Class AB Amplifier Topology With Local Common-Mode Feedback
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Solution Overview
Problem
Class AB amplifiers trade efficiency for better linearity, resulting in increased distortion and power wastage due to their complex three-stage configuration and high DC bias current consumption.
Innovation Solution
A dual-stage class AB amplifier design is implemented, combining the operational transconductance and buffer stages into a single stage, and utilizing a local common mode feedback circuit to reduce the number of transistors and DC bias current, while maintaining amplification efficiency and reducing crossover distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a class AB amplifier uses a three-stage configuration with high DC bias current to eliminate crossover distortion, then linearity is improved, but power consumption increases and efficiency decreases
Solution Approach 1:
The patent extracts and removes the buffer stage from the traditional three-stage class AB amplifier configuration, reducing it to a dual-stage design. This elimination of the redundant buffer stage reduces the number of transistors and DC bias current requirements while maintaining the essential amplification and distortion compensation functions through the remaining operational transconductance stage and output stage
Solution Approach 2:
The patent implements a local common mode feedback circuit that performs multiple functions simultaneously: it compensates for crossover distortion, stabilizes the operating point, and improves linearity. This multi-functional approach eliminates the need for separate dedicated circuits for each function, thereby reducing overall power consumption and component count while maintaining reliability
2Reliability
If a class AB amplifier uses a three-stage configuration with multiple transistors to compensate for distortion, then distortion compensation is improved, but device complexity increases
Solution Approach 1:
The patent merges the distortion compensation function into the local common mode feedback circuit within the operational transconductance stage, combining it with the primary amplification function. This integration eliminates the need for separate distortion compensation circuits and reduces the total number of transistors while maintaining effective distortion compensation through the unified feedback mechanism
Solution Approach 2:
The patent extracts and removes the buffer stage entirely from the amplifier configuration, eliminating the transistors associated with that stage. The essential distortion compensation and amplification functions are maintained in the reduced dual-stage configuration, achieving simpler device architecture without sacrificing distortion compensation performance
3Reliability
If a class AB amplifier uses high DC bias current to operate transistors in linear region, then crossover distortion is reduced, but current consumption increases
Solution Approach 1:
The patent implements a local common mode feedback circuit that dynamically adjusts the operating point of the transistors to maintain optimal linear operation. This feedback mechanism ensures adequate bias current is provided only when needed to prevent crossover distortion, rather than maintaining constantly high DC bias current, thereby reducing overall current consumption while maintaining reliability
Solution Approach 2:
The patent uses dynamic biasing through the local common mode feedback circuit that adjusts transistor operating conditions in real-time based on signal conditions. This dynamic approach provides sufficient bias current to prevent crossover distortion during signal transitions while reducing bias current during steady-state operation, achieving the trade-off between distortion reduction and current consumption
Data Source
AI summary
An amplifier includes a first stage and a second stage. The first stage includes a floating current source to maintain current within a threshold. The first stage also includes a local common mode feedback configured to provide gain to an input signal. Moreover, the second stage includes a driver that provides a load current to a load coupled to the amplifier.