The operational amplifier is the building block of analog electronics.

What is an operational amplifier?

Exercise — ideal opamp model

Exercise — realistic opamp model

Non-inverting op-amp

Exercise — non-inverting opamp

Feedback

Inverting op-amp

Exercise — inverting opamp

Virtual ground

Virtual ground — examples

Exercise — unity-gain buffer

Summing op-amp

Exercise — summing opamp

Further study

One of the best sources of information about analog circuit design and operational amplifiers is the design library at Analog Devices. This company is one of the leaders in analog integrated circuits. Over the years their design engineers have written great tutorials and detailed guides about their product line and, more importantly, about the fundamentals of analog design and signal sensing. This is a highly trusted source.