1/f noise up-conversion issue [help]

[trashbox]

Hi guys,
When designing the ring osc in PLL, I read a paper who mentions that:
making the waveform be as symmetric as possible will help reduce the 1/f noise up-conversion.

How to understand this topic? would you pls give me any hints?
Thank very much.

 

[Hooda]

symmetric as possible ----> assymetry in waveform could lead to dc offset in the oscillator output
at mixer
a)this could make feedthrough of the flicker noise of the transconductor stage to the output
b)VCO output that commutate the switching of the mixer as more symmetric as less flicker noise contribution to the output

more simpler answer :most of Mixers are differential so symmetry is a key in differential circuits otherwise mismatch and direct feedthrough of the 1/f noise to the mixer o/p
hope this help

Added after 3 minutes:

if my answer not clear check the famous paper of Asad Abidi & Homan Darabi in "Flicker noise in mixers , Physical model "
you can find it eazy on internet , no need to upload it .
Regards;

 

[hrkhari]

A symmetry differential architecture can minimize flicker noise up-conversion, as unbalanced oscillator results in 2ω common mode oscillation, which is mixed with fundametal oscillator frequency, resulting in phase noise at the oscillator frequency. Hope this helps....

Rgds[/list]