[time-nuts] Is a crystal likely to change frequency by 3% ?

Bob Camp kb8tq at n1k.org
Sat Sep 13 08:18:37 EDT 2014


In this era of “everything runs at GHz” it’s a bit tough to reach back to the sort of process used for watch IC’s.

The idea is to optimize for low power / low leakage. They make enough of them that an application specific process can be used. The divide side of the chip may have an Fmax of 60 KHz at full battery voltage. By the time the battery gets to 1/2 voltage, the Fmax may have dropped to 30 KHz. The boundary is never an exact thing. It’s a “probability of working” kind of limit. 

Lots of possibilities. 


On Sep 12, 2014, at 6:52 PM, Dr. David Kirkby (Kirkby Microwave Ltd) <drkirkby at kirkbymicrowave.co.uk> wrote:

> Dr David Kirkby
> Managing Director
> Kirkby Microwave Ltd
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> On 12 Sep 2014 12:18, "Bob Camp" <kb8tq at n1k.org> wrote:
>> Hi
> Hi,
>> If this is an RTC, it’s probably running off of a battery when the
> machine is powered down. It is far more likely that the oscillator is
> dropping out (stopping) rather than shifting frequency.
> Good point,  I never thought of that. I have however noticed that analogue
> quartz clocks slow as the battery goes flat. But maybe too they stop and
> start. It would make an interesting experiment to check it, but one would
> need some method of logging the time from the hands.  Conceptually that is
> not difficult,  but it needs more work than I want to do. One could do it
> with a video camera and a fair bit of work writing the software. Probably
> easier is logging battery voltage and current as that should show if it
> starts and stops.
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