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

On Jul 27, 9:47 am, Tiger <howyoul...@xxxxxxx> wrote:
On 7月27日, 上午1时12分, Tom Bruhns <k7...@xxxxxxx> wrote:



On Jul 26, 8:30 am, Tiger <howyoul...@xxxxxxx> wrote:

Now i need a high-power T-R switch that can switch state in two
microseconds. Drive outputs: +12 volts(current ,0.5 ampers) , +700
volts , -12volts(-0.5 ampers), -12 volts. Tx path may stand 600
watts
(peak). I want to use PIN driver IC,but don't find IC that may output
+700 volt. So i have to design the switch by myself.
I am going to employ discrete MOSFET as driver . Input to the
MOSFET is TTL logic.
some specification of my switch is :
working frequency band : 3 - 30 MHz
T - R isolation : > -80 dB (when transmitting)

Anyone ever do this? Can i get so fast speed(< 2 microseconds)?
Would you give me some suggestions? Any help will be appreciated!

What's the carrier lifetime of the PIN switches you'll be using? That
probably has more to do with how fast you'll be able to switch between
T and R than the FETs you use. What carrier lifetime do you need to
do a good job with your 600W at 3MHz? But I'd also like to know why
you think you need to switch so quickly for that frequency band, since
the transmission modes allowed are not particularly broadband. Also--
why do you need so much isolation? 50dB gets you below 10mW, and I'd
consider it a pretty poor receiver front end that couldn't handle that
without damage. 80dB attenuation won't be as easy over a decade of
frequencies as it would if you were dealing with a single frequency or
a narrow band, though you can add however many stages of low power PIN
or simple diode switches or other RF switches to get to whatever
attenuation you need, after your high power PIN switch. Note that 10
amps in an FET will slew 1000pF 10 volts per nanosecond...

Have you looked for ap notes on the web sites of manufacturers of high
power PIN diodes?

The carrier lifetime of PIN diode i use is 10microseconds(Typ.) .
Part number is UM4010,manufactured by Microsemi Corp. I have read some
ap notes of PIN Diodes, and got to know that switching speed of my
antenna switch is not only related to carrier lifetime of PIN
diodes ,but also related to driver . A good driver may get faster
switching speed:may up to one fifth or one tenth of carrier
lifetime(please refer to great book "Semiconductor control',writen by
White J F. ,1977) . In order to switch the RF signal(3 - 30 MHz) with
less distortion, accroding to calculation , the carrier lifetime must
longer than 8 microseconds, So i choose UM4010.
The reason of switch speed < 2 microseconds is that transmitting
signal will reach receving antenna in 2 microseconds.
I agree with you , it is not easy to gain 80 dB isolation over a
decade of frequencies. That high isolation may improve the recept
signal to noise ratio ，avoid Saturation of recept preamplifer. I am
going to take CPW technology to improve isolation besides care of
designing bias circuits.
Yes , My switch is used as a key assembly of ionospheric sounding
system (HF band) .

PS：UM4010, Carrier lifetime,10 microseconds; Rs(IF=100 mA@100MHz),
0.5 ohms; Vr(breakdown voltage),1000 volts;
PD(dissipation power),20 watts.
http://www.microsemi.com/catalog/parmlist.asp?P0_CAT=RF&P1_TYPE=PIN&L...

So the receiving antenna and transmitting antenna are separate, and
about 2000 feet apart?? If that is the case, why do you need a TR
switch? I trust that the transmitter is not so high power that the
receiving antenna is trying to deliver 600 watts to the receiver...and
even if it were, you wouldn't need to reverse-bias the PIN by several
hundred volts. Maybe I'm reading too much into what you wrote.

In any event, it seems like it should be reasonably easy to switch
~700V in well under a microsecond. It's not so different from what
switching power supplies do using half-bridge configurations, and in
your case, you mainly need to supply the current to charge/discharge
capacitance, and the DC current to bias the PIN "on" is modest. For
example, see the data *** for the Fairchild FQH8N100C 1kV 8A power
mosfet; switching times listed (rise, fall, delays) are in the range
of a few tens of nanoseconds up to 250nsec max.
.

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