Re: Amplifier
Basic operation of operational amplifier
The amplifier's differential inputs consist of an inverting input and a non-inverting input, and ideally the op-amp amplifies only the difference in voltage between the two. This is called the "differential input voltage". In its most common use, the op-amp's output voltage is controlled by feeding a fraction of the output signal back to the inverting input. This is known as negative feedback. If that fraction is zero, i.e., there is no negative feedback, the amplifier is said to be running "open loop" and its output is the differential input voltage multiplied by the total gain of the amplifier, as shown by the following equation:
where V+ is the voltage at the non-inverting terminal, V− is the voltage at the inverting terminal and G is the total open-loop gain of the amplifier.
Because the magnitude of the open-loop gain is typically very large and not well controlled by the manufacturing process, op-amps are not usually used without negative feedback. Unless the differential input voltage is extremely small, open-loop operation results in op-amp saturation (see below in Nonlinear imperfections). An example of how the output voltage is calculated when negative feedback exists is shown below in Basic non-inverting amplifier circuit.
Another typical configuration of op-amps is the positive feedback, which takes a fraction of the output signal back to the non-inverting input. An important application of it is the comparator with hysteresis