Spread Spectrum PWM Controller for EMI Reduction
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Solution Overview
Problem
Switching power converters suffer from switching noise and electromagnetic interference (EMI), which existing methods fail to adequately mitigate due to frequency sensitivity, particularly when using noisy quantization clocks or relying on complex noise shaping techniques.
Innovation Solution
A controller employing a spread spectrum pulse width modulation (PWM) signal generator that uses a clean clock to create a pulse width modulation centering signal with a 50% duty ratio and varying period, effectively distributing the switching frequency across a wider spectrum, thereby reducing EMI without requiring explicit ramp signals or high-speed quantization clocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a noisy quantization clock is used to distribute switching frequency, then EMI is reduced, but the clock signal quality deteriorates and produces uncontrolled emissions
Solution Approach 1:
The patent introduces a clean quantization clock as an intermediary signal that drives a noise shaping circuit. This mediator generates the frequency-varying PWM clock signal without introducing the noise and instability problems of using a noisy clock directly, thus reducing EMI while maintaining signal quality and controllability
Solution Approach 2:
The patent replaces the mechanical approach of using a noisy physical clock signal with an electronic/software-based noise shaping algorithm. Instead of relying on physical clock imperfections to spread frequency, the system uses digital processing to intentionally vary the PWM clock frequency, achieving EMI reduction while maintaining clean and controllable timing signals
2Object-affected harmful factors
If complex noise shaping techniques are employed to mitigate EMI, then EMI is reduced, but device complexity increases
Solution Approach 1:
The patent implements a universal noise shaping algorithm that can be applied to various PWM converter topologies and frequency ranges without requiring complex hardware modifications. The technique uses a general-purpose frequency variation approach that works across different operating conditions, reducing the need for topology-specific complex EMI mitigation circuits
Solution Approach 2:
The patent changes the frequency parameter of the PWM clock signal dynamically over time according to a noise shaping pattern. By varying the frequency parameter in a controlled manner rather than maintaining a fixed frequency, the system spreads EMI energy across a broader spectrum, reducing peak emissions without requiring complex additional hardware
3Object-affected harmful factors
If switching frequency is distributed over wider spectrum to reduce EMI, then EMI is mitigated, but switching noise control becomes less precise
Solution Approach 1:
The patent employs periodic frequency variation where the PWM clock frequency is modulated in a regular, predictable pattern. This periodic action spreads the switching energy across multiple frequency components while maintaining overall control, as the variations follow a defined cycle rather than being random or uncontrolled
Solution Approach 2:
The system uses feedback mechanisms to monitor and adjust the PWM operation based on the frequency variations introduced by noise shaping. This feedback ensures that despite the distributed frequency spectrum, the converter maintains proper regulation and the switching noise remains within acceptable bounds through active control
Data Source
AI summary
A switching power converter converts an input DC voltage to an output DC voltage using a switch to selectively connect an input DC voltage energy source. A switching controller controls the switch. A pulse width modulation centering signal is generated by a spread spectrum clock signal generator. An error amplifier of the switching controller generates an analog error signal based on a switching voltage measured after the switching of the switching power converter, the output voltage of the switching power converter, the pulse width modulation centering signal and a reference. A pulse width modulated signal generator generates the pulse width modulation signal to control the switch of the switching power converter based on the pulse width modulation centering signal and the analog error signal.