Pseudo-Random PWM Modulation for Lower EMI Spectral Peaks
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Solution Overview
Problem
Pulse width modulation (PWM) techniques generate electromagnetic interferences due to spectral components in the radio frequency band, requiring complex filter circuits to reduce ripple voltage and improve electromagnetic compatibility (EMC) in applications like switched power supplies and Class D amplifiers.
Innovation Solution
A digital pulse width modulator that incorporates a modulating unit, a random number generator, and a flipping unit to generate a pseudo-random sequence, randomly modifying the PWM output signal, thereby reducing the spectral components at the PWM frequency and harmonics, improving EMC by distributing power over a broader spectral range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional PWM modulation is used, then digital-to-analog conversion is achieved, but electromagnetic interference and spectral components in radio frequency band are generated
Solution Approach 1:
The patent applies spread spectrum modulation by periodically varying the PWM signal phase according to a pseudo-random code sequence. This periodic variation with changing phase distributes the spectral energy across a broader frequency range, reducing concentrated electromagnetic interference while maintaining the digital-to-analog conversion function.
Solution Approach 2:
The patent changes the phase parameter of the PWM carrier signal dynamically based on pseudo-random code. By modulating the phase parameter rather than keeping it fixed, the spectral components are spread across multiple frequencies, reducing electromagnetic interference in any single frequency band while preserving conversion accuracy.
2Object-generated harmful factors
If filter circuits are added to reduce ripple voltage and improve EMC, then electromagnetic compatibility is improved, but device complexity increases
Solution Approach 1:
The patent replaces the mechanical/electrical filter circuit approach with a digital signal processing approach. Instead of adding physical filter components to reduce electromagnetic interference, the system uses digital spread spectrum modulation to inherently distribute spectral energy, achieving improved EMC without increasing hardware complexity.
3Object-generated harmful factors
If PWM frequency and harmonics are suppressed, then electromagnetic interference is reduced, but power distribution becomes concentrated
Solution Approach 1:
By applying periodic phase variations based on pseudo-random codes, the patent distributes the power spectrum across a wide frequency range. This prevents concentration of power at any single frequency or harmonic, while simultaneously suppressing prominent spectral components that cause electromagnetic interference.
Data Source
AI summary
A pulse width modulator for modulating a rectangular carrier signal in accordance with an input signal includes a modulating unit that receives the input signal and provides a digital output word. The output word has a pre-defined number of digits comprising a first contiguous set of binary ones (“1”) and a second contiguous set of binary zeroes (“0”) and in which the fraction of the binary ones (“1”) represents the digital input signal. The modulator also includes a random number generator that generates a pseudo-random sequence, and a flipping unit configured to flip, or not, the output word provided by the modulating unit in accordance with the pseudo-random sequence thus providing a randomly modified digital pulse width modulated output signal.