Integrated circuit technology allows construction of many amplifier circuits on a single composite "chip" of semiconductor material. One key to the success of an operational amplifier is the "cascading" of a number of transistor amplifiers to create a very large total gain. That is, the number A in Eq.(1-2A-1)can be on the order of 100,00 or more.(For example, cascading of fiver transistor amplifiers, each with a gain of 10, would yield this value for A.) A second important factor is that these circuits can be built in such a way that the current flow into each of the inputs is very small. A third important design feature is that the output resistance of the operational amplifier (R0) is very, small. This in turn means that the output of the device acts likean ideal voltage source.
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