Dual-Stage Source/Sink Amplifier for Quiescent Current Control
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Solution Overview
Problem
Class-AB output stages in amplifiers face complexity in determining and maintaining quiescent current, leading to inefficiencies and high short-circuit currents due to limitations in tracking fast-changing signals and requiring complex circuitry.
Innovation Solution
The implementation of an amplifier circuit with two driver transistors that automatically switch between sourcing and sinking modes based on digital control signals, allowing the quiescent current to be based on a constant current source similar to class-A stages, minimizing high short-circuit currents by reversing transistor roles during mode changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If class-AB output stage is used to improve efficiency and reduce quiescent current, then power efficiency is improved, but determining and maintaining quiescent current becomes complex and requires additional circuitry
Solution Approach 1:
The patent inverts the conventional approach by using the output stage transistors themselves to determine quiescent current through their on-resistance measurements, rather than using separate sensing circuits. The roles of the transistors are reversed between measurement mode (determining quiescent current) and drive mode (sourcing/sinking current), eliminating the need for additional determination circuitry.
Solution Approach 2:
The output stage transistors serve multiple functions: they act as both the drive elements for sourcing/sinking current and as the measurement elements for determining quiescent current. The same transistors are used in both measurement mode and drive mode, eliminating the need for separate dedicated circuits for quiescent current determination.
2Loss of energy
If class-AB output stage is used to reduce quiescent current, then power efficiency is improved, but high short-circuit currents occur due to inability to track fast-changing signals
Solution Approach 1:
The patent performs preliminary measurement of the quiescent current and on-resistance values before the actual drive operation. By determining the quiescent current in advance during a measurement mode, the system can quickly switch to drive mode without experiencing high short-circuit currents, as the transistors are already in the correct operating state.
Solution Approach 2:
The patent implements dynamic switching between measurement mode and drive mode based on the operating conditions. The system can quickly transition between states to track fast-changing signals, preventing the transistors from remaining in a static class-AB state that causes high short-circuit currents during rapid transitions.
3Measurement precision
If additional feedback loop is added to determine quiescent current, then measurement precision is improved, but device complexity increases and three-stage amplifier is required
Solution Approach 1:
The patent merges the quiescent current determination function with the existing two-stage amplifier architecture. The measurement is performed using the same transistors and basic circuit elements already present in the amplifier, combining multiple functions into the existing structure rather than adding separate determination stages.
Solution Approach 2:
The output stage transistors themselves perform the quiescent current determination by utilizing their own on-resistance characteristics. The system uses self-measurement through the transistor channels rather than requiring external sensing circuits, allowing the amplifier to determine its own quiescent current without additional dedicated measurement stages.
Data Source
AI summary
An amplifier circuit includes a first stage that receives a signal input and a control input and that generates first stage outputs. A second stage that communicates with the first stage and the control input and that includes a current source drivers. Each of the current source drivers have a constant current source mode and a driver mode. The constant current source mode and the driver mode are selected based on the signal input and the control input. A comparator circuit compares current through the current source drivers with a reference current. A control circuit generates the control input based on the comparison.