Programming instructions

Analog Components
Multisim Component Reference Guide 5-2 ni.com
compensated Opamps, the -3 dB corner frequency can be changed by adding an external
capacitor.
unity-gain bandwidth
This is the frequency at which the gain of the opamp is equal to 1. This is the highest
frequency at which the opamp can be used, typically as a unity gain buffer.
common mode rejection ratio (CMRR)
This is the ability of an opamp to reject or to not amplify a signal that is applied to both its
input pins expressed as a ratio (in dBs) of its common mode gain to its open loop gain.
slew rate
This is the rate of change of output voltage expressed in volts per microsecond.
5.1.2 Opamp: Background Information
The operational amplifier is a high-gain block based upon the principle of a differential
amplifier. It is common to applications dealing with very small input signals.
The open-loop voltage gain (A) is typically very large (10e+5 to 10e+6). If a differential input
is applied across the “+” and “-” terminals, the output voltage will be:
V = A * (V+ - V-)
The differential input must be kept small, since the opamp saturates for larger signals. The
output voltage will not exceed the value of the positive and negative power supplies (Vp), also
called the rails, which vary typically from 5 V to 15 V. This property is used in a Schmitt
trigger, which sets off an alarm when a signal exceeds a certain value.
Other properties of the opamp include a high input resistance (Ri) and a very small output
resistance (Ro). Large input resistance is important so that the opamp does not place a load on
the input signal source. Due to this characteristic, opamps are often used as front-end buffers
to isolate circuitry from critical signal sources.
Opamps are also used in feedback circuits, comparators, integrators, differentiators, summers,
oscillators and wave-shapers. With the correct combination of resistors, both inverting and
non-inverting amplifiers of any desired voltage gain can be constructed.
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