Fast And Gate, 1 Ghz
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From: Joerg on 16 Feb 2010 12:30 John Larkin wrote: > 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$. The Pulse ranges from 4 to 20 Nanoseconds, and his current >>> idea is use the photodiode current to gate open a source of 1 ghz >>> pulses and integrate,. The 2 Ghz source is the easy part< I have >>> that.. The question is how to gate it. Sadly this is a single shot >>> event at 1-4 hz and thus a sampling scope is out. I have no >>> problem getting a photodiode with 47 picosecond rise time.. >>> >>> Suggestions, other then finding friends with higher salaries? My >>> friend is a independent field service engineer on medical lasers. He >>> has a idea for a replacement product to get him off the road, the >>> cost of travel is slaughtering his once profitable business. He wants >>> to build the prototype, and see if his idea works compared to a known >>> working pulsed laser source. >>> >>> Some modern form of ECL? >>> >>> Steve >> Seems like a job for a single-slope integrating A/D. Integrate a >> current onto a cap while the pulse flies, then de-integrate at your >> leisure in-between pulses. > > That's the classic pulse stretcher, used to get picosecond resolution > edge measurements. That suggests an interesting and cheap circuit to > solve the OP's problem. But my camera broke so I can't post it now. > But I found it hard to convince folks to do it that way. Nowadays many seem almost hell-bent on doing it digitally. Maybe because the analog world is too close to voodoo for younger engineers ;-) -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: John Larkin on 16 Feb 2010 12:50 On Tue, 16 Feb 2010 09:30:27 -0800, Joerg <invalid(a)invalid.invalid> wrote: >John Larkin wrote: >> On Sun, 14 Feb 2010 10:00:39 -0800 (PST), dagmargoodboat(a)yahoo.com >> wrote: >> >>> On Feb 14, 11:19 am, o...(a)uakron.edu wrote: >>>> Can anyone suggest a fast AND gate at 1-2 Ghz. A friend of mine needs >>>> to measure a laser pulse duration on almost no budget, perhaps >>>> 200-300$. 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. >> > >But I found it hard to convince folks to do it that way. Nowadays many >seem almost hell-bent on doing it digitally. Maybe because the analog >world is too close to voodoo for younger engineers ;-) It's tough to do picosecond time measurements all-digitally, although it has been done. How about a semi-logarithmic pulse width detector: Input comparator steers a current blip into a capacitor. The cap has a resistor to ground and a comparator working against some small positive DC bias. An input pulse charges the cap, voltage proportional to pulse width. The comparator tells you that you had a pulse, and the comparator pulse width is a (nonlinear) reflection of the much faster input pulse width; measure that with a reasonable counter. That's pretty simple and doesn't need a pretrigger or reset or separate pulse-start detector. You could do the same thing with a constant-current discharge and a negative-swing catch diode and get a linear stretch, but the catcher should be temp compensated for best results. ---- | | in | | -------------- ------------------------------------ ________ / \__________ / \___________ / \_________ / / fast charge slow discharge / ------------- ___________________________________________ | | | comp output | _____________| |__ John
From: Joerg on 16 Feb 2010 14:36 John Larkin wrote: > On Tue, 16 Feb 2010 09:30:27 -0800, Joerg <invalid(a)invalid.invalid> > wrote: > >> John Larkin wrote: >>> 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. >>> >> But I found it hard to convince folks to do it that way. Nowadays many >> seem almost hell-bent on doing it digitally. Maybe because the analog >> world is too close to voodoo for younger engineers ;-) > > It's tough to do picosecond time measurements all-digitally, although > it has been done. > > How about a semi-logarithmic pulse width detector: > > Input comparator steers a current blip into a capacitor. The cap has a > resistor to ground and a comparator working against some small > positive DC bias. An input pulse charges the cap, voltage proportional > to pulse width. The comparator tells you that you had a pulse, and the > comparator pulse width is a (nonlinear) reflection of the much faster > input pulse width; measure that with a reasonable counter. > > That's pretty simple and doesn't need a pretrigger or reset or > separate pulse-start detector. > > You could do the same thing with a constant-current discharge and a > negative-swing catch diode and get a linear stretch, but the catcher > should be temp compensated for best results. > > > ---- > | | in > | | > -------------- ------------------------------------ > > ________ > / \__________ > / \___________ > / \_________ > / > / fast charge slow discharge > / > ------------- > > ___________________________________________ > | | > | comp output | > _____________| |__ > > Yes, a "time stretcher" like this could get it into the realms of regular speed digital counters. FPGA and such. However, since Steve wrote about 1-4Hz PRF I don't see anything wrong with the classic integrate and hold approach. You've got tons of time to read it out, issue a text message that a pulse has come, turn on the coffeemaker ... :-) I'd do this analog -> ADC. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: John Larkin on 16 Feb 2010 15:17 On Tue, 16 Feb 2010 11:36:06 -0800, Joerg <invalid(a)invalid.invalid> wrote: >John Larkin wrote: >> On Tue, 16 Feb 2010 09:30:27 -0800, Joerg <invalid(a)invalid.invalid> >> wrote: >> >>> John Larkin wrote: >>>> 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. >>>> >>> But I found it hard to convince folks to do it that way. Nowadays many >>> seem almost hell-bent on doing it digitally. Maybe because the analog >>> world is too close to voodoo for younger engineers ;-) >> >> It's tough to do picosecond time measurements all-digitally, although >> it has been done. >> >> How about a semi-logarithmic pulse width detector: >> >> Input comparator steers a current blip into a capacitor. The cap has a >> resistor to ground and a comparator working against some small >> positive DC bias. An input pulse charges the cap, voltage proportional >> to pulse width. The comparator tells you that you had a pulse, and the >> comparator pulse width is a (nonlinear) reflection of the much faster >> input pulse width; measure that with a reasonable counter. >> >> That's pretty simple and doesn't need a pretrigger or reset or >> separate pulse-start detector. >> >> You could do the same thing with a constant-current discharge and a >> negative-swing catch diode and get a linear stretch, but the catcher >> should be temp compensated for best results. >> >> >> ---- >> | | in >> | | >> -------------- ------------------------------------ >> >> ________ >> / \__________ >> / \___________ >> / \_________ >> / >> / fast charge slow discharge >> / >> ------------- >> >> ___________________________________________ >> | | >> | comp output | >> _____________| |__ >> >> > >Yes, a "time stretcher" like this could get it into the realms of >regular speed digital counters. FPGA and such. > >However, since Steve wrote about 1-4Hz PRF I don't see anything wrong >with the classic integrate and hold approach. You've got tons of time to >read it out, issue a text message that a pulse has come, turn on the >coffeemaker ... :-) > >I'd do this analog -> ADC. Sure. You'll need to trigger the ADC and discharge the ramp. That's all easy if there is a reasonable event pretrigger available. John
From: Joerg on 16 Feb 2010 15:42
John Larkin wrote: > On Tue, 16 Feb 2010 11:36:06 -0800, Joerg <invalid(a)invalid.invalid> > wrote: > >> John Larkin wrote: >>> On Tue, 16 Feb 2010 09:30:27 -0800, Joerg <invalid(a)invalid.invalid> >>> wrote: >>> >>>> John Larkin wrote: >>>>> 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. >>>>> >>>> But I found it hard to convince folks to do it that way. Nowadays many >>>> seem almost hell-bent on doing it digitally. Maybe because the analog >>>> world is too close to voodoo for younger engineers ;-) >>> It's tough to do picosecond time measurements all-digitally, although >>> it has been done. >>> >>> How about a semi-logarithmic pulse width detector: >>> >>> Input comparator steers a current blip into a capacitor. The cap has a >>> resistor to ground and a comparator working against some small >>> positive DC bias. An input pulse charges the cap, voltage proportional >>> to pulse width. The comparator tells you that you had a pulse, and the >>> comparator pulse width is a (nonlinear) reflection of the much faster >>> input pulse width; measure that with a reasonable counter. >>> >>> That's pretty simple and doesn't need a pretrigger or reset or >>> separate pulse-start detector. >>> >>> You could do the same thing with a constant-current discharge and a >>> negative-swing catch diode and get a linear stretch, but the catcher >>> should be temp compensated for best results. >>> >>> >>> ---- >>> | | in >>> | | >>> -------------- ------------------------------------ >>> >>> ________ >>> / \__________ >>> / \___________ >>> / \_________ >>> / >>> / fast charge slow discharge >>> / >>> ------------- >>> >>> ___________________________________________ >>> | | >>> | comp output | >>> _____________| |__ >>> >>> >> Yes, a "time stretcher" like this could get it into the realms of >> regular speed digital counters. FPGA and such. >> >> However, since Steve wrote about 1-4Hz PRF I don't see anything wrong >> with the classic integrate and hold approach. You've got tons of time to >> read it out, issue a text message that a pulse has come, turn on the >> coffeemaker ... :-) >> >> I'd do this analog -> ADC. > > Sure. You'll need to trigger the ADC and discharge the ramp. That's > all easy if there is a reasonable event pretrigger available. > Why does it need a pre-trigger event? Start two ramps when the leading edge of the pulse arrives. One stops integrating into the little cap when the short pulse is over. The other keeps integrating into another cap until a threshold is reach and that is then your "timer". Or just skip the whole timer thing and have the ADC triggered by the falling edge of the laser pulse and discharge the one cap if the caps don't need much tempco correction. Basically needs a simple delay circuit that makes sure the ADC has done its acquisition job before the cap is reset. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |