 # Periodic Signals

## Introduction

Periodic signals are more commonly identified by their frequency (usually abbreviated as f ), rather than their period. The frequency of a signal is the inverse of the period. Mathematically, this means that:

$f = \frac{1}{T}$

The frequency of a signal tells us how many times the signal repeats itself during one second. Units of frequency are in cycles per second, or Hertz (abbreviated as Hz). Therefore, a signal with a frequency of 100Hz goes through 100 cycles (periods) in one second—the period of the signal is 0.01 seconds. Higher frequency signals change more rapidly, and have shorter periods than lower frequency signals. Figure 1. Periodic signal. The period of the signal is “T”.

Although any repetitious signal is periodic, there are a few specific signals which are very commonly used in the analysis and testing of electrical circuits. Three examples of common voltage signals are shown in Fig. 2. Periodic voltages are typically classified according to:

1. Their overall shape (e.g. “sinusoidal”, “triangular”, or “square” in Fig. 2).
2. Their frequency (the inverse of the periods indicated in Fig. 2).
3. Their amplitude, or the “height” of the signal, (e.g. “A”, in Fig. 2).