Non-linear distortion in transistor class-A amplifiers at low and medium frequencies

Abstract

Non-linear distortion in junction transistors at low signal levels is investigated over a range of frequencies extending up to about 0-2 times the cut-off frequency. Theoretical expressions are developed for the second-and third-harmonic distortion as a function of d.c. conditions, frequency, and load and generator impedances. An alloyjunction transistor is studied under a range of different working conditions, the calculated results then being compared with those of experimental measurements. LIST OF PRINCIPAL SYMBOLS A = Average cross-section area of transistor.A c = Collector-base junction area. C c = Total collector capacitance ( = C d + C,). C d = Collector diffusion capacitance. C, = Capacitance corresponding to the base-collector transition layer. D p = Diffusion constant for holes. e = Electronic charge. fa. = Cut-off frequency. n» ^i2> ^21» ^22 ~ /^-parameters. i e{ , i e2 , i e3 = First, second and third harmonics of emitter current in symbolic notation. i ela , i e2a , i e3a = Amplitudes of first, second and third harmonics of emitter current. I e = Direct emitter current. 'cu 'c2> hi = First, second and third harmonics of collector current in symbolic notation. i cla , i c2a , i c3a = Amplitudes of first, second and third harmonics of collector current. K { -K 6 = Quantities proportional to first derivatives of the A-parameters. K 7 -K i4 = Quantities proportional to second derivatives of the A-parameters. Kf 0 , K$ o , k h X = Characteristic quantities of the transistor. k = Boltzmann's constant. k 2 = Second-harmonic distortion factor in common-base transistor. k 3 = Third-harmonic distortion factor in common-base transistor. N = Concentration of donors in the base layer. P c = Collector dissipation. R g = Internal resistance of generator. Ri = Load resistance. r' b = Base spreading resistance. T = Absolute temperature. V Q = Built-in potential at the base-collector junction. v cl ,v c2 ,v c3 = First, second and third harmonics of collector voltage in symbolic notation. v cia , v c2a , v c3a = Amplitudes of first, second and third harmonics of collector voltage.Dr. Meyer is at the Teleteknisk Forskningslaboratorium, Copenhagen.v el ,v e2 ,v e3 = First, second and third harmonics of emitter voltage in symbolic notation. v ela , v e2a , v e3a = Amplitudes of first, second and third harmonics of emitter voltage. V c = Direct collector voltage. w = Effective base-width. vf 0 = Metallurgical base-width. Z g = Internal impedance of generator. Zi = Load impedance. K = Thermal resistance of the transistor. rj = Output efficiency, i.e. the ratio between the a.c. and d.c. output powers. co = Angular frequency. to a = 2-nfa.-o>°0 = Value of cu a corresponding to I e -0 and w = w 0 .(1) INTRODUCTION The non-linear distortion in transistor class-A amplifiers has been treated previously in some detail 1 -2 for frequencies so low that the transistor parameters can be considered to be real and frequency-independent. In practice, however, transistor amplifiers are often used in a frequency range where the imaginary ...