alt Hacker NewsThe digital part of TCXO is interesting. It must be some simple microncontroller with lookup table that steers the frequency back to nominal value. These days you really have computation in many basic components, from crystals to flash memories.
The digital part of TCXO is interesting. It must be some simple microncontroller with lookup table that steers the frequency back to nominal value. These days you really have computation in many basic components, from crystals to flash memories.
Yes, the typical way this works is that the lookup table is programmed during device calibration and that the microcontroller has a temperature sensor attached and uses a varicap to drive one of the two capacitors attached to the crystal (usually through a coupling capacitor to avoid loading up the circuit too much).
This is nice because it will help to keep the crystal on track but a lot depends on the time constants of the control circuit whether or not the Allan Deviation of the circuit as a whole is going to be acceptable across all applicable timescales.
As a domain this is both fascinating and far more complex than I had ever imagined it to be, but having spent the last couple of months researching this and building (small) prototypes I've learned enough to have holy respect for anything that doesn't have an atomic clock in it and that does better than 10^-7. That is a serious engineering challenge especially when you're on a tiny budget.
If you can use a GPS disciplined oscillator then that's one possible solution, but there to you may see short term deviations that are unacceptable even if the system is long term very precise.