Differential GaN-power oscillator for compact high power 2.45 GHz generators
Fig. 1. Prototype of the oscillator module (top) and concept of the differential circuit (bottom)
New applications in the fields of microwave heating and plasma technology require compact generators at power levels from 10 W to 100 W. Today’s conventional microwave generators employ either magnetrons or small signal oscillators connected to a cascade of multiple power amplifiers. Due to their physical size both concepts cannot be used if only a small volume is available as it may occur in various industrial systems. By combining the signal generation and amplification in a single small circuit, power oscillators can contribute significantly to the miniaturization of future generators.
With this goal a new power oscillator was developed at FBH. Its differential circuit concept consists of a pair of FBH GaN powerbars, each containing five transistor cells with 0.5 micron gate length, that are coupled by a special feedback network. The microwave signal is delivered to two separate 50 Ω outputs with 180° phase shift. Fig. 1 depicts the circuit and the prototype of the power oscillator.
At an oscillation frequency of 2.45 GHz the module delivers an output power of approximately 40 W with an efficiency of about 40%. The required circuit area is merely 10 cm². Consequently the introduced microwave generator features the smallest form factor for this power level. The results were presented at the European Microwave Conference 2013 in Nueremberg. In a future industrial collaboration the described generator principle is to be used in highly integrated plasma modules to realize a multi-jet plasma source.
Publication:
C. Bansleben, W. Heinrich, "Compact High-Power GaN Oscillator with 2.45 GHz Differential Output" Proc. 43th European Microwave Conf. (EuMC 2013), Nuremberg, Germany, Oct. 7-10, pp. 818-821 (2013).
FBH research: 20.11.2013