PWM Amplifier Calibration Using Fixed Duty Cycle Offset Measurement
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Solution Overview
Problem
Existing pulse width modulation amplifier systems face challenges in accurately correcting signal offsets, leading to signal distortion and inaccuracy due to inherent integrator stage offsets and resistor mismatches.
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 offsets, including isolating mismatches between input and feedback resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If class-D amplifier with PWM modulation is used to improve power efficiency, then power dissipation is reduced, but signal offset and distortion increase 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 stage offsets and resistor mismatches, thereby eliminating signal accuracy problems before they affect performance
Solution Approach 2:
The calibration system uses feedback by measuring the actual output of the amplifier system, comparing it to the expected output based on the forced input value, and using this information to determine and correct offsets. The system continuously monitors and adjusts correction factors to maintain signal accuracy while preserving the power efficiency benefits of class-D operation
2Manufacturing precision
If calibration system is added to correct signal offsets, then signal accuracy is improved, but device complexity increases
Solution Approach 1:
The calibration system is merged with the existing amplifier circuitry, sharing common components such as the integrator stage, feedback network, and output stage. The calibration functionality is integrated into the existing control logic, allowing offset correction to be performed using already-present hardware resources rather than adding completely separate calibration equipment
Solution Approach 2:
The calibration system is designed to perform multiple functions: it measures offset, determines correction factors, and applies compensation across different operating conditions. The same calibration infrastructure serves both offset correction and potential future calibration needs, maximizing the utility of the added complexity while maintaining signal accuracy
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 solution effectively minimizes signal offsets, reducing distortion and inaccuracy by accurately determining and correcting for both overall and resistor-related offsets, thereby enhancing the performance of the amplifier system.
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 and include 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.