[time-nuts] questions on uncompensated crystal oscillators

Ulrich Bangert df6jb at ulrich-bangert.de
Wed Jul 5 11:50:31 EDT 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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