Phase-Adjusted PWM Signal Generation for Lower EMI
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Solution Overview
Problem
Digital power amplifiers using pulse width modulation (PWM) circuits suffer from significant electromagnetic interference (EMI) due to noise components concentrating at carrier frequencies, which affects the quality of the output signal.
Innovation Solution
A signal generating apparatus comprising a signal modulating unit, a selection signal generating unit, and a phase adjusting unit that processes an input signal to perform phase modulation, adjusting the pulse width of the modulated signal to generate an output signal, thereby dispersing energy across various frequencies and reducing EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If pulse width modulation (PWM) is used to generate the output signal, then the efficiency of the digital power amplifier is improved, but electromagnetic interference (EMI) and noise components concentrate at carrier frequencies
Solution Approach 1:
The patent applies periodic phase shifting to the PWM signal by introducing delay signals with different phase shifts (e.g., 0°, 180°) and selectively combining them. This periodic modification of the signal phase disperses the energy that would otherwise concentrate at carrier frequencies, reducing EMI while preserving the high efficiency benefit of PWM operation
Solution Approach 2:
The patent combines multiple PWM signals with different phase shifts into a composite output signal. By superimposing these phase-shifted signals and selectively outputting certain phases, the resulting composite signal maintains the efficiency advantages of PWM while distributing spectral energy to reduce electromagnetic interference
2Object-generated harmful factors
If the pulse width of the modulated signal is adjusted to disperse energy across frequencies, then electromagnetic interference is reduced, but the complexity of the signal generating apparatus increases
Solution Approach 1:
The patent segments the PWM signal generation process into distinct functional blocks: a signal modulating unit for generating the base PWM signal, a delay unit for creating phase-shifted versions, and a selection unit for combining them. This segmentation allows the system to reduce EMI through phase manipulation while maintaining modular architecture that limits overall complexity
Solution Approach 2:
The patent introduces delay signals as intermediary elements that facilitate phase shifting without requiring complex modulation circuits. These delay signals act as mediators between the original PWM signal and the final output, enabling EMI reduction through simple time-delay-based phase shifts and selective combination
Data Source
AI summary
The signal generating apparatus includes a signal modulating unit, a selection signal generating unit, and a phase adjusting unit. The signal modulating unit is utilized for processing a modulation upon an input signal to generate a modulated signal. The selection signal generating unit is utilized for generating at least a first selection signal. The phase adjusting unit is coupled to the signal modulating unit and the selection signal generating unit, and is utilized for receiving the modulated signal and adjusting a pulse width of the modulated signal to generate an output signal according to the first selection signal.