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Design >> RF Design >> Active Mixer Flicker Noise Corner
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Message started by aaron_do on Nov 28^th, 2007, 1:35am

Title: Active Mixer Flicker Noise Corner
Post by aaron_do on Nov 28^th, 2007, 1:35am

Hi all,

I'm designing an active mixer, and i found the flicker noise corner frequency to be over 10 MHz. This seems to unusually high. Isn't the corner frequency supposed to be closer to 1 MHz? Any thoughts on why or how i can reduce it? Also is it possible that the thermal noise is simply lower than normalresulting in a high corner?

thanks,
Aaron

Title: Re: Active Mixer Flicker Noise Corner
Post by ACWWong on Nov 28^th, 2007, 3:31am

the flicker noise corner is just where the 1/f noise meets the thermal noise of your circuit, so given a low thermal floor and excessive flicker noise, the corner could be very high. The opposite is true where very high levels of thermal noise would mean a very low (or even no) flicker corner.

In your case you might like to reduce the flicker noise contibutions due to the switching LO transistors. This is best achieved by faster slew drive (and more gate area unfortunately means more power....) to switch the transitors more effectively.

cheers
aw

Title: Re: Active Mixer Flicker Noise Corner
Post by RFICInDaHouse on Dec 1^st, 2007, 6:19pm

Hi Aaron,

You might initially want to examine the corner frequency of the switching transistors when biased at the balance point as well as for any transistors in your circuit. That can be easily done via AC analysis....

Depending on the frequency planning, i.e., Frf, FLO... the flicker noise of the transconductor stage (TS) might be significant. Using a large-area transconductor device helps but that trade-offs with the TS linearity at a constant bias current. You can, however, significantly reduce the flicker noise contribution of the switching transistors by:

1- Resonating the parasitic capacitance at the tail node (common-source node of the switching transistors) with a spiral at Flo.
2- reduce the overdrive voltage of the switching transistors by running a parallel DC current branch feeding the transconductor stage from the supply voltage. Consult Abidi's paper on noise analysis in active mixers.

-Ibrahim