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.

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

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

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 + V_sat or – V_sat 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.