Zero-if receiver mixers !!

[eng-a-hesham]

1- When designing a zero if receiver will one mixer be enough for my design .. or should i use two I&Q mixers?
2- if two, there should be a phase shift by 90 between the LO signals feeding them... what are the other design differences between them?
3- to avoid 2nd order distortion i will use differential ended mixer is that good or bad !!!

 

[BigBoss]

1-If you use two I/Q Mixers, it will be easy to seperate wanted and unwanted sidebands at the output.You can use a polyphase filter to discriminate them..
2-Yes, 90 degree phase shift is necessary to drive I/Q mixer combination..
3-Yes, differential structures have theoritically no even mode harmonics.

 

[eng-a-hesham]

2-are they identical or there should be some differences in design !!

 

[BigBoss]

2-are they identical or there should be some differences in design !!

They must be identical.

 

[mtwieg]

I also am trying to do a zero-IF homodyne setup. I was looking at active mixers from analog devices as a possibility, and some of them specify their IF range as working down to DC, but none of them really give any specific examples of using them for homodyne receivers.

For example, I was looking at the AD8343: https://www.analog.com/static/imported-files/data_sheets/AD8343.pdf

But I can't see a good way to get the signal off the differential (which are biased high) outputswithout AC coupling (which I can't do, need the thing to work all the way down to DC). Has anyone used active mixers like these for zero-IF receivers, or should I stick with doubly balanced mixers?

My frequency is low (8-50MHz), btw.

Also, if I use two doubly balanced mixers, it is okay if I use a two way power splitter to feed my RF into both of them directly? Or should I have some kind of buffer or attenuator pad between the splitter outputs and the mixer RF ports?