[EMAIL PROTECTED] wrote: > 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. > > Said
Actually the interpolator in the PRS10 has 200 picosec resolution. However they have not provide a means of accurate autocalibration of the interpolator offset and gain. >> 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. > > Not exactly the point, the entire counter complexity and PCB area was reduced by using a single chip for the counters etc., and it was easy to incorporate an interpolator with sufficient resolution for the target market. One doesn't usually add a synchroniser with more than the required resolution even if it only costs a few dollars, if a device with adequate resolution can be obtained at very little added cost when its incorporated within the counter chip itself. Having decided to implement the counter in a CMOS chip, the jitter due to internal cross coupling and noise within the chip would have made it difficult to achieve a usable resolution much better than the 150ps actually achieved even if a cheap high resolution external interpolator were used. > 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 > Bruce _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
