loose-electron wrote on Nov 18th, 2006, 11:44am:AW:
I have seen multi-tan structiures used in the differential pairs of Gilbert cell mixers to improve linearity a bit.
Care to comment on that? (Like I said, seen them, but not designed one using that architecture)
Jerry
PS - in total agreement on NMOS gain structure, and AC coupling into the mixer. Don't deal with DC coupling and offset control unless you have to.
Yes, the classic Gilbert paper "the Multi-tanh principle" explains it all very well...
Anyway, i have used them in MOS and bjt forms in gilbert cell style cells for modulator and mixers... because of the increased input capacitance & fast gm roll off outside of the flat (linearised) gm section, perhaps not the best method for linearising high frequency first downconversion mixer in a wireless receiver....
More suited for well defined signal excursions in a modulator of a wireless transmitter... extremely flat gm characteristic gives for very low distortion products ... pretty robust to corners, mismatch etc.
Used them extensively in gmC filters (triplet forms) for receiver channel filtering.
All in all I like the technique...
Used them extensively in gmC continuous-time filters (in triplet form) for receiver channel filtering.