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Digital frequency dithering for switched-mode power supplies (SMPS) using triangular, asymmetric cubic, or random cubic spread spectrum oscillators
Digital frequency dithering for switched-mode power supplies (SMPS) using triangular, asymmetric cubic, or random cubic spread spectrum oscillators
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机译:用于开关模式电源的数字频率抖动(SMPS)使用三角形,非对称立方体或随机立方扩频振荡器
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摘要
A modulator spreads the spectrum of a generated clock to reduce Electro-Magnetic Interference (EMI). A capacitor is charged by a variable current to generate a ramp voltage that is compared to a reference to end a clock cycle and discharge the capacitor. An up-down counter drives a Digital-to-Analog Converter (DAC) that controls the variable charging current to provide triangle modulation. A smaller offset current is added or subtracted for cubic modulation when the up-down counter reaches its minimum count. A frequency divider that clocks the up-down counter also clocks a Linear-Feedback Shift-Register (LFSR) to that controls pseudo-random current sources that further modulate variable current and frequency. The LFSR is clocked with the up-down counter to modulate each frequency step, or only at the minimum count to randomly modulate at the minimum frequency. Binary-weighted bits from the up-down counter to the DAC are swapped to modulate the frequency step size.
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