Fri May 16 20:44:32 EDT 2014

1/3 DAC and 2/3 DAC_REF ?

Did I loose some notes?  Basically, use a Vcc -> R -> diode followed
by a buffer as REF voltage for a DAC.  Send DAC output to a summing
amp with 1R coming from REF and 2R coming from DAC.  Summing gain set
to 1/3 DAC, 2/3 DC (e.g. just a buffer).

This should give ballpark voltage levels.  As long as OSC/CONTROL
transistors are thermally coupled, digital comp can be used to
calibrate the pair.