From: "Bill Hawkins" <[EMAIL PROTECTED]> Subject: RE: [time-nuts] Interfacing a 8dBm sine output of an OCXO toadigital logic standard Date: Fri, 16 Sep 2005 18:42:36 -0500 Message-ID: <[EMAIL PROTECTED]>
> Magnus Danielson wrote, in part, > > "I wonder if that chip isn't really a DLL after all. They usually are." > > When my brain parses DLL I get data linked library. > > Did you mean phase locked loop? No, I mean Delay Locked Loop. A Delay Locked Loop is a quite different animal than what we usually perceive as a PLL, but have similar behaviours. Wonderfull for CMOS implementation, but the drawback is the jitter. > How do you measure jitter? What instrument? I use a high BW undersampling scope with high resolution time base, such as a Tek CSA 803, CSA 8000 or Agilent 86100. You need to use a power-splitter to get a trigger signal (for all three you need a separate trigger) and the other to the sampling head but only after being delayed through a cable to compensate for the trigger delay in the scope as they are not compensated within, that is only done in real-time sampling scopes which just samples and store before the trigger kicks in. The delay-cable needs to be longer than the delay-time, so that one clearly can view the trigger point. This is necessary in order to establish the trigger jitter. Tek made a box called DL-11 which was a delay- line intended for this purpose, but I use a standard cable cut into a suitable delay. I can use the reading from the next rising edge directly, but I should really compensate it by taking the root of the squared value minus the squared trigger noise to get a more accurate measure. There are other scopes that can be used too. Notice that I use scopes to get the cycle-to-cycle jitter measure, which is not the same as a normal phase-noise analysis. You can take a phase-noise plot and convert it over, but it is so easy to measure it with a scope you have standing around in the lab anyway, so that is what I choose to use. Wouln't mine a real phase-noise system, but it really isn't needed. Cheers, Magnus _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
