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OPA180 and OPA2188 Simulation models

Other Parts Discussed in Thread: OPA180, OPA2188, OPA2180, TINA-TI

Does anyone know if the OPA180 (or dual version OPA2180) is the same silicon as the OPA2188?  If it is, I have noticed a marked difference in these two parts during noise simulation.  The OPA180 displays the correct noise voltage characteristics as listed by the data sheet.  However, the OPA2188 does not.  If you test the noise voltage of the OPA2188 it appears to have 1/f noise like a normal OpAmp.  Also, unlike the OPA180 where the noise decreases at high frequencies the OPA2188 noise increases at higher frequencies.  

  • George,

    Are you using the TINA-TI simulation for the comparison? I did see an increase in both at frequencies higher than 1MEG, however, the OPA2188 seems to go up much more dramatically. I'll check with the team to see if there is a reason for this behavior.

  • Yes, I am using TINA-TI simulation to measure the noise voltage of the OPA2180 and OPA2188.  I am mainly interested in correct modeling for low frequency noise of these two parts.  The OPA2180 simulation model appears to have very little 1/f (near flat) noise which is expected for these zero-drift Op Amps.  However, the OPA2188 simulation model displays an increasing noise for decreasing frequency, as in a typical Op Amp.      

  • Hello George,

    We do not disclosed proprietary information about our integrated circuit die. When I simulated and compare the OPA180 and OPA2188 voltage noise spectral density curves I do see that the OPA2188 model does show an increase in noise at very low frequency and that towards the high end of the range. I would agree that the noise shouldn't increase quite so much on the low end, but in actuality the noise does increase at high frequency as the op amp begins to run out of open-loop gain (Aol). Often, the noise graph scale cuts off before that occurs.

    Even though it appears that the OPA2188 model will not provide as near-ideal noise behavior as the OPA180, in reality their noise performances are quite close. This is revealed when the integrated output noise is simulated for each of them and then overlaid on the same graph. This can be seen in the graph at the bottom of the diagram below where the two curves lay on top of each other.

    Regards, Thomas

    PA - Linear Applications Engineering