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Differential GaN-power oscillator for compact plasma-sources in the 2.45 GHz ISM frequency band

FBH research: 18.12.2014

Differential circuit

Fig. 1: Concept of the differential circuit

Prototype of the oscillator module

Fig. 2: Prototype of the oscillator module

New applications in the fields of microwave heating and plasma technology require very 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. In an industrial cooperation with the company SENTECH Instruments a power oscillator is applied as the key component of a highly integrated plasma source module which can be arranged in arrays in order to generate large area plasmas.

Its differential circuit concept consists of a pair of FBH GaN powerbars, each containing five transistor cells with 0.5 micron gate length. These bars are coupled by a special feedback network. The microwave signal is delivered to two separate 50 Ω outputs with 180 ° phase shift and thus feeds its energy into two resonators inside the plasma source module. Fig. 1 depicts the power oscillator Fig. 2 the the SENTECH design of the plasma source module into which it is included.

For the first time, FBH has developed a power oscillator with mechanical frequency tuning capability inside the 2.4 GHz ISM band. The module delivers a peak output power of 57 W and a peak efficiency of about 54%. Circuit area requirements are 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 2014 in Rome.

Publication:  

C. Bansleben and W. Heinrich, "Compact High-Power High Efficiency Microwave Generator With Differential Outputs", Proc. 44th European Microwave Conf. (EuMC 2014), Rome, Italy, Oct. 6-9, pp. 723-726 (2014).

FBH research: 18.12.2014