Re: [time-nuts] HP5061B Peak to Valley Ratios
> We are having trouble getting beam current on our #2 HP5061B. Ion > current has gone down in a week from 10 to zero. It looks like the rf > chain is working normally. Both HV power supplies had to repaired. > Beam current is all the way up and which gives 2 on the meter. We are > preparing to do the Low Frequency Coil test mentioned on page 5-22 > section 5-175. > > I got this idea from that procedure. On our good #1 instrument we set > the beam current at 20 with normal lock. The middle coax J2 which > carries 12.631 mc to the harmonic generator was removed next. The > beam current instantly dropped to 2. We set the beam current with the > front panel control at 10 to 30 and all three settings dropped about > 10 to one when the cable was pulled. This ratio seems to be a good > indicator of beam tube quality. Other useful cues are the effect on the beam current when you turn the modulation off -- it should rise a bit -- and the stability of the meter needle in the beam-current position as an indicator of tube noise. In that regard, excess noise from A13CR1 could potentially be mistaken for noise in the tube itself. It could stand a bit more bypassing IMHO. > I don't see it in the manual, but the > fine five turn pot oscillator control works much better than the > course adjustment for setting peak beam current. It also works better > for setting the control voltage to zero. The push to turn course > frequency control slot has been chewed up by the previous owner. It's a good idea to remove that contraption altogether. You don't want anything poking into the 10811's trimmer access hole or otherwise touching it. Drill a hole in the panel that will let you reach the 10811's trimmer directly with an alignment tool. It will then be easy to follow the guidelines in the manual -- i.e., set the OCXO trimmer to the central peak with the pot at 250. The intent was probably to achieve a consistent operating point at a linear spot in the EFC curve, while discouraging technicians from setting the 5-turn pot near either extreme. By specifying a midscale setting for the pot, they were able to maintain a consistent damping factor between units while incidentally making it easier to return to the central peak after any temporary adjustments. The 10811-60109s are all labeled with a factory-selected resistor value for the same reason. Overkill, but that's how HP rolled. -- john, KE5FX Miles Design LLC ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] HP5061B Peak to Valley Ratios
We are having trouble getting beam current on our #2 HP5061B. Ion current has gone down in a week from 10 to zero. It looks like the rf chain is working normally. Both HV power supplies had to repaired. Beam current is all the way up and which gives 2 on the meter. We are preparing to do the Low Frequency Coil test mentioned on page 5-22 section 5-175. I got this idea from that procedure. On our good #1 instrument we set the beam current at 20 with normal lock. The middle coax J2 which carries 12.631 mc to the harmonic generator was removed next. The beam current instantly dropped to 2. We set the beam current with the front panel control at 10 to 30 and all three settings dropped about 10 to one when the cable was pulled. This ratio seems to be a good indicator of beam tube quality. I don't see it in the manual, but the fine five turn pot oscillator control works much better than the course adjustment for setting peak beam current. It also works better for setting the control voltage to zero. The push to turn course frequency control slot has been chewed up by the previous owner. We are planning to get an oscilloscope display of the main and secondary lobes similar to page 4-31 Figure 4-43. If it works we will post it. It should show both the dc and ac parts of the beam current as the 137 cps sweep goes from one extreme to the other. Will anyone having any experience with the Low Frequency Coil test kindly post on the subject? This is NOT the Zeeman frequency test. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS first LO need to be locked?
Hi > On Apr 1, 2017, at 11:18 AM, paul swed wrote: > > Thanks everyone but I am working on an austron 2201a so all the discussions > on modern methods won't help. Whats is interesting is indeed the 2201 down > converts to 80KHz and the does sample in an IQ fashion. Its all discreet > chips and such. If you have a free running VCO in the head end, then indeed you need to lock it to something. An unlocked VCO will not be close enough to frequency to do you any good. The 8660 may or may not be close enough in free run mode. It depends a lot on what standard you have in yours. > Easily traceable and logical. > I think I have what I asked for and am experimenting with active mixers and > IFs made of minicircuit gain stages. > I am using a commercial antenna with 34 db of gain. It says 50db I question > that. That is a very normal antenna gain spec and it was quite common in the era the device you have was designed. I run a number of GPS gizmos that need a 50 db antenna on them. They *might* work with a 40 db setup. They do not work with something in the 20 to 30 db range. If you watch for a while (as in 6 to 12 months) you can indeed get good old 50 db gain antennas on eBay pretty cheap. Bob > But lots of gain to a HP IAM 81008 active mixer low drive LO. Then a 40db > at least 75 MHz IF. (Pretty sure this is overkill.) > The LO is a HP 8660c for now. Locked to a TBolt. > Thats the reason for the question. I can shift the 8660 to the ausytron 10 > MHz. > Regards > Paul. > WB8TSL > > On Fri, Mar 31, 2017 at 7:47 PM, Bob kb8tq wrote: > >> Hi >> >> >> There are a lot of GPS chips that do an I/Q mix down to a low IF. It’s >> then (re) sampled from there. The “LO” in this case would down convert to >> the low IF …. >> >> Bob >> >>> On Mar 31, 2017, at 6:08 PM, Magnus Danielson < >> mag...@rubidium.dyndns.org> wrote: >>> >>> God natt Attila, >>> >>> On 03/31/2017 11:29 PM, Attila Kinali wrote: God kväll Magnus, On Fri, 31 Mar 2017 21:19:00 +0200 Magnus Danielson wrote: > Still fills the function of LO, as the sample and hold operates as a > mixer and the fold-down can be seen as an overtone mix followed by a > sampling of the mix product, so well, it's about the same thing. "Harmonic mixer" is the word you are looking for :-) >>> >>> Not necessarily. It could be a locked oscillator too. >>> Harmonic mixer is another way to go. >>> >>> Cheers, >>> Magnus >>> ___ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to https://www.febo.com/cgi-bin/ >> mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/ >> mailman/listinfo/time-nuts >> and follow the instructions there. >> > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] TAPR TICC boxed
Hi The whole delay difference thing does get into a “do you care?” sort of category. The testing process you are doing may well calibrate out (or ignore) an offset of this nature. This is quite true in a number of TimeNut sort of tests. Bob > On Apr 1, 2017, at 4:02 AM, Bruce Griffiths > wrote: > > The common mode propagation delay dispersion is also likely to be significant > unless one uses an SiGe ECL/CML comparator. > > Calibrating this or actually the differential dispersion between channels is > an interesting but not insoluble issue. > > Bruce > >> >>On 01 April 2017 at 18:49 Scott Stobbe wrote: >> >>Also interesting the LTC6752 is rail-rail input. Any rail-rail input opamp >>I've used ends up with an ugly bump in input offset voltage transitioning >>from the nmos or npn diff pair to the pmos or nmos. I'm not sure how good >>or bad a rail-rail comparator may behave when common-mode biased in that >>region. >> >>On Fri, Mar 31, 2017 at 11:22 PM Bruce Griffiths >> >>wrote: >> >>>Attempting sub nanosecond timing with an actual 1Mohm source is an >>>exercise in futility. There are very few cases where one would want >>> to >>>attempt precision timing measurements with such a high impedance >>> source. >>>The 1M pulldown on the TICC input is merely intended to maintain a >>> valid >>>logic input should the user leave that input disconnected. In actual >>> use >>>with PPS signals the source impedance is in most cases a few tens of >>> ohms. >>>If one wishes to have a 1Mohm input impedance for use with AC coupled >>>signals then a low noise FET input buffer preceding the comparator is >>>required. >>> >>>Protection diodes in this application not only need to have low >>> leakage, >>>they also need to turn on and off fast enough to be useful. >>> >>>The propagation delay dispersion (both vs common mode and vs >>> overdrive) >>>also need to be considered along with the comparator jitter. >>> >>>Bruce >>> >>>and overdrive (both vs overdrive and vs input common modeOn 01 April >>> 2017 >>>at 15:34 Scott Stobbe wrote: >>> >>>Fwiw, for a precision comparator you'll probably want a bipolar >>> front end >>>for a lower flicker corner and better offset stability over cmos. For >>>high-speeds the diffpair is going to be biased fairly rich for >>> bandwidth. >>>So you will more than likey have input bias currents of 100's of nA >>> to uA >>>on your comparator. Which is not great with a 1 megohm source. >>> >>>On Fri, Mar 31, 2017 at 9:08 PM Charles Steinmetz >>> >>>wrote: >>> >>>Mark wrote: >>> >>>I thought about using the clamp diodes as protection but was a bit >>>worried about power supply noise leaking through the diodes and >>> adding some >>>jitter to the input signals... >>> >>>It is a definite worry even with a low-noise, 50 ohm input, and a >>>potential disaster with a 1Mohm input. Common signal diodes (1N4148, >>>1N914, 1N916, 1N4448, etc.) are specified for 5-10nA of reverse >>> current. >>>Even a low-leakage signal diode (e.g., 1N3595) typically has several >>>hundred pA of leakage. Note that the concern isn't just power supply >>>noise -- the leakage current itself is quite noisy. >>> >>>For low-picoamp diodes at a decent price, I use either (1) the B-C >>> diode >>>of a small-signal BJT, or (2) the gate diode of a small-geometry >>> JFET. >>>A 2N5550 makes a good high-voltage, low-leakage diode with leakage >>>current of ~30pA. Small signal HF transistors like the MPSH10 and >>>2N5179 (and their SMD and PN variants) are good for ~5pA, while the >>> gate >>>diode of a PN4417A JFET (or SMD variant) has reverse leakage current >>> of >>>~1pA (achieving this in practice requires a very clean board and good >>>layout). >>> >>>I posted some actual leakage test results to Didier's site, which >>> can be >>>downloaded at >>>< >>> >>> >>> http://www.ko4bb.com/getsimple/index.php?id=download&file=03_App_Notes_-_Proceedings/Reverse_leakage_of_diode-connected_BJTs_and_FETs_measurement_results.pdf >>> >>> http://www.ko4bb.com/getsimple/index.php?id=download&file=03_App_Notes_-_Proceedings/Reverse_leakage_of_diode-connected_BJTs_and_FETs_measurement_results.pdf >>> >>>. >>>This document shows the connections I used to obtain the data. >>> >>>The TICC doesn't have the resolution for it to matter or justify a >>>HP5370 or better quality front end. I'll probably go with a fast >>>comparator to implement the variable threshold input. >>> >>>Properly applied, a fast comparator will have lower jitter than the >>> rest >>>
Re: [time-nuts] GPS first LO need to be locked?
Thanks everyone but I am working on an austron 2201a so all the discussions on modern methods won't help. Whats is interesting is indeed the 2201 down converts to 80KHz and the does sample in an IQ fashion. Its all discreet chips and such. Easily traceable and logical. I think I have what I asked for and am experimenting with active mixers and IFs made of minicircuit gain stages. I am using a commercial antenna with 34 db of gain. It says 50db I question that. But lots of gain to a HP IAM 81008 active mixer low drive LO. Then a 40db at least 75 MHz IF. (Pretty sure this is overkill.) The LO is a HP 8660c for now. Locked to a TBolt. Thats the reason for the question. I can shift the 8660 to the ausytron 10 MHz. Regards Paul. WB8TSL On Fri, Mar 31, 2017 at 7:47 PM, Bob kb8tq wrote: > Hi > > > There are a lot of GPS chips that do an I/Q mix down to a low IF. It’s > then (re) sampled from there. The “LO” in this case would down convert to > the low IF …. > > Bob > > > On Mar 31, 2017, at 6:08 PM, Magnus Danielson < > mag...@rubidium.dyndns.org> wrote: > > > > God natt Attila, > > > > On 03/31/2017 11:29 PM, Attila Kinali wrote: > >> God kväll Magnus, > >> > >> On Fri, 31 Mar 2017 21:19:00 +0200 > >> Magnus Danielson wrote: > >> > >>> Still fills the function of LO, as the sample and hold operates as a > >>> mixer and the fold-down can be seen as an overtone mix followed by a > >>> sampling of the mix product, so well, it's about the same thing. > >> > >> "Harmonic mixer" is the word you are looking for :-) > > > > Not necessarily. It could be a locked oscillator too. > > Harmonic mixer is another way to go. > > > > Cheers, > > Magnus > > ___ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > > and follow the instructions there. > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] TAPR TICC boxed
Hi There are low(fish) leakage / low capacitance / high speed transient suppressor diodes out there. The aren’t going to do anything good in a 1 megohm environment. They are quite useful in lower impedance circuits. Bob > On Apr 1, 2017, at 1:49 AM, Scott Stobbe wrote: > > Also interesting the LTC6752 is rail-rail input. Any rail-rail input opamp > I've used ends up with an ugly bump in input offset voltage transitioning > from the nmos or npn diff pair to the pmos or nmos. I'm not sure how good > or bad a rail-rail comparator may behave when common-mode biased in that > region. > > On Fri, Mar 31, 2017 at 11:22 PM Bruce Griffiths > wrote: > >> Attempting sub nanosecond timing with an actual 1Mohm source is an >> exercise in futility. There are very few cases where one would want to >> attempt precision timing measurements with such a high impedance source. >> The 1M pulldown on the TICC input is merely intended to maintain a valid >> logic input should the user leave that input disconnected. In actual use >> with PPS signals the source impedance is in most cases a few tens of ohms. >> If one wishes to have a 1Mohm input impedance for use with AC coupled >> signals then a low noise FET input buffer preceding the comparator is >> required. >> >> Protection diodes in this application not only need to have low leakage, >> they also need to turn on and off fast enough to be useful. >> >> The propagation delay dispersion (both vs common mode and vs overdrive) >> also need to be considered along with the comparator jitter. >> >> >> Bruce >> >> and overdrive (both vs overdrive and vs input common modeOn 01 April 2017 >> at 15:34 Scott Stobbe wrote: >> >> Fwiw, for a precision comparator you'll probably want a bipolar front end >> for a lower flicker corner and better offset stability over cmos. For >> high-speeds the diffpair is going to be biased fairly rich for bandwidth. >> So you will more than likey have input bias currents of 100's of nA to uA >> on your comparator. Which is not great with a 1 megohm source. >> >> On Fri, Mar 31, 2017 at 9:08 PM Charles Steinmetz >> wrote: >> >> Mark wrote: >> >> I thought about using the clamp diodes as protection but was a bit >> worried about power supply noise leaking through the diodes and adding some >> jitter to the input signals... >> >> It is a definite worry even with a low-noise, 50 ohm input, and a >> potential disaster with a 1Mohm input. Common signal diodes (1N4148, >> 1N914, 1N916, 1N4448, etc.) are specified for 5-10nA of reverse current. >> Even a low-leakage signal diode (e.g., 1N3595) typically has several >> hundred pA of leakage. Note that the concern isn't just power supply >> noise -- the leakage current itself is quite noisy. >> >> For low-picoamp diodes at a decent price, I use either (1) the B-C diode >> of a small-signal BJT, or (2) the gate diode of a small-geometry JFET. >> A 2N5550 makes a good high-voltage, low-leakage diode with leakage >> current of ~30pA. Small signal HF transistors like the MPSH10 and >> 2N5179 (and their SMD and PN variants) are good for ~5pA, while the gate >> diode of a PN4417A JFET (or SMD variant) has reverse leakage current of >> ~1pA (achieving this in practice requires a very clean board and good >> layout). >> >> I posted some actual leakage test results to Didier's site, which can be >> downloaded at >> < >> >> http://www.ko4bb.com/getsimple/index.php?id=download&file=03_App_Notes_-_Proceedings/Reverse_leakage_of_diode-connected_BJTs_and_FETs_measurement_results.pdf >> >> . >> This document shows the connections I used to obtain the data. >> >> The TICC doesn't have the resolution for it to matter or justify a >> HP5370 or better quality front end. I'll probably go with a fast >> comparator to implement the variable threshold input. >> >> Properly applied, a fast comparator will have lower jitter than the rest >> of the errors, and is an excellent choice. Bruce suggested the LTC6752, >> which is a great part if you need high toggle speeds (100s of MHz) or >> ultra-fast edges. But you don't need high toggle rates and may not need >> ultra-fast edges. Repeatability and stability are more important than >> raw speed in this application. The LT1719, LT1720, or TLV3501 may work >> just as well for your purpose, and they are significantly less fussy to >> apply. >> >> Note that the LTC6752 series is an improved replacement for the ADCMP60x >> series, which itself is an improved replacement for the MAX999. Of >> these three, the LTC6752 is the clear winner in my tests. If you do >> choose it (or similar), make sure you look at the transitions with >> something that will honestly show you any chatter at frequencies up to >> at least several GHz. It only takes a little transition chatter to >> knock the potential timing resolution of the ultra-fast comparator way >> down. Do make sure to test it with the slowest input edges you need it >> to handle. >> >> Best regards, >> >> Charles >> >>
Re: [time-nuts] TAPR TICC boxed
The common mode propagation delay dispersion is also likely to be significant unless one uses an SiGe ECL/CML comparator. Calibrating this or actually the differential dispersion between channels is an interesting but not insoluble issue. Bruce > > On 01 April 2017 at 18:49 Scott Stobbe wrote: > > Also interesting the LTC6752 is rail-rail input. Any rail-rail input opamp > I've used ends up with an ugly bump in input offset voltage transitioning > from the nmos or npn diff pair to the pmos or nmos. I'm not sure how good > or bad a rail-rail comparator may behave when common-mode biased in that > region. > > On Fri, Mar 31, 2017 at 11:22 PM Bruce Griffiths > > wrote: > > > > > > Attempting sub nanosecond timing with an actual 1Mohm source is an > > exercise in futility. There are very few cases where one would want > > to > > attempt precision timing measurements with such a high impedance > > source. > > The 1M pulldown on the TICC input is merely intended to maintain a > > valid > > logic input should the user leave that input disconnected. In > > actual use > > with PPS signals the source impedance is in most cases a few tens > > of ohms. > > If one wishes to have a 1Mohm input impedance for use with AC > > coupled > > signals then a low noise FET input buffer preceding the comparator > > is > > required. > > > > Protection diodes in this application not only need to have low > > leakage, > > they also need to turn on and off fast enough to be useful. > > > > The propagation delay dispersion (both vs common mode and vs > > overdrive) > > also need to be considered along with the comparator jitter. > > > > Bruce > > > > and overdrive (both vs overdrive and vs input common modeOn 01 > > April 2017 > > at 15:34 Scott Stobbe wrote: > > > > Fwiw, for a precision comparator you'll probably want a bipolar > > front end > > for a lower flicker corner and better offset stability over cmos. > > For > > high-speeds the diffpair is going to be biased fairly rich for > > bandwidth. > > So you will more than likey have input bias currents of 100's of nA > > to uA > > on your comparator. Which is not great with a 1 megohm source. > > > > On Fri, Mar 31, 2017 at 9:08 PM Charles Steinmetz > > > > wrote: > > > > Mark wrote: > > > > I thought about using the clamp diodes as protection but was a bit > > worried about power supply noise leaking through the diodes and > > adding some > > jitter to the input signals... > > > > It is a definite worry even with a low-noise, 50 ohm input, and a > > potential disaster with a 1Mohm input. Common signal diodes (1N4148, > > 1N914, 1N916, 1N4448, etc.) are specified for 5-10nA of reverse > > current. > > Even a low-leakage signal diode (e.g., 1N3595) typically has several > > hundred pA of leakage. Note that the concern isn't just power supply > > noise -- the leakage current itself is quite noisy. > > > > For low-picoamp diodes at a decent price, I use either (1) the B-C > > diode > > of a small-signal BJT, or (2) the gate diode of a small-geometry > > JFET. > > A 2N5550 makes a good high-voltage, low-leakage diode with leakage > > current of ~30pA. Small signal HF transistors like the MPSH10 and > > 2N5179 (and their SMD and PN variants) are good for ~5pA, while the > > gate > > diode of a PN4417A JFET (or SMD variant) has reverse leakage > > current of > > ~1pA (achieving this in practice requires a very clean board and > > good > > layout). > > > > I posted some actual leakage test results to Didier's site, which > > can be > > downloaded at > > < > > > > > > http://www.ko4bb.com/getsimple/index.php?id=download&file=03_App_Notes_-_Proceedings/Reverse_leakage_of_diode-connected_BJTs_and_FETs_measurement_results.pdf > > > > http://www.ko4bb.com/getsimple/index.php?id=download&file=03_App_Notes_-_Proceedings/Reverse_leakage_of_diode-connected_BJTs_and_FETs_measurement_results.pdf > > > > . > > This document shows the connections I used to obtain the data. > > > > The TICC doesn't have the resolution for it to matter or justify a > > HP5370 or better quality front end. I'll probably go with a fast > > comparator to implement the variable threshold input. > > > > Properly applied, a fast comparator will have lower jitter than the > > rest > > of the errors, and is an excellent choice. Bruce suggested the > > LTC6752, > > which is a great part if you need high toggle speeds (100s of MHz) > > or > > ultra-fast edges. But you don't need high toggle rates and may not
Re: [time-nuts] TAPR TICC boxed
Also interesting the LTC6752 is rail-rail input. Any rail-rail input opamp I've used ends up with an ugly bump in input offset voltage transitioning from the nmos or npn diff pair to the pmos or nmos. I'm not sure how good or bad a rail-rail comparator may behave when common-mode biased in that region. On Fri, Mar 31, 2017 at 11:22 PM Bruce Griffiths wrote: > Attempting sub nanosecond timing with an actual 1Mohm source is an > exercise in futility. There are very few cases where one would want to > attempt precision timing measurements with such a high impedance source. > The 1M pulldown on the TICC input is merely intended to maintain a valid > logic input should the user leave that input disconnected. In actual use > with PPS signals the source impedance is in most cases a few tens of ohms. > If one wishes to have a 1Mohm input impedance for use with AC coupled > signals then a low noise FET input buffer preceding the comparator is > required. > > Protection diodes in this application not only need to have low leakage, > they also need to turn on and off fast enough to be useful. > > The propagation delay dispersion (both vs common mode and vs overdrive) > also need to be considered along with the comparator jitter. > > > Bruce > > and overdrive (both vs overdrive and vs input common modeOn 01 April 2017 > at 15:34 Scott Stobbe wrote: > > Fwiw, for a precision comparator you'll probably want a bipolar front end > for a lower flicker corner and better offset stability over cmos. For > high-speeds the diffpair is going to be biased fairly rich for bandwidth. > So you will more than likey have input bias currents of 100's of nA to uA > on your comparator. Which is not great with a 1 megohm source. > > On Fri, Mar 31, 2017 at 9:08 PM Charles Steinmetz > wrote: > > Mark wrote: > > I thought about using the clamp diodes as protection but was a bit > worried about power supply noise leaking through the diodes and adding some > jitter to the input signals... > > It is a definite worry even with a low-noise, 50 ohm input, and a > potential disaster with a 1Mohm input. Common signal diodes (1N4148, > 1N914, 1N916, 1N4448, etc.) are specified for 5-10nA of reverse current. > Even a low-leakage signal diode (e.g., 1N3595) typically has several > hundred pA of leakage. Note that the concern isn't just power supply > noise -- the leakage current itself is quite noisy. > > For low-picoamp diodes at a decent price, I use either (1) the B-C diode > of a small-signal BJT, or (2) the gate diode of a small-geometry JFET. > A 2N5550 makes a good high-voltage, low-leakage diode with leakage > current of ~30pA. Small signal HF transistors like the MPSH10 and > 2N5179 (and their SMD and PN variants) are good for ~5pA, while the gate > diode of a PN4417A JFET (or SMD variant) has reverse leakage current of > ~1pA (achieving this in practice requires a very clean board and good > layout). > > I posted some actual leakage test results to Didier's site, which can be > downloaded at > < > > http://www.ko4bb.com/getsimple/index.php?id=download&file=03_App_Notes_-_Proceedings/Reverse_leakage_of_diode-connected_BJTs_and_FETs_measurement_results.pdf > > . > This document shows the connections I used to obtain the data. > > The TICC doesn't have the resolution for it to matter or justify a > HP5370 or better quality front end. I'll probably go with a fast > comparator to implement the variable threshold input. > > Properly applied, a fast comparator will have lower jitter than the rest > of the errors, and is an excellent choice. Bruce suggested the LTC6752, > which is a great part if you need high toggle speeds (100s of MHz) or > ultra-fast edges. But you don't need high toggle rates and may not need > ultra-fast edges. Repeatability and stability are more important than > raw speed in this application. The LT1719, LT1720, or TLV3501 may work > just as well for your purpose, and they are significantly less fussy to > apply. > > Note that the LTC6752 series is an improved replacement for the ADCMP60x > series, which itself is an improved replacement for the MAX999. Of > these three, the LTC6752 is the clear winner in my tests. If you do > choose it (or similar), make sure you look at the transitions with > something that will honestly show you any chatter at frequencies up to > at least several GHz. It only takes a little transition chatter to > knock the potential timing resolution of the ultra-fast comparator way > down. Do make sure to test it with the slowest input edges you need it > to handle. > > Best regards, > > Charles > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and foll
