On Thu, September 7, 2017 10:56 am, Mark Sims wrote:

Could you send me a snip of what that looks like?  Or a link to the
schematic if you have it already.  I need to take 10MHz in and was going
to generate 24MHz with a PLL, but probably 20MHz will be acceptable, and I
think just a couple of gates would work a lot better from a space and
power layout perspective.

If I need 50/50 duty cycle I would need to double again to 40MHz and use a
flip-flop to divide by 2, right?  Does the XOR circuit still work OK with
a narrow duty cycle?

thanks,
Chris Caudle

Chris wrote:

Depending on your application and its tolerance for jitter/PN, you may
want to use a fast analog comparator to do the initial sine-square
conversion.  The difference in jitter/PN compared to a biased CMOS gate
can be 10-20dB over a wide range of tau/BW (even worse if the gate has a
Schmidt trigger input, which has WAY, WAY too much hysteresis for a
sine-square converter).  I recommend the TLV3501, LT1719, and LT1720 out
of extensive experience with them.  These comparators have just the
right amount of internal hysteresis for squaring a 10MHz sine wave, with
10MHz jitter around 10-15pSrms for jitter bandwidths from 10Hz-5MHz.

Of course, if your multiplier/divider chain has more jitter than a CMOS
squarer, it won't make much difference which squarer you use -- so be
careful with its design and construction.

Best regards,

Charles

I've used some LT1719s in a project to discipline a 100MHz OCXO using an
HMC1031. They work really well in squaring up the 10MHz sine from my Rb
reference.

Neil G4DBN

On 08/09/2017 23:15, Charles Steinmetz wrote:

On Fri, September 8, 2017 5:15 pm, Charles Steinmetz wrote:

I think there have been several discussions on squaring circuits, I was
more interested in the XOR doubler.  That seems like it might be pretty
simple to implement since I will have power supplies for CMOS gates easily
available.  I don't remember seeing discussions on that technique.

--
Chris Caudle

Hi

Quick and simple on the XOR doubler:

Buffer up your square wave. Output goes direct to one input of the XOR. Other
input goes through a filter to give you a phase shift. Low pass is one option. Band
pass is another option. Both benefit from being tunable. Net result is that you can get
the sub-harmonics down to about the -40 db level. Phase noise will floor out at whatever
the floor of the logic you use is. ( = it’s not magic)

Bob