There is no doubt that gallium-nitride (GaN) technology has clearly made a huge impact in the RF/microwave industry. In comparison to older technology, GaN offers various benefits that have already been discussed. Of course, when it comes to GaN, power amplifiers (PAs) are usually the first thing that comes to mind—and rightfully so.
But one company, Custom MMIC, decided to explore what else GaN could be used for beyond simply amplifiers. The end result of its efforts: GaN-based high-linearity mixers.
To demonstrate the capability of GaN-based mixers, Dr. Charles Trantanella, a chief scientist at Custom MMIC, delivered a presentation at EDI CON 2016 titled, “Reaching New Heights in Mixer Linearity with GaN MMIC Technology.” In it, Trantanella noted the three important properties of a mixer: in his own words, linearity, linearity, and everything else (conversion loss/gain, isolation, etc.). He stated that GaN offers the linearity performance “to boldly go where no passive mixer has gone before.”
Trantanella described the two main mixing element options when it comes to monolithic-microwave-integrated-circuit- (MMIC-) based mixers. The first is a two-terminal diode, while the second is a three-terminal field-effect transistor (FET). He explained how most GaN processes can support both of these types of mixers. Trantanella then went on to compare GaN with gallium-arsenide (GaAs) pseudomorphic-high-electron-mobility-transistor (pHEMT) technology, demonstrating that GaN can achieve a higher third-order intercept point (IP3)—at the expense of requiring a higher local-oscillator (LO) drive level.
Back in May, at IMS 2016, the company demonstrated a series of GaN mixers that achieved input IP3 levels in excess of +30 dBm. Three new mixers with even better performance have been developed since that time: an S-band GaN FET mixer, an X-band GaN diode mixer, and a Ku-band GaN FET mixer.
To sum up, Custom MMIC is showing that GaN-based mixers can now achieve input IP3 levels ranging from +35 to +40 dBm. While these mixers do have the drawback of requiring a higher LO drive level, the company maintains that this issue can be resolved by integrating an amplifier on the same MMIC die. With all of this being said, we shall see what the future has in store for GaN-based mixers.