DC-DC type converter- the low power

[whirl7wind77]

Which DC-DC converter is best for stepping down the voltage from 1.2 V - 0.8V/0.6 V ( depending on input_referred_mode, the output is a variable and can be either 0.8 or 0.6 ) ? [Assume that a reference voltage of 0.6V is provided.]
It should consume low power ( < 20 uW ).
Assuming that it is driving (1) analog circuit (2) digital circuit .

 

[whirl7wind77]

Please, Someone help me out here

 

[BradtheRad]

This volt range is near the turn-on thresholds for everyday diodes and transistors.

Then there is the low power requirement (20 uW).

These factors create a tough spec to work with.

It should be possible to devise a series voltage regulator around a transistor (maybe a germanium type)...
but this is a resistive drop method which will waste power.

Or you can obtain voltage regulation from a silicon diode (it's the same as a 0.6V zener)...
however you'll waste power that way too.