Bias Techniques for GaN and pHEMT Depletion Mode Devices

Advances in process technology have led to GaN depletion mode devices finding their way out of research labs and into communications markets. In many microwave wave applications for example, the LDMOS devices that have dominated power amplifier designs are giving way to GaN solutions, particularly the final output stage where efficiency and linearity are key requirements. The high power density, high efficiency capability of GaN makes it valuable for microwave applications, and the trend of GaN devices finding their way into future communication systems is predicted to continue. As a result, there are incentives to develop novel bias techniques that provide proper bias control and temperature compensation for depletion mode devices. These techniques must be compatible with communication applications where stable operation into high capacitance loads is necessary for the wide video bandwidths found in Doherty configured amplifiers that carry 4G and LTE signals. As pHEMT devices are well established in numerous applications, the approach is to develop universal techniques that work for any type of depletion mode device.