What is the difference between Configuration A and Configuration B on mixers?

Configuration A vs. B does not reflect a different option that you need to order when you specify the part number, it is two different ways to use the same mixer. The reason that you would use it is to get the very best spurious performance out of the mixer. If you are just looking for low conversion loss and good bandwidth, then just use Configuration A and don’t worry about it. If you are obsessed with getting the lowest spurs, however, then it may be worth looking into Configuration B.

Many Marki mixers (currently all Microlithic and MMIC non-IQ mixers) are passive, double-balanced, diode ring based mixers. That means that they can be used as up or downconverters. It also means that the ports are totally interchangeable: the LO can be driven into any port that supports that frequency, and the conversion will take place. Configuration A and B just reflect the option to drive the LO into either of the high frequency ports.

It is useful to think of a double balanced mixer as having a filter at each port; the LO and RF ports have bandpass filters (from 3 to 20 GHz or 10 to 40 GHz, for example), while the IF port has a low pass filter (DC to 5 GHz or DC to 15 GHz in this example). Since the ports are interchangeable, and the LO and RF ports have the same frequency range, this means that the LO and RF ports can be swapped. Configuration A vs. Configuration B refer to these two ways to operate the mixer. Lets look at the typical double balanced mixer structure:

As you can see, the LO side and the RF side are not identical. One side uses a balun (in this case the LO), and the other case uses a magic-tee, where the IF comes from. For the mixer user, this is not set in stone. You can swap the LO and the RF, and the mixer will still work, but with different performance.

But how different? When would I use one vs. the other? Lets look at the MM1-0320H datasheet to decide. The first thing you notice is that in the A configuration, the conversion loss is better, but the B configuration requires less LO drive. This is because the one balun is less lossy than the other balun, so it can be used to reduce the conversion loss or lower the LO drive requirements, depending on which configuration is used. You will also see that the RF-IF isolation becomes the LO-IF isolation if the ports are switched, while the LO-RF isolation is the same either way.

On nonlinear specs is where the real benefit can be had, but it depends on the specific frequency and power plan of your conversion. The B configuration has slightly better IP3, but only at specific frequencies. Look at the 2IF x 1 LO spurious suppression:

If you are operating between 12 and 14 GHz, then configuration A is better. If you are operating between 14 and 16 GHz, then configuration B is better. The best way to determine which is best is to plug each mixer in and try it. Alternatively you can use the Marki PDK to compare the mixer spur levels, although we do not guarantee the accuracy of spur levels predicted at this time. Since these are physics-based models we expect them to be very good.

So in conclusion Configuration A vs. B simply gives system designers an extra degree of freedom when it comes to getting the absolution best nonlinear performance out of the mixer.