|M.Sc Student||Burdo Gennady|
|Subject||Linear Broadband Amplifier in InP HBT Technology|
|Department||Department of Electrical Engineering||Supervisor||Professor Dan Ritter|
|Full Thesis text - in Hebrew|
Indium Phosphide based HBTs are ultra fast devices, which can operate at frequencies of several hundreds of GHz. Another attractive feature of this technology is the capability to integrate fast electronic circuits with lasers, optical sensors and light modulators on the same chip.
This research concentrates on the design and characterization of a broadband power amplifier using the InP HBT technology developed at Technion with emphasis on reduced third order distortion. The Technion InP HBT technology has already proven its maturity by successful design and fabrication of several high-speed circuits; including broadband power-amplifiers with a record bandwidth of 75 GHz. Previous designs did not attempt, however, to obtain a good linearity performance
The linearity of power amplifiers is a crucial requirement in communication systems and measurement instrumentation. Combined with thermal noise, distortion is the limiting factor of system efficiency. For example, the number of channels in a given frequency band is usually limited by distortion and jitter. An effective way to solve this problem is to reduce distortion.
In this work I suggest and demonstrate a new method for 3rd order linearity enhancement of amplifiers based on a common-emitter (CE) gain stage.
The proposed linearization method is based on the sign reversal in 3rd order non-linear coefficient of the CE gain stage. The proposed circuit is composed of two parts. The first part is the main CE gain stage, the purpose of which is to supply high voltage-to-current gain within a wide frequency range a negative 3rd order non-linear coefficient since it is operating at high current densities. The second part is the correction circuit which is also based on the CE stage but operates at very low current densities and achieves a positive 3rd order non-linear coefficient. The incoming voltage signal is applied to both stages in such a way that when both received currents are summed together on the shared resistor, the resultant voltage is free of the 3rd order distortion if the distortion parts of the two currents are equal in amplitude and opposite in phase.
A 4-stage distributed amplifier based on the described method was designed and fabricated in InP HBT technology developed in the Technion. Measurements proved the proposed linearization method to be functional although slightly different behavior was examined. Improvement of 10 to 20 [dB] in the 3rd order intermodulation distortion and 25 to 30 [dB] in the 2nd order intermodulation distortion was observed.