Time-domain characterization of transistors.

Large-signal performance of GaAs based pHEMT devices were investigated using a combination of analytical models and measured data from a novel, time-domain active load-pull measurement system. A method for developing large-signal circuits from a collection of small-signal circuits was implemented using a nonlinear least-squares fitting technique. Small-signal circuits were extracted using a combination of coldFET and hotFET techniques with a new modification that more accurately models the bonding pad capacitance on the drain side of the device. Five common large-signal models used in the study. The novel, time-domain measurement system simultaneously measures data at the fundamental and harmonic frequencies. New vector error correction techniques were developed transform raw measured data into vector voltages and impedances at the device terminals. The system is different from any other time-domain system since it incorporates an active load which is capable of independently tuning the impedances at the fundamental and the second harmonic. Large-signal measurements were taken of a 12 x 100 mum Raytheon pHEMT at a fundamental frequency of 4 GHz for class A and AB operating points. The load was tuned to 50 O and the maximum transducer gain point. It was shown that tuning the fundamental load to the maximum gain point increased the gain by 13%, PAE by 30%, and drain efficiency by 38% over a 50 O load condition for the class AB operation. Comparisons between the measured data and the five models showed good agreement with the RF data, and DC agreement in error due to smaller than predicted drain current at low drive levels. The 12 x 100 mum pHEMTS were then measured with their second harmonic load tuned with their fundamental load fixed. The class A operating point showed an improvement of 11% in the drain efficiency and 10% in the PAE, compared to measured results when both the fundamental and the second harmonic load were fixed at 50 O. Transducer gain was reduced by 9% for this bias point. Similarly, the class AB operating point had an 12% increase in both the drain efficiency and the PAE.Ph.D.Applied SciencesElectrical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/132172/2/9959795.pd