[SOLVED] Ring Oscillator with dominant cap

[patricky]

Hi,
If we have a ring oscillator composed of 3 inverters in a loop, but in one of the nodes we stick a reasonable size cap (10-100 times larger than usual gate capacitance), how will this effect the transient? Will the oscillator now run at ~ tinv*(Cin/Cg) instead of 3*tinv?
THanks.

 

[Milad-D]

It depends. Actually as you increase the loading capacitor, the oscillation frequency will decrease as you suggested. But interestingly, as you increase the loading capacitor, you producing a dominant pole which is stabilize the loop.

Therefore, if the capacitor is very large, the chance that you don't get an oscillation is very high unless you increase the loop gain by adding more stages.