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Title: Intermodulation distortion characterisation and analysis of InGaP/GaAs HBTs
Author: Khan , Asif
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2007
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Minimisation of Intermodulation Distortion (IMD), and in particular the third order IMD, in communication systems is key to developing linearisation methods. The first step in the minimisation process is the characterisation of the extrinsic and intrinsic device nonlinearities that give rise to the IMD phenomena. Many conventional analytical characterisation methods are too complex to interpret whilst schematic characterisation provides very little information as to how the results are derived. The above issues are addressed in this thesis through the development of an analytical IMD model for the microwave InGAP/GaAs DHBT. The model is based on Taylor series expansion of intrinsic device nonlinearities, mainly the base› emitter dynamic resistance (Rbe), base-emitter diffusion capacitance (Cciff), voltage controlled current source (VCCS) and the base-collector depletion capacitance (Cbe). Data derived from this model is compared with measurements, calculations and simulations of both weak and relatively strong nonlinearities. It is shown that a simple diode model is robust enough to account for the IMD behaviour at low powers and frequencies. However, at higher powers and frequencies the Taylor series based model needs to be adopted. Through this model it is found that the VCCS non linearity is reasonably sufficient in explaining IMD phenomena at low powers. However, at higher input signal power levels and frequencies the Cbe nonlinearity is found to dominate to such an extent that it almost completely accounts for the characteristics of the dip in the third order IMD. Another area where very little research is conducted is the thermal analysis of nonlinear behaviour. Hence, third order IMD (which is the most problematic from a filtering viewpoint) measurements are made as a function of temperature. These results are compared with the data derived using the Taylor series based model as well as the purely resistive diode model. The relationship between device parameters, biasing and IMD behaviour is critical when designing for linearity. Hence, during this project a novel method is developed for the extraction of thermal resistance, directly at the point of optimum bias (where third order IMD is minimised). This technique is compared with the traditional methods of extracting thermal resistance and it is found to have the added advantage of being able to extract thermal resistance at lower power dissipations and temperatures.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available