a question about the amplitude of vco
I am confused that some pappers say the maximum output of the vco is 2VDD.
the vco ,e.g with nmos or complementary differential-couple LC oscillator operated in voltage-limitted region , the maximum differential output of it is from -VDD to + VDD,thus the maximum differential output amplitude is VDD rather than 2VDD,what 's wrong with my result?
thanks a lot.
Well, you said it yourself. If the differential voltage goes from -V to +V, then the peak to peak voltage across a load will be 2 V. It is a little clearer if you add a balun to the output pins and convert to a single ended output, like a lot of wireless chips do.
Another way to get a higher voltage than the supply is to use some sort of tank circuit. The transistor only conducts for a short portion of the sine wave, and the L-C or other tank circuit "rings" at a high voltage.
thank you for your replying,biff44.
i found the error of my thought.Indeed,the maximum single-end output range is from 0 to 2VDD rather than 0 to VDD.
in my previous calculation ,i use the drain current of the differential-coupled pair multiply Rp to calculate the output voltage.
The current is comprise of quiescent current and transient current and the Rp is short to the quiescent current.