[time-nuts] questions on uncompensated crystal oscillators
Ulrich Bangert
df6jb at ulrich-bangert.de
Wed Jul 5 15:50:31 UTC 2006
Hi Stan,
perhaps you can construct yourself something similar to this
http://www.kuhne-electronic.de/english/special.htm
Choose "Chrystal heater" from the menu on the left
Regards
Ulrich Bangert
> -----Ursprüngliche Nachricht-----
> Von: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Stan Searing
> Gesendet: Dienstag, 4. Juli 2006 18:53
> An: 'Discussion of precise time and frequency measurement'
> Betreff: [time-nuts] questions on uncompensated crystal oscillators
>
>
> Hello,
> Please excuse the fact that this is not what we all
> consider precise frequency. I am selecting crystals to use
> for a medium to high volume application.
> The basic criterion are:
> - used with a VLSI inverter based oscillator with
> 3.3 V supply, but somewhat high impedance output.
> - frequency: 27.000 MHz fundamental within 40 (or so) ppm over
> temperature including 7 to 10 years of aging.
> - HC49S case
> - no production line trimming
> - low cost
>
> After looking at the design issues, I wonder if some of you
> haven't faced similar designs and have some suggestions
> regarding the following issues:
>
> - Is there a free (or inexpensive) spice that works well
> simulating crystal oscillators?
> (I did see the submissions to this email list last September
> on LTSpice.)
> (I have tried using the SIMetrix Intro package,
> and it generally seems to produce good results,
> but I found it's awkward or impossible to measure
> frequency to lots of precision (taking an FFT helps),
> and some results regarding oscillator frequency
> shifts as a result of small delay changes in the
> inverter seemed questionable to me.)
>
> - Are there some good papers dealing with the practical aspects of:
> - transforming the Q limiting element of the design from
> a series R to a parallel R
> - Rs vs. ESR
> - exceeding the correlation drive level of a crystal
> - measuring the drive level & calculating the maximum drive level
> - negative R and oscillator startup margin
> - consumer video color subcarrier tolerance
>
> - Do you have any suggested suppliers for crystals with the
> following specifications:
> - HC49S
> - 27.000 MHz
> - 10 ppm tolerance
> - 10 ppm stability
> - 18 pF load
> - trim sensitivity less than 15 ppm/pF
> - 7 (or better yet 10) year aging less than 10 ppm
> - drive level up to 1 mW (may not need to be this high if
> the ESR is < 30 ohms or I better understand our maximum
> inverter output voltage)
>
> If someone is interested in providing comments on the app
> note I'm working on, that would also be appreciated.
>
> Thanks
> Stan Searing
>
>
>
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