Some very insightful engineers suggested many decades ago that applying a square-wave LO drive instead of a sine wave LO drive would improve the intermodulation performance of the mixer. Owing to remarkable innovations made in the design of ultra-wideband traveling wave amplifiers, it is now possible to drive the mixer LO with near-square wave signals. The bottom line is that the LO drive acts like an “ideal” switching function that opens and shorts the mixer diodes within a few picoseconds. By limiting the “intermittent” period when the mixer diodes are partially open and partially short, intermodulation distortion can be drastically reduced. For optimal results, Marki Microwave engineers have determined that square-wave LO drivers should be used with any triple balanced mixer family—especially with T3 mixers. When used with a T3 mixer, square-wave LO driving can yield an input third order intercept of +40 dBm with an LO drive around +23 to +25 dBm! When using single quad double balanced mixers such as those found in the ML1 mixer family, square-wave LO drivers are not required and the standard sine wave LO drive will produce optimal results.
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