I have integrated the spice model for the OPA657 into my simulation in Altium, but when I run the simulation, I find a persistent oscillation at about 100 MHz whenever I simulate a simple amplifier. I think that the basic connections are correct: we’ve both checked them over; also my simulations indicate correct 10 MHz amplification, even though there are superimposed 100 MHz oscillations. Low-value feedback resistors don’t help. A capacitor (of up to 100 pF!) in the feedback doesn’t help. I’ve seen reference in TI’s self-help group to deficiencies of this model, and the comments from some revision levels back mention “fixing oscillation in input stage.” Any suggestions?
100pF is very large for a compensation capacitor in the feedback path which could be a source of oscillation. Typical values are around 1pF or less. The applications section starting on page 11 of the OPA657 shows how to calculate the correct value for the compensation cap.
A similar post has already been addressed on the forums: http://e2e.ti.com/support/amplifiers/high_speed_amplifiers/f/10/p/163943/596734.aspx#596734
Additionally I tested the OPA657 in TINA-TI and did not notice any oscillations with a properly selected feedback capacitor so the model appears to be working ok.
If you upload your schematic I can verify your values for you if you'd like.
Regards,Luke LaPointeHigh Speed Amplifiers
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