Methods and circuits for frequency modulation that reduce...

Oscillators – Electrical noise or random wave generator

Reexamination Certificate

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C363S013000

Reexamination Certificate

active

07362191

ABSTRACT:
The present invention comprises methods and circuits for spread spectrum frequency modulation that reduce peak spectral noise at the outputs or inputs of switching regulators. More specifically, the present invention modulates the operating frequency of the switching regulator in accordance with a frequency modulation waveform having a shape coordinated to a peak noise amplitude waveform that describes the correlation between the operating frequency of a switching regulator and the peak noise amplitude at the regulator's input or output absent spread spectrum frequency modulation.

REFERENCES:
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patent: 5929620 (1999-07-01), Dobkin et al.
patent: 2005/0243894 (2005-11-01), Chen et al.
Hardin, K., Fessler, J. and Bush, D., “Spread Spectrum Clock Generation for the Reduction of Radiated Emissions”, 1994 IEEE International Symposium on Electromagnetic Compatibility, pp. 227-231 (Aug. 22-26, 1994).
Lin, F. and Chen, D.Y., “Reduction of Power Supply EMI Emission by Switching Frequency Modulation”, IEEE Transactions on Power Electronics, pp. 132-137 (Jan. 1994).
Linear Technology, “LTC1735 High Efficiency Synchronous Step-Down Switching Regulator”, Datasheet (1998).
Linear Technology, “LTC3251/LTC3251-1.2/LTC3251-1.5 500mA High Efficiency, Low Noise, Inductorless Step-Down DC/DC Converter”, Datasheet (2003).
Linear Technology, “LTC6902 Multiphase Oscillator with Spread Spectrum Frequency Modulation”, Datasheet (2003).
Seago, J., “LTC1436-PLL Low Noise Switching Regulator Helps Control EMI”, Linear Technology Design Note 141 (1996).
Stone, D., Chambers, B. and Howe, D., “Random Carrier Frequency Modulation of PWM Waveforms to Ease EMC Problems in Switched Mode Power Supplies”, Proceedings of IEEE Power Electronics and Drive Systems Conference, pp. 16-21 (1995).
Yang, K., “Spread-Spectrum DC—DC Converter Combats EMI”, Electronic Design Magazine, pp. 86, 88. (Nov. 5, 2001).

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