Transistor Distortion Analysis Using Volterra Series Representation

Solid-state long-haul analog communication systems are being designed for higher frequencies to meet the growth in demand. One of the more critical and significant problems facing the system designer is intermodulation noise arising from transistor nonlinearities. Thus, an analysis of transistor distortion at higher frequencies is a practical problem; this paper investigates the transistor distortion using the Volterra series as an analysis tool. Transistor distortion has been investigated in some detail previously. Many authors have considered the exponential nonlinear relation between emitter current and emitter-to-base voltage which is important 991 992 TI-IE BELL SYSTEM T E C H N I C A L J O U R N A L , M A Y - J U N E 1967 at low currents. 1,2,3 ' 4,5 The effect of frequency 011 this nonlinear source alone has been reported. 5 Three nonlinearities (exponential, avalanche, and hFE at dc) have been examined by Riva, Beneteau and Dallavolta. 0 For currents up to 20 mA and frequencies up to 100 kHz, Meyer 7 ' 8 ' 0 has developed a more accurate and complex model obtaining the nonlinearities from /i-parameters. However, he takes into account the frequency dependence by assuming that the ^-parameters can be written as h' + jwh". Moreover, he does not take into account avalanche distortion, nor has he extended the model to higher currents (100 mA) and frequencies (20 MHz). The model described here considers four nonlinearities; they are, exponential, avalanche, hFE , and collector capacitance nonlinearities.