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OPA1637: Input current noise model testing, 1/f corner seems off on the current OPA1637 model,

Part Number: OPA1637
Other Parts Discussed in Thread: THS4561

Morning Iwata-san if you are still looking at this, 

Well this noise model issue has been continuing over on the amplifier forum comparing the simulated input current noise on the THS4561 to the OPA1637. 

To summarize, the original 2018 THS4561 TINA model was a bit off on the voltage noise flatband while the current noise had a 1/f corner in the model far higher than the final PDS plot shows. This older model uses a macro I recognize (not so obvious in the most recent models), so it is easy to modify - here is what that looks like in the original 2018 THS4561 model release, The 1st number on each row is a frequency for the low frequency noise value (1Hz normally), the 2nd is that noise value, the last is the flatband value. (I am pulling this from the models in the 3 FDA comparison file that Iwata sent earlier - which was the 2018 model). From these numbers that actual 1/f corner frequency can be calculated than compared to the PDS lot - neither the voltage or current noise are very close to PDS in the THS4561 2018 model, 

Here is the PDS plot for the THS4561 that the model should be matching, the flatband values here are both lower than the spec table? Use the curves for now, 

From these curves, 

En = 3.8nV with 1/f = 9Hz

In = 3.6pA with 1/f = 500Hz, 

Here are the modified model lines to match this, current noise must be in femto, voltage in nV

So focusing in on just the current noise, that is easy to get by inserting current meter into the summing lines and running and output noise sim, here is that from Iwata's original file looking at just the OPA1637 and modified THS4561 models. The modified THS4561 model lines appear to match the PDS plot now, the OPA1637 is close on flatband but way low on 1Hz noise, should be about 0.8pA at 1Hz. So, in those early sim efforts that Iwata was doing, the TINA model for the THS4561 was way high on low F current noise and the OPA1637 is a bit low. Not sure how to change the OPA1637 model, but the 2018 THS4561 model is easily updated. 

And then here is that file with the corrected THS4561 noise models, 

Audio-FDA_comparizon05 Iwata original comparison updated THS4561 noise models.TSC