Estimating the Amplitude Reduction of Clock Harmonics Due to Frequency Modulation

Simple formulae were theoretically derived for estimating the reduction in amplitude of clock harmonics, as measured in electromagnetic interference (EMI) tests, due to clock frequency modulation (FM). They show how the amplitude reduction is related to the clock FM parameters and resolution bandwidth (RBW) in spectrum measurement. Numerical simulations and experiments clearly demonstrated the validity of this analysis. Because clock FM does not reduce the actual power of the clock harmonics, the apparent decrease in the harmonic amplitude must be carefully treated when evaluating the potential of the radiated harmonics interfering with wireless systems