PWM Modulator Feedback Circuit for Lower-EMI Class-D Amplifiers
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Solution Overview
Problem
Class-D amplifiers face issues with switching noise and high switching peak voltage, leading to increased electromagnetic interference (EMI) due to rapid changes in output current and harmonic components, which can cause malfunctions in surrounding circuits.
Innovation Solution
A PWM modulator design incorporating an integrator, low pass filter, comparator, and power stage with delay circuits to reduce switching noise and peak voltage, featuring an integrator with capacitors and resistors, and a power stage with inverters and delay cells to manage signal phases and buffering, thereby minimizing EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional PWM modulator with ramp generator is used, then PWM signal generation is achieved, but the structure becomes complicated and switching noise is generated
Solution Approach 1:
The patent removes the ramp generator from the PWM modulator structure, extracting the problematic component that caused both structural complexity and switching noise. The simplified modulator achieves PWM signal generation through alternative means without the ramp generator, thereby eliminating the source of switching noise while reducing device complexity.
Solution Approach 2:
The patent converts the harmful switching noise into a beneficial self-oscillation mechanism. By allowing the power stage to self-oscillate at its natural frequency, the previously harmful noise becomes the operating frequency of the system, eliminating the need for external ramp signals and complex modulation circuits while reducing overall noise pollution.
2Use of energy by moving object
If switching speed is increased to improve efficiency, then power efficiency improves, but electromagnetic interference increases
Solution Approach 1:
The patent implements feedback by feeding the output signal back to the integrator input. This feedback mechanism allows the system to self-regulate the switching frequency and amplitude, maintaining high efficiency while reducing EMI through automatic adjustment of operating parameters based on actual output conditions.
Solution Approach 2:
The patent dynamically changes operating parameters through the self-oscillation mechanism, where the switching frequency and duty cycle automatically adjust based on the load and input conditions. This parameter adaptation allows the system to maintain optimal efficiency across different operating points while minimizing EMI through frequency modulation.
3Power
If output power is increased to improve performance, then amplifier capability improves, but switching peak voltage increases causing EMI
Solution Approach 1:
The patent employs dynamic operation where the power stage operates in a self-oscillating mode rather than fixed-frequency switching. The switching frequency and voltage levels dynamically adapt to the output power requirements, allowing high output power when needed while automatically reducing peak voltages during low-power operation, thus minimizing EMI across all power levels.
Data Source
AI summary
A pulse width modulation (PWM) modulator includes an integrator generating an integrated signal based on an input signal and an output signal, a low pass filter (LPF) receiving the integrated signal and performing low pass filtering, a comparator receiving an output signal of the LPF and a predetermined reference signal, comparing the received signals, and outputting a PWM signal, a dead time setup block outputting a first signal and a second signal having a predetermined phase difference therebetween based on the PWM signal, and a power stage buffering the first and second signals and generating the output signal based on a result of buffering. In the PWM modulator and a class-D amplifier having the PWM modulator, EMI can be reduced.