Super fast sample & hold under $10?

[Joerg]

John Larkin wrote:

On Fri, 07 Feb 2014 07:53:59 -0800, Joerg <invalid@invalid.invalid> wrote:

John Larkin wrote:
On Fri, 07 Feb 2014 18:02:08 +1100, Chris Jones <lugnut808@spam.yahoo.com
wrote:

On 07/02/2014 15:32, John Larkin wrote:
On Thu, 06 Feb 2014 10:32:17 -0800, Joerg <invalid@invalid.invalid> wrote:

John Larkin wrote:
On Thu, 06 Feb 2014 07:55:31 -0800, Joerg <invalid@invalid.invalid> wrote:

John Larkin wrote:
On Thu, 6 Feb 2014 01:08:51 -0500, "Tom Miller" <tmiller11147@verizon.net
wrote:

"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news:h496f9lnspapejoj41btps9ebihu2qnk52@4ax.com...
On Wed, 05 Feb 2014 13:01:54 -0800, Joerg <invalid@invalid.invalid> wrote:

Folks,

Need to sample stuff again. Essentially an equivalent time deal like on
older generation digital scopes where you have a 20MHz or so ADC and
GHZ-bandwidth on the scope. Can take as long as it has to but ... the
sampling must be accurate and the sample gate should ideally close and
open in a few hundred picosends, 1nsec at the most. So far I've always
done this stuff in discretes, diode quads, brute-force driver, the
usual. But this gets old and now I need something small and cheap.

Aren't there any ICs in that domain or am I the only one with such
desires?

Also looking for a timer chip to run this but that's easier.
Some ADCs have screaming fast multi-GHz front-end s/h speeds, intended for
sub-Nyquist sampling of RF stuff. 1 ns isn't especially fast in that
world.


--

John Larkin Highland Technology Inc
For $10 ? Put me down for one.

Tom
AD9204-20 has 700 MHz s/h bw, maybe 500 ps, $5.

But when looking at the fine print in here ...

http://www.analog.com/static/imported-files/data_sheets/AD9204.pdf

... it says quote "The user can sample any fs/2 frequency segment from
dc to 200 MHz". Something doesn't seem to compute with the data on page
7 where the fastest version (AD9204-80) still requires 6.25nsec high
phase for the clock. The -20 is 25nsec. How can they do 625MHz with that?
The data sheet is a tad ambiguous about what that 700 MHz thing means.

The min clock pulse width kind of gives it away. I don't think the
sampler could possible be fast enough with that. It'll integrate over
many nsec and that totally spoils the soup here.

I'll put you down for two.

Do you know any cheap one that's faster? I sure wish that instead of all
the no-connect pins they'd pipe out the analog output of the S&H so
people could use it sans the ADC section.
The s/h may not actually exist as such inside.

That could be a problem unless there is a true flash ADC inside.

Do you need a s/h alone, or could you use an adc with a fast s/h inside? There
are probably more ads with fast front ends... I just nabbed that one as an
example.

I don't quite understand the application.

This one I really can't talk about but essentially I need to be able to
digitize a very high frequency event in an equivalent time fashion, like
on old DSOs. Or very fast new ones. A very fast ADC is far from ideal
here but could work if nothing else is there. And it seems there ain't.


Could you use a diode mixer and a narrow pulse generator? That could be cheap.

Yes, but diodes still have almost a pF when operated as quads, even the
fancy Skyworks ones. Too much leakage when off. The only way to make
that work would be a slew of T-configuration sections. Gets big and
expensive. In an IC that would be easy to do but there seems to be not
enough market. There are some boutique chips but those cost hundreds of
Dollars.
There is the 1-bit sampler thing, namely using a d-flop as an equivalent-time
sampler, sort of a tracking ADC. It takes a lot of samples to build the
waveform, but it's potentially cheap. A differential-input D flop, like an
EL/EP52, can do that.


Yes, well I had always thought of doing it with a clocked comparator
like the ADCMP572 etc., and the other input connected to a slow DAC. The
tricky part is generating the clock pulse to the comparator, with
accurately variable timing relative to the trigger input, but this might
be easy if you control the stimulus to the circuit.

Another guy seems to have also thought of it:
https://www.kickstarter.com/projects/1855991221/10-ghz-usb-oscilloscope
though he says the Hittite comparators are faster than the ADI ones.

Chris
I did it with tunnel diodes in 1969, inspired by a circuit in the GE Transistor
Manual.

The advantage of the EL flop is that it's within Joerg's budget. ...

It could do it but it would be a potentially long iterative process per
sample time slot. An option may be to use some clever seek method
instead of a stair-step ramp. Go to full, if not there go to half. If
there go to 3/4, if not there go to 1/4, and so on. In my case the
computational overhead would jinx it though.


You can do a feedback loop on the go/nogo decisions of the comparator/flipflop,
so the thing becomes a tracking ADC of sorts. That's not too awful if the
equivalent-time sweep is fairly slow.

If the clock rate is constant, the feedback loop could be just an RC or RLC from
Q to \D, something like that.

Might be an option, I'll have to think that through. The sweep time is
several hundred times the sampling window and can be made constant.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

John Larkin wrote:

On Wed, 05 Feb 2014 13:01:54 -0800, Joerg <invalid@invalid.invalid> wrote:

Folks,

Need to sample stuff again. Essentially an equivalent time deal like on
older generation digital scopes where you have a 20MHz or so ADC and
GHZ-bandwidth on the scope. Can take as long as it has to but ... the
sampling must be accurate and the sample gate should ideally close and
open in a few hundred picosends, 1nsec at the most. So far I've always
done this stuff in discretes, diode quads, brute-force driver, the
usual. But this gets old and now I need something small and cheap.

Aren't there any ICs in that domain or am I the only one with such desires?

Also looking for a timer chip to run this but that's easier.

The classic sampling-scope circuit can be built cheap. SRD, clip lines, 2-diode
sampler, charge amp.

This got about 5 GHz bandwidth:

https://dl.dropboxusercontent.com/u/53724080/Protos/Sampler1.JPG

I was mulling a 2-diode sampler because then you don't get that 100%
sampling pulse feed-through that you have with single-diode sampling.
But it doubles the capacitance. Doesn't it leak too much?

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

Robert Lacoste wrote:

"Joerg" wrote in message news:blfn65F5qnhU1@mid.individual.net...
the sampling must be accurate and the sample gate should ideally close
and
open in a few hundred picosends, 1nsec at the most. So far I've always
done this stuff in discretes, diode quads, brute-force driver, the
usual. But this gets old and now I need something small and cheap.
Aren't there any ICs in that domain or am I the only one with such
desires?

Came also per PM

Hello Joerg,
If you are ready to accept, well, a significant waiver on the chip cost
target, look at Hittite. A chip like the HMC760LC4B would probably
nicely fit the technical specs (trak&hold with a 5GHz bandwidth, clock
up to 4Gsps, 66dB SFDR, etc) but would cost 30 times more than planned...
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

That was the reason I didn't consider it. If I had to build something
like the Bay Bridge a 6x cost overrun would not be a problem, but here
it would be.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[John Larkin]

On Fri, 07 Feb 2014 10:04:23 -0800, Joerg <invalid@invalid.invalid>
wrote:

John Larkin wrote:
On Wed, 05 Feb 2014 13:01:54 -0800, Joerg <invalid@invalid.invalid> wrote:

Folks,

Need to sample stuff again. Essentially an equivalent time deal like on
older generation digital scopes where you have a 20MHz or so ADC and
GHZ-bandwidth on the scope. Can take as long as it has to but ... the
sampling must be accurate and the sample gate should ideally close and
open in a few hundred picosends, 1nsec at the most. So far I've always
done this stuff in discretes, diode quads, brute-force driver, the
usual. But this gets old and now I need something small and cheap.

Aren't there any ICs in that domain or am I the only one with such desires?

Also looking for a timer chip to run this but that's easier.

The classic sampling-scope circuit can be built cheap. SRD, clip lines, 2-diode
sampler, charge amp.

This got about 5 GHz bandwidth:

https://dl.dropboxusercontent.com/u/53724080/Protos/Sampler1.JPG


I was mulling a 2-diode sampler because then you don't get that 100%
sampling pulse feed-through that you have with single-diode sampling.
But it doubles the capacitance. Doesn't it leak too much?

Schottky diodes don't leak badly. You have to read it out in a few us
after the sample.

There is also "blow-by", which is capacitive feedthrough of the
diodes. That is easily compensated with an opamp.

Sampling efficiency of a fast sampler (the output voltage over the
input voltage) is low, a few per cent maybe, but gain is cheap.

The classic HP 2-diode feedback sampler is well documented.

4-diode samplers are slower, and don't need blowby compensation and
can be very simple. These are generally in the 1 or maybe 2 GHz range.


--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Joerg]

John Larkin wrote:

On Fri, 07 Feb 2014 10:04:23 -0800, Joerg <invalid@invalid.invalid
wrote:

John Larkin wrote:
On Wed, 05 Feb 2014 13:01:54 -0800, Joerg <invalid@invalid.invalid> wrote:

Folks,

Need to sample stuff again. Essentially an equivalent time deal like on
older generation digital scopes where you have a 20MHz or so ADC and
GHZ-bandwidth on the scope. Can take as long as it has to but ... the
sampling must be accurate and the sample gate should ideally close and
open in a few hundred picosends, 1nsec at the most. So far I've always
done this stuff in discretes, diode quads, brute-force driver, the
usual. But this gets old and now I need something small and cheap.

Aren't there any ICs in that domain or am I the only one with such desires?

Also looking for a timer chip to run this but that's easier.
The classic sampling-scope circuit can be built cheap. SRD, clip lines, 2-diode
sampler, charge amp.

This got about 5 GHz bandwidth:

https://dl.dropboxusercontent.com/u/53724080/Protos/Sampler1.JPG

I was mulling a 2-diode sampler because then you don't get that 100%
sampling pulse feed-through that you have with single-diode sampling.
But it doubles the capacitance. Doesn't it leak too much?

Schottky diodes don't leak badly. You have to read it out in a few us
after the sample.

There is also "blow-by", which is capacitive feedthrough of the
diodes. That is easily compensated with an opamp.

That's what I meant, the capacitance. Even at 0.3pF or so that doubles
to 0.6pF for a 2-diode sampler. If you have a lot of clanging or a major
step going on in the source after the sampling that feeds through and
can mess up the reading.

Sampling efficiency of a fast sampler (the output voltage over the
input voltage) is low, a few per cent maybe, but gain is cheap.

That's not a problem as long as one doesn't use this as a sensitive
receiver.

The classic HP 2-diode feedback sampler is well documented.

I've got some papers about it that were hand-typed. From the days when
HP was really HP, the founders were still alive and the Beatles played
on the radio.

4-diode samplers are slower, and don't need blowby compensation and
can be very simple. These are generally in the 1 or maybe 2 GHz range.

That's how I have done it until now, mostly. But yeah, above a GHz it
becomes tough.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Fred Abse]

On Fri, 07 Feb 2014 08:37:37 -0800, John Larkin wrote:

The classic sampling-scope circuit can be built cheap. SRD, clip lines,
2-diode sampler, charge amp.

This got about 5 GHz bandwidth:

https://dl.dropboxusercontent.com/u/53724080/Protos/Sampler1.JPG

I like that...

--
"Design is the reverse of analysis"
(R.D. Middlebrook)

 

[John Larkin]

On Fri, 07 Feb 2014 10:55:46 -0800, Joerg <invalid@invalid.invalid>
wrote:

John Larkin wrote:
On Fri, 07 Feb 2014 10:04:23 -0800, Joerg <invalid@invalid.invalid
wrote:

John Larkin wrote:
On Wed, 05 Feb 2014 13:01:54 -0800, Joerg <invalid@invalid.invalid> wrote:

Folks,

Need to sample stuff again. Essentially an equivalent time deal like on
older generation digital scopes where you have a 20MHz or so ADC and
GHZ-bandwidth on the scope. Can take as long as it has to but ... the
sampling must be accurate and the sample gate should ideally close and
open in a few hundred picosends, 1nsec at the most. So far I've always
done this stuff in discretes, diode quads, brute-force driver, the
usual. But this gets old and now I need something small and cheap.

Aren't there any ICs in that domain or am I the only one with such desires?

Also looking for a timer chip to run this but that's easier.
The classic sampling-scope circuit can be built cheap. SRD, clip lines, 2-diode
sampler, charge amp.

This got about 5 GHz bandwidth:

https://dl.dropboxusercontent.com/u/53724080/Protos/Sampler1.JPG

I was mulling a 2-diode sampler because then you don't get that 100%
sampling pulse feed-through that you have with single-diode sampling.
But it doubles the capacitance. Doesn't it leak too much?

Schottky diodes don't leak badly. You have to read it out in a few us
after the sample.

There is also "blow-by", which is capacitive feedthrough of the
diodes. That is easily compensated with an opamp.


That's what I meant, the capacitance. Even at 0.3pF or so that doubles
to 0.6pF for a 2-diode sampler. If you have a lot of clanging or a major
step going on in the source after the sampling that feeds through and
can mess up the reading.


Sampling efficiency of a fast sampler (the output voltage over the
input voltage) is low, a few per cent maybe, but gain is cheap.


That's not a problem as long as one doesn't use this as a sensitive
receiver.


The classic HP 2-diode feedback sampler is well documented.


I've got some papers about it that were hand-typed. From the days when
HP was really HP, the founders were still alive and the Beatles played
on the radio.


4-diode samplers are slower, and don't need blowby compensation and
can be very simple. These are generally in the 1 or maybe 2 GHz range.


That's how I have done it until now, mostly. But yeah, above a GHz it
becomes tough.

The 7S14 got 2 GHz typical bandwidth from a 4-diode sampler driven by
an avalanche transistor! Most of the HP and Tek 4-diode samplers were
spec'd at 1 GHz.

Tek published "Sampling Oscilloscope Circuits", part of their Tek
Concept series of white paperbacks. It's probably online somewhere, or
I could loan you mine with a suitably huge security deposit.

I actually own an HP185 sampling scope, mostly tubes, early 60's
monster. It was the first modern 2-diode feedback sampler gadget.

It would take a little fiddling, but a 2-GHz sampler could be done for
$10, maybe for $5. I don't know anything about your specific
application, but if you email me privately I could deliver any number
of wild opinions.




--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Phil Hobbs]

On 02/06/2014 01:39 PM, Joerg wrote:

John Larkin wrote:
On Thu, 06 Feb 2014 08:01:30 -0800, Joerg <invalid@invalid.invalid> wrote:

Klaus Kragelund wrote:
On Thursday, February 6, 2014 12:00:06 PM UTC+1, Klaus Kragelund
wrote:
On Wednesday, February 5, 2014 10:01:54 PM UTC+1, Joerg wrote:

Folks, Need to sample stuff again. Essentially an equivalent time
deal like on older generation digital scopes where you have a
20MHz or so ADC and GHZ-bandwidth on the scope. Can take as long
as it has to but ... the sampling must be accurate and the sample
gate should ideally close and open in a few hundred picosends,
1nsec at the most. So far I've always done this stuff in
discretes, diode quads, brute-force driver, the usual. But this
gets old and now I need something small and cheap. Aren't there
any ICs in that domain or am I the only one with such desires?
Also looking for a timer chip to run this but that's easier.
I have never done fast S/H, so I'll excuse my suggestion forehand:



Wrap the sample and hold around a very fast comparator, like the:



http://www.analog.com/static/imported-files/data_sheets/ADCMP572_573.pdf




You probably need an open drain output type, let a cap ride on the
output. Charge the cap, Then enable the comparator which in turn
via a resistor discharges the cap and the comparator shuts of its
own discharge. Start AD conversion.....

The problem is the switch, making the pulse is not a problem. The
comparator doesn't have any switch but you must disconnect the cap from
the signal source. Even Skyworks diodes are still 0.5pF (and unobtanium
...) which presents a ton of leakage at a GHz. Making a T or double-T
switch out of something like that gets really big and unwieldy.

We use SMS7621 diodes, around 0.25 pF. I can send you some.


That's better than 0.5pF. I might take you up on that if I can't find a
better solution. And they have SPICE parameters published which is
really nice.


Of course, the precision is perhaps not up to your requirements,
since it has 150ps prop delay...

What is the requirement for accuracy?

The prop delay does not matter. I need 100psec or so accuracy in pulse
position but the delay is not a concern.

A PHEMT might make an interesting series switch. They behave like jfets on
steroids. An NE8509 has about 0.35 pF drain capacitance and is about 6 ohms Rds
at zero gate bias. The capacitance could be "neutralized" with a balun
transformer inverter and another cap, or some dual-phemt balanced thingie.


Some sort of gated active stage would work, maybe. Because reading the
S&H cap may take some time.

If you use the pHEMTs in cascode, you can get the effective C_dg way down.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Joerg]

John Larkin wrote:

On Fri, 07 Feb 2014 10:55:46 -0800, Joerg <invalid@invalid.invalid
wrote:

John Larkin wrote:
On Fri, 07 Feb 2014 10:04:23 -0800, Joerg <invalid@invalid.invalid
wrote:

John Larkin wrote:
On Wed, 05 Feb 2014 13:01:54 -0800, Joerg <invalid@invalid.invalid> wrote:

Folks,

Need to sample stuff again. Essentially an equivalent time deal like on
older generation digital scopes where you have a 20MHz or so ADC and
GHZ-bandwidth on the scope. Can take as long as it has to but ... the
sampling must be accurate and the sample gate should ideally close and
open in a few hundred picosends, 1nsec at the most. So far I've always
done this stuff in discretes, diode quads, brute-force driver, the
usual. But this gets old and now I need something small and cheap.

Aren't there any ICs in that domain or am I the only one with such desires?

Also looking for a timer chip to run this but that's easier.
The classic sampling-scope circuit can be built cheap. SRD, clip lines, 2-diode
sampler, charge amp.

This got about 5 GHz bandwidth:

https://dl.dropboxusercontent.com/u/53724080/Protos/Sampler1.JPG

I was mulling a 2-diode sampler because then you don't get that 100%
sampling pulse feed-through that you have with single-diode sampling.
But it doubles the capacitance. Doesn't it leak too much?
Schottky diodes don't leak badly. You have to read it out in a few us
after the sample.

There is also "blow-by", which is capacitive feedthrough of the
diodes. That is easily compensated with an opamp.

That's what I meant, the capacitance. Even at 0.3pF or so that doubles
to 0.6pF for a 2-diode sampler. If you have a lot of clanging or a major
step going on in the source after the sampling that feeds through and
can mess up the reading.


Sampling efficiency of a fast sampler (the output voltage over the
input voltage) is low, a few per cent maybe, but gain is cheap.

That's not a problem as long as one doesn't use this as a sensitive
receiver.


The classic HP 2-diode feedback sampler is well documented.

I've got some papers about it that were hand-typed. From the days when
HP was really HP, the founders were still alive and the Beatles played
on the radio.


4-diode samplers are slower, and don't need blowby compensation and
can be very simple. These are generally in the 1 or maybe 2 GHz range.

That's how I have done it until now, mostly. But yeah, above a GHz it
becomes tough.

The 7S14 got 2 GHz typical bandwidth from a 4-diode sampler driven by
an avalanche transistor! Most of the HP and Tek 4-diode samplers were
spec'd at 1 GHz.

But their budget was "the sky is the limit", probably all gold-plated on
alumina and hand-signed by Agoston Agoston.

Tek published "Sampling Oscilloscope Circuits", part of their Tek
Concept series of white paperbacks. It's probably online somewhere, or
I could loan you mine with a suitably huge security deposit.

I guess my wooden beer Dollar won't count as collateral. Plus you gave
that to me.

Seems this Concept Series never made it onto the web. I do have tons
from HP though so I am pretty well covered for samplers. Over the years
I've built/designed several so I am fairly aware of the trade-offs. That
is one area where there seriously are no free lunches.

I actually own an HP185 sampling scope, mostly tubes, early 60's
monster. It was the first modern 2-diode feedback sampler gadget.

That sure is a piece of history. My GHz workhorse here is a HP-54110D.
Not comparable to very fast sampling scopes but has four HP-samplers in
there. It is remarkable how easy such vintage HP equipment can be
operated. I haven't ever pulled out the manual, not once. Looks like new.

It would take a little fiddling, but a 2-GHz sampler could be done for
$10, maybe for $5. I don't know anything about your specific
application, but if you email me privately I could deliver any number
of wild opinions.

Thanks. Can't reveal all that much at this point though.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Spehro Pefhany]

On Fri, 07 Feb 2014 11:30:16 -0800, John Larkin
<jlarkin@highlandtechnology.com> wrote:

Tek published "Sampling Oscilloscope Circuits", part of their Tek
Concept series of white paperbacks. It's probably online somewhere, or
I could loan you mine with a suitably huge security deposit.

Looks like a good copy here:

http://www.davmar.org/TE/TekConcepts/TekSamplingCircuits.pdf

254 pages!

--sp

 

[Joerg]

Phil Hobbs wrote:

On 02/06/2014 01:39 PM, Joerg wrote:
John Larkin wrote:
On Thu, 06 Feb 2014 08:01:30 -0800, Joerg <invalid@invalid.invalid
wrote:

Klaus Kragelund wrote:

[...]

Of course, the precision is perhaps not up to your requirements,
since it has 150ps prop delay...

What is the requirement for accuracy?

The prop delay does not matter. I need 100psec or so accuracy in pulse
position but the delay is not a concern.

A PHEMT might make an interesting series switch. They behave like
jfets on
steroids. An NE8509 has about 0.35 pF drain capacitance and is about
6 ohms Rds
at zero gate bias. The capacitance could be "neutralized" with a balun
transformer inverter and another cap, or some dual-phemt balanced
thingie.


Some sort of gated active stage would work, maybe. Because reading the
S&H cap may take some time.


If you use the pHEMTs in cascode, you can get the effective C_dg way down.

Yes, the "Miller" effect goes way down to the point where it's hardly
existing anymore. But in a sampler one has to connect and disconnect
from the sampling capacitor somehow. That's where even very few tenths
of pF begin to hurt.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

Spehro Pefhany wrote:

On Fri, 07 Feb 2014 11:30:16 -0800, John Larkin
jlarkin@highlandtechnology.com> wrote:

Tek published "Sampling Oscilloscope Circuits", part of their Tek
Concept series of white paperbacks. It's probably online somewhere, or
I could loan you mine with a suitably huge security deposit.

Looks like a good copy here:

http://www.davmar.org/TE/TekConcepts/TekSamplingCircuits.pdf

254 pages!

Thanks! That is a reallynice blast from the past. Haven't heard the word
snap-off diode in a long time.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Phil Hobbs]

On 02/07/2014 03:45 PM, Joerg wrote:

Phil Hobbs wrote:
On 02/06/2014 01:39 PM, Joerg wrote:
John Larkin wrote:
On Thu, 06 Feb 2014 08:01:30 -0800, Joerg <invalid@invalid.invalid
wrote:

Klaus Kragelund wrote:

[...]


Of course, the precision is perhaps not up to your requirements,
since it has 150ps prop delay...

What is the requirement for accuracy?

The prop delay does not matter. I need 100psec or so accuracy in pulse
position but the delay is not a concern.

A PHEMT might make an interesting series switch. They behave like
jfets on
steroids. An NE8509 has about 0.35 pF drain capacitance and is about
6 ohms Rds
at zero gate bias. The capacitance could be "neutralized" with a balun
transformer inverter and another cap, or some dual-phemt balanced
thingie.


Some sort of gated active stage would work, maybe. Because reading the
S&H cap may take some time.


If you use the pHEMTs in cascode, you can get the effective C_dg way down.


Yes, the "Miller" effect goes way down to the point where it's hardly
existing anymore. But in a sampler one has to connect and disconnect
from the sampling capacitor somehow. That's where even very few tenths
of pF begin to hurt.

Sure, but if it's independent of the input, you can fix it afterwards,
as with blow-by in a diode sampler.

An ordinary dual gate Si MOSFET, circa 1975, has a typical C_dg1 of
something like 0.02 pF. I used to use 3N201s for samplers back in the
day. They worked great.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[John Larkin]

On Fri, 07 Feb 2014 12:43:10 -0800, Joerg <invalid@invalid.invalid>
wrote:

John Larkin wrote:
On Fri, 07 Feb 2014 10:55:46 -0800, Joerg <invalid@invalid.invalid
wrote:

John Larkin wrote:
On Fri, 07 Feb 2014 10:04:23 -0800, Joerg <invalid@invalid.invalid
wrote:

John Larkin wrote:
On Wed, 05 Feb 2014 13:01:54 -0800, Joerg <invalid@invalid.invalid> wrote:

Folks,

Need to sample stuff again. Essentially an equivalent time deal like on
older generation digital scopes where you have a 20MHz or so ADC and
GHZ-bandwidth on the scope. Can take as long as it has to but ... the
sampling must be accurate and the sample gate should ideally close and
open in a few hundred picosends, 1nsec at the most. So far I've always
done this stuff in discretes, diode quads, brute-force driver, the
usual. But this gets old and now I need something small and cheap.

Aren't there any ICs in that domain or am I the only one with such desires?

Also looking for a timer chip to run this but that's easier.
The classic sampling-scope circuit can be built cheap. SRD, clip lines, 2-diode
sampler, charge amp.

This got about 5 GHz bandwidth:

https://dl.dropboxusercontent.com/u/53724080/Protos/Sampler1.JPG

I was mulling a 2-diode sampler because then you don't get that 100%
sampling pulse feed-through that you have with single-diode sampling.
But it doubles the capacitance. Doesn't it leak too much?
Schottky diodes don't leak badly. You have to read it out in a few us
after the sample.

There is also "blow-by", which is capacitive feedthrough of the
diodes. That is easily compensated with an opamp.

That's what I meant, the capacitance. Even at 0.3pF or so that doubles
to 0.6pF for a 2-diode sampler. If you have a lot of clanging or a major
step going on in the source after the sampling that feeds through and
can mess up the reading.


Sampling efficiency of a fast sampler (the output voltage over the
input voltage) is low, a few per cent maybe, but gain is cheap.

That's not a problem as long as one doesn't use this as a sensitive
receiver.


The classic HP 2-diode feedback sampler is well documented.

I've got some papers about it that were hand-typed. From the days when
HP was really HP, the founders were still alive and the Beatles played
on the radio.


4-diode samplers are slower, and don't need blowby compensation and
can be very simple. These are generally in the 1 or maybe 2 GHz range.

That's how I have done it until now, mostly. But yeah, above a GHz it
becomes tough.

The 7S14 got 2 GHz typical bandwidth from a 4-diode sampler driven by
an avalanche transistor! Most of the HP and Tek 4-diode samplers were
spec'd at 1 GHz.


But their budget was "the sky is the limit", probably all gold-plated on
alumina and hand-signed by Agoston Agoston.

Like this:

https://dl.dropboxusercontent.com/u/53724080/SD-24/SD-24.zip

Tek published "Sampling Oscilloscope Circuits", part of their Tek
Concept series of white paperbacks. It's probably online somewhere, or
I could loan you mine with a suitably huge security deposit.


I guess my wooden beer Dollar won't count as collateral. Plus you gave
that to me.

Seems this Concept Series never made it onto the web. I do have tons
from HP though so I am pretty well covered for samplers. Over the years
I've built/designed several so I am fairly aware of the trade-offs. That
is one area where there seriously are no free lunches.


I actually own an HP185 sampling scope, mostly tubes, early 60's
monster. It was the first modern 2-diode feedback sampler gadget.


That sure is a piece of history. My GHz workhorse here is a HP-54110D.
Not comparable to very fast sampling scopes but has four HP-samplers in
there. It is remarkable how easy such vintage HP equipment can be
operated. I haven't ever pulled out the manual, not once. Looks like new.

We have a bunch of (about a dozen) Tek 11801s, ca early 90s. Big, nice
scopes. I have some 20 GHz TDR heads, and a 50 GHz single-channel
sampling head with funny connectors. Picoseconds are fun.

It would take a little fiddling, but a 2-GHz sampler could be done for
$10, maybe for $5. I don't know anything about your specific
application, but if you email me privately I could deliver any number
of wild opinions.


Thanks. Can't reveal all that much at this point though.

Harumph.



--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Fri, 07 Feb 2014 15:45:46 -0500, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

On Fri, 07 Feb 2014 11:30:16 -0800, John Larkin
jlarkin@highlandtechnology.com> wrote:


Tek published "Sampling Oscilloscope Circuits", part of their Tek
Concept series of white paperbacks. It's probably online somewhere, or
I could loan you mine with a suitably huge security deposit.

Looks like a good copy here:

http://www.davmar.org/TE/TekConcepts/TekSamplingCircuits.pdf

254 pages!

--sp

Nice scan. Thanks.


--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Fri, 07 Feb 2014 12:52:05 -0800, Joerg <invalid@invalid.invalid>
wrote:

Spehro Pefhany wrote:
On Fri, 07 Feb 2014 11:30:16 -0800, John Larkin
jlarkin@highlandtechnology.com> wrote:

Tek published "Sampling Oscilloscope Circuits", part of their Tek
Concept series of white paperbacks. It's probably online somewhere, or
I could loan you mine with a suitably huge security deposit.

Looks like a good copy here:

http://www.davmar.org/TE/TekConcepts/TekSamplingCircuits.pdf

254 pages!


Thanks! That is a reallynice blast from the past. Haven't heard the word
snap-off diode in a long time.

They were first called Boff Diodes.


--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Phil Hobbs]

On 02/07/2014 03:43 PM, Joerg wrote:

John Larkin wrote:
On Fri, 07 Feb 2014 10:55:46 -0800, Joerg <invalid@invalid.invalid
wrote:

John Larkin wrote:
On Fri, 07 Feb 2014 10:04:23 -0800, Joerg <invalid@invalid.invalid
wrote:

John Larkin wrote:
On Wed, 05 Feb 2014 13:01:54 -0800, Joerg <invalid@invalid.invalid> wrote:

Folks,

Need to sample stuff again. Essentially an equivalent time deal like on
older generation digital scopes where you have a 20MHz or so ADC and
GHZ-bandwidth on the scope. Can take as long as it has to but ... the
sampling must be accurate and the sample gate should ideally close and
open in a few hundred picosends, 1nsec at the most. So far I've always
done this stuff in discretes, diode quads, brute-force driver, the
usual. But this gets old and now I need something small and cheap.

Aren't there any ICs in that domain or am I the only one with such desires?

Also looking for a timer chip to run this but that's easier.
The classic sampling-scope circuit can be built cheap. SRD, clip lines, 2-diode
sampler, charge amp.

This got about 5 GHz bandwidth:

https://dl.dropboxusercontent.com/u/53724080/Protos/Sampler1.JPG

I was mulling a 2-diode sampler because then you don't get that 100%
sampling pulse feed-through that you have with single-diode sampling.
But it doubles the capacitance. Doesn't it leak too much?
Schottky diodes don't leak badly. You have to read it out in a few us
after the sample.

There is also "blow-by", which is capacitive feedthrough of the
diodes. That is easily compensated with an opamp.

That's what I meant, the capacitance. Even at 0.3pF or so that doubles
to 0.6pF for a 2-diode sampler. If you have a lot of clanging or a major
step going on in the source after the sampling that feeds through and
can mess up the reading.


Sampling efficiency of a fast sampler (the output voltage over the
input voltage) is low, a few per cent maybe, but gain is cheap.

That's not a problem as long as one doesn't use this as a sensitive
receiver.


The classic HP 2-diode feedback sampler is well documented.

I've got some papers about it that were hand-typed. From the days when
HP was really HP, the founders were still alive and the Beatles played
on the radio.


4-diode samplers are slower, and don't need blowby compensation and
can be very simple. These are generally in the 1 or maybe 2 GHz range.

That's how I have done it until now, mostly. But yeah, above a GHz it
becomes tough.

The 7S14 got 2 GHz typical bandwidth from a 4-diode sampler driven by
an avalanche transistor! Most of the HP and Tek 4-diode samplers were
spec'd at 1 GHz.


But their budget was "the sky is the limit", probably all gold-plated on
alumina and hand-signed by Agoston Agoston.


Tek published "Sampling Oscilloscope Circuits", part of their Tek
Concept series of white paperbacks. It's probably online somewhere, or
I could loan you mine with a suitably huge security deposit.


I guess my wooden beer Dollar won't count as collateral. Plus you gave
that to me.

Seems this Concept Series never made it onto the web. I do have tons
from HP though so I am pretty well covered for samplers. Over the years
I've built/designed several so I am fairly aware of the trade-offs. That
is one area where there seriously are no free lunches.

It's out there. See e.g. http://tinyurl.com/pm2k5s6

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[David Platt]

In article <b3caf9t2kmba65h4p70ricia3rfhaadg4f@4ax.com>,
John Larkin <jlarkin@highlandtechnology.com> wrote:

Tek published "Sampling Oscilloscope Circuits", part of their Tek
Concept series of white paperbacks. It's probably online somewhere, or
I could loan you mine with a suitably huge security deposit.

http://www.davmar.org/TE/TekConcepts/TekSamplingCircuits.pdf

Thanks - this looks like interesting reading!

 

[John Larkin]

On Fri, 7 Feb 2014 14:33:05 -0800, dplatt@coop.radagast.org (David
Platt) wrote:

In article <b3caf9t2kmba65h4p70ricia3rfhaadg4f@4ax.com>,
John Larkin <jlarkin@highlandtechnology.com> wrote:

Tek published "Sampling Oscilloscope Circuits", part of their Tek
Concept series of white paperbacks. It's probably online somewhere, or
I could loan you mine with a suitably huge security deposit.

http://www.davmar.org/TE/TekConcepts/TekSamplingCircuits.pdf

Thanks - this looks like interesting reading!

That was a whole series of books: probes, timebases, CRT circuits,
vertical amplifiers. Ten-ish books? I have them at home.



--

John Larkin Highland Technology, Inc

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Phil Hobbs]

On 2/7/2014 6:12 PM, John Larkin wrote:

On Fri, 7 Feb 2014 14:33:05 -0800, dplatt@coop.radagast.org (David
Platt) wrote:

In article <b3caf9t2kmba65h4p70ricia3rfhaadg4f@4ax.com>,
John Larkin <jlarkin@highlandtechnology.com> wrote:

Tek published "Sampling Oscilloscope Circuits", part of their Tek
Concept series of white paperbacks. It's probably online somewhere, or
I could loan you mine with a suitably huge security deposit.

http://www.davmar.org/TE/TekConcepts/TekSamplingCircuits.pdf

Thanks - this looks like interesting reading!



That was a whole series of books: probes, timebases, CRT circuits,
vertical amplifiers. Ten-ish books? I have them at home.

I have scans of all of them, I think. The TV, CRT, and horizontal
circuits are pretty much historical interest only.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net