Didier Juges wrote: > Bruce, > > Thanks for the reminder. That was my intention. I was planning to use a > 74HC74, and whatever dividers I can get my hands on. I am not looking > forward to daisy chain seven 7490s, so I will probably try something > else. With the D flip-flop, the dividers don't really matter, as long as > the delay is below 100nS. > I need to find the best way to go from the 10 MHz sinewave to the > divider, probably through an LM119 comparator with modest hysteresis. > The need for a low jitter divider is the same for the GPS disciplined > oscillator, so I should be able to reuse the divider for my frequency > standard. > > Thanks > > Didier > > Dr Bruce Griffiths wrote: > >> Didier >> >> If you are going to use a PPS divider to divide the oscillator frequency >> down to 1Hz, you will need to measure the inherent jitter of the divider >> to ensure that it doesn't degrade the measurement resolution. It may be >> necessary to resynchronise the divided output using a fast D flipflop to >> reduce the inherent divider jitter to less than the 20ps resolution of >> the 5370. >> >> Bruce >> >> > > > _______________________________________________ > time-nuts mailing list > time-nuts@febo.com > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > Didier
You can use a set of cascaded 74HC4017 Johnson counters to divide 10MHz down to 1 Hz as long as you use a 2 stage (74AC74??) resynchroniser to reduce the PPS jitter and reduce the effective propagation delay. With an extra gate or 2 this will even work for a 5MHz input. It is not necessary to have a 50% duty cycle signal to drive the HP5370 allowing more flexibility in the divider design. I have designed a circuit using 74HC4017's to do this with a 5MHz input. If you want I can send it to you. Satisfactory drivers for the HP5370 START and STOP inputs can also be built by using a 270 ohm resistor in series with an ACMOS gate or flipflop output. This produces a swing of around 800mV into a 50 ohm load which is more than sufficient. The load current ratings of the driver device are not exceeded even if the load is shorted. Bruce _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
