In a message dated 4/29/2007 16:40:44 Pacific Daylight Time, [EMAIL PROTECTED] writes:
>Try studying a little history, its been possible to achieve 25 >picosecond accuracy and resolution for over 30 years. >Such resolution is routine in Nuclear instrumentation. State of the art >nuclear instrumentation strives for subpicosecond resolution and accuracy. Hi Bruce, never doubted that it was technically possible to get this type of resolution/accuracy. I myself mentioned the 15 year old Wavecrest units achieve 800 femtoseconds resolution, single shot. The point was A) that type of resolution is not needed in a TI unit where the intrinsic pk to pk noise on the TI intervall is >100ns (more than three orders of magnitude above 100ps). B) that implementing it with that kind of resolution and getting a meaningful accuracy (say 250ps 6-sigma accuracy) is not easy while at the same time keeping the cost to "Three-four transistors and a handfull of caps and resistors." In mass production a handfull of caps and transistors/resistors cost less than $0.20. Again if it was that easy and cheap, HP would have done it in their 5334A's or even the 5335A for example which have 1 or 2ns resolution I believe SRS would have given us 100ps resolution on their PRS10 time-stamping input - what better place to do it than in a highly-accurate frequency reference. >The reason that the 53132A doesn't have resolution and accuracy better >resolution than 150ps, is that a design choice was made to implement it >all (counters plus interpolators) in a CMOS chip using the delay of a >CMOS inverter to set the resolution. This reduces the cost and >complexity significantly and allows faster cycling of the interpolator Bingo. QED. People choose not to do 100ps resolution in their products because of cost and complexity, even in >$3K products such as the 53132A - let alone in $750 products. C) I don't believe the Z3801A has 100ps single shot resolution and accuracy (for resolution doesn't do anything without accuracy) until someone will prove it to me. And even then it would be wasted resolution since the GPS 1PPS source noise will totally swamp out any benefit a 100ps resolution would give. On top of that, all GPSDO's do heavy averaging of this time intervall, with a PRS10 typically doing 7 hours or more of averaging. 100ps per-second resolution in that kind of averaging window is meaningless, since the OCXO cannot perform that well - it would require 4E-015 stability in a 7 hour window. Not possible without a high-end Cs/Rb/H source. Certainly not possible with the 10811 that's inside a Z3801A. Still hoping someone knows the TI hardware used in the Z3801A's... bye, Said ************************************** See what's free at http://www.aol.com. _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts