Class AB Output Stage With Current-Mirror Quiescent Control
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Solution Overview
Problem
Class AB amplifier circuit arrangements face challenges in operating at low supply voltages with high power supply rejection ratio and minimal current consumption, often suffering from harmonic distortion and mismatch issues during handoff between active elements.
Innovation Solution
The implementation of a class AB amplifier output stage circuit using PMOS and NMOS transistor current mirrors, coupled with monitoring circuits such as operational transconductance amplifiers or differential amplifiers, to regulate quiescent current and equalize voltage drops across impedances, thereby minimizing current consumption and improving power supply rejection ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a stack of two diodes is used to adjust quiescent current in Class AB amplifier, then quiescent current can be controlled, but the circuit cannot operate well at low supply voltages
Solution Approach 1:
The patent changes the operating parameters by using transistors instead of diodes, allowing the circuit to operate at low supply voltages while maintaining quiescent current control through the transistor's current mirror configuration
Solution Approach 2:
The patent introduces an intermediary current mirror circuit using transistors that mediates between the power supply and the output stage, enabling low-voltage operation while still providing effective quiescent current adjustment
2Use of energy by moving object
If current mirrors are used to generate and mirror current to the output, then low supply voltage operation is achieved, but current consumption is doubled
Solution Approach 1:
The patent segments the current mirror function into separate PMOS and NMOS circuits, with each handling half of the output waveform, thereby reducing the simultaneous current draw compared to a single high-current mirror configuration
Solution Approach 2:
The patent implements periodic action by having PMOS and NMOS circuits alternate in active mode according to the input waveform, with each circuit active for half the cycle, reducing peak current consumption while maintaining continuous output
3Object-generated harmful factors
If Class AB amplifier uses two active elements in active mode more than 50% of the time, then harmonic distortion is decreased, but adjustment of output quiescent current becomes problematic
Solution Approach 1:
The patent implements feedback by monitoring the voltage drops across impedances in the PMOS and NMOS circuits and using operational transconductance amplifiers to generate compensating currents that equalize the voltage drops, thereby maintaining proper quiescent current balance
Solution Approach 2:
The patent introduces intermediary monitoring circuits and operational transconductance amplifiers that mediate between the PMOS and NMOS current mirror circuits, automatically balancing the quiescent current by detecting and compensating for mismatches
4Loss of energy
If low supply voltage operation is implemented with low current consumption, then power efficiency is improved, but power supply rejection ratio deteriorates
Solution Approach 1:
The patent uses feedback through operational transconductance amplifiers that monitor voltage drops and generate compensating currents, creating a regulation mechanism that rejects power supply variations while maintaining low current consumption
Data Source
AI summary
The present disclosure relates to a class AB amplifier output stage.