Dear Colleagues from Analog Devices,
My current scientific interest is related to determination of crossover frequency of operational amplifiers; and especially ADA4898-2, which we often use in our University. The search in the literature revealed that the crossover frequency is poorly described. Actually in some textbooks some methods for determination of this important parameter are described but in newer specifications of commercial operational amplifiers we do not find histograms of the crossover frequency of operational amplifiers. We have even submitted to a journal the following article uploaded in the Cornell University library https://arxiv.org/abs/1802.09342 (version 2, which will become visible tomorrow), but since the engineering science is concentrated on the industry, we do not expect any reliable response from the referees of the journal. Journals become tools for career instead of forums for exchange of scientific information. That is why I took the liberty to address Analog Devices.
As a university teacher I will appreciate a report from Analog Devices concerning our method for determination of the crossover frequency of ADA4898-2 and Probability Distribution Function (PDF) determined using 200 double amplifiers. This is already a reliable statistics and the result, which we have obtained is that PDF corresponds to Gaussian distribution of the crossover frequency. We are kindly asking Analog Devices whether our method and results looks acceptable. Still we have hundred ADA4898-2 and can make additional measurements using a digital lock-in voltmeter. It will be nice if in future some tutorial article in Analog Dialog can give clarity on the problem for determination of crossover frequency of operational amplifiers. Now for example, in the specification of ADA4817 are given some theoretical formulas for the frequency response of the main circuits (equations (4) and (7) in Rev. F) but without reference to any textbook or monograph in electronics. The relation between time dependent output and input voltages has also never been published.
In short, I am suggesting an Analog Dialog concerning the problem of method of determination and statistical properties of crossover frequency of Analog Devices operational amplifiers.
Professor in Physics,
University of Sofia, Bulgaria