Its been so long since you started the post I've forgotten what the aim was, but your right there will be a V drop across the const current source, and that will affect the minimum o/p voltagem dont forget though if your using a darlington it will drop 1.2V itself, so your 2V becomes 0.8v, and you could always bodge this a little putting a diode in series with the o/p dropping it another 0.6V and protecting the transistor.
The ad654 looks like an interesting device, never used one of those.
Heres a link to a calc for the 4046 vco if you need another option, one benefit is it has a programmable minimum frequency:
https://www.changpuak.ch/electronics/calc_03.php
The ad654 looks like an interesting device, never used one of those.
Heres a link to a calc for the 4046 vco if you need another option, one benefit is it has a programmable minimum frequency:
https://www.changpuak.ch/electronics/calc_03.php