[sdiy] Idea - Triangle wave DCO core

[David G Dixon]

> Couldn't we use a leaky integrator? The DC drift problem is 
> likely to occur over longer periods (seconds) and the lowest 
> frequency is going to be in the tenths of seconds, say. So 
> highpass the integrator to lose any DC. Or is that nonsense? 
> I've only ever done it in the digital domain.
> 
> The idea was to do the vast majority of the work in the 
> software and have almost no hardware. If I start adding 
> comparators and switches and such like, it loses its charm 
> and I might as well build a sensible VCO circuit.

How about a tri-square VCO with back-to-back zener reference, and simply use
the zener square wave through a fixed resistor to define the current
reference into a bipolar current DAC?  We're talking about two opamps, one
cap, three resistors, and two zeners (which exert no temperature effect, by
the way, no matter their voltage).  Do HF compensation in software.