Dr Bruce Griffiths wrote: > Didier Juges wrote: > >> Dr Bruce Griffiths wrote: >> >> >>> Didier Juges wrote: >>> >>> >>> >>>> Dr Bruce Griffiths wrote: >>>> >>>> >>>> >>>> >>>>> In principle this measurement could be made with a time interval counter: >>>>> PPS -> START >>>>> delayed 10KHz -> STOP >>>>> >>>>> Vary the delay and watch the jitter jump when the leading edge of the >>>>> PPS signal occurs during the 10KHz burst which was phase coherent with >>>>> the previous PPS pulse. >>>>> The only problem is finding a suitable variable delay device with >>>>> sufficiently low (<=1ns??) jitter. >>>>> >>>>> >>>>> >>>>> >>>>> >>>>> >>>> The delay device can be triggered by the 1 PPS, then will drive the ARM >>>> input of the counter, so as long as the delay device's jitter is less >>>> than the 10 kHz period, if we adjust the delay to 0.99985 second >>>> (between the last 2 periods of 10 kHz before the 1 PPS), then the TI >>>> counter will START on the last 10 kHz pulse before the pps, and STOP on >>>> the 1 PPS. >>>> Tek has some time delay generators in the TM-500 and 7000 plug-in >>>> series. I knew one day I would need one of those, I now know why :-) >>>> >>>> Didier >>>> >>>> >>>> _______________________________________________ >>>> time-nuts mailing list >>>> time-nuts@febo.com >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> >>>> >>>> >>>> >>>> >>> Since the HP5370 arm input is high impedance(1 Megohm) and its input >>> range lies betwen -2V and +2V its desirable to drive it from a back >>> terminated source with an amplitude of 2V or less to avoid overdriving >>> (the comparators are better behaved if the input signal remains within >>> the specified range) the input and ensure that the pulse at the ARM is >>> relatively clean and reflection free. A suitable buffer can be built >>> using 3 74AC04 inverters as depicted below: The 74AC04 inverters load >>> currents are well within the specified limits even if the buffer output >>> is shorted to ground. Thus the driver should have a long service life. >>> ARM driver >>> >>> >>> Bruce >>> ________________ >>> >>> >> The trigger levels on the 5370 are strange. The normal inputs have >> trigger levels that can be adjusted between -1.5 and +0.6 V or something >> like that. >> I am not sure where that is coming from. >> For the ARM input, if someone is going to drive it with long coax >> cables, the best would be a 50 ohm termination right at the instrument's >> input. >> The schematic did not make it, but I believe I understand what you mean: >> 3 gates with common input, each output has a 150 ohm series resistor and >> the outputs (far end of the resistors) are tied together, to provide a >> good 50 ohm drive to the cable. A series capacitor would probably be >> recommended to center the signal around ground (assuming it's 50% duty >> cycle). >> >> Didier >> _______________________________________________ >> time-nuts mailing list >> time-nuts@febo.com >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> >> >> > Didier > > The trigger level limits are derived from the input amplifier and > trigger circuit characteristics for the START and STOP inputs. > > The ARM input feeds directly (via a 1X FET buffer) to an ECL comparator > ((MC1651). > This comparator has an NPN longtailed pair input stage the > characteristics of which determines the usable input signal range. > Driving an amplifier or comparator input stage into saturation degrades > its timing characteristics somewhat. > > Bruce > > I understand that the levels are what they are due to the use of ECL logic, I was wondering from a user's perspective, was the 5370 intended to be used only with ECL logic circuits? I am surprised that they did not design a trigger range that included at least the "old" normal TTL levels 0 to 5V. TTL was very common when the 5370 was designed (it uses a lot of it internally, not so much in the timing circuits though)
Didier _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts