Non-linear distortion in transistor amplifiers at low signal levels and low frequencies

Abstract

An analysis is made with the purpose of establishing analytical methods of calculating the non-linear distortion of sinusoidal signals in the input and output circuits of transistor amplifiers at low frequencies and low distortion levels. The transistor is regarded as an ‘almost linear’ four-pole, and characterizing matrix equations and T-network equivalent circuits are developed under the further assumption that the second harmonic is of greater magnitude than the higher harmonics. By using these equations or the equivalent circuits it is possible to calculate second-harmonic distortion of the signals by wellknown methods from the linear theory, and it is indicated how the principle may be extended to allow calculation of the third-harmonic distortion also. The principle is used to calculate the output distortion factor for some simple amplifiers, and it is shown that the input and output distortion of the common-emitter amplifier may cancel under special working conditions of the amplifier. From the analytical expressions developed it is possible to fix these conditions so that a considerable reduction of the second harmonic in the output signal is obtained. The expressions developed have been verified experimentally.