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:
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