Hi Even back in the 1970’s we used computing counters to read the 32 KHz. You get 7 digits in about 10 ms these days. It will take you longer to power up the module and stabilize it than the frequency reading takes.
The semiconductor process for the watch chips has always been a bit odd. They never need anything faster than 32 KHz for a clock. They are after *very* low leakage. Back in the old days having it run at 1 V was considered strange. It’s pretty common today. They use the same tricks to dump an analog function into a digital process as the MCU people. It’s not a *great* analog sub system, but it’s good enough for the purpose. They may even calibrate the temperature and voltage when the set the frequency. That would let them get away with a *lot* of slop on those sub systems. If they digitize the temperature range from 0 to 50 C, that’s plenty for any normal environment the watch will see. A 5 bit ADC would be good enough for that task (with the proper full scale input). The same thing likely applies to the voltage. The circuit is unlikely to function below half voltage on the battery. Again a few bits of ADC will tell you everything you need to know to drive the table. I’d bet that they run a sigma delta and are quite happy with information at a “once a minute” sort of rate. There’s not a lot of “analog” stuff in that case. It would be pretty easy to dump onto the die. Bob > On Jun 30, 2015, at 4:42 PM, Andy <ai.egrps...@gmail.com> wrote: > > Measuring a 32kHz frequency to ~100 PPB accuracy takes some time, even for > ATE. Time is money. > > I didn't think the hardware to do the computations and the digital offset > was any problem. I thought the temperature and voltage sensors might be, > since they are analog. But you can integrate them into a good mixed > technology IC process. I just didn't think that was what they are using. > > Andy > _______________________________________________ > 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. _______________________________________________ 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.
