Amplifiers and Operational Amplifier Circuits 5.1
An ampliﬁer is a device which magniﬁes signals. The heart of an ampliﬁer is a source controlled by an input signal. A simpliﬁed model of a voltage ampliﬁer is shown in Fig. 5-1(a). The input and output reference terminals are often connected together and form a common reference node. When the output terminal is open we have v2 ¼ kv1 , where k, the multiplying factor, is called the open circuit gain. Resistors Ri and Ro are the input and output resistances of the ampliﬁer, respectively. For a better operation it is desired that Ri be high and Ro be low. In an ideal ampliﬁer, Ri ¼ 1 and Ro ¼ 0 as in Fig. 5-1(b). Deviations from the above conditions can reduce the overall gain.
Published on May 10, 2013