[time-nuts] ? phase comparison or other device
Dr Bruce Griffiths
bruce.griffiths at xtra.co.nz
Wed May 9 19:42:31 EDT 2007
Bill Janssen wrote:
> I thought that someone was designing a circuit that could be used to compare
> two oscillators.
> What happened to that project? I now have a HP 5370A so I have
> something, but
> I would like to make simultaneous measurements on three or four "precision"
> clocks.I am not qualified to design a "state of the art" device, so I am
> looking for others
> to do that.
> Bill K7NOM
> time-nuts mailing list
> time-nuts at febo.com
Ulrich and I have designed and Ulrich is currently testing a CPLD
implementation of the improved version of the HP K34-5991A linear phase
It includes programmable prescalers (1-256) so that frequency like 10MHz
and 5MHz for example can be compared. The maximum input frequency is
It has 2 quadrature phase outputs. The prescalers also allow the phase
detector gain to be adjusted. The phase detector has a triangular wave
characteristic with a period of 4 cycles of the input frequency to the
phase detector (ie at the built in prescaler output).
Preliminary results using a very crude kitchen table "breadboard"
indicate that instabilities of a few parts in 1E12 are easily seen
within an hour or so.
Sensitivity is likely to be much better than this but a 10X prescaler
was used on each 10MHz input.
Comparing 3 or 4 standards requires using a set of distribution
amplifiers plus a set of linear phase comparators to achieve the desired
This is more flexible than trying to anticipate exactly how many
channels a user may want, it also has less crosstalk than an
implementation with more than 2 input frequencies to a single board or CPLD.
With external prescalers the maximum input frequency can be extended to
100MHz or more.
More information about the time-nuts