nandy wrote on Jul 6th, 2007, 10:12am:I have an inverting amplifier with gain and delay modeled as -A/(1+s/w), where 'w' is the 3dB BW. Say I have 3 such amplifiers in a ring oscillator. So the VCO gives a signal which is delayed by 60 degrees (or T/6) by every amplifier in the loop (to get the total delay to 180 degrees or T/2). My argument is that even if you increase the gain of the amplifiers, the signal frequency which undergoes 60 degree shift musn't change as the magnitude transfer function doesnt affect phase transfer function, or in other words the 3dB BW is still the same.
...
Just to add to the above point, while simulating I only changed the gain without varying the delay. For example
-A/(1+s/w) becomes -2A/(1+s/w).
If you increase the gain you also increase the unity gain bandwidth of your amplifier, so, yes, it gets faster...
And the amplifiers in a VCO always clamp, so you cannot derive the oscillation frequency from the phase shift of the small-signal transfer function.
BOE