# [time-nuts] Frequency Comparator Ideas needed.

David C. Partridge david.partridge at perdrix.co.uk
Wed Aug 10 14:29:03 UTC 2011

```OK, you've described what you think of as the solution to your problem, but what actually is your problem?  In other words what is your objective.

Are we looking at something like a phased array radar here?  If so there is probably quite a bit of stuff out there that isn't classifed by now as the technology is no longer bledding edge military only stuff.

Dave
-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Dan Kemppainen
Sent: 10 August 2011 15:20
To: time-nuts at febo.com
Subject: [time-nuts] Frequency Comparator Ideas needed.

Hi All,

Been lurking here for a while, some neat traffic going around. I'm thinking this may be a question for this list...

I'm wondering if there are any ways to compare two frequencies and tell if one is lower or higher than the other, at a very high rate of speed with a digital output. I would like to know how each cycle of the signals compare in terms of frequency, basically is one higher than the other or not. Ideally this returned signal would be a digital logic signal (high or low) and be glitch free.

Basically I have a relatively high frequency signal, say around 50Mhz
+/- 150Khz that I would like to compare to a reference frequency
(50Mhz) on a cycle by cycle basis. The two signals are not locked together, and the signals should never be exactly the same with the exception of transitions of the input signal across the reference frequency. I'd like to know when the transition happens to within a few tens of nanoseconds if possible.

I've currently been looking at digital Phase/Frequency type detectors, and am considering building a discrete unit based on high speed 74AUP or ECL/PECL type logic.

Just wondering if I'm missing something obvious, that you guys may know about!

Thanks!
Dan Kemppainen

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