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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.

Fig. 5-1

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