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Dennis Feucht

Fully-Differential Amplifiers and the Leading Edge in Electronics

Dennis Feucht
D Feucht
D Feucht
9/12/2018 5:04:52 PM
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Re: FDA's been around for awhile
Mike,

Your chronology about FDAs is right, of course, and it reveals my age. The main point is that FDAs have been around in oscilloscope vertical amplifiers since at least the late 1940s. Because CRT deflection plates are inherently differential, there was an impetus for them back then, but my point of amazement is that they didn't show up in IC amplifiers in the 1970s, in other than in-house Tektronix ICs. "Glacial pace" puts it accurately.

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TucsonMike
TucsonMike
9/12/2018 10:09:19 AM
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Newbie
FDA's been around for awhile
Nice post Dennis, but to clarify, what has come to be called the Fully Differential Amplifier has been available commercially since I think about 1999 - almost 20years. We were working on one inside BurrBrown starting in 1998 while ADI beat us out with the first one in 1999 - I believe it was the AD8138 or AD8132. TI was also aggressively developing FDA's in this time period, where I think the THS4130 might have been the first released. With the TI acquisition of BurrBrown in 2001, we stopped our FDA development for a few years picking it up again with the THS4521 typed device around 2008. The distinquishing characteristic for this class of device is the seperate output common mode control loop. Diff I/O stages can be done very easily with dual op amps, but the 2nd loop makes a whole new creature. Looking at my high speed amplifier parametric data base, I now see somewhere around 75 devices that are called FDA's where most are from ADI, LTC, and TI. This is not including a whole range of internally fixed gain FDA topologies mainly from LTC. 

Analog Signal chain seems to change at a glacial pace, I am not sure we can call these FDA's recent or new any more. 

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