Filter-Less Class-D Amplifier EMI Cancellation via Inverse Common-Mode
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Solution Overview
Problem
Class-D audio amplifiers generate high-frequency switching noise that leads to significant electromagnetic interference (EMI), which is difficult to mitigate without increasing complexity or cost, especially in filter-less designs that require compliance with FCC and European Standards.
Innovation Solution
An integrated circuit (IC) chip with a class-D PWM modulator and an inverse common-mode signal generator, which includes transistors and resistors configured to produce inverse common-mode signals that can be radiated through PCB traces or wires to compensate and reduce EMI, thereby minimizing electromagnetic interference without the need for additional filters or components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If filter-less class-D amplifier design is used, then system cost and size are reduced, but EMI increases making regulatory compliance difficult
Solution Approach 1:
The patent generates common-mode current through PCB traces or wires that intentionally radiate inverse common-mode signals to cancel the harmful EMI from the amplifier outputs. This converts the potentially harmful radiation from trace currents into a beneficial cancellation mechanism, eliminating the need for external filters while meeting EMI standards
2Object-affected harmful factors
If traditional EMI filtering components are added, then EMI is reduced, but system cost and complexity increase
Solution Approach 1:
The amplifier system generates its own EMI cancellation signal using the existing output traces and common-mode current paths. The inverse common-mode signal generator uses the same PCB traces or wires that carry the differential output signals to radiate the cancellation signal, making the EMI mitigation self-contained without external filter components
3Object-affected harmful factors
If common-mode current is generated through PCB traces, then EMI cancellation is achieved, but trace length requirements increase
Solution Approach 1:
The patent modifies the electrical characteristics of the PCB traces by controlling the common-mode current magnitude and frequency to optimize radiation efficiency. By adjusting these parameters, the system achieves effective EMI cancellation with minimal trace length, eliminating the need for intentionally long antenna traces
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
Effectively reduces EMI by compensating common-mode signals with inverse common-mode signals, minimizing the need for costly filters and maintaining efficiency, while adhering to regulatory standards.
Implementation Method 1
which includes transistors and resistors configured to produce inverse common-mode signals that can be radiated through PCB traces or wires to compensate and reduce EMI
Data Source
AI summary
An audio system includes a speaker and a class D amplifier with a class-D PWM (pulse width modulation) modulator configured for generating first and second PWM signals forming a differential signal with three differential output levels with three differential output levels. The class-D amplifier also has a differential output driver configured for driving a first and a second output signals onto a first and a second output terminals in response to the first and the second PWM signals, wherein the first and the second output signals form a differential output signal having three differential output levels. An inverse common-mode signal generator is coupled to first and second output signals for providing an inverse common-mode signal. The audio system also includes one or more output terminals for providing the inverse common mode signal, and further includes a wire or a trace on a PCB (printed circuit board).