Fast And Gate, 1 Ghz
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From: Jon Slaughter on 15 Feb 2010 14:53 John Larkin wrote: > On Mon, 15 Feb 2010 09:31:21 -0800, Joerg <invalid(a)invalid.invalid> > wrote: > >> John Larkin wrote: >>> On Sun, 14 Feb 2010 08:19:11 -0800 (PST), osr(a)uakron.edu wrote: >>> >>>> Can anyone suggest a fast AND gate at 1-2 Ghz. A friend of mine >>>> needs to measure a laser pulse duration on almost no budget, >>>> perhaps 200-300$. The Pulse ranges from 4 to 20 Nanoseconds, and >>>> his current idea is use the photodiode current to gate open a >>>> source of 1 ghz pulses and integrate,. The 2 Ghz source is the >>>> easy part< I have that.. The question is how to gate it. Sadly >>>> this is a single shot event at 1-4 hz and thus a sampling scope >>>> is out. I have no problem getting a photodiode with 47 >>>> picosecond rise time.. >>>> >>>> Suggestions, other then finding friends with higher salaries? My >>>> friend is a independent field service engineer on medical lasers. >>>> He has a idea for a replacement product to get him off the road, >>>> the cost of travel is slaughtering his once profitable business. >>>> He wants to build the prototype, and see if his idea works >>>> compared to a known working pulsed laser source. >>>> >>>> Some modern form of ECL? >>>> >>>> Steve >>> >>> The Eclips Plus gates would be about right, if you really need >>> gates. ON and Micrel make them. >>> >>> But one of the Analog Devices fast (ecl/pecl) comparators might be >>> all you need. It could discriminate the photodiode signal, and you >>> could use its ECL output and a couple of transistors to steer a >>> current into an integrating cap to give pulse width. >>> >>> If you count a 2 GHz source, the resolution will be 500 ps, so >>> you'll only get 8 to 40 ticks. An analog trick could give lots >>> better resolution. >>> >> >> Fully agree, this really calls for the analog integrator. With a 2GHz >> source you'd also get tons of "amplitude jitter". Sometimes it >> catches three pulses, sometimes only two, stuff like that. > > How accurate is this integrator method with regards to repeatability? I would imagine any simple implementation would be rather inaccurate? (due to temperature issues, etc...)
From: Tim Wescott on 15 Feb 2010 15:16 On Sun, 14 Feb 2010 10:00:39 -0800, dagmargoodboat wrote: > On Feb 14, 11:19 am, o...(a)uakron.edu wrote: >> Can anyone suggest a fast AND gate at 1-2 Ghz. A friend of mine needs >> to measure a laser pulse duration on almost no budget, perhaps >> 200-300$. The Pulse ranges from 4 to 20 Nanoseconds, and his current >> idea is use the photodiode current to gate open a source of 1 ghz >> pulses and integrate,. The 2 Ghz source is the easy part< I have that.. >> The question is how to gate it. Sadly this is a single shot event at >> 1-4 hz and thus a sampling scope is out. I have no problem getting >> a photodiode with 47 picosecond rise time.. >> >> Suggestions, other then finding friends with higher salaries? My friend >> is a independent field service engineer on medical lasers. He has a >> idea for a replacement product to get him off the road, the cost of >> travel is slaughtering his once profitable business. He wants to build >> the prototype, and see if his idea works compared to a known working >> pulsed laser source. >> >> Some modern form of ECL? >> >> Steve > > Seems like a job for a single-slope integrating A/D. Integrate a > current onto a cap while the pulse flies, then de-integrate at your > leisure in-between pulses. That was my thought. Or just integrate a current into the cap while the pulse flies, then measure the resulting voltage with a plain ol' ADC. -- www.wescottdesign.com
From: John Larkin on 15 Feb 2010 20:20 On Mon, 15 Feb 2010 13:53:24 -0600, "Jon Slaughter" <Jon_Slaughter(a)Hotmail.com> wrote: >John Larkin wrote: >> On Mon, 15 Feb 2010 09:31:21 -0800, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>> John Larkin wrote: >>>> On Sun, 14 Feb 2010 08:19:11 -0800 (PST), osr(a)uakron.edu wrote: >>>> >>>>> Can anyone suggest a fast AND gate at 1-2 Ghz. A friend of mine >>>>> needs to measure a laser pulse duration on almost no budget, >>>>> perhaps 200-300$. The Pulse ranges from 4 to 20 Nanoseconds, and >>>>> his current idea is use the photodiode current to gate open a >>>>> source of 1 ghz pulses and integrate,. The 2 Ghz source is the >>>>> easy part< I have that.. The question is how to gate it. Sadly >>>>> this is a single shot event at 1-4 hz and thus a sampling scope >>>>> is out. I have no problem getting a photodiode with 47 >>>>> picosecond rise time.. >>>>> >>>>> Suggestions, other then finding friends with higher salaries? My >>>>> friend is a independent field service engineer on medical lasers. >>>>> He has a idea for a replacement product to get him off the road, >>>>> the cost of travel is slaughtering his once profitable business. >>>>> He wants to build the prototype, and see if his idea works >>>>> compared to a known working pulsed laser source. >>>>> >>>>> Some modern form of ECL? >>>>> >>>>> Steve >>>> >>>> The Eclips Plus gates would be about right, if you really need >>>> gates. ON and Micrel make them. >>>> >>>> But one of the Analog Devices fast (ecl/pecl) comparators might be >>>> all you need. It could discriminate the photodiode signal, and you >>>> could use its ECL output and a couple of transistors to steer a >>>> current into an integrating cap to give pulse width. >>>> >>>> If you count a 2 GHz source, the resolution will be 500 ps, so >>>> you'll only get 8 to 40 ticks. An analog trick could give lots >>>> better resolution. >>>> >>> >>> Fully agree, this really calls for the analog integrator. With a 2GHz >>> source you'd also get tons of "amplitude jitter". Sometimes it >>> catches three pulses, sometimes only two, stuff like that. >> >> > > >How accurate is this integrator method with regards to repeatability? I >would imagine any simple implementation would be rather inaccurate? (due to >temperature issues, etc...) If you did it carefully, I'd think you could get repeatability of 20 ps or less for a 20 ns full-scale. Steer a good current source with fairly fast transistors, and use an NPO cap, follow with a good low-bias-current opamp. John
From: dagmargoodboat on 15 Feb 2010 22:39 On Feb 15, 3:16 pm, Tim Wescott <t...(a)seemywebsite.com> wrote: > On Sun, 14 Feb 2010 10:00:39 -0800, dagmargoodboat wrote: > > On Feb 14, 11:19 am, o...(a)uakron.edu wrote: > >> Can anyone suggest a fast AND gate at 1-2 Ghz. A friend of mine needs > >> to measure a laser pulse duration on almost no budget, perhaps > >> 200-300$. The Pulse ranges from 4 to 20 Nanoseconds, and his current > >> idea is use the photodiode current to gate open a source of 1 ghz > >> pulses and integrate,. The 2 Ghz source is the easy part< I have that... > >> The question is how to gate it. Sadly this is a single shot event at > >> 1-4 hz and thus a sampling scope is out. I have no problem getting > >> a photodiode with 47 picosecond rise time.. > > >> Suggestions, other then finding friends with higher salaries? My friend > >> is a independent field service engineer on medical lasers. He has a > >> idea for a replacement product to get him off the road, the cost of > >> travel is slaughtering his once profitable business. He wants to build > >> the prototype, and see if his idea works compared to a known working > >> pulsed laser source. > > >> Some modern form of ECL? > > >> Steve > > > Seems like a job for a single-slope integrating A/D. Integrate a > > current onto a cap while the pulse flies, then de-integrate at your > > leisure in-between pulses. > > That was my thought. Or just integrate a current into the cap while the > pulse flies, then measure the resulting voltage with a plain ol' ADC. Sure. That's just as good and what with today's uC's and a/d's, possibly more convenient. -- Cheers, James Arthur
From: John Larkin on 15 Feb 2010 23:10
On Sun, 14 Feb 2010 10:00:39 -0800 (PST), dagmargoodboat(a)yahoo.com wrote: >On Feb 14, 11:19�am, o...(a)uakron.edu wrote: >> Can anyone suggest a fast AND gate �at 1-2 Ghz. A friend of mine needs >> to measure a laser pulse duration on almost no budget, perhaps >> 200-300$. The Pulse ranges from 4 to 20 Nanoseconds, and his current >> idea is use the photodiode current to gate open a source of 1 ghz >> pulses and integrate,. The 2 Ghz source is the easy part< I have >> that.. The question is how to gate it. Sadly this is a single shot >> event at 1-4 hz and �thus a sampling scope is out. � �I have no >> problem getting a photodiode with 47 picosecond rise time.. >> >> Suggestions, other then finding friends with higher salaries? My >> friend is a independent field service engineer on medical lasers. He >> has a idea for a replacement �product to get him off the road, the >> cost of travel is slaughtering his once profitable business. He wants >> to build the prototype, and see if his idea works compared to a known >> working pulsed laser source. >> >> Some modern form of ECL? >> >> Steve > >Seems like a job for a single-slope integrating A/D. Integrate a >current onto a cap while the pulse flies, then de-integrate at your >leisure in-between pulses. That's the classic pulse stretcher, used to get picosecond resolution edge measurements. That suggests an interesting and cheap circuit to solve the OP's problem. But my camera broke so I can't post it now. John |