The Operational Amplifier or OP-AMP is a high performance linear amplifier with an amazing variety of uses. The OP-AMP has two inputs, inverting(-) and Non-Inverting(+), and one output . The Polarity of a signal applied to the inverting input is reversed at the output. A Signal applied to the Non-Inverting input retains its polarity at the output.
The Gain (Degree of amplification) of an OP-AMP os determined by a feedback resistor that feeds . some of the amplified signal from the output to the inverting input, This reduces the amplitude of the output signal, hence the Gain. The smaller the resistor, the lower the Gain.
The Gaun is independent of the supply voltage. Note that the unused input is grounded. Therefore the OP-AMP amplifies the difference between the Input (Vin) and Ground (0 Volts). The OP-AMP is then a differential amplifier.
The feedback resistor (Rf) and an OP-AMP form a closed feedback loop, when Rf is omitted, the OP-AMP os said to be in its open loop mode. The OP-AMP then exhibits maximum Gain, buit its output then swings from full on to full off or vice versa for very small changes in input voltage. Therefore the open loop mode is not practical for linear amplification. Instead this mode is used to indicate when the voltage at one input differs from that at the other, In this mode the OP-AMP is called a comparator since it compares one input voltage with other.
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