[time-nuts] fast edge, rise time.

David C. Partridge david.partridge at perdrix.co.uk
Thu Dec 26 17:26:21 UTC 2013


Look at the Jim Williams application note
<http://cds.linear.com/docs/en/application-note/an47fa.pdf>


Regards,
David Partridge 
-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of ct1dmk
Sent: 26 December 2013 16:08
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] fast edge, rise time.

Hello,

I'm willing to generate a pulse (of some few hundred volts) by discharging a
capacitor into a pulse transformer I'm solely interested is the active edge
(call it either rise or fall depending on the wiring of the output of the
transformer).

The target is 4ns, while ideas seemed to be clear at some point, now I'm
having doubts if better to use a MOSFET or a bipolar transistor as the
switch element. Experiments with MOSFETs presented me some difficulties
charging the gate capacitance having some trouble to achieve something in
the 4ns region. Well 4ns seems hard whatever device anyway.

I would be happy to receive some comments/ideas that may pop out of your
heads.
Thanks.

hope that my quest for fast rise "time" is not too off topic on this "time"
list...
but... there are so many experts on this list that I could not resist ;-)

Luis Cupido
ct1dmk.


p.s. ( I switch a capacitor to GND with a transistor (fet or bipolar). 
that capacitor has a charging resistor to 48V, transformer has a 9:1 voltage
ratio. Pulse average power is quite low a few watt only. At the primary side
some 20A of peak current for less than 100ns... and very low duty cycle. )
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