[time-nuts] Frequency referenced temperature regulator

Charles P. Steinmetz charles_steinmetz at lavabit.com
Mon Nov 8 15:36:44 UTC 2010


Poul-Henning Kamp wrote:

 > But since I happen to have access to much more stable frequencies
 > than voltages, I thought of a different way:
 >
 > 1. Mount a X-tal-osc with really lousy tempco inside the enclosure.
 >
 > 2. Compare its output to a stable reference frequency.
 >
 > 3. Use the output of the phase comparator to drive the Peltier.
 >
 > It is basically a PLL where temperature is used as EFC...
 >
 > Has anybody tried that ?

Frequency comparison between two oscillators, one a low-tempco and 
the other a high-tempco, is used by Dallas in the new version of the 
infamous (to Time Nuts) DS1620 temperature sensor.  See the current 
datasheet and Dallas AN-105.  I assume neither is an XO, nor do they 
phase lock them.  Instead, they count the higher-frequency, 
low-tempco oscillator using the lower-frequency, high-tempco 
oscillator as a time base, then correct for nonlinearities.

Best regards,

Charles






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