5.1 Introduction

The concept of signal amplification finds numerous uses in the field of electronics. This includes applications such as boosting the signal level from a sensor or driving loads like loudspeakers or antennas. Reduced to its most simple terms, amplification is just multiplication. The ideal amplifier multiplies the amplitude of the input signal by a constant. It should not change the frequency of the signal, alter its shape, add noise or in any other way warp or distort the signal.

Amplifiers can be designed to be voltage sensing or current sensing and can be modeled as either controlled voltage sources or controlled current sources. As a functional block, we are primarily interested in describing an amplifier in terms of its amplification factor, input impedance and output impedance. The amplification factor is also referred to as the gain and may be expressed in terms of voltage gain, current gain or power gain, depending on the application. Other items of interest include the maximum output level or compliance, useful frequency range, noise and distortion characteristics.