Spread-Spectrum Clocking in Switching Regulators for EMI Reduction

Takayuki DAIMON  Hiroshi SADAMURA  Takayuki SHINDOU  Haruo KOBAYASHI  Masashi KONO  Takao MYONO  Tatsuya SUZUKI  Shuhei KAWAI  Takashi IIJIMA  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E86-A    No.2    pp.381-386
Publication Date: 2003/02/01
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Analog Circuit Techniques and Related Topics)
switching regulator,  DC-DC converter,  spread spectrum,  EMI,  switching noise,  

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This paper describes a simple, inexpensive technique for intentionally broadening and flattening the spectrum of a DC-DC converter (switching regulator) to reduce Electro-Magnetic Interference (EMI). This noise spectrum broadening technique involves intentionally introducing pseudo-random dithering of control clock timing, which can be achieved by adding simple digital circuitry. This technique can significantly reduce noise power spectrum peaks at the DC-DC converter output. For our test case circuit, measurements showed that noise power was reduced by 5.7 dBm at the main peak, by 15.6 dBm at the second peak and by 12.8 dBm at the third peak. This simple, inexpensive technique can be applied to most conventional switching regulators by adding simple digital circuitry, and without any modification of the design of other parts.