Bruce Griffiths skrev: > Hej Magnus > > Magnus Danielson wrote: >> Hej Bruce, >> >> Bruce Griffiths skrev: >> >>> Magnus >>> >>> Magnus Danielson wrote: >>> >>>> Bruce Griffiths skrev: >>>> >>>> >>>>> Magnus >>>>> >>>>> For examples of the use of crystals in filters for cleaning up the >>>>> output of a crystal oscillator look at the circuit schematics for some >>>>> of the early crystal frequency standards. >>>>> Crystal filters were used quite liberally in some of these to clean up >>>>> the outputs. >>>>> >>>>> >>>> It's used in the step-up chain of the SR620 for instance. The SR620 has >>>> a 10 MHz oscillator (TCXO or as in my case a Wenzel OCXO) which is >>>> stepped up to 90 MHz using a fairly ordinary odd-order stepup and >>>> filtering chain. The ECL logic counter frontend use this as coarse >>>> counter frequency. The analog interpolators is a bit interesting in a >>>> few peculiarities but nothing really exciting. >>>> >>>> >>>> >>> Except if you believe that they actually use a Z5U capacitor (specified >>> in the parts list) for the interpolator TDC ramp capacitor. >>> If so, this would make for some interesting linearity and dielectric >>> absorption compensation software. >>> >> The caps listed as Z5U in the part list is not the timing caps. C701 and >> C711 both being 100 pF NP0 is the timing caps. If you look careful you >> will see it referenced. A 7 us sample pulse will charge a polypropylen >> cap with the buffered value for a sligthly later performed 12 bit ADC >> conversion. >> >> > > The online version of the manual specifies both of these caps as Z5U > (see attachment). > This may be an error in this version of the manual, or perhaps early > versions used Z5U?? > 100pF NP0 surface mount caps have been available for decades.
My manual specifies NP0 for these. Maybe a hardware revision that occured between the manuals. >> Autocalibration will adjust the discharge current, measure the voltage >> bias and adjust the linearization data (65 bytes per channel). >> >> > Dielectric absorption and voltage dependence correction for Z5U caps > would be very challenging. I do not disagree with you on that, but we do not know how it actually works. I could lift the lid and try to identify what is really sitting in there. It could be that the online manual reflects the original mistake. >> Agree. Any temperature effects will occur with very flat slopes as the >> tuning is far away from the frequency of interest. >> >> A number of shunting LCRs can be used, infact a suitable crystal could >> be used to shunt into ground. >> >> > > Series tuned LC shunts are generally better as at resonance their ESR > can be much lower than that of a crystal, the signal level that they can > handle without damage is also much higher. > Although a single LC series tuned shunt wont provide large attenuation > one can always use one tuned to each significant harmonic per filter > section. It needs to be combined with a general low-pass filter of a few poles. Cheers, Magnus _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.