Re: [time-nuts] Phase Noise of 74AC gates
I've been following the discussion of the noise introduced by 74AC gates with some interest. In an attempt to achieve a clean transition, I've been using gates from http://potatosemi.com/ Lacking the test equip. to verify the results, I've been taking the claimed specs at face value. I must admit that by TN thread standards, my needs are quite modest, but I don't see why I should compromise based on need! Has anyone had a look at the output of these to see if they are an improvement over 74AC Potato also do a range of Clock Buffer/Fanout drivers (GHz+), but don't seem make any claims about isolation or crosstalk. Has anyone put these on the bench and measured real performance? 73, ian _ View photos of singles in your area! Browse profiles for FREE http://clk.atdmt.com/NMN/go/150855801/direct/01/ ___ 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] Phase Noise of 74AC gates
I wrote: “The input uses a LT1016 10ns comparator as the input stage that drives several CD74AC00E quad nand gates” and got this response. “This is a terrible design. The comparator will add considerable jitter. What were they thinking? Rick Karlquist N6RK“ While my post was to show that commercial designs can use 74AC chips as was being discussed and was not to comment on the use of the LT1016 comparator, here is another point of view. First, you have to consider what the design parameters of this distribution amplifier were. The unit I described could use an external input or use an internal OCXO with a panel mounted pot to adjust EFC. The internal OCXO is an average single oven unit that I’m sure isn’t that great so the unit probably wasn’t designed to NIST standards. To use a Rolls Royce where a Ford would serve the purpose wouldn’t make much sense so my uneducated guess is the LT1016 worked fine in this application. Second, the statement that a comparator design is terrible is generic and may not apply to the LT1016. On this list you can find the following info from others who have used the LT1016 comparator. New TAPR TADD kit in the works -- are you interested? http://www.febo.com/pipermail/time-nuts/2005-December/019773.html “Each input can be selected to drive either a 74AC14 Schmitt trigger (TTL level) or an LT1016 high-speed comparator (with trigger point adjustable from 0 to 5 volts). The LT1016 has less than 10ns delay, and initial tests show jitter that's not much worse than driving the 74AC14 directly; it's a good chip.” ___ 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] Phase Noise of 74AC gates - application
Hi We do indeed make some assumptions when talking about frequency distribution. If the need it to drive the standard input on a couple of conventional counters and an economy class signal generator, that's one end of the output spectrum. If I want to use the signal to drive one side of a high resolution heterodyne system that's another end of the output spectrum. If I'm driving it out of an OCXO that was cheap when it was brand new that's one end of the input spectrum. If I'm driving it with a hydrogen maser That's a pretty big space, even looking at two basic dimensions. There certainly are a number of other dimensions you could toss in. For a lot of people a hand full of logic gates and some coils will do a very nice job. For others anything short of a full discrete design just isn't going to cut it. Different problems will indeed tend towards different solutions. Bob On Feb 20, 2010, at 11:46 AM, Arthur Dent wrote: I wrote: “The input uses a LT1016 10ns comparator as the input stage that drives several CD74AC00E quad nand gates” and got this response. “This is a terrible design. The comparator will add considerable jitter. What were they thinking? Rick Karlquist N6RK“ While my post was to show that commercial designs can use 74AC chips as was being discussed and was not to comment on the use of the LT1016 comparator, here is another point of view. First, you have to consider what the design parameters of this distribution amplifier were. The unit I described could use an external input or use an internal OCXO with a panel mounted pot to adjust EFC. The internal OCXO is an average single oven unit that I’m sure isn’t that great so the unit probably wasn’t designed to NIST standards. To use a Rolls Royce where a Ford would serve the purpose wouldn’t make much sense so my uneducated guess is the LT1016 worked fine in this application. Second, the statement that a comparator design is terrible is generic and may not apply to the LT1016. On this list you can find the following info from others who have used the LT1016 comparator. New TAPR TADD kit in the works -- are you interested? http://www.febo.com/pipermail/time-nuts/2005-December/019773.html “Each input can be selected to drive either a 74AC14 Schmitt trigger (TTL level) or an LT1016 high-speed comparator (with trigger point adjustable from 0 to 5 volts). The LT1016 has less than 10ns delay, and initial tests show jitter that's not much worse than driving the 74AC14 directly; it's a good chip.” ___ 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] Phase Noise of 74AC gates
Hi All, I read Garry's email about using the 74AC04 as a distribution amplifier. Did I read it right, does Gary say you will get -178 dBc/Hz at 10 kHz offset??? Being one of only 3 or 4 companies in the world that manufactures distribution amplifiers that break the -170 dBc/Hz region at 10 kHz offset, in my experience any logic gate or Op amp will limit you to about -155 dBc/Hz at offsets of 10 kHz and beyond. I've tested many competitive units and very few people get below -155 dBc. I'm not about to say how we achieve -170 dBc/Hz phase noise, but we definitely don't use op amps or logic gates!! Regards Martyn ___ 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] Phase Noise of 74AC gates
I picked up a used 10 Mhz distribution amplifier made by an English company. The input uses a LT1016 10ns comparator as the input stage that drives several CD74AC00E quad nand gates. The output from each AC00 I.C. is fed through filters to recreate a pretty good sinewave. ___ 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] Phase Noise of 74AC gates
From: Martyn Smith mar...@ptsyst.com Subject: [time-nuts] Phase Noise of 74AC gates I'm not about to say how we achieve -170 dBc/Hz phase noise, but we definitely don't use op amps or logic gates!! Regards Martyn Is this an advertisement? I don't think anybody believes a logic gate provides state-of-the-art reference buffering. ___ 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] Phase Noise of 74AC gates
Martyn Smith wrote: Hi All, I read Garry's email about using the 74AC04 as a distribution amplifier. Did I read it right, does Gary say you will get -178 dBc/Hz at 10 kHz offset??? Being one of only 3 or 4 companies in the world that manufactures distribution amplifiers that break the -170 dBc/Hz region at 10 kHz offset, in my experience any logic gate or Op amp will limit you to about -155 dBc/Hz at offsets of 10 kHz and beyond. I've tested many competitive units and very few people get below -155 dBc. I'm not about to say how we achieve -170 dBc/Hz phase noise, but we definitely don't use op amps or logic gates!! Regards Martyn Actually the phase noise was supposedly -178dBc/Hz or lower for offsets of 100kHz or more. This is potentially possible if a high Q (1000?? for a 10MHz input ) tuned circuit suitable bandpass filter were used. Extrapolating the measured phase noise of a divider to that of an inverter doesn't predict the inverter noise accurately as the divider output includes noise due to aliasing of its wide band input noise etc. One actually has to measure it with an accurately calibrated phase noise measurement setup. Bruce ___ 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] Phase Noise of 74AC gates
Bruce Griffiths wrote: He's made similar comments before. It actually isnt that difficult to achieve an isolation amplifier phase noise floor below -170dBc/Hz if one is careful to use appropriate parts, design techniques, and the input signal level is high enough. The real problem is verifying that performance. The 10811 production engineers searched for a long time for a low noise buffer amplifier and settled on the ANZAC AMC-123. The data sheet refers to a patent that reads like a construction article. You can make your own if you can find an old 2N5109 transistor. Rick Karlquist N6RK ___ 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] Phase Noise of 74AC gates
Arthur Dent wrote: I picked up a used 10 Mhz distribution amplifier made by an English company. The input uses a LT1016 10ns comparator as the input stage that drives several CD74AC00E quad nand gates. The output from each AC00 I.C. is fed through filters to recreate a pretty good sinewave. This is a terrible design. The comparator will add considerable jitter. What were they thinking? Rick Karlquist N6RK ___ 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] Phase Noise of 74AC gates
Rick Karlquist wrote: Bruce Griffiths wrote: He's made similar comments before. It actually isnt that difficult to achieve an isolation amplifier phase noise floor below -170dBc/Hz if one is careful to use appropriate parts, design techniques, and the input signal level is high enough. The real problem is verifying that performance. The 10811 production engineers searched for a long time for a low noise buffer amplifier and settled on the ANZAC AMC-123. The data sheet refers to a patent that reads like a construction article. You can make your own if you can find an old 2N5109 transistor. Rick Karlquist N6RK The Tyco/MAcom version of the AMC-123 datsheet doesn't refer to a patent. Is a variant of a Norton CB transformer feedback amplifier? One would need to cascade a number of these to achieve a reverse isolation of 120dB. Whilst I dont have any 2N5109's, I do have several 2N5943's. Bruce ___ 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.
