PIN diode bias question... - RF Cafe Forums
Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
you would like to post something on RF Cafe's
page, please do.
Below are all of the forum threads, including all
the responses to the original posts.
Post subject: PIN diode bias question... Posted: Wed Nov 23, 2005 6:29 am
Joined: Fri Aug 27, 2004 11:25 am
Location: Cape Town, R.S.A.
fundamental question regarding PIN diodes and their biasing – How does one calculate the minimum DC voltage
required to ensure that a PIN diode remains OFF in the presence of RF?
In a specific system implementation,
where a PIN diode RF switch is used to cold switch 500 W RF pulsed signal, a shunt diode configuration is used. In
this existing system a reverse bias of 50V is used to switch the diodes OFF, but it was shown experimentally that
the reverse voltage could be dropped as low as 25V before the RF began to bias the diodes ON.
First of all
I understand that 500W RF power corresponds to a RF voltage swing of 450Vp-p, if 50 ohm is assumed. This on top of
a -50V bias (for switching the diodes OFF) means that the signal is swinging between -275V and +175V, which one
would think would bias the diodes ON during the positive cycle. The minority carrier lifetime of the PIN diode
however is related to the fact that this does not happen and the diode remains OFF for the complete duration.
The question then remains, what is the relationship between minority carrier lifetime, RF power, frequency and
other PIN diode specifications and this minimum reverse bias voltage to ensure that the diodes remain OFF.
Am I missing something obvious? I’ve searched through various application notes and other literature, which
somehow always seem to ignore this requirement.
Post subject: Posted: Wed Nov 23, 2005 11:44 pm
Joined: Tue Sep 07,
2004 3:09 pm
This is an interesting question.
As I know when used as
attenuators, pin diode long minority carrier lifetime drives the hability of the diode to provide good
In a two tone intermodulation test the enveloppe being non-constant, I see
this also as the hability to resist bias change by the enveloppe modulation.
I wonder if the equations for
linearity of a pin diode attenuator in high attenuation condition would be useful... like the one from MACOM or
Alpha. You would be using a criterion for extremely low distortion meaning the diode absorbs no power.