Random-Dithered Clock Oscillator for EMI-Safe Switching Regulators
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for reducing electromagnetic interference (EMI) from switching regulators, such as spread spectrum frequency modulation, face challenges in generating optimal random signals that effectively reduce EMI at both fast and slow clocking frequencies without introducing amplitude modulation that can corrupt electronic circuits.
Innovation Solution
A spread spectrum frequency modulated oscillator circuit that includes a reference component, a controlled oscillator, and circuits for supplying a random signal to cause frequency dithering, with a fixed percentage rate of change and frequency change, ensuring reliable tracking by switching regulators while reducing EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If periodic sinusoidal frequency modulation is used to spread interference energy, then EMI at clocking frequency is reduced, but large amplitude low frequency components are added that can corrupt electronic circuits
Solution Approach 1:
The patent inverts the conventional approach by using random frequency modulation instead of periodic sinusoidal modulation. This inversion transforms the deterministic amplitude modulation problem into a stochastic process where the interference spectrum is flattened across a wide frequency range without creating harmful low-frequency components, thereby resolving the contradiction between EMI reduction and avoidance of corrupting artifacts
Solution Approach 2:
The patent changes the modulation parameter from periodic sinusoidal variation to random variation with controlled statistics. By controlling the mean and variance of the random modulation signal, the system achieves spectrum spreading while maintaining bounded amplitude variations that do not corrupt electronic circuits, thus resolving the technical contradiction
2Object-affected harmful factors
If random frequency hopping is used to spread interference, then EMI reduction is improved, but optimal random signal generation becomes difficult to achieve for both fast and slow hopping rates
Solution Approach 1:
The patent simplifies random signal generation by controlling only the mean and variance parameters of the modulation signal rather than generating complex optimal random sequences. This parameter-based approach works effectively across both fast and slow hopping rates without requiring complex signal generation circuitry, thus resolving the contradiction between EMI reduction and device complexity
Solution Approach 2:
The system allows the random modulation to naturally adapt to different operating conditions through its statistical properties alone, without requiring external optimization or complex control mechanisms. The inherent randomness combined with parameter control provides effective EMI reduction across varying clock frequencies and regulator speeds, eliminating the need for complex optimal signal generation
3Stability of the object's composition
If lowpass filtering is applied to random modulation signal, then output ripple is reduced, but the benefit of random modulation for EMI reduction is negated
Solution Approach 1:
The patent resolves this contradiction by carefully controlling the variance parameter of the random modulation signal and its correlation time to match the tracking capability of the switching regulator. This parameter optimization allows the system to maintain the EMI reduction benefits of random modulation while keeping output ripple within acceptable limits, eliminating the need for aggressive lowpass filtering that would negate the modulation benefits
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution generates a wide range of frequencies with random frequency modulation that effectively reduces EMI across various switching regulator applications, maintaining reliable operation by ensuring a flat frequency spectrum and constant modulation index.
Implementation Method 1
a controlled oscillator and a first circuit coupled to the reference component and controlled oscillator and configured to supply a first control signal to the oscillator to cause the oscillator to oscillate at a frequency corresponding to a value of the reference component
Implementation Method 2
a second circuit configured to supply a random signal to the oscillator to cause the frequency of the oscillator to dither
Data Source
AI summary
A spread spectrum frequency modulated oscillator circuit usable as a clock comprises a reference component such as a resistor, a voltage controlled oscillator and a first circuit coupled to the reference component and voltage controlled oscillator and configured to supply a first control signal to the oscillator to cause the oscillator to oscillate at a frequency corresponding to a value of the reference component. A second circuit configured to supply a random signal to the oscillator causes the frequency of the oscillator to dither. To cause the oscillator to exhibit random frequency modulation that is fast enough to reduce EMI but not too fast for controlled devices such as switching regulators to track, the oscillator includes a third circuit configured to control (1) a rate of change of the oscillator frequency such that the rate of change is a fixed percentage of the oscillator frequency, and (2) an amount of frequency change in the oscillator frequency such that the amount of frequency change is a fixed percentage of the oscillator frequency.