We were talking about TCXOs. One measures temperature and drives a varicap through some nonlinear transfer function to get minumum net TC.
We don't want a digital design (ADC, lookup table or polynomial, DAC) because that might add phase noise. I guess you could use a static polynomial with the equivalent of nonvolatile DPOTS as the coefficients.
This occurred to me, not as anything practical maybe but as an interesting architecture.
It's sort of a thermometer-code ADC, but each comparator incrementally adds + or - one increment to the output.
As the temperature increases, we jog the output up or down one increment at a time.
The sequence of switch settings become a delta-sigma code to make the output.
The comparators could be sort of linear, not step outputs, to kind of interpolate a bit. Some flash ADCs did something like that, soft comparators.