Co-investigator Eugene Fitzgerald
Highly integrated GaN RF power amplifiers (PAs) have been developed for mobile devices and connected cars applications using the physics-based RF transistor compact model, MIT Virtual Source GANFET (MVSG). RF power amplifiers are required to operate in a linear region to prevent signal distortion and resultant data loss, which is mainly affected by inherent device-level nonlinear behavior. Since the second derivative of transconductance, g3, is an intrinsic source of intermodulation distortion, many studies aimed to cancel it, especially in CMOS technology. However, the high mobility and thermal effect of GaN devices make the device nonlinearity compensation harder than in CMOS devices. Thus, we have looked into the large signal linearization considering both power gain and third-order harmonics rather than g3 alter- ation techniques that cannot be properly functional in a high-power amplifier with large signal input.
In our previous design, the Class-AB + Class-C configuration was proposed for a fully integrated GaN RF amplifier, demonstrating improved linearity and efficiency. Recently, we designed another GaN RF power amplifier with the Common-Source & Common Gate (CS-CG) configuration to further improve the intermodulation distortion by optimizing the third order harmonics performance from the viewpoint of compensating for the large signal distortion. The CS-CG outperforms the Class-AB + Class-C in terms of the third order harmonics and intermodulation distortion, which means that the average time-varying composite g3 of the CS–CG is lower than that of the Class-AB + Class-C.
To study the impact of the device and technology parameters on the circuit performance, we used both the MVSG model and the CS-CG amplifier and isolated some device parameters which affect the DC and RF performance at both device and circuit levels. We show the circuit implementation using 0.25μm GaN technology and its gain and third-order harmonics with varying DIBL, delta. Intermodulation distortion is further investigated with varying δ, short channel effects such as moderate punch-through, nd, and parasitics, i.e., Cds, and Cdg.