Evaluation of Differential Amplifier Circuits in Electrophysiological Research

摘要

For quality characteristics of the individual differential stages, it is useful to examine two quantities: (a) the rejection coefficient which represents the relation of the amplification of the cascades with and without consideration of negative feedback on cathode resistance. This coefficient increases with the coupling of several additional differential cascades. (b) the symmetry coefficient, which shows the degree to which the paired tubes are matched in a symmetrical cascade. It gives the amount of out-of-phase voltage at the output of the cascade when inphase voltage is applied to the input terminals. Since the out-of-phase signal does not change with coupling of additional cascades, this coefficient is determined by the first cascade. The quality of a multicascade differential amplifier can be characterized by the noise suppression coefficient, which depends on both coefficients cited above. From the point of view of their use in clinical physiological experiments and diagnoses, investigation shows that because noise voltage under actual conditions is not absolutely identical, large coefficients of noise suppression can be realized only by additional balancing of these voltages at the input of the amplifiers. (Author)