Spread-Spectrum PWM Circuit With Baseband Noise Notching
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Solution Overview
Problem
Conventional PWM circuits generate carrier noise with a wide frequency spectrum that affects other circuit blocks, especially in miniaturized devices, due to the spreading of harmonic components across a wide range of frequencies, including the baseband, leading to interference with other signals.
Innovation Solution
A method and circuit that generate a spread spectrum waveform with a shaped frequency spectrum distribution, using a clock and PN code with varying frequencies, and conducting logical operations to create a pulse-width modulated signal with a spectrum component reducing part in at least one band, such as the baseband, thereby reducing noise and interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional PWM modulator uses a triangle wave with fixed period, then the circuit structure is simple, but the carrier noise concentrates at specific frequencies causing interference to other circuits
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed-frequency triangle wave to a variable-frequency triangle wave whose frequency changes over time according to a spread spectrum sequence. This dynamic frequency variation causes the carrier noise to spread across a wide frequency range rather than concentrating at specific frequencies, thereby reducing interference to other circuits while maintaining relatively simple circuit structure
Solution Approach 2:
The patent changes the frequency parameter of the triangle wave from constant to variable by modulating it with a spread spectrum sequence. This parameter change transforms the noise spectrum from concentrated to spread out, solving the interference problem without significantly increasing circuit complexity
2Object-generated harmful factors
If a PWM modulator uses a triangle wave with varying frequency to spread spectrum, then carrier noise is distributed over wide range reducing peaks, but noise is also spread uniformly in baseband where signal is present
Solution Approach 1:
The patent applies local quality by using a shaped spectrum sequence that has different spectral characteristics at different frequencies. The sequence is designed to have reduced energy in the baseband region while maintaining spread spectrum characteristics in higher frequencies. This creates non-uniform noise distribution where the baseband region has lower noise levels, thus reducing both carrier noise peaks and baseband noise simultaneously
3Area of stationary object
If device is miniaturized, then integration density increases, but harmonic components of triangle wave affect other circuit blocks due to spectrum spreading
Solution Approach 1:
The patent uses dynamic frequency variation of the triangle wave according to spread spectrum sequencing. This causes the harmonic components to move continuously across the frequency spectrum rather than remaining at fixed frequencies. When the device is miniaturized, this dynamic spreading prevents harmonic radiation from consistently affecting specific adjacent circuit blocks, thereby enabling compact design while reducing interference
Data Source
AI summary
The objective of this invention is to provide a circuit that generates a spread frequency spectrum waveform with shaped frequency spectrum distribution. The waveform generator has a spread spectrum waveform generating circuit that generates a waveform with a spread spectrum and frequency spectrum distribution shaping circuit that shapes the frequency spectrum distribution of the spread spectrum waveform. In one embodiment, distribution shaping circuit can perform shaping such that the spread spectrum waveform has a frequency spectrum distribution having a spectrum reducing part in at least one band. Also, in one embodiment, the frequency of the spread spectrum waveform can vary periodically or nonperiodically.