Fully Differential Class AB Speaker Amplifier With Ripple Immunity
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Solution Overview
Problem
Current audio amplifier designs face challenges such as noise propagation from power supplies, complex design requirements for intermediate stages, especially in class-G operation, and difficulty in protecting gates of low voltage PMOS devices, leading to inefficiencies and area constraints.
Innovation Solution
A fully differential amplifier topology operating in class AB mode with a differential drive intermediate stage, common mode regulation, and class AB regulation, using dual differentiation of input error signals and current sensing to regulate quiescent currents, allowing for area savings and improved immunity to supply ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If rail-to-rail intermediate stage is used to drive high/low side power devices, then the amplifier can operate in class AB mode, but noise from power supplies propagates through Miller compensation capacitors degrading PSR
Solution Approach 1:
The patent introduces a dedicated intermediate stage that acts as a mediator between the power supply and output stage. This intermediate stage processes the error signal and drives the high/low side power devices without directly connecting the noisy power supply to the Miller compensation capacitors, thereby blocking noise propagation while maintaining class AB operation efficiency.
2Loss of energy
If supply voltage varies widely as in class-G operation, then power efficiency improves, but it becomes much more difficult to keep the intermediate stage biased in linear mode requiring complex and larger design
Solution Approach 1:
The patent implements dynamic biasing control for the intermediate stage that automatically adjusts the bias conditions based on the instantaneous supply voltage. This dynamic adaptation allows the intermediate stage to remain properly biased in linear mode across wide supply variations without requiring complex protective circuitry or larger design margins.
3Loss of energy
If cascaded low voltage PMOS devices are used, then power efficiency improves, but it becomes much more complicated to protect their gates from seeing the full supply especially at start-up
Solution Approach 1:
The patent applies preliminary protection actions by implementing gate voltage clamping and protection circuitry that prevents the full supply voltage from appearing at the PMOS gate terminals during start-up and transient conditions. This preliminary protection is built into the circuit architecture, eliminating the need for complex external protection mechanisms.
4Object-affected harmful factors
If fully differential amplifier topology is implemented, then immunity against supply ripple improves, but design complexity of intermediate stage increases
Solution Approach 1:
The patent segments the intermediate stage into distinct functional blocks: a differential error amplifier section and a differential drive section. This segmentation allows each block to be optimized independently for its specific function, simplifying the overall design while maintaining the supply ripple immunity benefits of the fully differential topology.
Data Source
AI summary
Circuits and methods to achieve a new fully differential amplifier topology in class AB mode are disclosed. In a preferred embodiment of the disclosure the differential amplifier is diving dynamic speakers. An differential intermediate stage combines four different feedbacks, all sharing four high impedance nodes: main loop regulation feedback, common mode regulation feedback, and output stage quiescent current regulation for both differential output stage branches.