PWM Amplifier Feed-Forward Filter Mismatch Correction
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Solution Overview
Problem
Conventional audio power amplifiers using Pulse Width Modulation (PWM) face errors due to component variation, particularly in power supply rejection, which are not adequately addressed by existing correction methods that rely on the quality of analog to digital conversion and filter performance.
Innovation Solution
A digital PWM amplifier system with a power supply feed-forward path that includes analog filters and correction circuitry to modify digital audio signals based on power supply measurements, correcting component mismatch errors by scaling and summing power supply differences and common modes to reduce errors in the feed-forward signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If power supply feed forward techniques are used to improve power supply rejection, then power supply rejection is improved, but component variation errors are introduced
Solution Approach 1:
The patent implements a feedback mechanism where the system measures its own power supply ripple and distortion through ADCs, processes this information through digital signal processing, and uses the corrected data to compensate for power supply errors in real-time. This closed-loop feedback approach allows the system to actively correct component variation errors while maintaining improved power supply rejection.
Solution Approach 2:
The patent changes the operating parameters of the power supply measurement system by using multiple ADCs with different reference voltages and processing their outputs through digital signal processing. By measuring the same physical quantity (power supply ripple) under different parameter conditions (different references, different paths) and combining the results, the system achieves both high power supply rejection and immunity to component variations.
2Measurement precision
If multiple ADCs with different references are used to measure power supply ripple, then measurement capability is improved, but system complexity increases
Solution Approach 1:
The patent makes the digital signal processor perform multiple functions: it processes measurements from multiple ADCs, corrects for component variations, calculates power supply ripple, and generates compensation signals. By making the DSP multi-functional, the patent avoids adding separate dedicated circuits for each function, thereby improving measurement precision without proportionally increasing system complexity.
Solution Approach 2:
The patent introduces digital signal processing as an intermediary between the ADC measurements and the final power supply correction. The DSP acts as a mediator that receives raw measurements from multiple ADCs with different references, processes and reconciles the data, and produces a unified corrected measurement. This intermediary layer simplifies the integration of multiple ADCs by providing a centralized processing point.
3Object-affected harmful factors
If conventional analog filters are used in the feed forward path, then filtering is achieved, but component mismatch errors are introduced
Solution Approach 1:
The patent replaces the mechanical/analog filter system with a digital filtering approach. Instead of using physical resistors, capacitors, and inductors that are subject to component tolerance and drift, the system uses digital signal processing to achieve the same filtering function. The DSP digitally filters the measured power supply ripple and distortion, eliminating the harmful effects of analog component mismatch while maintaining effective ripple rejection.
Solution Approach 2:
The patent changes the domain in which filtering is performed from the analog time-domain to the digital frequency-domain. By converting the analog measurements to digital signals and applying digital filtering algorithms, the system achieves precise filtering characteristics that are determined by software rather than physical component values. This allows for exact filter responses without the tolerance accumulation inherent in analog filter designs.
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 errors caused by component variation, improving system performance by compensating for power supply common mode and difference issues, leading to enhanced fidelity and reduced distortion in audio output.
Implementation Method 1
The feed-forward path includes an analog filter configured to filter the power supply measurement
Data Source
AI summary
Systems and methods for minimizing errors due to component variation in switching amplifiers utilizing power supply feed forward techniques. One embodiment comprises a digital PWM amplifier having an amplification subsystem for receiving a digital audio signal and producing an analog output signal. The amplifier includes a power supply feed-forward path configured to modify the digital audio signal based on a power supply measurement. The feed-forward path includes an analog filter configured to filter the power supply measurement, as well as correction circuitry configured to correct component mismatch errors introduced by the filter. The power supply measurement may be a power supply difference, a power supply common mode, or both. In either case, the power supply measurement is corrected by multiplying the measurement by an appropriately scaled power supply difference.