What is a square-wave LO driver amplifier and when should I use it?
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!
For more information consult the T3 Mixers Video, T3 Mixers Presentation (video), T3 Mixers presentation (slides), or the T3 Mixers Primer.