AOE 3054 Self-Taught Unit 1

1.7 Operational Amplifiers (contd.)

Consider, for example, the inverting amplifier circuit. Applying rule (i) we see that i₁ = i₂. Applying rule (ii) we see that the negative input voltage is zero, since the positive input is connected to the ground. We therefore have
i₁ = v_in / R₁ and i₂ = -v_out / R₂ and so,
v_out / v_in = -R₂ / R₁ i.e. this circuit inverts the input voltage signal and multiplies it by R₂ / R₁ - hence 'inverting amplifier'.

As you can imagine it is possible to build many other types of amplifiers using this component. Note that Op amps can be built to behave as filters. These are usually called 'active' filters to distinguish them from the 'passive' filters described later in the review.