Chapter 4 - Linear Circuits

Abstract

A linear circuit is a type of analog circuit that is designed to make a scaled copy of a waveform meaning that the amplitude of the output of the linear circuit is a fraction, or a multiple of the amplitude of the input waveform. The output amplitude is greater than the input amplitude, and the circuit is an amplifier. If the circuit is truly linear, the output waveform has the same frequency and the same waveshape as the input waveform—it is a true copy at a different amplitude scale, and the ratio of the output amplitude to the input amplitude is called the gain. The name of linear circuit arises from the shape of graphs of output amplitude plotted against input amplitude. For a perfectly linear amplifier, this graph should be a straight line, hence the name linear. An amplifier carries out the action of making an enlarged copy of the waveform that is used as its input signal, and the ratio of the output signal to the input signal is called the gain of the amplifier. Broadband amplifiers have a much wider frequency response than the ordinary audio amplifier. Power amplifiers are usually current amplifiers that are needed when a load, such as a loudspeaker or electric motor, has to be supplied with a waveform that has been electronically generated. An oscillator is a circuit that is designed to generate wave signals from a steady voltage supply, with no wave input. A tuned circuit can also be used as a frequency multiplier.