Re: how to design PIN diode driver - high voltage and high speed


Yes, I would certainly agree that proper filtering to separate thePIN
bias from the RF is a good idea.  The faster you need to switch, the
more critical that becomes.  It should be an advantage to consider not
only a low-pass filter for the bias but a high pass filter for the RF--
or other methods to reduce the capacitance that thePINswitch must
drive.  Of course, be careful about the return path for the current
that charges the capacitance especially on the receiver side, so that
you do not expose the receiver input to excessive current.  A power
mosfet that switches several hundred volts in a few tens of
nanoseconds will be generating quite a bit of available energy to a 50
ohm 3-30MHz input!  If there exists between the fastPINdriver
circuit and thePINdiodes a low pass filter, and also between thePIN
switches and the receiver input (or transmitter output) a high pass
filter, and the filter passbands do not overlap, then there should be
decent isolation to protect the receiver input.  I can tell you that I
also usePINdiodeclamps on the input to a receiver I recently put
into production, and they are able to absorb transient energy quite
nicely.  They are just diodes normally reverse-biased by several
volts.  In a switched system, I would consider driving them actively,
using differential drive so that there is no (or very low) transient
on the RF input that they shunt to ground when they are "on."  If the
diodes are matched (as they are in a packaged pair, such as Avago
HSMP-3822) and you drive them to the "off" state symmetrically, they
should inject very low pulse energy into the line they are switching.
The data sheet for the HSMP-3822 has several ideas for getting very
good isolation on the receiver side, once you've gotten isolation from
the high power with a high voltagePINdiode, and there are otherPINdiodeap notes on the Avago site.

Cheers,
Tom

Hi,Tom
Thank you for your reply in my news group"how to design PIN diode
driver - high voltage and high speed ?"! I got so much in your answer!
In my Antenna switch, in order to avoid input overload of my
receiver, a power limiter will be utilized. In your reply , you
mentioned that you also use PIN diode clamps on the input to your
receiver . My question is , is it able to absorb transient voltage >1
mV (the maximum value of receiver's pre-amp is 1mV )? According your
suggestion , i am going to use HSMP-3822 diode pair with 5 volts
forward bias(when transmitting ),-5 volts reverse bias(when
receiving), on the input of my receiver. Do you think the power
limiter plan can absorb the transient energy above 1 mV for the
receiver during both the receiving state "ON" and "OFF"?
Any suggestions will be appreciated!
.

Relevant Pages