MMIC amps: Input impedance

Joerg · 2006-11-30T21:04:50+00:00

Hello Folks,The BGA2001 from NXP looks like a good deal at around $0.30/1k. Hard to justify rolling your own amp at that price, plus it's got a really nice noise figure of under 1.5dB.I am planning to use it well under 100MHz, actually down to maybe 5-10MHz. Looking at figure 12 the input impedance seems to exceed 500ohms down there (they don't show anything below 100MHz). Except for 500MHz its input is pretty far off 50ohms on most bands. Is this normal?I wonder why they spec input intercept and other things in dBm then. Not complaining here since a higher Rin actually helps my photodiode app because I won't need a RF transformer. Just wondering. I have always rolled my own, first time I am considering a MMIC.-- Regards, Joerg

Nov 30, 2006 22 Replies

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Don't remember but we came really close to the advertised noise figures of the transistors. It was ultrasound, same range as shortwave but noise really matters there.

Most pathetic was that we were told back at the alma mater that using a FET in common gate is the stupidest thing an RF engineer can do. Of course I did not believe that. Actually I was sitting at the front of the auditorium and to the dismay of the prof I burst into laughter. Couldn't help it because I had just built one for my ham radio station. Then my very first project after getting my degree was, guess what?

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