Digitally Controlled Driver Amplifier With DC Offset Equalization
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Solution Overview
Problem
Conventional AB class amplifiers face challenges in balancing efficiency and crossover distortion due to the need for accurate bias current control, which can result in shoot-through currents and complex circuitry.
Innovation Solution
An operational amplifier with digital control circuits that automatically switch drivers based on load current polarity and include bias circuits and offset equalization to manage DC offset, simplifying circuitry and reducing current carried by drivers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional AB class amplifiers use biasing current to ensure smoother crossover, then crossover distortion is reduced, but shoot-through current from the power supply is generated and circuit complexity increases
Solution Approach 1:
The amplifier circuit is divided into two separate operational amplifiers (first op-amp for PMOS driver, second op-amp for NMOS driver) with independent bias control. This segmentation allows each driver to be controlled independently, preventing simultaneous conduction and eliminating shoot-through current while maintaining reduced crossover distortion through individual biasing.
Solution Approach 2:
A digital control circuit with current sensing provides feedback to dynamically control the bias current. The circuit monitors the current carried by the PMOS and NMOS drivers and adjusts the bias current accordingly, ensuring optimal crossover performance while preventing shoot-through conditions through active feedback control.
2Reliability
If accurate control of bias current is implemented, then crossover distortion is reduced and efficiency is improved, but circuit complexity increases
Solution Approach 1:
The digital control circuit automatically senses the current carried by each driver and self-adjusts the bias current without requiring external intervention or complex manual calibration. This self-service mechanism simplifies the overall system by eliminating the need for precise external bias control while maintaining optimal performance.
Solution Approach 2:
The bias current is dynamically changed based on the operating conditions and current carried by the drivers. The digital control circuit adjusts the bias current parameter in real-time, allowing the amplifier to adapt to different signal levels and load conditions, thereby reducing crossover distortion without requiring fixed complex biasing circuitry.
3Device complexity
If DC offset is not compensated, then circuit simplicity is maintained, but output accuracy and signal fidelity deteriorate
Solution Approach 1:
DC offset compensation is performed in advance through the offset equalization circuit before the amplified signal is output. The circuit pre-adjusts any DC offset generated by the operational amplifiers or drivers, ensuring that the output signal maintains high accuracy and fidelity without requiring complex post-processing or additional compensation stages.
Data Source
AI summary
A driving amplifier circuit includes: a first driver for sourcing a load current to a load; a second driver for sinking the load current from the load; a first operational amplifier (op-amp) for driving the first driver; a second operational amplifier for driving the second driver; a first bias circuit for biasing the first driver; a second bias circuit for biasing the second driver; an enabling circuit for enabling either the first bias circuit or the second bias circuit according to a control signal; a digital control circuit for monitoring currents of the first driver and the second driver to generate the control signal; and an offset equalization circuit, coupled between an internal node of the first operational amplifier and an internal node of the second operational amplifier, for adjusting DC offset of at least one of the first operational amplifier and the second operational amplifier.