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From: "John Jardine"
Subject: Re: 100Hz from 25.6kHz crystal.
Date: Tue, 3 Dec 2002 22:16:50 -0000
References: <5Q1H9.32847$zX3.email@example.com> <firstname.lastname@example.org> <email@example.com>
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John Fields wrote in message
> On Tue, 3 Dec 2002 16:05:03 -0000, "John Jardine"
> >Yes ... The watch crystals keep 'customer acceptable' good time.
> >Xtal wise, the watch manufacturers are limited in what they can choose to
> >use and this is set by the power required by the xtal oscillator circuit
> >the following binary divider chains needed to get down to 1HZ. This
> >in the 32768Hz compromise.
> >Compare this 32768Hz timekeeping, against that of the clock in your auto,
> >where the designers didn't have to worry about power consumption.
> >The vehicle clock will invariably be fitted with a higher frequency 4Mhz
> >xtal. This xtal is naturally much more stable over time and temperature
> >results in about 10X better timekeeping!.
> I've got the data sheets for an Epson C-2 type 32768Hz and an Epson
> CA-310 4MHz crystal in front of me and here are some interesting
> TYPE FREQ TOL TEMPCO AGING SHOCK
> C-2 20ppm -0.04ppm/°C² 5ppm/yr 5ppm
> CA-310 30ppm +/- 0.714ppm/°C 5ppm/yr 10ppm
> In the tempco column, the C-2 data is exactly as taken from their
> data sheet, while the CA-310 is represented as +/-50ppm over the
> range of -10 to 60°C. on their data sheet. I don't really
> understand the notation for the C-2 tempco and that's the only
> reference they make to it on the data sheet, but if it really _is_
> 0.04ppm, then it seems the C-2 is clearly a better crystal at
> 32768Hz than the CA-310 is at 4MHz! Here's Epson's URL for
> John Fields
> Professional circuit designer
That C-2 is one hell of a good xtal !. I'm staggered. I'll keep my eye
(Yes I agree about the tempco presentation but I can't see them really
moving away from a standard data format ).
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