From: "Stephan Sandenbergh" <[EMAIL PROTECTED]> Subject: Re: [time-nuts] Some results of PRS10 and Trimble Resolution Date: Wed, 28 Jun 2006 18:22:58 +0200 Message-ID: <[EMAIL PROTECTED]>
Stephan, > So, the only option is to go for a higher clock speed. What are your > experiences with the resulting EMI? Is it a problem? How do you combat it? You interpolate using analogue interpolators. Take a look into the HP5335A counter for instance. It happilly acheives 1 ns single-shot resolution but it counts at a mear 10 MHz clock. The analog interpolators of the HP5335A acts like pulse-stretchers and will make the pulse 200 times longer. It will see a pulse which is 100-200 ns long, but will convert it into a pulse which is 20-40 us long, which turns into 200 to 400 counts long in its 10 MHz clock. These interpolator counters is actually in normal TTL in the HP5335A, and is actually only 8-bit, so they will wrap-around, but the software will de-wrap it since there is no ambiguity in reality. The cost for the interpolators themselfs is not very high, not compared to all the fancy stuff around them anyway. It will cost some additional logic for error-pulse generation and also for the additional counters (you usually have one start and one stop counter). Another cost is the longer conversiontime. However, if you work on PPS clocks, then a conversion-time of 40 us is very quick anyway and not much of a problem. If you scale this design a little, getting 200 ps or 100 ps should be reachable without too much of an effort. Infact, I suspect that this is exactly what HP did in the Z3801. Their measurement FPGA was really not up to any magic in speeds. Soo, if you want to improve your measurement resolution only, it is simple. In a very similar fashion, you can actually do the revese, in order to compensate for the time error of a signal in your clock. However, thus designs you can buy canned if you don't want to DIY. A DAC working as a programable current source (preferably through a current mirror) and a cap with a buffer and comparator aught to do it. Cheers, Magnus _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
