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

On Jul 28, 11:29 am, Tiger <howyoul...@xxxxxxx> wrote:
I am sorry ,because i express unclear. in my system ,Transmitter
and receiver share one antenna.
Accounting for RF choke in DC bias path, A low path filter must
be used. thus in order to get faster switch wave rising edge ,we have
to decrease time constant of circuit . The filter's cutoff frequency
is closer to 3MHz, better rising edge or falling edge of switch wave
we achieve. Do you agree with me?
As to FQH8N100C you mentioned , i am reading it. Thank you for your
advice!

Yes, I would certainly agree that proper filtering to separate the PIN
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 the PIN switch 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 fast PIN driver
circuit and the PIN diodes a low pass filter, and also between the PIN
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 use PIN diode clamps 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 voltage PIN diode, and there are other PIN
diode ap notes on the Avago site.

Cheers,
Tom

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