Replacing PIN diode with Schotty diode...

[Mark]

Hi all,

I'm basically looking for views on why a Schotty BAR43 diode would work as a
PIN diode and provide a better NF than a RN731V PIN diode.

It's just that there is a modification for a Kenwood TS-2000 bandpassfilter
that says replacing the PIN's with BAR43's will lower the noise floor
from -24db to -34db.

Could it just be the though resistance difference not adding to the noise
figure?

Could the use of BAR43's introduce other problems??

Any suggestions/ideas welcome,

Regards,

Mark

 

[Tim Wescott]

Mark wrote:

Hi all,

I'm basically looking for views on why a Schotty BAR43 diode would work as a
PIN diode and provide a better NF than a RN731V PIN diode.

It's just that there is a modification for a Kenwood TS-2000 bandpassfilter
that says replacing the PIN's with BAR43's will lower the noise floor
from -24db to -34db.

Could it just be the though resistance difference not adding to the noise
figure?

Could the use of BAR43's introduce other problems??

Any suggestions/ideas welcome,

Regards,

Mark

I'm not sure about the noise -- it could be that the shot noise would be
lower with a Schottky because of the lower forward voltage drop, or the
lower on-resistance.

I _do_ know that one uses a PIN diode for signal switching applications
because it has a long carrier lifetime. This means that it takes a
while to switch off and will not rectify RF (if you've selected the
right one, at least). A Schottky turns on and off very fast, so if the
bias current wasn't sufficient for the signal levels you may see serious
distortion, intermodulation products, etc., that you wouldn't see with a
PIN diode.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com