PWM Amplifier Offset Calibration Using Filtered Quantizer Output
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Solution Overview
Problem
Existing pulse width modulation amplifier systems face challenges in minimizing signal offsets, which can lead to signal distortion and inaccuracy.
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, determines the offset, and corrects for it.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a class-D amplifier uses pulse-width modulation to amplify audio signals, then power efficiency is improved, but signal offsets and distortion may occur
Solution Approach 1:
The calibration system performs preliminary offset measurement and correction before normal audio signal processing. The system forces the integrator input to a fixed known value, measures the resulting offset at the amplifier output, and stores correction values that are applied during subsequent audio amplification operations.
Solution Approach 2:
The calibration system uses feedback by measuring the actual output signal at the amplifier output when the integrator input is forced to a known value. This measured output is compared against the expected value to determine the offset, which is then used to correct future amplification operations.
2Measurement precision
If offset correction is performed in amplifier systems, then signal accuracy is improved, but device complexity increases
Solution Approach 1:
The calibration system is self-contained within the amplifier circuitry, using the existing integrator and amplifier components to perform offset measurement and correction. The system calibrates itself during initialization or factory testing without requiring external calibration equipment, thereby minimizing added complexity.
Solution Approach 2:
The calibration system uses the existing amplifier components (integrator, PWM modulator, output stage) for dual purposes: normal audio signal amplification and offset calibration measurement. This multi-functionality reduces the need for separate dedicated calibration hardware.
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 reduces or eliminates signal offsets in pulse width modulation amplifier systems, thereby improving signal accuracy and reducing distortion.
Implementation Method 1
the output pulse train may be converted to an unmodulated analog signal by passing through a passive low-pass filter
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, include a loop filter configured to generate a digital loop filter output, include a quantizer configured to generate a pulse-width modulated representation of the digital loop filter 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, 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, determine an offset of the switched mode amplifier system based on the filtered quantizer output signal, and correct for the offset.