Super fast sample & hold under $10?

[John Larkin]

On Thu, 06 Feb 2014 11:52:38 -0500, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

On Thu, 06 Feb 2014 08:14:43 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> 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.

"Analog input bandwidth is the analog input frequency at which the
spectral power of the fundamental frequency (as determined by the FFT
analysis) is reduced by 3 dB."

Small-signal? All the real data stops at 200 MHz.




--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

 

[Spehro Pefhany]

On Thu, 06 Feb 2014 08:14:43 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> 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.

"Analog input bandwidth is the analog input frequency at which the
spectral power of the fundamental frequency (as determined by the FFT
analysis) is reduced by 3 dB."

 

[Klaus Kragelund]

On Thursday, February 6, 2014 10:16:30 PM UTC+1, Joerg wrote:

Klaus Kragelund wrote:

On Thursday, February 6, 2014 7:42:28 PM UTC+1, Joerg wrote:

Klaus Kragelund wrote:



Wrt the switch, the idea was to use an open drain type, so it

pulls low but when the output reaches the threshold, it switches

so the cap is isolated with the body diode. The input of the SH

does not "see" the cap that way at all





Maybe I misunderstand this, but there is no threshold. The signal

is not



known and must be sampled to find out what the amplitude is at each

time



slot. That can change significantly within a few hundred psec.





Implementation with sloooooooow comparator and emulation of reset of

capacitor (open/closed switches):



https://dl.dropboxusercontent.com/u/44228185/FastSH.pdf



For actual application you would need a comparator with enable input

and rescale values





Hmm, I think you lost me there. How can it sample the signal off of a

sensor and store that sample value in a capacitor for later pickup? With

the sampling time being a fraction of a nanosecond.

The procedure, hope nothing is wrong:

Use a micro output or whatever to charge the capacitor on the output of the comparator (node OUT)
Hi-state the micro output (node OUT)
Enable the comparator for 500ps (you need a fast comparator). The comparator slews the output to the input value. When node OUT is equal to the input signal, node OC rises.
When OC rises, use that to Disable the comparator (needs perhaps level translation circuit)
Use the OC rise to trigger the microcontroller to start ADC conversion.

Cheers

Klaus

 

[Joerg]

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.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

Phil Hobbs wrote:

On 02/06/2014 11:01 AM, Joerg 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.


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.


Sounds like a job for a couple of pHEMTs in cascode. The SKY65050 is a
very nice device if its high 1/f corner (~50 MHz) doesn't worry you too
much.

Noise almost doesn't matter at all in this case. But the package of the
SKY65050 somehow tells me that it's not a low capacitance device.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

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.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

Klaus Kragelund wrote:

Wrt the switch, the idea was to use an open drain type, so it pulls
low but when the output reaches the threshold, it switches so the cap
is isolated with the body diode.

The input of the SH does not "see" the cap that way at all

Maybe I misunderstand this, but there is no threshold. The signal is not
known and must be sampled to find out what the amplitude is at each time
slot. That can change significantly within a few hundred psec.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

Klaus Kragelund wrote:

On Thursday, February 6, 2014 7:42:28 PM UTC+1, Joerg wrote:
Klaus Kragelund wrote:

Wrt the switch, the idea was to use an open drain type, so it
pulls low but when the output reaches the threshold, it switches
so the cap is isolated with the body diode. The input of the SH
does not "see" the cap that way at all


Maybe I misunderstand this, but there is no threshold. The signal
is not

known and must be sampled to find out what the amplitude is at each
time

slot. That can change significantly within a few hundred psec.


Implementation with sloooooooow comparator and emulation of reset of
capacitor (open/closed switches):

https://dl.dropboxusercontent.com/u/44228185/FastSH.pdf

For actual application you would need a comparator with enable input
and rescale values

Hmm, I think you lost me there. How can it sample the signal off of a
sensor and store that sample value in a capacitor for later pickup? With
the sampling time being a fraction of a nanosecond.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

Klaus Kragelund wrote:

On Thursday, February 6, 2014 10:16:30 PM UTC+1, Joerg wrote:
Klaus Kragelund wrote:

On Thursday, February 6, 2014 7:42:28 PM UTC+1, Joerg wrote:
Klaus Kragelund wrote:
Wrt the switch, the idea was to use an open drain type, so it
pulls low but when the output reaches the threshold, it switches
so the cap is isolated with the body diode. The input of the SH
does not "see" the cap that way at all
Maybe I misunderstand this, but there is no threshold. The signal
is not
known and must be sampled to find out what the amplitude is at each
time
slot. That can change significantly within a few hundred psec.
Implementation with sloooooooow comparator and emulation of reset of
capacitor (open/closed switches):
https://dl.dropboxusercontent.com/u/44228185/FastSH.pdf
For actual application you would need a comparator with enable input
and rescale values


Hmm, I think you lost me there. How can it sample the signal off of a

sensor and store that sample value in a capacitor for later pickup? With

the sampling time being a fraction of a nanosecond.


The procedure, hope nothing is wrong:

Use a micro output or whatever to charge the capacitor on the output of the comparator (node OUT)
Hi-state the micro output (node OUT)
Enable the comparator for 500ps (you need a fast comparator). The comparator slews the output to the input value. When node OUT is equal to the input signal, node OC rises.
When OC rises, use that to Disable the comparator (needs perhaps level translation circuit)
Use the OC rise to trigger the microcontroller to start ADC conversion.

That is a clever method. With comparators there is one problem though:
When a very fast comparator sees little change or too slow a change on
the input side it can burst into oscillation. If it doesn't see
10mV/nsec or more it can go berserk, they are meant more for digital stuff.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Phil Hobbs]

On 2/6/2014 1:35 PM, Joerg wrote:

Phil Hobbs wrote:
On 02/06/2014 11:01 AM, Joerg 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.


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.


Sounds like a job for a couple of pHEMTs in cascode. The SKY65050 is a
very nice device if its high 1/f corner (~50 MHz) doesn't worry you too
much.


Noise almost doesn't matter at all in this case. But the package of the
SKY65050 somehow tells me that it's not a low capacitance device.

Read the datasheet.

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 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.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

 

[Chris Jones]

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

 

[Klaus Kragelund]

On Thursday, February 6, 2014 11:29:39 PM UTC+1, Joerg wrote:

Klaus Kragelund wrote:

On Thursday, February 6, 2014 10:16:30 PM UTC+1, Joerg wrote:

Klaus Kragelund wrote:



On Thursday, February 6, 2014 7:42:28 PM UTC+1, Joerg wrote:

Klaus Kragelund wrote:

Wrt the switch, the idea was to use an open drain type, so it

pulls low but when the output reaches the threshold, it switches

so the cap is isolated with the body diode. The input of the SH

does not "see" the cap that way at all

Maybe I misunderstand this, but there is no threshold. The signal

is not

known and must be sampled to find out what the amplitude is at each

time

slot. That can change significantly within a few hundred psec.

Implementation with sloooooooow comparator and emulation of reset of

capacitor (open/closed switches):

https://dl.dropboxusercontent.com/u/44228185/FastSH.pdf

For actual application you would need a comparator with enable input

and rescale values





Hmm, I think you lost me there. How can it sample the signal off of a



sensor and store that sample value in a capacitor for later pickup? With



the sampling time being a fraction of a nanosecond.





The procedure, hope nothing is wrong:



Use a micro output or whatever to charge the capacitor on the output of the comparator (node OUT)

Hi-state the micro output (node OUT)

Enable the comparator for 500ps (you need a fast comparator). The comparator slews the output to the input value. When node OUT is equal to the input signal, node OC rises.

When OC rises, use that to Disable the comparator (needs perhaps level translation circuit)

Use the OC rise to trigger the microcontroller to start ADC conversion.





That is a clever method. With comparators there is one problem though:

When a very fast comparator sees little change or too slow a change on

the input side it can burst into oscillation. If it doesn't see

10mV/nsec or more it can go berserk, they are meant more for digital stuff.

You can do it with an opamp also, just add a diode in the output

As for precision, route the reference to the input occationally, so you can do ratiometric calibration of offsets and propagation delays

Cheers

Klaus

 

[Robert Lacoste]

"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?

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...
Robert
www.alciom.com

 

[John Larkin]

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. The ADI
comparators are expensive, and Hittite's pricing is insane.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

 

[Joerg]

Klaus Kragelund wrote:

On Thursday, February 6, 2014 11:29:39 PM UTC+1, Joerg wrote:
Klaus Kragelund wrote:

On Thursday, February 6, 2014 10:16:30 PM UTC+1, Joerg wrote:
Klaus Kragelund wrote:
On Thursday, February 6, 2014 7:42:28 PM UTC+1, Joerg wrote:
Klaus Kragelund wrote:
Wrt the switch, the idea was to use an open drain type,
so it pulls low but when the output reaches the
threshold, it switches so the cap is isolated with the
body diode. The input of the SH does not "see" the cap
that way at all
Maybe I misunderstand this, but there is no threshold. The
signal is not known and must be sampled to find out what
the amplitude is at each time slot. That can change
significantly within a few hundred psec.
Implementation with sloooooooow comparator and emulation of
reset of capacitor (open/closed switches):
https://dl.dropboxusercontent.com/u/44228185/FastSH.pdf For
actual application you would need a comparator with enable
input and rescale values
Hmm, I think you lost me there. How can it sample the signal
off of a sensor and store that sample value in a capacitor for
later pickup? With the sampling time being a fraction of a
nanosecond.
The procedure, hope nothing is wrong: Use a micro output or
whatever to charge the capacitor on the output of the comparator
(node OUT) Hi-state the micro output (node OUT) Enable the
comparator for 500ps (you need a fast comparator). The comparator
slews the output to the input value. When node OUT is equal to
the input signal, node OC rises. When OC rises, use that to
Disable the comparator (needs perhaps level translation circuit)
Use the OC rise to trigger the microcontroller to start ADC
conversion.


That is a clever method. With comparators there is one problem
though:

When a very fast comparator sees little change or too slow a change
on

the input side it can burst into oscillation. If it doesn't see

10mV/nsec or more it can go berserk, they are meant more for
digital stuff.

You can do it with an opamp also, just add a diode in the output

I've look at opamps instead but that may be a few years off. There are
reasonably priced ones with GBWs in excess of 15GHz but they are only
stable at gains of 10 or so. That results in too low bandwidth for this
application. In a few years that can be different.

As for precision, route the reference to the input occationally, so
you can do ratiometric calibration of offsets and propagation delays

Calibaration is not problem because test signals can be generated. That
would calibrate the whole path.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Joerg]

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.

... The ADI
comparators are expensive, and Hittite's pricing is insane.

Insane as in >$300 a pop :-(

--
Regards, Joerg

http://www.analogconsultants.com/

 

[John Larkin]

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.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

 

[John Larkin]

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


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation

 

[whit3rd]

On Thursday, February 6, 2014 10:39:58 AM UTC-8, Joerg wrote:

[about a sample/hold for 800 MHz, nonastronomical price]

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

An OTA might be the right kind of gated gizmo; TI's OPA860 has a buffer/
follower and the OTA, and at least some response out at that frequency
(gain of 5 at 80 MHz is claimed).