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Op-amp simulation

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Full Member level 5
May 10, 2020
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I am not sure what's the mistake I am making on the below simulation.

Below is a Non-inverting op-amp (IC Link) with Gain as 3.

Case1 : Input: 1MHz; Offset:0.5V; Pk-pk Amplitude: 0.2V

enter image description here


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The output gain is close to 3. And the input and output frequencies are same.

But if I increase the input frequency alone to 5MHz,

Below is the result:

enter image description here

Why is there a 60mV additional increase in the output voltage? Shouldn't it be the same 600mV?

I am trying to test the GBWP and slew rate with this op-amp.

Maybe spice model is not 100% accurate ?

And you have not included parasitics in your schematic.

I would have guessed gain peaking but your Cload = 0 so thats out.

Regards, Dana.

Dear FreshmanNewbie,
Why is there a 60mV additional increase in the output voltage? Shouldn't it be the same 600mV?
Even if the external load capacitance is not included in your test bench for the MCP660 op-amp, I examined its model and found it does include a 2 pf capacitance at its load. Hence, I suspect the reason you are observing a 60 mV increase in output amplitude with a 5 MHz input relative to the input amplitude and do not observe the 60 mV increase in amplitude relative to the input amplitude at 1 MHz is the transfer characteristic of the op-amp and its peripheral circuitry in your test bench.

Two options to attempt to confirm this hypothesis are:
1. Perform a small-signal AC analysis of your circuit with the input set to 1 V AC and observe the output voltage over frequency. This will illustrate the transfer function over frequency.
2. Apply a series of input frequencies and measure the gain at each frequency in a series of transient simulations to assemble the gain characteristic as a function of input frequency.

I hope this helps FreshmanNewbie!
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