Differential LC VCO regarding the inductor

[calculus_cuthbert]

Differential LC VCO

I had a question about differential LC VCO. The inductor used in the differential LC VCO is a differential inductor, so for a particular frequency if the equivalent inductance 2L ?

for eg. I need to design a differential LC VCO for 900 MHz and the value of inductance I am provided with is 4nH. When designing it, I am deigning a PMOS current source and NMOS cross coupled transistors. There are two inductors one for each leg. Would the value of the inductance be 2nH for each leg or 4nH for each leg?

 

[saro_k_82]

Re: Differential LC VCO

In the differential LC VCO, if you use an inductance of L for one leg, then the equivalent inductance of the tank is 2L.., if that is what you are asking for

 

[E-design]

Re: Differential LC VCO

Theoretically slightly more than 2L because of the mutual inductance in a optimum symmetrical layout..

 

[calculus_cuthbert]

Differential LC VCO

So then the frequency of oscillation would be 1/2pi(squroot(2LC) right?

And regarding the mutual inductance it also depends how they are coupled so the inductance could be more or less i.e +k or -k

 

[E-design]

Differential LC VCO

On chip layout is always to increase L per unit area