This next topic focuses on the operational amplifier, which is one of the most widely used electronic components in the analog world. The operational amplifier, also known as an op-amp, is a type of differential amplifier. The output voltage of an op-amp is:
Op-amps are used in a variety of applications, which perform many different operations, hence the name. External passive elements – such as resistors, caps, inductors, etc – are used to determine the end function. Before continuing into any applications, you should consider the following properties of an ideal op-amp.
Ideal OP-AMPs have:
Infinite input impedance
Zero Output Impedance
Infinite Differential Gain
Zero Offset Voltage
Zero Input Bias Current
Zero Common Mode Gain
Recalling our previous equation and substituting Aol=∞ produces the following relationship for the non-inverting and inverting inputs.
This equation merely demonstrates that for an ideal op-amp, both inputs are the same voltage value, so in a sense both inputs are virtually shorted to each other.
Using these properties, you can solve any ideal op-amp circuit configuration. To get you started in op-amp analysis, I’ve provided a simple circuit below, which is an inverting op-amp configuration.
Using KCL, let’s guess the current direction and solve for node 2.
What happens when I substitute a voltage for the V+ input?
I’ll leave this next configuration as homework: