polyphase network

Low-IF receiver, mixer+polyphase filter to reject image.

Between mixer output and polyphase filter, do we need a buffer?

For low power operation, a emitter follower buffer driver has very bad linearity. How to design the buffer?

Hi _RFIC_,

Yes it is necessaryto have buffer between polyphase network and source Also it is importan that you have a high impadance load. Emitter follower is bad solution it have a limitted dinamic range. Best solution is to put some low comsuption OPAMP and that you put it in +1 follower schematics. Than you can obtain controlled performances from audio poly-phase network.OP type dual AD8079 10mA (noise 2nV/SQRT Hz and AD 8137 3.6mA........

GL XTASA

Hi xtasa,
Thanks a lot. But I still have questions.
You mean the buffer is realized by an opamp connected as a follower? Can this method be applied to a single chip receiver? In IC design, is this a practical solution? 10mA is very close to the current consumption spec of the whole receiver chip, in low power design, what is the better solution?

Could you draw a sketch for your system that you consider, I can help you..

Thanks BigBoss, here is the sketch. In fact we are investigating the architecture of the Low-IF receiver. Two options: I/Q mixer + Polyphase + IF filter. Another is I/Q mixer + Complex Filter. Low power is the main concern. I have no idea which one is better: power consumption, noise, dynamic range, chip size ...

As shown in the pic, the block R is a PPF driver. What I am asking is the actual implementation of this block. How to make it low power and high dynamic range? I have two papers, both from ST. The first one use an VGA Amp and the other one is just a voltage follower (I really doubt its performance).

Anyone can help?

Hi _RFIC_,
Do you design the circuit in IC level?
If so,a differential amlipifier input stage usually can do this job.It consumes resonabel power.
Hope this helpful.

hanm