Hi Suresh,

This isn't really going to be helpful with regard to the specifics of your question, but I think it's valuable to know and it very well could be helpful in that it will give you a more complete understanding of opamps.

The reason opamps are called opamps, which is short for OPerational AMPlifier, is because they were intended to perform mathematical operations. They go back to the days of analog computers and field artillery. This history is manifest today in instrumentation, wherein the output of an opamp may be a sum of multiple inputs, or the integral or derivative of an input. Remember that PID stands for Proportional Integral Derivative.

Richard's advise to review the literature concerning basics is probably the most direct route to your specific answer. But maybe this will help it make a bit more sense as you study those basics and wonder why. That's my hope anyway.

Good luck,

Joe