Operational Amplifiers (Op-Amps)

Op-amps and transistors are the staples of analog circuit design. Internally, op-amps consist of many transistors, capacitors, and resistors; all crammed onto a small integrated circuit.

The symbol for an op-amp:

Each op-amp has an inverting input, a non-inverting input, and an output. In practice, op-amps also must be powered by a positive and negative voltage, but since the power and ground won't affect our schematic design, the leads are usually omitted in the drawings.

Ideal Op-Amps

Op-amps are generally very well described the their ideal model.There are several basic rules for ideal op-amps:

1. There is no voltage difference across the inputs. Although the open-loop gain of an ideal op-amp is considered to be infinitely large, the op-amp will try to keep the inputs at the same voltage if it can somehow send the output signal back to the input to push or pull the input voltages to the same level.

2. The input current draw is zero. In real op-amps, there will be a small current draw because the op-amp does not have infinite resistance (maybe $10^{1}2\Omega$ for FETs and $10^{8}\Omega$ for BJTs).

3. The output impedance is zero. This means that the output current does not affect the output voltage.

The 741 and 411 Type Op-Amps

The 741 (bipolar) and 411 (FET) families of op-amps are popular chips made by many manufacturers. The model number is often preceded by a modifier/identifier, such as "LM741" or "LF411". These op-amps also come in varieties where you get multiple op-amps on a single package.

[here for the data sheet of the LM471]

Click here for the data sheet of the LM148 quad 471

Click here for the data sheet of the LF411

For now, we can ignore the "offset" pins. These are used to make very fine adjustments in the reference voltages.