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

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.