We're designing some laser driver boards, and I thought it would be cool to add test points to some of the interesting circuit nodes. Regular scope probes don't work at ps speeds, and probe grounding is difficult. There are multi-GHz active probes, at roughly $1 per Hz. So I was thinking that I could add a small, 0603 maybe, resistor to a signal to be snooped, run a 50 ohm trace some small distance, and end up at some structure that had a signal test point and a ground. Something roughly like this: http://db.tt/6rRcagTt The resistor could be 450 or 950 ohms, for a 10:1 or 20:1 ratio. The "probe" would be a piece of hardline coax that runs to a sampling scope input, with some provision for grounding. Something like a 3-5 GHz bandwidth should be feasible. This looks promising if a little klunky. Any other ideas? -- John Larkin, President Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
picosecond test points
Started by ●February 11, 2012
Reply by ●February 11, 20122012-02-11
On Sat, 11 Feb 2012 12:57:53 -0800, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:> > >We're designing some laser driver boards, and I thought it would be >cool to add test points to some of the interesting circuit nodes. >Regular scope probes don't work at ps speeds, and probe grounding is >difficult. There are multi-GHz active probes, at roughly $1 per Hz.Per MHz, actually. -- John Larkin, President Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Reply by ●February 11, 20122012-02-11
John Larkin a �crit :> > We're designing some laser driver boards, and I thought it would be > cool to add test points to some of the interesting circuit nodes. > Regular scope probes don't work at ps speeds, and probe grounding is > difficult. There are multi-GHz active probes, at roughly $1 per Hz. > > So I was thinking that I could add a small, 0603 maybe, resistor to a > signal to be snooped, run a 50 ohm trace some small distance, and end > up at some structure that had a signal test point and a ground. > Something roughly like this: > > http://db.tt/6rRcagTt > > The resistor could be 450 or 950 ohms, for a 10:1 or 20:1 ratio. > > The "probe" would be a piece of hardline coax that runs to a sampling > scope input, with some provision for grounding. Something like a 3-5 > GHz bandwidth should be feasible. > > This looks promising if a little klunky. Any other ideas? > >SD14? -- Thanks, Fred.
Reply by ●February 11, 20122012-02-11
On 11 Feb., 21:57, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> We're designing some laser driver boards, and I thought it would be > cool to add test points to some of the interesting circuit nodes. > Regular scope probes don't work at ps speeds, and probe grounding is > difficult. There are multi-GHz active probes, at roughly $1 per Hz. > > So I was thinking that I could add a small, 0603 maybe, resistor to a > signal to be snooped, run a 50 ohm trace some small distance, and end > up at some structure that had a signal test point and a ground. > Something roughly like this: > > http://db.tt/6rRcagTt > > The resistor could be 450 or 950 ohms, for a 10:1 or 20:1 ratio. > > The "probe" would be a piece of hardline coax that runs to a sampling > scope input, with some provision for grounding. Something like a 3-5 > GHz bandwidth should be feasible. > > This looks promising if a little klunky. Any other ideas? >something like this: http://www.idinet.com/IdiNet/media/PDF/94.pdf?ext=.pdf think mouser have them -Lasse
Reply by ●February 11, 20122012-02-11
John Larkin wrote:> > We're designing some laser driver boards, and I thought it would be > cool to add test points to some of the interesting circuit nodes. > Regular scope probes don't work at ps speeds, and probe grounding is > difficult. There are multi-GHz active probes, at roughly $1 per Hz. > > So I was thinking that I could add a small, 0603 maybe, resistor to a > signal to be snooped, run a 50 ohm trace some small distance, and end > up at some structure that had a signal test point and a ground. > Something roughly like this: > > http://db.tt/6rRcagTt > > The resistor could be 450 or 950 ohms, for a 10:1 or 20:1 ratio. > > The "probe" would be a piece of hardline coax that runs to a sampling > scope input, with some provision for grounding. Something like a 3-5 > GHz bandwidth should be feasible. > > This looks promising if a little klunky. Any other ideas?Looks good. Another approach would be something like a BFP650 follower, with the 50-ohm coax forming the emitter load when the probe is connected. You'd need a very small base inductor to keep it from oscillating. 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 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●February 11, 20122012-02-11
On Sat, 11 Feb 2012 22:55:54 +0100, Fred Bartoli <" "> wrote:>John Larkin a �crit : >> >> We're designing some laser driver boards, and I thought it would be >> cool to add test points to some of the interesting circuit nodes. >> Regular scope probes don't work at ps speeds, and probe grounding is >> difficult. There are multi-GHz active probes, at roughly $1 per Hz. >> >> So I was thinking that I could add a small, 0603 maybe, resistor to a >> signal to be snooped, run a 50 ohm trace some small distance, and end >> up at some structure that had a signal test point and a ground. >> Something roughly like this: >> >> http://db.tt/6rRcagTt >> >> The resistor could be 450 or 950 ohms, for a 10:1 or 20:1 ratio. >> >> The "probe" would be a piece of hardline coax that runs to a sampling >> scope input, with some provision for grounding. Something like a 3-5 >> GHz bandwidth should be feasible. >> >> This looks promising if a little klunky. Any other ideas? >> >> > >SD14?I have a couple, but the tip is nasty and it's hard to ground. John -- John Larkin, President Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Reply by ●February 11, 20122012-02-11
On Sat, 11 Feb 2012 14:20:24 -0800 (PST), "langwadt@fonz.dk" <langwadt@fonz.dk> wrote:>On 11 Feb., 21:57, John Larkin ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> We're designing some laser driver boards, and I thought it would be >> cool to add test points to some of the interesting circuit nodes. >> Regular scope probes don't work at ps speeds, and probe grounding is >> difficult. There are multi-GHz active probes, at roughly $1 per Hz. >> >> So I was thinking that I could add a small, 0603 maybe, resistor to a >> signal to be snooped, run a 50 ohm trace some small distance, and end >> up at some structure that had a signal test point and a ground. >> Something roughly like this: >> >> http://db.tt/6rRcagTt >> >> The resistor could be 450 or 950 ohms, for a 10:1 or 20:1 ratio. >> >> The "probe" would be a piece of hardline coax that runs to a sampling >> scope input, with some provision for grounding. Something like a 3-5 >> GHz bandwidth should be feasible. >> >> This looks promising if a little klunky. Any other ideas? >> > >something like this: http://www.idinet.com/IdiNet/media/PDF/94.pdf?ext=.pdf > >think mouser have them > >-LasseOK, that leads to... http://www.idinet.com/Test-Probes/Specialty-Probes/Coaxial-Probes/ What I don't understand is that all the inner probes seem to be flush with the outer shell, which doesn't look like it would make a reliable connection to the board. The PCB layout for these would be an outer ground ring and an inner via, with the signal trace on an inner or bottom layer. Or maybe an outer broken/c-shaped ring for grounding, and the signal/pad on top. -- John Larkin, President Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Reply by ●February 11, 20122012-02-11
On 11 Feb., 23:39, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> On Sat, 11 Feb 2012 14:20:24 -0800 (PST), "langw...@fonz.dk" > > > > > > > > > > <langw...@fonz.dk> wrote: > >On 11 Feb., 21:57, John Larkin > ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> We're designing some laser driver boards, and I thought it would be > >> cool to add test points to some of the interesting circuit nodes. > >> Regular scope probes don't work at ps speeds, and probe grounding is > >> difficult. There are multi-GHz active probes, at roughly $1 per Hz. > > >> So I was thinking that I could add a small, 0603 maybe, resistor to a > >> signal to be snooped, run a 50 ohm trace some small distance, and end > >> up at some structure that had a signal test point and a ground. > >> Something roughly like this: > > >>http://db.tt/6rRcagTt > > >> The resistor could be 450 or 950 ohms, for a 10:1 or 20:1 ratio. > > >> The "probe" would be a piece of hardline coax that runs to a sampling > >> scope input, with some provision for grounding. Something like a 3-5 > >> GHz bandwidth should be feasible. > > >> This looks promising if a little klunky. Any other ideas? > > >something like this:http://www.idinet.com/IdiNet/media/PDF/94.pdf?ext=.pdf > > >think mouser have them > > >-Lasse > > OK, that leads to... > > http://www.idinet.com/Test-Probes/Specialty-Probes/Coaxial-Probes/ > > What I don't understand is that all the inner probes seem to be flush > with the outer shell, which doesn't look like it would make a reliable > connection to the board. >both outer and inner are spring loaded, from the datasheet: Spring Force: Signal Conductor: 2.3 oz. @ .107 (2.72) travel Shielding Plunger: 5.8 oz. @ .107 (2.72) travel> The PCB layout for these would be an outer ground ring and an inner > via, with the signal trace on an inner or bottom layer. Or maybe an > outer broken/c-shaped ring for grounding, and the signal/pad on top. >yes something like that, maybe just a standard round test point with a big enough void in the soldermask to get to the ground plane btw. seen this?: http://koti.mbnet.fi/jahonen/Electronics/DIY%201k%20probe/ -Lasse
Reply by ●February 11, 20122012-02-11
On Feb 11, 5:39=A0pm, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> On Sat, 11 Feb 2012 14:20:24 -0800 (PST), "langw...@fonz.dk" > > > > > > <langw...@fonz.dk> wrote: > >On 11 Feb., 21:57, John Larkin > ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> We're designing some laser driver boards, and I thought it would be > >> cool to add test points to some of the interesting circuit nodes. > >> Regular scope probes don't work at ps speeds, and probe grounding is > >> difficult. There are multi-GHz active probes, at roughly $1 per Hz. > > >> So I was thinking that I could add a small, 0603 maybe, resistor to a > >> signal to be snooped, run a 50 ohm trace some small distance, and end > >> up at some structure that had a signal test point and a ground. > >> Something roughly like this: > > >>http://db.tt/6rRcagTt > > >> The resistor could be 450 or 950 ohms, for a 10:1 or 20:1 ratio. > > >> The "probe" would be a piece of hardline coax that runs to a sampling > >> scope input, with some provision for grounding. Something like a 3-5 > >> GHz bandwidth should be feasible. > > >> This looks promising if a little klunky. Any other ideas? > > >something like this:http://www.idinet.com/IdiNet/media/PDF/94.pdf?ext=3D=.pdf> > >think mouser have them > > >-Lasse > > OK, that leads to... > > http://www.idinet.com/Test-Probes/Specialty-Probes/Coaxial-Probes/ > > What I don't understand is that all the inner probes seem to be flush > with the outer shell, which doesn't look like it would make a reliable > connection to the board.It's a spring loaded plunger...
Reply by ●February 11, 20122012-02-11
On Feb 11, 11:24=A0pm, Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> wrote:> John Larkin wrote: > > > We're designing some laser driver boards, and I thought it would be > > cool to add test points to some of the interesting circuit nodes. > > Regular scope probes don't work at ps speeds, and probe grounding is > > difficult. There are multi-GHz active probes, at roughly $1 per Hz. > > > So I was thinking that I could add a small, 0603 maybe, resistor to a > > signal to be snooped, run a 50 ohm trace some small distance, and end > > up at some structure that had a signal test point and a ground. > > Something roughly like this: > > >http://db.tt/6rRcagTt > > > The resistor could be 450 or 950 ohms, for a 10:1 or 20:1 ratio. > > > The "probe" would be a piece of hardline coax that runs to a sampling > > scope input, with some provision for grounding. Something like a 3-5 > > GHz bandwidth should be feasible. > > > This looks promising if a little klunky. Any other ideas? > > Looks good. =A0Another approach would be something like a BFP650 follower=,> with the 50-ohm coax forming the emitter load when the probe is > connected. =A0You'd need a very small base inductor to keep it from > oscillating.I did something like that on the little up-grade board that put ECLinPS into the critical bit of an old TTL-based pulse generator for electron spin resonance - that would have been back around 1996. The original designer wanted buffered test points so that he could probe the critical signals without loading the trace, so I buffered the relevant traces with BFR92A emitter-followers. We didn't bother with a base-stopping inductor - something like an 0603 33R hard up against the base did the job perfectly adequately. -- Bill Sloman
