Normal LNA working below -100 celsius?

[Hadi-Alik]

Hi all,

Similar to what is done in all Radio-Telescopes, I want to reduce noise by putting my LNA in a very cooled (cryogenic) system around -100 deg . Normal LNA's (cheap or connectorized) datasheet say -40 normally as the lowest working temperature. My question is what happens below this temperature and if I can them in such application or I have to use a specially designed Cryogenic LNA?

Thanks
Hadi

 

[vfone]

Most of the minimum temperatures given by transistor manufacturers are limited by their possibilities (and desired interest) to go below about -40 deg.
I think that transistors from various fabrication processes would work fine at -100 deg.

 

[Hadi-Alik]

Many thanks, Would you please give me more details on the mentioned limitations of going beyond -40 deg?

 

[G4BCH]

While the semiconductor die may still be capable of operating at cryo temperatures, an amplifier designed for 'normal temperatures' may not be biased to be able to operate there and still give optimum performance. The noise match may alter negating any improvment from the lower temperature, and the reliability of the components may be compromised. Differential rates of expansion, or in this case contraction may cause the components to break appart. I'm not sure anout the long term reliablilty of soldered joints below -60C either.
I don't want to sound pessimistic and say it will not work or that you should not try, just to be aware that the amplifier may not survive, but then it might. Keep the moisture out as much as possible, expanding ice crystals can cause a lot of damage if in the 'wrong' place.
Peter

 

[biff44]

the plastic housing may break open at the lower temperature. If it does not....it will probably work electrically just fine. cool a LNA down to that temp, and reheat and inspect it. If good, then try it with RF signals.