Output Stage Amplifier Control for Higher PSRR and Lower THD
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Solution Overview
Problem
Low-power amplifier designs suffer from increased Total Harmonic Distortion (THD) at high frequencies due to insufficient loop gain and noisy supply voltages, which result in signal distortion, necessitating enhanced Power Supply Rejection Ratio (PSRR) at the output stage.
Innovation Solution
The implementation of a detection circuit and a control amplifier circuit that adjust voltages at specific control nodes to mitigate disturbances in supply voltages, using a different path gain control amplifier circuit to manage quiescent current and enhance PSRR, thereby preventing output signal distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If low-power amplifier design is used, then power consumption is reduced, but Total Harmonic Distortion increases at high frequencies due to insufficient loop gain
Solution Approach 1:
The amplifier is divided into multiple stages including a first output stage, a second output stage, and a control amplifier stage. Each stage has specific functions: the first output stage provides initial amplification, the control amplifier detects disturbances and generates correction signals, and the second output stage delivers the final output. This segmentation allows the low-power design to maintain sufficient loop gain through the distributed architecture while keeping overall power consumption low.
Solution Approach 2:
The control amplifier stage performs preliminary detection of disturbances in the supply voltage before they reach the output stage. By detecting these disturbances early and generating correction signals in advance, the system can compensate for potential THD issues before they manifest in the final output, maintaining signal quality without increasing power consumption.
2Device complexity
If conventional output stage is used, then device complexity is low, but Power Supply Rejection Ratio is insufficient causing signal distortion from noisy supply voltage
Solution Approach 1:
A control amplifier stage is introduced as an intermediary between the supply voltage and the output stage. This control amplifier detects disturbances in the supply voltage and generates correction signals that are applied to the output stage, effectively mediating the harmful effects of noisy supply voltage and improving PSRR without requiring complex changes to the basic output stage structure.
Solution Approach 2:
The control amplifier stage implements a feedback mechanism by continuously monitoring the supply voltage for disturbances and generating correction signals that are fed back to the output stage. This feedback loop enables the system to automatically compensate for supply voltage variations and improve PSRR while maintaining a relatively simple overall structure.
Data Source
AI summary
An amplifier circuit is disclosed. The amplifier circuit includes a detection circuit, a control amplifier circuit and an output stage. The detection circuit detects disturbances occurring in a first supply voltage and provides detection results. The control amplifier circuit controls a first voltage provided to a first control node and a second voltage provided to a second control node in response to the detection results. The output stage circuit includes a first output power transistor coupled to the control amplifier circuit at the first control node and a second output power transistor coupled to the control amplifier circuit at the second control node. The first voltage and the second voltage are controlled differently when a disturbance is detected to have occurred.