AD8000 .cir emulation not working in LTSPICE

Robz  Before we start troubleshooting the model, I want to make sure your circuit is behaving as expected with an ideal opamp.

/cfs-file/__key/communityserver-discussions-components-files/1020/Basic-Circuit-with-ideal-opamp.asc

I've redrawn your schematic, with the following changes:

- I've replaced the AD8000 with an ideal opamp

- I've replaced the Rser in the input voltage with an actual resistor - just helps me to visualize.

- I've remove supply bypass caps - not needed for this sim, just trying to simplify as much as I can.

I'm using an input signal with a lower frequency, just to make sure I understand the behavior of the circuit.

The opamp DC bias at In+ is set by the 27k resistor divider to Vcc/2 - that looks fine.

The opamp is going to drive the DC bias of the output to 4.4V - since it's trying to drive that 430 resistor divider connecting to IN- to Vcc/2, to drive the opamp inputs to the same voltage.

Can we work this this simpler schematic to ensure it's behaving as expected before switching out to the more complex macromodel?  One thing that is going to give us trouble when we switch this ideal model with a more realistic model is that the opamp is trying to drive the output to the supply rail.  One possibility is to replace the GND of the 430 resistor divider with VCM = 2.2V?

Why didn't you just use the AD8000 model, the circuit is just as simple as using the 5532.

The interface on LTSpice is not exactly intuitive, so its faster for you, someone who knows the tricks, to add the AD8000 than for a new user, me, to set up an alternative op amp.

If you can't add the AD8000 and get it to work, what hope do I have?

Why didn't you just use the AD8000 model, the circuit is just as simple as using the 5532.

The interface on LTSpice is not exactly intuitive, so its faster for you, someone who knows the tricks, to add the AD8000 than for a new user, me, to set up an alternative op amp.

If you can't add the AD8000 and get it to work, what hope do I have?

I also need to test from 100KHz to 160 MHz, and a 0.2uV input signal, that is the goal, anything less is worthless, and as this isn't rocket science, it really should work.

Robz I'm peeling layers of an onion.  You have a simulation that isn't working, and I'm trying to help you figure out why.

You are correct - adding a part like the AD8000 is not intuitive - we have lots of op amps included in the LTspice library that would be easy to add to a schematic, but the AD8000 isn't one of them.  So that is one of the things that's making this complicated - I understand the frustration.

But I'm also trying to understand the circuit you've built, and what it's supposed to be doing.  The original schematic you attached had R3 set to an incorrect value, I believe, so that was one issue.  I'm also trying to understand if you're going to violate the limits of the opamp that are dictated by the supply voltages that are being fed to the opamp - that's another potential issue.

If we can get something working the way you expect with an ideal opamp model, it gets us closer to feeling good about the circuit topology overall - then we can examine if things work as expected when we switch out the ideal opamp with the AD8000.