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. )
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 have seen recently two kinds of devices for similar task: MOSFETs and
avalanche breakdown transistors. Try the second ones, might be a good fit
if the pulsing is not very frequent (say, kHz range).
Regards,
Marek
On 12/26/13 8:07 AM, ct1dmk wrote:
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).
ns risetime pulses sounds like fairly straight forward radar stuff.
the inductance of the transformer is going to be your challenge,
depending on the energy level. What about a non-transformer
alternative? Can you just charge your cap up to the few hundred volts
and have a switch that can take the voltage?
How much energy do you need? You said a few hundred volts, but is that
microjoules, joules, or kilojoules?
A small triggered spark gap would be one way. There's also the ever
popular krytron, which has very good timing accuracy.
YOu might look for circuits used for exploding bridge wires (EBW)
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.
You want some sort of RF transistor here. What about one of the new
LDMOS FETs: some have fairly impressive voltage handling, and if they
work at 1 GHz for radar applications, they will work for you.
What about stacking a bunch of MMIC RF amplifiers (e.g. like the ERA or
GAL from minicircuits)
Other traditional approaches to fast pulse generation are avalanche
transistors.
There's also a variety of interesting pulse forming networks that can
generate fast rise time high voltage pulses. Blumlein arrangements are
one. Your 100ns pulse is fairly long for a transmission line scheme,
though (20-30 m of coax)
On Thu, 26 Dec 2013 16:07:49 +0000
ct1dmk ct1dmk@gmail.com wrote:
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.
First idea that comes to mind is using a bipolar transistor in avalanche
mode. There are specialized transistors for this, like the ZTX415[1,2], but
you can use 0-8-15 tranistors like a BC548 as well. If using a general
purpose transistor, then the avalanche voltage will vary quite a bit
from transistor to transistor. Easiest way to get around this is to use
a "small" resistor from base to emiter to drain any charge generated,
then insert a fast rising spike into the base. Using this, you can enter
the range of the avalanche voltage while surpressing the effect until
you want to trigger it. With this you should be able to get into the low ns
range, if not even below 1ns. The limiting factor is usually how fast the
base voltage can rise. The avalanche voltage for BC548 in my experiments
was in the vincinity of 200V.
I took the idea from [3], which contains a description of such a pulse
generator with a general purpose transistor on page 32. Almost the same
circuit can be found in [4].
Attila Kinali
[1] ZTX415 datasheet
http://www.diodes.com/datasheets/ZTX415.pdf
[2] ZTX415 avalanche mode transistore application note 8,
by Neil Chadderton, 1996
http://www.diodes.com/_files/products_appnote_pdfs/zetex/an8.pdf
[3] "A seven-nanosecond comparator for single supply operation",
by Jim Williams, 1998
http://cds.linear.com/docs/Application%20Note/an72f.pdf
[4] "Slew rate verification for wide band amiplifier",
by Jim Williams, 2003
http://cds.linear.com/docs/Application%20Note/an94f.pdf
--
1.) Write everything down.
2.) Reduce to the essential.
3.) Stop and question.
-- The Habits of Highly Boring People, Chris Sauve
Hi
If you go the Krytron route you probably will need some fairly fancy transformers as well….
Bob
On Dec 26, 2013, at 11:19 AM, Jim Lux jimlux@earthlink.net wrote:
On 12/26/13 8:07 AM, ct1dmk wrote:
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).
ns risetime pulses sounds like fairly straight forward radar stuff.
the inductance of the transformer is going to be your challenge, depending on the energy level. What about a non-transformer alternative? Can you just charge your cap up to the few hundred volts and have a switch that can take the voltage?
How much energy do you need? You said a few hundred volts, but is that microjoules, joules, or kilojoules?
A small triggered spark gap would be one way. There's also the ever popular krytron, which has very good timing accuracy.
YOu might look for circuits used for exploding bridge wires (EBW)
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.
You want some sort of RF transistor here. What about one of the new LDMOS FETs: some have fairly impressive voltage handling, and if they work at 1 GHz for radar applications, they will work for you.
What about stacking a bunch of MMIC RF amplifiers (e.g. like the ERA or GAL from minicircuits)
Other traditional approaches to fast pulse generation are avalanche transistors.
There's also a variety of interesting pulse forming networks that can generate fast rise time high voltage pulses. Blumlein arrangements are one. Your 100ns pulse is fairly long for a transmission line scheme, though (20-30 m of coax)
time-nuts mailing list -- time-nuts@febo.com
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and follow the instructions there.
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@febo.com [mailto:time-nuts-bounces@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. )
time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to
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and follow the instructions there.
On 26 December 2013 16:07, ct1dmk ct1dmk@gmail.com wrote:
Hello,
I'm willing to generate a pulse (of some few hundred volts)
by discharging a capacitor into a pulse transformer
There are probably more modern approaches, but a thryatron is one
possibility. Shame I put on in the dump a few months ago. Maybe though
they are more suitable for higher voltages.
Dave
Can you say more about your application? What does your load look like?
What pulse shape? There are well-known solutiuons for most problems.
As Jim said, a lot depends on the energy you need per pulse. What works
for a few mJ will not work for MJ
BTW, SCRs probably switch a lot faster than thyratrons. Years ago, I
cobbled up a high-current SCR pulser with a few thousand uF cap and stud
mounted SCR. It would drive enough current through a length of hook up
wire so that the wire would jump off the desk when pulsed.
-John
=================
On 26 December 2013 16:07, ct1dmk ct1dmk@gmail.com wrote:
Hello,
I'm willing to generate a pulse (of some few hundred volts)
by discharging a capacitor into a pulse transformer
There are probably more modern approaches, but a thryatron is one
possibility. Shame I put on in the dump a few months ago. Maybe though
they are more suitable for higher voltages.
Dave
time-nuts mailing list -- time-nuts@febo.com
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https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On Thu, 26 Dec 2013 16:07:49 +0000, ct1dmk wrote:
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.
Have a look here "Jim Williams" on eevblog
https://tinyurl.com/nhyvtc3
CFO
Am 26.12.2013 17:07, schrieb 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. )
We once built an ultrasonic pipeline pig with 1024 transmit/receive
channels,
so everything had to be quite compact. The transmitting parts of the
transducers
were hit with 350V pulses with a few ns risetime and 50 Ohm source impedance
and they rang on their favourite frequency. No transformer at all.
We used avalanche transistors to produce the pulses, a small smd bipolar
made by Zetex (afaik that's now bought up by Diodes, inc). Old 2N3904 are
said to avalanche also quite good.
The drawback is the repetition rate.
Doing it as a 'normal' amplifier w/o transformer will require a cascode
stage
but should work also.
But then I think you know that already since I've seen your presentation
of the TWT switcher PS on the EME meeting in Paris 15?? years ago. :-)
73, Gerhard
On Thu, 26 Dec 2013 19:38:08 +0000 (UTC)
cfo xnews3@luna.dyndns.dk wrote:
Have a look here "Jim Williams" on eevblog
https://tinyurl.com/nhyvtc3
I advice to be cautious with EEVblog. Dave Jones has a lot of half
knowledge and presents that like he knew exactly what he is talking
about. His videos usally contain a lot of errors. The videos are usally
good enough to get you started with something you dont know anything
about, but please double check every information you get from there.
Attila Kinali
--
1.) Write everything down.
2.) Reduce to the essential.
3.) Stop and question.
-- The Habits of Highly Boring People, Chris Sauve
Many thanks to all for the nice tips.
I may narrow down by saying a few more specs as suggested.
The pulse would see a somehow unknown load but for a start I
was suggested to have my source with 50ohm impedance so worst
case would be a short circuit and therefore the pulse would be a current
pulse
and would have some 10Amp. Pulse length about 100ns so only some 0.5mJ
energy that would die inside the pulse source( this would be the worst
case).
The 100us repetition rate make a a very small duty cycle of 1/1000 so
average power
maximum 5W.
Since the amplitude and timing parameters are to be controlled (pulse
timing come from an FPGA) I really need a solution using that trivial
switching element fet or bipolar (and can't really do a more exotic
scheme if I cant electronically control the parameters) also I must use
a transformer because these short pulse are to be superimposed to
another voltage and a transformer becomes very handy to do that. I
interrupt the wire and insert the secondary there to add the pulses.
The challenge I'm facing is on the device either RF FET or Biplolar tr
etc. and
surrounding circuits, transformer, etc. this to achieve the 4ns (or 5ns).
(the transformer I have in mind is something very similar to those
transformers
on the final stages of HF/VHF ham radio amps, coax cables and ferrite cores)
any suggestion regarding devices etc ?...
Thanks for all comments.
Luis Cupido.
Are only the amplitude and rep rate variable, or do you vary the width too?
-John
=============
Many thanks to all for the nice tips.
I may narrow down by saying a few more specs as suggested.
The pulse would see a somehow unknown load but for a start I
was suggested to have my source with 50ohm impedance so worst
case would be a short circuit and therefore the pulse would be a current
pulse
and would have some 10Amp. Pulse length about 100ns so only some 0.5mJ
energy that would die inside the pulse source( this would be the worst
case).
The 100us repetition rate make a a very small duty cycle of 1/1000 so
average power
maximum 5W.
Since the amplitude and timing parameters are to be controlled (pulse
timing come from an FPGA) I really need a solution using that trivial
switching element fet or bipolar (and can't really do a more exotic
scheme if I cant electronically control the parameters) also I must use
a transformer because these short pulse are to be superimposed to
another voltage and a transformer becomes very handy to do that. I
interrupt the wire and insert the secondary there to add the pulses.
The challenge I'm facing is on the device either RF FET or Biplolar tr
etc. and
surrounding circuits, transformer, etc. this to achieve the 4ns (or 5ns).
(the transformer I have in mind is something very similar to those
transformers
on the final stages of HF/VHF ham radio amps, coax cables and ferrite
cores)
any suggestion regarding devices etc ?...
Thanks for all comments.
Luis Cupido.
time-nuts mailing list -- time-nuts@febo.com
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https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hi
Unless you want run for < 1 second, that rules out a Krytron.
Length of operation also impacts some of the other implementations.
Bob
On Dec 26, 2013, at 9:16 PM, ct1dmk ct1dmk@gmail.com wrote:
Many thanks to all for the nice tips.
I may narrow down by saying a few more specs as suggested.
The pulse would see a somehow unknown load but for a start I
was suggested to have my source with 50ohm impedance so worst
case would be a short circuit and therefore the pulse would be a current pulse
and would have some 10Amp. Pulse length about 100ns so only some 0.5mJ energy that would die inside the pulse source( this would be the worst case).
The 100us repetition rate make a a very small duty cycle of 1/1000 so average power
maximum 5W.
Since the amplitude and timing parameters are to be controlled (pulse timing come from an FPGA) I really need a solution using that trivial switching element fet or bipolar (and can't really do a more exotic scheme if I cant electronically control the parameters) also I must use a transformer because these short pulse are to be superimposed to another voltage and a transformer becomes very handy to do that. I interrupt the wire and insert the secondary there to add the pulses.
The challenge I'm facing is on the device either RF FET or Biplolar tr etc. and
surrounding circuits, transformer, etc. this to achieve the 4ns (or 5ns).
(the transformer I have in mind is something very similar to those transformers
on the final stages of HF/VHF ham radio amps, coax cables and ferrite cores)
any suggestion regarding devices etc ?...
Thanks for all comments.
Luis Cupido.
time-nuts mailing list -- time-nuts@febo.com
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and follow the instructions there.
There are some good alternatives to krytrons. Just don't expect to be able to afford or export them. ;)
On Dec 26, 2013, at 21:26, Bob Camp lists@rtty.us wrote:
Hi
Unless you want run for < 1 second, that rules out a Krytron.
Length of operation also impacts some of the other implementations.
Bob
On Dec 26, 2013, at 9:16 PM, ct1dmk ct1dmk@gmail.com wrote:
Many thanks to all for the nice tips.
I may narrow down by saying a few more specs as suggested.
The pulse would see a somehow unknown load but for a start I
was suggested to have my source with 50ohm impedance so worst
case would be a short circuit and therefore the pulse would be a current pulse
and would have some 10Amp. Pulse length about 100ns so only some 0.5mJ energy that would die inside the pulse source( this would be the worst case).
The 100us repetition rate make a a very small duty cycle of 1/1000 so average power
maximum 5W.
Since the amplitude and timing parameters are to be controlled (pulse timing come from an FPGA) I really need a solution using that trivial switching element fet or bipolar (and can't really do a more exotic scheme if I cant electronically control the parameters) also I must use a transformer because these short pulse are to be superimposed to another voltage and a transformer becomes very handy to do that. I interrupt the wire and insert the secondary there to add the pulses.
The challenge I'm facing is on the device either RF FET or Biplolar tr etc. and
surrounding circuits, transformer, etc. this to achieve the 4ns (or 5ns).
(the transformer I have in mind is something very similar to those transformers
on the final stages of HF/VHF ham radio amps, coax cables and ferrite cores)
any suggestion regarding devices etc ?...
Thanks for all comments.
Luis Cupido.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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and follow the instructions there.
On Fri, 27 Dec 2013 02:16:26 +0000
ct1dmk ct1dmk@gmail.com wrote:
Since the amplitude and timing parameters are to be controlled (pulse
timing come from an FPGA) I really need a solution using that trivial
switching element fet or bipolar (and can't really do a more exotic
scheme if I cant electronically control the parameters) also I must use
a transformer because these short pulse are to be superimposed to
another voltage and a transformer becomes very handy to do that. I
interrupt the wire and insert the secondary there to add the pulses.
If you are already using an FPGA, you can use it for pulse forming.
Just use some delay line (or two) and an AND "gate". This should give
you an easily changable pulse from sub-1ns to an aribtrary long
pulse. The problem here is that your delay line will not have the
same step sizes for each step of the delay line (varies from 10ps
to ~100ps on a Virtex-4). [1] gives a small overview of the problem
and where it comes from. There are other papers on TDCs that deal
with this and might give a solution how to linearize it. Googling
for "vernier delay line linearization" sould give you some results.
As output from the FPGA you probably want to use some differntial
format, to increase the "steepness" of the rising/falling edge.
When you have the pulse you can use some standard RF amplifier circuit
that drivers your transformer. Setting the amplitude should be easy too.
Attila Kinali
[1] "A High Resolution (<10 ps RMS) 48-Channel Time-to-Digital Converter
(TDC) Implemented in a Field Programmable Gate Array(FPGA)",
by Bayer and Traxler, 2011
--
1.) Write everything down.
2.) Reduce to the essential.
3.) Stop and question.
-- The Habits of Highly Boring People, Chris Sauve
On Fri, 27 Dec 2013 11:30:00 +0100
Attila Kinali attila@kinali.ch wrote:
When you have the pulse you can use some standard RF amplifier circuit
that drivers your transformer. Setting the amplitude should be easy too.
I just reread your first mail and realized that this amplifier might
be your problem. If you use a differntial, current-coupled structure
(similar to current mode logic) with GHz RF bipolar transistors, you
should be able to get your pulse with good shape into the transformer.
Attila Kinali
--
1.) Write everything down.
2.) Reduce to the essential.
3.) Stop and question.
-- The Habits of Highly Boring People, Chris Sauve
Thank you all for your comments on this subject.
Happy new year.
Luis Cupido.
ct1dmk.
Hi,
Since you guys are interested in fast pule generators, I have one you may be
interested in.
I got it in govt. auction about 25 years ago for ~ $ 50.00. I will sell it
to anyone for $ 50.00 plus shipping.
I prefer to sell to someone who will restore and use it rather than parting
it. It has more than $ 50.00 parts in it.
There are a 30 turn 6.5 inch diameter hard line, wide band hybrid coupler,
diode assembly and several adapters and attenuators.
I believe the hard line discharges into a step diode. The power supply
includes 200 V plus other voltages.
If I remember correctly ( I have no high speed scope now ) the pulse is 2
nanoseconds wide with a 280 picosecond rise time and and 2.5 Vpp.
I checked with a 200 MHz digital scope and can see a pulse that verifies my
scopes bandwidth. The rate generator works but has problems.
See facebook (reedbn@otelco.net) for pictures under Impulse.
Bill Reed 256 586-3446
-----Original Message-----
From: ct1dmk
Sent: Sunday, December 29, 2013 7:36 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] fast edge, rise time.
Thank you all for your comments on this subject.
Happy new year.
Luis Cupido.
ct1dmk.
time-nuts mailing list -- time-nuts@febo.com
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https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hi,
Since there is no interest in my pulse generator maybe one of you knows
someone at NBS who can provide a schematic of the generator.
It has " NBS Impulse Generator SN 3-75-2 " engraved on the front panel and
is ~ 10 x 16 x 17.
Thanks,
Bill Reed
-----Original Message-----
From: Bill Reed
Sent: Tuesday, January 07, 2014 7:53 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] fast edge, rise time.
Hi,
Since you guys are interested in fast pule generators, I have one you may be
interested in.
I got it in govt. auction about 25 years ago for ~ $ 50.00. I will sell it
to anyone for $ 50.00 plus shipping.
I prefer to sell to someone who will restore and use it rather than parting
it. It has more than $ 50.00 parts in it.
There are a 30 turn 6.5 inch diameter hard line, wide band hybrid coupler,
diode assembly and several adapters and attenuators.
I believe the hard line discharges into a step diode. The power supply
includes 200 V plus other voltages.
If I remember correctly ( I have no high speed scope now ) the pulse is 2
nanoseconds wide with a 280 picosecond rise time and and 2.5 Vpp.
I checked with a 200 MHz digital scope and can see a pulse that verifies my
scopes bandwidth. The rate generator works but has problems.
See facebook (reedbn@otelco.net) for pictures under Impulse.
Bill Reed 256 586-3446
-----Original Message-----
From: ct1dmk
Sent: Sunday, December 29, 2013 7:36 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] fast edge, rise time.
Thank you all for your comments on this subject.
Happy new year.
Luis Cupido.
ct1dmk.
time-nuts mailing list -- time-nuts@febo.com
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