# Ideal Op Amp model in PSpice capture

I am trying to simulate a comparator in pspice capture student version. The problem that I am facing is that circuit is not working for higher frequencies because the opamp I am using is not ideal.

I downloaded opamp.olb and opamp.lib from this link http://robustdesignconcepts.com/files/pspice/pmindex.htm and tried many opamp modals from this library.

I have searched some other libraries from this page too but I cant find an ideal opamp modal.

Can anyone share any pspice libraries which has ideal opamp or guide me how to build one.

I am using also PSpice - however with a schematic entry package called "SCHEMATICS". In this library there is a part called "opamp" which is the model of an ideal opamp without any frequency-dependence.

Take a step back. What is an opamp ?

You want an ideal opamp yet you search for models of real opamps which (assuming the model is any good) include non ideal properties.

The same non ideal properties (like bandwidth) you're trying to get rid of !?!?!

See the contradiction ?

Now back to my question, what actually is an opamp. What would be the behavour of an ideal opamp ?

In literature you can find:

$$V_{out} = A * (V_{in+} - V_{in-})$$

where $V_{in+}$ and $V_{in-}$ are the voltages at the non-inverting and inverting inputs of the opamp. And $V_{out}$ is the output voltage obviously. A is the gain which we often want to be as high as possible.

Now how would one make this in a simulator ? That is actually quite easy, the Voltage controlled Voltage source does just that. You can set the gain as high as you like but in practice, start with 1000 and see how that goes. A higher gain might confuse the simulator.

You can simulate it using a voltage controlled voltage source vcvs or a voltage controlled current source vccs followed by an output resistance.

The two-port equivalent circuit of an OpAmp will help you understand it better since it is a simple representation of what is really happening in a differential amplifier (OpAmp is basically composed by a diff.amp and a common drain). The pair of transistors convert the differential input voltage into current by a factor of "gm" and then this current flows through an equivalent output resistance, causing a voltage drop (output voltage)