P A P E R    T I T L E
The Effects of Feedback Capacitance on Thermally Shunted Heterojunction Bipolar Transistor's Linearity

A U T H O R  /  C R E D I T S
R. Welch, T. Jenkins, L. Kehias, C. Bozada, C. Cerny, G. DeSalvo, R. Dettmer, J. Ebel, J. Gillespie, K. Nakano, C. Pettiford, T. Quach, J. Sewell, D. Via, and R. Anholt*
Air Force Research Laboratory, AFRL/SNDD
2241 Avionics Circle C2G69 Wright-Patterson AFB OH 45433-7322
Phone: (937) 255-1874 x3473, email: welch@el.wpafb.af.mil
*Gateway Modeling, Inc., 1604 East River Terrace, Minneapolis, Minnesota 55414

A B S T R A C T
The effects of feedback capacitance on linearity of thermally shunted heterojunction bipolar transistors (HBTs) were experimentally determined through power load pull measurements. The results show state-of-the-art linearity performance of devices biased and matched for power operation at X-band. Gain is easily traded for increased linearity by increasing the feedback capacitance in the device design. The data shows that a self-aligned process is necessary to maximize power performance (gain and efficiency), but an advantage of a re-aligned process is the ability to trade gain for linearity by increasing the emitter-to-base metal separation. With this additional design flexibility in a fixed technology, circuit performance can be optimized through layout variations only. For example, one HBT technology would be suitable for a Transmit/Receive module and each block could be easily optimized for different performance specifications.