The operational amplifier (op-amp) is a most versatile integrated circuit, originally designed to perform mathematical operations on analog voltages such as addition, differentiation and integration.

An op-amp is a differential amplifier with an inverting V_- input, non-inverting V₊ input and open loop gain A_v. The output voltage V_o = A_v*(V₊ - V_-). To derive approximate theoretical equations for op-amp circuits, the op-amp is assumed to be an ideal device having the following electrical characteristics:

• the inputs draw no current, i₊ = i _- = 0, hence the input impedance Z₊ = Z_- = ∞ ;
• the output current is infinite, hence the output impedance Z_o = 0,
• the open-loop gain, or voltage amplification A_v = ∞ so that from the gain equation one can conclude that V_- = V₊.

In open-loop configuration, since A_v of the op-amp is very large, a tiny voltage difference between the inputs causes the output to swing between the power supply limits, or saturate. This effect can be used to implement a voltage comparator or level detector.

To implement a comparator, one input is set to a reference voltage. The output changes state as the voltage at the other input swings above and below the reference voltage. For example, with a +5V power supply: when V₊ > V_-, then V_o ≈ +5V; when V₊ < V_-, then V_o ≈ 0V. Note that in practice, due to input signal noise and non-ideal op-amp operation, when V₊ and V_- differ by less than a few millivolts, the comparator output may oscillate or otherwise behave in an erratic fashion.

In closed-loop configuration, feedback is applied from V_o to V_-. The op-amp gain can be analytically determined from the circuit components, assuming that ideally V_- = V₊.

The MCP6002 8-pin chip includes two op-amps in the same package. Each op-amp has rail-to-rail outputs, meaning that the output voltage can range between the two power supply limits, in your case, between V_ss=0V and V_dd=+5V. The MCP6002 data sheet can be found here.

Prelab preparation:

Review your lecture notes and this document so that you understand how to apply the ideal op-amp characteristic V_- = V₊ to derive an op-amp transfer function. Then derive the equations that will be used during this lab session.