Forums

150 ps TDR sampler--dead bug!

Started by Phil Hobbs December 2, 2016
ChesterW and I have spent the last couple of days doing a dead-bug proto
of a single-diode TDR front end I designed for a mutual client.  It uses
all SOT23, SC-70, 0603, and a super small (0402ish) sampling diode.   It
includes the TX pulse generator, sample pulse generator, sampling diode,
and a ~100~MHz bandwidth buffer and voltage amplifier

Connectors are MMCX to minimize pigtail inductance.  Nice clean sampling
response, 150-ps 10%-90% (probably 100 ps FWHM), 17 ps p-p jitter, BOM
cost $1.30 excluding connectors.  (I cheated slightly by replacing the
BJT pulse generators with pHEMTs--an extra 80 cents--to make up for the
higher stray inductances, so it's really $2.10.)

Chester's bit is the delay generator, back end, and all the  secret
sauce in the actual transducer we're measuring.  It's all done, so he
came up from Dallas to lend a shoulder to the prototyping wheel, which
was great.

For the test, we used one of JL's very nice P400 digital delay
generators to do the timing.  That 17 ps jitter number is pretty good, I
think, especially since there's no shielding and a bunch of cell phones
around.  It's neat to be able to tune the delay by 10 ps and see the
sampler output change.

Prototyping is sure slow when you're fighting the surface tension of the
solder and the tendency of all of the midair solder joints to melt at
once.  0603-pitch pad board with ground plane is a big win for this sort
of job, but some of the hairiest mid-air things took 10 tries to get
right, even under a Mantis.

Fun doing my first-ever sampler, though!

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
On Fri, 2 Dec 2016 16:13:49 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>ChesterW and I have spent the last couple of days doing a dead-bug proto >of a single-diode TDR front end I designed for a mutual client. It uses >all SOT23, SC-70, 0603, and a super small (0402ish) sampling diode. It >includes the TX pulse generator, sample pulse generator, sampling diode, >and a ~100~MHz bandwidth buffer and voltage amplifier > >Connectors are MMCX to minimize pigtail inductance. Nice clean sampling >response, 150-ps 10%-90% (probably 100 ps FWHM), 17 ps p-p jitter, BOM >cost $1.30 excluding connectors. (I cheated slightly by replacing the >BJT pulse generators with pHEMTs--an extra 80 cents--to make up for the >higher stray inductances, so it's really $2.10.) > >Chester's bit is the delay generator, back end, and all the secret >sauce in the actual transducer we're measuring. It's all done, so he >came up from Dallas to lend a shoulder to the prototyping wheel, which >was great. > >For the test, we used one of JL's very nice P400 digital delay >generators to do the timing. That 17 ps jitter number is pretty good, I >think, especially since there's no shielding and a bunch of cell phones >around. It's neat to be able to tune the delay by 10 ps and see the >sampler output change. > >Prototyping is sure slow when you're fighting the surface tension of the >solder and the tendency of all of the midair solder joints to melt at >once. 0603-pitch pad board with ground plane is a big win for this sort >of job, but some of the hairiest mid-air things took 10 tries to get >right, even under a Mantis. > >Fun doing my first-ever sampler, though! > >Cheers > >Phil Hobbs
I just got the assembled proto (a 4-layer PC board) of a TDR. It will cost a bit more than yours, but I'm hoping to get down around 50 ps. I expect the step response to be sorta ugly, but that can be deconvolved for beauty, and maybe a bit faster risetime. A couple of the chips are leadless QFNs, so a hand-wired proto wasn't appealing. https://dl.dropboxusercontent.com/u/53724080/TDR/Z394_TDR_Blur.jpg Maybe I'll fire it up this weekend. Then find a use for it. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On 12/02/2016 05:22 PM, John Larkin wrote:
> On Fri, 2 Dec 2016 16:13:49 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> ChesterW and I have spent the last couple of days doing a dead-bug proto >> of a single-diode TDR front end I designed for a mutual client. It uses >> all SOT23, SC-70, 0603, and a super small (0402ish) sampling diode. It >> includes the TX pulse generator, sample pulse generator, sampling diode, >> and a ~100~MHz bandwidth buffer and voltage amplifier >> >> Connectors are MMCX to minimize pigtail inductance. Nice clean sampling >> response, 150-ps 10%-90% (probably 100 ps FWHM), 17 ps p-p jitter, BOM >> cost $1.30 excluding connectors. (I cheated slightly by replacing the >> BJT pulse generators with pHEMTs--an extra 80 cents--to make up for the >> higher stray inductances, so it's really $2.10.) >> >> Chester's bit is the delay generator, back end, and all the secret >> sauce in the actual transducer we're measuring. It's all done, so he >> came up from Dallas to lend a shoulder to the prototyping wheel, which >> was great. >> >> For the test, we used one of JL's very nice P400 digital delay >> generators to do the timing. That 17 ps jitter number is pretty good, I >> think, especially since there's no shielding and a bunch of cell phones >> around. It's neat to be able to tune the delay by 10 ps and see the >> sampler output change. >> >> Prototyping is sure slow when you're fighting the surface tension of the >> solder and the tendency of all of the midair solder joints to melt at >> once. 0603-pitch pad board with ground plane is a big win for this sort >> of job, but some of the hairiest mid-air things took 10 tries to get >> right, even under a Mantis. >> >> Fun doing my first-ever sampler, though! >> >> Cheers >> >> Phil Hobbs > > I just got the assembled proto (a 4-layer PC board) of a TDR. It will > cost a bit more than yours, but I'm hoping to get down around 50 ps. I > expect the step response to be sorta ugly, but that can be deconvolved > for beauty, and maybe a bit faster risetime. > > A couple of the chips are leadless QFNs, so a hand-wired proto wasn't > appealing. > > https://dl.dropboxusercontent.com/u/53724080/TDR/Z394_TDR_Blur.jpg > > Maybe I'll fire it up this weekend. Then find a use for it.
Fun. I think mine is limited by the voltage gain of the pHEMTs, because I'm driving their gates with a 1.5 ns edge. A couple of those nice ECL comparators you're using would be nice, or even two stages of pHEMT, but that would blow the budget for this one. A TDR accuracy of a quarter inch is easily good enough for this job. 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
Phil Hobbs wrote:
> ChesterW and I have spent the last couple of days doing a dead-bug proto > of a single-diode TDR front end I designed for a mutual client. It uses > all SOT23, SC-70, 0603, and a super small (0402ish) sampling diode. It > includes the TX pulse generator, sample pulse generator, sampling diode, > and a ~100~MHz bandwidth buffer and voltage amplifier > > Connectors are MMCX to minimize pigtail inductance. Nice clean sampling > response, 150-ps 10%-90% (probably 100 ps FWHM), 17 ps p-p jitter, BOM > cost $1.30 excluding connectors. (I cheated slightly by replacing the > BJT pulse generators with pHEMTs--an extra 80 cents--to make up for the > higher stray inductances, so it's really $2.10.) > > Chester's bit is the delay generator, back end, and all the secret > sauce in the actual transducer we're measuring. It's all done, so he > came up from Dallas to lend a shoulder to the prototyping wheel, which > was great. > > For the test, we used one of JL's very nice P400 digital delay > generators to do the timing. That 17 ps jitter number is pretty good, I > think, especially since there's no shielding and a bunch of cell phones > around. It's neat to be able to tune the delay by 10 ps and see the > sampler output change. > > Prototyping is sure slow when you're fighting the surface tension of the > solder and the tendency of all of the midair solder joints to melt at > once. 0603-pitch pad board with ground plane is a big win for this sort > of job, but some of the hairiest mid-air things took 10 tries to get > right, even under a Mantis. > > Fun doing my first-ever sampler, though! > > Cheers > > Phil Hobbs >
Will these be available to the great unwashed? Price,qty?
>Will these be available to the great unwashed? &nbsp;Price,qty?
As part of a low cost gauging application. Dunno about other stuff. For lab use, Tek 1180x stuff and (especially) HP 70820A units are available cheap, and have far better performance--a SD-24 head does 30 ps-ish TDR. Cheers Phil Hobbs