Amplifier Satisfies Demanding Infrastructure Applications

July 23, 2009
much debate exists about whether galliumnitride (GaN) devices can replace or even outperform devices based on other technologies, such as laterally diffused metal oxide semiconductor (LDMOS) devices. In an application note titled, "GaN For ...

much debate exists about whether galliumnitride (GaN) devices can replace or even outperform devices based on other technologies, such as laterally diffused metal oxide semiconductor (LDMOS) devices. In an application note titled, "GaN For LDMOS Users," Nitronex Corp. compares LDMOS against GaN for RF power-amplifier (PA) stages. The 15-page document evaluates equivalent outputpower devices to illustrate both the differences and similarities between LDMOS and GaN.

The input and output impedances of GaN devices can be estimated and modeled the same way as LDMOS and gallium-arsenide (GaAs) ferroelectric transistors (FETs). For power devices, however, small-signal stability can be a difficult problem. Vertical metal-oxide semiconductor (VMOS), LDMOS, and GaAs FETs as well as GaN high-electron mobility transistors (HEMTs) have large amounts of gain at low frequencies and similar challenges from a stabilization standpoint. When designing amplifiers in both small- and large-signal scenarios, careful attention must therefore be paid to stability.

In terms of capacitance-voltage characteristics, GaN HEMTs have some of the same capacitance behaviors as other FET devices. Compared to the other technologies, however, GaN's higher power density results in smaller devices and thus smaller absolute capacitance values. Output capacitance plays a significant role in determining the bandwidth limitations. To compare various devices, it is best to compare capacitance per watt of output power.

From a biasing perspective, GaN has two special requirements: The gate and drain must be sequenced during startup and shutdown and the designer must accommodate current flow both into and out of the gate. Otherwise, bias network topology and general design practices are the same for LDMOS and GaN devices. Compared to silicon LDMOS devices, the paper asserts that GaN HEMT linearity is less sensitive to changes in the bias point.

The note advises GaN users to possibly operate their devices above P1dB for continuouswave (CW) applications. For the firm's devices to be used past the 1-dB compression point, three criteria need to be considered: junction temperature, gate current, and device variation over process and temperature. The paper ends with a discussion of insertion-phase variation, which impacts how multiple devices are combined. Although GaN HEMT devices are very different from LDMOS devices, this application note asserts that they can be designed and treated just like LDMOS FETs.

Nitronex Corp., 2305 Presidential Dr., Durham, NC 27703; (919) 807-9100, Fax: (919) 807-9200, Internet: www.nitronex.com.

About the Author

Nancy Friedrich | RF Product Marketing Manager for Aerospace Defense, Keysight Technologies

Nancy Friedrich is RF Product Marketing Manager for Aerospace Defense at Keysight Technologies. Nancy Friedrich started a career in engineering media about two decades ago with a stint editing copy and writing news for Electronic Design. A few years later, she began writing full time as technology editor at Wireless Systems Design. In 2005, Nancy was named editor-in-chief of Microwaves & RF, a position she held (along with other positions as group content head) until 2018. Nancy then moved to a position at UBM, where she was editor-in-chief of Design News and content director for tradeshows including DesignCon, ESC, and the Smart Manufacturing shows.

Sponsored Recommendations

Forging the Future of Defense

Oct. 11, 2024
Raytheon’s Advanced Technology team incubates capabilities that fuel the future of defense. Together with leading research and development organizations, def...

Phase-Matched Cable Assemblies

Oct. 8, 2024
Phase-matched cable assemblies are ubiquitous, and growing in popularity. Electrical length matching requirements continue to tighten and the mechanical precision of cable construction...

3 New Wideband MMIC LNAs Cover 5.5 to 20 GHz

Oct. 8, 2024
Mini-Circuits’ expanded PMA3-series of wideband, ultra-low NF MMIC amplifiers operates in ranges between 5.5 and 20 GHz.

Wideband Amplifiers Variable and Temperature-Compensated Gain

Oct. 8, 2024
Many types of RF systems and applications that span from the upper end of microwave frequencies to the lower end of mmWave have arisen in recent years. Meeting system requirements...