gilbert vs. passive mixer in cmos

[estradasphere]

what are the main advantages and disadvantages of gilbert and passive mixers? could you please make a compasison (linearity, supply voltage etc.)? thanks.

 

[elbadry]

Generally, passive mixers would have higher linearity . However, higher noise figures and negative gain are major drawbacks. So, in general, it'd not be preferable to use a passive mixer as the 1st mixer in the Rx chain ( or as a direct down-conversion mixer ) or otherwise overall system noise figure would be degraded. It'd be more suitable for use where the signal is healthy.

Gilbert Cell mixer has lower linearity in general. However, it's possible to get reasonable gain from it. it requires higher supply voltages of course. Low voltage versions are usually pseudo-differential ( tail source is eliminated ).
However, it's very popular and well-stablished with tons of papers/references.

 

[estradasphere]

as far as i know one has to employ large input LO power to the switching quad of a passive mixer to switch them on and off. this seems to cause high nonlinearity at the mixer output. did anyone face similar problems, is there a solution to overcome this?

 

[Circuit_seller]

Hi

Another advantage of gilbert cell over passive mixer is Bandwidth. Active mixers potentially have wider BW than others.

Regards

 

[victoriya]

an important advantage of passive mixer is its too low flicker noise. the flicker noise has unfavorable effects on baseband specially in zero-if applications where the if frequency is lower than the 1/f noise corner frequency.also the passive one has no power dissipation but if we consider it wholly the lo buffers has some power dissipation that is comparable with the gilbert mixer power dissipation. passive mixers need larger lo drive amplitude than the active(in this case gilbert) one. the gilbert mixer has better port to port isolation than passive mixers. this is so important because for example lo to if feedthrough can desensitize the baseband function.also the lo to rf feedthrough can radiates to antenna.

 

[Milad-D]

Interestingly, the passive mixer has a very special ability. This goes back to n-pATH FILTERS. IF you have a low-pass impedance at baseband node, At the rf node you will see a band pass impedance.