is this model roughly correct? - power in ring oscillators

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svensl

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I was wondering about the power consumption of VCOs, i.e ring oscillators. Considering the acquisition range only we would expect the input the the VCO to change and thus the output frequency. Is it correct to assume that the power during acquisition bill be dynamic and can be expressed as P=Vdd²×C×fout_average?

Here, C would be the load of each cell, or rather the parasitic capacitance associated with a simple inverter cell and fout_average be the average output frequency of the VCO. I would also think that the above equation would have to multiplied by the number of stages in the ring oscillator.

Is it correct to use above equation for the power conumption of a VCO during acquisition?
 

Re: is this model roughly correct? - power in ring oscillato

in my opinion,
1. if ur ring oscillator is oscillated between Vdd and GND, then Pav=n*f*C*Vdd² is an estimation of the average power generating from rising pulse and falling pulse, cause each stage
P=(1/T)∫i(t)*v(t)dt =f*∫C*dv(t)/dt*v(t)dt =f*C*∫v(t)dv =f*C*v(t)²/2
and in every period, there are two change of v(t) , i.e. rising & falling, so
P=fCV², and for n stage it will be P=nfCV²
2. But, usually the real oscillator is not full swing, instead it will like a sine wave,
such that v(t)=vpk/2*cos(wt), and i(t) will be something like i(t)=ipk/2*cos(wt+Φ)
 

Re: is this model roughly correct? - power in ring oscillato

Thanks for your feedback Btrend. The VCO I have in mind would be output a square wave. Of course it will not be a full VSS-to-VDD swing but close to that. Thus P=nfCV²
would be approx corret, I suppose.

Thanks. I just needed some confirmation.
 

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