Class-D Amplifier Modulation to Suppress Low-Level EMI
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Solution Overview
Problem
Prior class-D amplifiers suffer from electromagnetic interference (EMI) when the audio input signal is zero or close to zero, leading to high frequency noise radiation and periods of silence in audio equipment due to noise removal methods that filter out audio signals.
Innovation Solution
A class-D amplifier circuit is designed to include a modulation signal that adjusts the amplitude of the input signal, ensuring a non-zero minimum peak-to-peak amplitude, which widens the current pulses to keep the EMI frequency spectrum below 30 MHz, preventing interference while maintaining audio integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If digital logic elements are used to remove noise above a certain frequency, then electromagnetic interference is reduced, but audio signals are also removed resulting in periods of complete silence
Solution Approach 1:
The patent changes the parameter of pulse width by adding a modulation signal to ensure the pulse width remains above a threshold value. This parameter change allows the system to reduce EMI (by keeping pulses wide enough to avoid high frequency radiation) while preserving audio signals (by not filtering out the modulated audio information), thus resolving the contradiction between reducing EMI and maintaining audio integrity.
2Use of energy by moving object
If the audio input signal value is zero or close to zero, then the amplifier operates at low signal levels, but high frequency noise radiates from the output due to small amounts of noise on the input signal
Solution Approach 1:
The patent applies preliminary action by adding a modulation signal to the audio input signal before amplification. This preliminary modulation ensures that even when the audio input is zero or close to zero, the modulated signal has sufficient amplitude to produce wide enough pulses that avoid high frequency noise radiation, thus preventing EMI before it occurs.
3Object-affected harmful factors
If current pulse width is increased to reduce EMI frequency spectrum below 30 MHz, then electromagnetic interference is suppressed, but the amplifier circuit complexity increases
Solution Approach 1:
The patent uses parameter changes by modulating the audio input signal with a modulation signal to control the pulse width parameter. This approach suppresses EMI frequency spectrum below 30 MHz through parameter control rather than complex circuit modifications, thereby reducing EMI while maintaining relatively simple amplifier circuit architecture.
Data Source
AI summary
In one embodiment, an amplification circuit receives an analog signal and adds another signal to the analog signal to modify the minimum amplitude of the analog input signal.