Do you need the accuracy of the frequency standard? Why not just buy a
little 4MHz CMOS crystal oscillator?

If jitter and accuracy were important I'd either (hobby use) build a VXCO
with an 8MHz crystal referenced to 2MHz from the standard or (for a customer
design) buy an integrated 4MHz VXCO and reference it to 2MHz from the
standard. In either case I'd use the phase comparator from a 74HC4046 or an
exclusive OR gate. You'll be using a divide-by 5 which can be had from a
74HC390 if they're still available, and a divide-by 2 or 4, which can be had
from just about anything -- including the same 74HC390 if your hookup is a
little perverse. All the logic _could_ be done on a PAL, of course.

Come to think of it if absolute accuracy is important but jitter isn't you
can just use the oscillator from the '4046 as well, with the same division
scheme.

--------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com


"Mike W" wrote in message
...
I have a need to produce an accurate 4Mhz 50% dutycycle TTL squarewave
to use as a timebase.

I have a 10Mhz IQD frequency standard of suitable accuracy. How can I
divide this to produce the 50% duty cycle 4Mhz signal?. Is it even
possible with logic alone?. I can see how to mix with either 6Mhz or
14Mhz, but this then detracts from the required accuracy.

atb Mikw