent current causing voltage overshoot and inability to absorb leakage current, leading to unstable output voltage, and slow response to transient variations due to Miller compensation, which limits the loop bandwidth and response speed.
Innovation Solution
The proposed multi-stage amplifier circuit incorporates an additional loop to control the bias current of output transistors, featuring a transconductance amplifier circuit with differential transistors and an impedance adjustment device, allowing for quick resistance adjustments based on feedback and reference signals, enhancing response speed and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If Miller compensation capacitor is used to enhance stability, then stability is improved, but response speed becomes slow
Solution Approach 1:
The amplifier circuit is divided into two independent control loops: a main feedback loop for stability and an adjustment loop for fast transient response. The main feedback loop includes the Miller compensation capacitor CM for stability, while the adjustment loop uses transistor MC14 and impedance adjustment device MC7 for rapid response to transient variations, allowing both stability and speed requirements to be met simultaneously
Solution Approach 2:
The adjustment loop acts as an intermediary mechanism that quickly responds to transient output voltage variations before the main feedback loop needs to act. The adjustment transistor MC14 and impedance adjustment device MC7 form a fast-acting intermediary control path that compensates for the slow response caused by Miller compensation, enabling both stability and fast response
2Use of energy by moving object
If quiescent current is reduced to save power, then power consumption is improved, but current sink function becomes insufficient causing voltage overshoot
Solution Approach 1:
The bias current of the output transistor is made dynamically adjustable through the adjustment loop. During transient states, the adjustment transistor MC14 increases the bias current to provide sufficient current sink capability and prevent voltage overshoot. During steady-state operation, the bias current is reduced to minimize power consumption. This dynamic adjustment allows the system to achieve both low power consumption and reliable output voltage stability
Solution Approach 2:
The adjustment loop provides feedback control for the output transistor bias current based on output voltage variations. When the output voltage deviates during transient states, the feedback mechanism activates to increase the bias current, ensuring sufficient current sink capability. This feedback control enables the system to maintain reliable output voltage stability while keeping power consumption low during normal operation
Data Source
AI summary
A multi-stage amplifier circuit includes: a front stage amplification circuit, for generating a front stage amplification signal according to a difference between a primary reference signal and a primary feedback signal; an output adjustment circuit, for generating a driving signal according to the front stage amplification signal; and an output transistor, controlled by the driving signal to generate an output signal. The output adjustment circuit includes: an adjustment transistor biased by a differential current of the front stage amplification signal; and an impedance adjustment device biased by the differential current. A resistance of the impedance adjustment device is determined by a difference between an adjustment feedback signal and an adjustment reference signal. The driving signal is determined by a product of a resistance of the impedance adjustment device multiplied by the differential current of the front stage amplification signal, and a drain-source voltage of the adjustment transistor.