One by one answers:
1) PIN diodes are characterized by the thickness of the intrinsic layer when
cut off. Exactly the same with silicone diodes: what sets those apart is the
parallel capacitance; bigger for regular diodes it causes more leakage
around the back biased junction. this has nothing to do with the dynamic
resistance of the back biased diode junction.
2) Linearity is a function of both the DC bias current when "ON" AND the
carrier lifetime of the diode (recombination time). This is much longer for
PIN diodes and is the reason for better linearity at low frequencies.
So, if you want all the best: rectifies are less linear although you can
alleviate to a point by increasing the bias current, which incidentally
reduces also the insertion loss.
For better isolation you need diodes with smaller parasitic capacitances for
less leakage. Since capacitance is proportional to the chip size, that means
smaller diodes that won't keep up with the power planned. The only
compromise that achieves both goals is a PIN diode!!!
Soooo, if you want the best use PIN diodes, if you're a ham use whatever you
have and and install more diodes in series, increase biases_ both forward
current and back voltage and experiment.
Alex 4Z5KS
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Steve Katz
Sent: Friday, August 07, 2009 6:35 PM
To: jtml@vla.com; amps@contesting.com
Subject: Re: [Amps] PIN diodes and QSK
Because they often "won't" do. P-N devices carefully selected for this
application still aren't as linear as PIN devices, don't have as much
isolation when turned off, and often won't work well down at lower
frequencies like 160 meters, which is the most challenging application.
WB2WIK/6
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]On
Behalf Of John Lyles
Sent: Friday, August 07, 2009 8:30 AM
To: amps@contesting.com
Subject: [Amps] PIN diodes and QSK
Thanks, Lon, k5jv, for the work on PIN diodes that you reported.. Makes me
think the same thing, why pay for the $$ diodes if silicon power rectifiers
will do?
73
john
K5PRO
New Mexico
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