For next-generation broadband amplifier designs, many engineers are now looking at gallium-nitride (GaN) device technology as an option. Yet some debate still exists about whether GaN high-electron-mobility-transistor (HEMT) technology is a viable option compared to gallium-arsenide (GaAs) field-effect transistor (FET) and silicon laterally diffused metal-oxide semiconductor (LDMOS). In the application note titled, "AN-013: Broadband Performance of GaN HEMTs," Nitronex compares GaN HEMT to GaAs FET and silicon LDMOS technologies to show each one's advantages in broadband applications. It then provides a broadband GaN example to illustrate the results that can be expected from the company's current devices.
The 15-page note delves into broadband matching limitations like the Bode-Fano Limit and quarter-wave matching. As a general rule of thumb for typical broadband designs, 15 dB return loss is excellent while 10 dB is good and 6 dB is roughly as poor as can be tolerated. By keeping these rules in mind and matching return-loss plots, the engineer can make an approximation across a given bandwidth for a given number of quarter-wave matching sections. The paper also details broadband design methodology including an output model using load-pull impedances and synthesis using a matching network. It then compares GaN, GaAs, and LDMOS and concludes that GaN's high operating voltage and high power density allow it to enable higher-power wideband designs. This abilitytogether with GaN's inherent robustnesswill continue to push it into more applications.
Nitronex Corp., 2305 Presidential Dr., Durham, nC 27703; (919) 807-9100, Fax: (919) 807-9200, internet: www.nitronex.com.
