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Design >> RF Design >> Buffer design for Passive differential mixer
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Message started by sandman on Aug 13^th, 2007, 4:24am

Title: Buffer design for Passive differential mixer
Post by sandman on Aug 13^th, 2007, 4:24am

Hi,

Would anyone have literature on the design of a buffer at the output of a passive double balanced mixer (with no DC voltage available at the output of the mixer as part of a zero-IF receiver) ? Any help would be appreciated.

Cheers!

Title: Re: Buffer design for Passive differential mixer
Post by aaron_do on Aug 13^th, 2007, 7:41am

I'm not sure about any papers, but one way to do it would be something like this...

----------output
__|
LO-----||----||__
| |
< |-----||-----input
Rlarge < |
< >
| > Rlarge
Vbb+Vth >
|
Vbb

where Vbb is the buffer biasing voltage and then you gotta do the whole double balancing and of course design the buffer. Note that you should be able to put Vbb and its Rlarge on the other side too.

Title: Re: Buffer design for Passive differential mixer
Post by sandman on Aug 14^th, 2007, 5:05am

Thanks aaron_do.

I think the one you've shown below is an LO buffer. I was looking for one that's used to interface the passive double balanced mixer with an off-chip measurement equipment. Would you know more abt it ?

Cheers !

Title: Re: Buffer design for Passive differential mixer
Post by aaron_do on Aug 14^th, 2007, 5:46pm

Hi,

i think you've misread me. Sorry for the confusion, that's supposed to be a switching transistor for your passive mixer. i.e you have to use 4 of those transistors in a double balanced mixer. The bias Vbb will go through the switching transistor and allow you to bias your buffer.

cheers,
Aaron