PWM Amplifier Gain Calibration for Integrator Offset Correction
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Solution Overview
Problem
Existing pulse width modulation amplifier systems face challenges in minimizing signal offsets, leading to signal distortion and inaccuracy due to inherent offsets in integrator stages and resistor mismatches, which are not effectively corrected by current calibration methods.
Innovation Solution
A switched mode amplifier system with a calibration system that forces the input of an analog integrator to a fixed known value, low-pass filters the pulse-width modulated representation of the digital loop filter output, determines, and corrects for the offset, using a feedback network and loop filter to generate a digital loop filter output and pulse-width modulated representation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a class-D amplifier with PWM modulation is used to improve power efficiency, then power dissipation is reduced, but signal offsets and distortion occur due to integrator stage offsets and resistor mismatches
Solution Approach 1:
The calibration system performs preliminary offset measurement and correction before normal amplifier operation. The system forces the integrator input to a fixed known value, measures the resulting output, determines the offset, and applies correction factors to compensate for integrator and resistor mismatches, thereby eliminating signal accuracy issues before they affect performance
Solution Approach 2:
The calibration system uses feedback by measuring the actual output of the PWM amplifier when the integrator input is forced to a known value. This measured output is compared against the expected value, and the difference (offset) is used to generate correction factors that are fed back into the system to compensate for the identified errors in integrator stages and resistors
2Manufacturing precision
If calibration methods are implemented to correct signal offsets, then signal accuracy is improved, but device complexity increases due to additional calibration circuitry and procedures
Solution Approach 1:
The calibration system is designed to perform multiple functions: it measures offsets, determines correction factors, and applies compensation for both integrator stage offsets and resistor mismatches using a unified calibration procedure. This multi-functional approach consolidates what could be separate complex subsystems into a single integrated calibration mechanism
Solution Approach 2:
The calibration system is self-contained and automatically performs offset measurement and correction without requiring external calibration equipment or manual adjustment. The system forces known input values, measures its own output, determines its own offsets, and applies its own corrections, thereby simplifying the overall device architecture by eliminating the need for external calibration tools
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The calibration system effectively reduces or eliminates signal offsets, improving the accuracy and reducing distortion in the amplifier system by determining and correcting for offsets based on filtered quantizer output signals, thereby enhancing the overall performance of the switched mode amplifier.
Implementation Method 1
low-pass filter the pulse-width modulated representation of the digital loop filter output generated by the quantizer to generate a filtered quantizer output signal
Data Source
AI summary
A switched mode amplifier system may include a switched mode amplifier having an amplifier input coupled to an output of an analog integrator and an amplifier output, include a feedback network coupled between the amplifier output and an input of the analog integrator, and a calibration system. The calibration system may be configured to force the input of the analog integrator to a fixed known input value, force the amplifier output to a fixed known duty cycle, measure an analog signal generated at the output of the analog integrator in response to forcing the input of the analog integrator to the fixed value, determine an offset of the switched mode amplifier system based on the analog signal, and correct for the offset.