I was looking for a way I could plot the output frequency of a ring oscillator versus an input tuning voltage. I did not find anything easy and fast in the literature but I think PSS is the key for the more formal methods. PSS = Periodic Steady State. I will look at this later most likely for other applications. To see what I did do for a useful plot of F versus Vtuning see below.
The current consumption of the ring oscillator is more or less proportional to frequency and thus can be used as a plot of frequency versus voltage. The tuning voltage goes into a gate of an mosfet. You can see most of the tuning action occurs just below the Vt of that mosfet since the fet is being used with such low currents.
- 500 kHz @ 69 nAmp
- 200 kHz @ 31 nAmp
Assuming current consumption directly proportional to frequency gives 0.000014 nAmp / Hertz. This checks out.