Open Loop Configuration of Op amp:

The simplest possible way to use an operational amplifier is in the open loop mode. The Fig. 2.13 shows an Open Loop Configuration of Op amp.Open Loop Configuration of Op amp

We know that the d.c. supply voltages applied to the op-amp are VCC and -VEE and the output varies linearly only between VCC and -VEE.

Since gain is very large in open loop condition, the output voltage Vo is either at its positive saturation voltage (+ Vsat) or negative saturation voltage (- Vsat) as V1 > V2 or V2 > V1 respectively. This is shown in the Fig. 2.14.

Open Loop Configuration of Op amp

Thus very small noise voltage present at the input also gets amplified due to its high open loop gain and operational amplifier gets saturated.

It can be seen from the Fig. 2.14, only for small range of input signal (from point a to b), it behaves linearly. This range is very small and practically due to high open loop gain, op-amp either shows + Vsat or – Vsat level.

This indicates the inability of op-amp to work as a linear small signal amplifier in the open loop mode.

Hence, the op-amp is generally not used in the open loop configurations.

Such an open loop behavior of the operational amplifier finds some rare applications like voltage comparator, zero crossing detector etc.