Frequency Spectra of Digital Signals

In mathematics, base 10 logarithm of a positive number A is defined as log₁₀A. In engineering, especially in EMC, the authors use a unit of decibel (dB) which is related to the base 10 logarithm. Any periodic function can be represented as an infinite sum of sinusoidal components. An expansion of this type is known as a Fourier Series Expansion. Clock signals can be represented as periodic trains of trapezoid‐shaped pulses. One of the most common measurement units expressed in decibels is dBm. Many spectrum analyzers display voltage amplitudes both in dBμV and in dBm, even though dBm is a unit of power. The authors present laboratory exercises which examine the spectrum of a digital clock signal and determines the impact of signal parameters on the spectrum. Reducing the fundamental frequency reduces the high‐frequency spectral content of the waveform, but does not affect the low‐frequency content.