Tuning speed of a laser diode

Hello Phil,

Thanks. Looks like Amazon then. I like your web article about the real story of photodiode front ends. Reminds me of a morning where I sat in a big auditorium at our university. The professor showed the various configurations of a transistor on the overhead projector (those projectors without a PC...). When he came to the MOSFET and said that common base configuration would be utter nonsense I couldn't help it anymore. I burst into laughter and everybody looked at me. Embarrassing. I had just built an amp like that and it worked like a champ. And you could find similar amps in lots of the better commercial radios.

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Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg
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Sure, "common base" is nonsense. They don't even _have_ a base. ;-)

Cheers! Rich

Reply to
Rich Grise

I'm partial to the common-gate U309 JFET myself--just about exactly 75 ohms input, high IP3, 10 dB gain, reasonably flat over HF and VHF, nearly bulletproof, lowish noise--perfect for block downconverters. (That's another part I have lots of in my drawer--probably a career's worth.)

Common-base stages are the bee's knees sometimes--besides the impedance transformation property, the small signal emitter resistance kT/(eIc) has a noise temperature of T/2--i.e. 150K at room temperature, or 1.8 dB NF.

Once or twice I've been told that there was no way of getting a noise temperature below ambient, 'due to thermodynamics'. I've noticed that when people say that they usually have a cold beer nearby--which came from a refrigerator that also couldn't be below ambient, by the same argument. ;)

I may build mostly one-offs these days, but I'm still very much in your camp when it comes to the designer's art--I'd far rather use a 3N3904 than an OPA656, even when I have both in the drawer. (Which is not to knock the OPA656.)

Cheers,

Phil Hobbs

Reply to
Phil Hobbs

Hello Phil,

Yes, the old jelly bean parts often do the trick and we can be pretty sure that they or something similar will be around 20 years from now. Less so for JFETs :-(

In this case I'll need well over 100MHz BW and low noise. While many nice RF transistors have gone lalaland Infineon features a good line-up, including their MOSFET tetrodes. But their parts can be dang hard to get a hold off. Their marketing is, well, don't get me started.

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Regards, Joerg

http://www.analogconsultants.com
Reply to
Joerg

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