OPA857: TINA AC Simulation

Olaf Wohlmann1

Part Number: OPA857

Hi,

I am using TINA-9 to simulate some basic OPA857 circuits. When i do a AC simulation based on the example downloaded from the TI website i am receiving the plot shown below. Unity gain is reached far above 10 GHz which doesn't sound reasonable to me. I already learned that some models are not ideal, but however i want to build up a simulation with this OPA as the first one and this diminishes my trust into this model.

Regards

sbom863a.tsc

over 5 years ago

0 Michael Steffes over 5 years ago

Guru 48395 points

Well Olaf

It is plotting in dB gain for a transimpedance value, you set up is at about 5kohm gain where it should be 125MHz 3dB down - and it is, low frequency gain is 73.58dBohms, and 3.01dB down is at 70.57dB at 125Mhz - exactly correct it seems.

0 Olaf Wohlmann1 over 5 years ago in reply to Michael Steffes

Prodigy 240 points

Hi,

Well, i am fine with the -3dB point but a colleague asked me how it is possible that there is still gain at GHz frequencies.

Thanks for the quick help on that.

0 Michael Steffes over 5 years ago in reply to Olaf Wohlmann1

Guru 48395 points

Your 0dB point way out there is equivalent to a gain of 1ohm for this transimpedance stage, yes the models are not super accurate above say about 2GHz due to every parasitic matter there - I doubt the package model is in the TINA model for instance. If you actually measured this and saw this, I would suspect feedthrough. Saw that quite clearly characterizing the CLC110 buffer.

But anyway, who cares really - something is following this stage that will bandlimit the response.

0 Olaf Wohlmann1 over 5 years ago in reply to Michael Steffes

Prodigy 240 points

Thanks!

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OPA857: TINA AC Simulation