Symmetric loads in VCO...

[asuprash]

Could any one tell me how the VCO with symmetric loads accomplishes the following
thing

1) High dynamic supply noise rejection -> The maneatis paper says that this is
due to the suppression of first order terms..

I can see how symmetric loads achieve better linearity. If u superimpose
Id-VD(for active) and Id- Vgs(for diode connected) curves then the net characteristic is that of a symmetric load buffer

Can anyone explain how nonlinear effects contribute towards noise. If I have nonlinear loads how does this convert differential mode signals to common mode signals ?

Regards Prashanth

 

[nandu]

Let us look at an example. Applying differential voltage v to a diff-amp, we get currents gm(v/2) and gm(-v/2) in the two branches. This is the linear current. Apart from this there are other non-linear currents k1(v/2)^2 and k1(-v/2)^2, k2(v/2)^3 and k2(-v/2)^3 etc. These non-linear portions are unwanted currents and can be thought of as noise.

Added after 1 minutes:

You can now see that the even order non-linear components cancel out as they only contribute to common mode change.

Added after 10 minutes:

Differential circuits reject all common mode noise including power supply noise is also common mode since it affects both branches in the same way