Auto-Biased Class AB Amplifier for Overshoot Control
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Solution Overview
Problem
Class AB amplifiers used in Ethernet physical layers suffer from signal distortion due to high stray inductance, leading to signal integrity issues and efficiency trade-offs, as they either experience overshoot/undershoot or crossover distortion when operating at class A or B modes.
Innovation Solution
A system that automatically adjusts the quiescent current of the amplifier to operate between pure class A and B modes based on stray inductance, using a comparator and control circuit to monitor and adjust the current, thereby reducing signal overshoot and optimizing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the amplifier operates at class AB mode, then efficiency is improved, but signal distortion increases due to overshoot and undershoot caused by stray inductance
Solution Approach 1:
The amplifier's operating class is made dynamic rather than fixed. The system continuously monitors output signals for overshoot/undershoot conditions and automatically adjusts the operating class between class A and class AB, allowing the amplifier to adapt its behavior based on real-time signal conditions and stray inductance levels.
Solution Approach 2:
A feedback mechanism is implemented where the output signal is monitored to detect overshoot and undershoot caused by stray inductance. This feedback information is used to control the adjustment of the amplifier's operating class, creating a closed-loop system that maintains signal integrity while optimizing efficiency.
2Reliability
If the amplifier operates at class A mode, then signal integrity is improved by reducing overshoot and undershoot, but efficiency deteriorates
Solution Approach 1:
The system dynamically adjusts the operating class based on detected signal conditions. When overshoot/undershoot is detected indicating high stray inductance impact, the system transitions toward class A operation to improve signal integrity. When signal conditions are favorable, it transitions to class AB to improve efficiency, avoiding continuous operation at the less efficient class A mode.
3Use of energy by moving object
If the amplifier operates at class B mode, then efficiency is improved, but crossover distortion is generated when the output signal changes polarity
Solution Approach 1:
The system dynamically selects between class AB and class A operation based on detected signal conditions. When crossover distortion is detected or when operating conditions indicate potential for crossover distortion, the system adjusts toward class A operation to eliminate the distortion, while maintaining class AB operation during normal conditions to preserve efficiency.
4Reliability
If wire bonding and packaging are designed with larger dimensions, then amplifier performance is improved, but stray inductance increases leading to higher signal distortion
Solution Approach 1:
The system implements feedback monitoring of the output signal to detect the effects of stray inductance (overshoot and undershoot). When these effects are detected, the system automatically adjusts the operating class to compensate for the inductance effects, allowing the amplifier to maintain performance despite the presence of stray inductance from wire bonding and packaging.
Data Source
AI summary
This disclosure relates to monitoring signal overshoot of an amplifier generated signal and automatically adjusting a quiescent current of the amplifier as a function of the monitored signal overshoot.