Some transistor building blocks for analogue computers

MANY analogue computers of the electronic type include combinations of a few “building blocks” called operational amplifiers. This paper analyzes the basic properties of voltage and current operational amplifiers and discusses some of the problems of designing the circuitry using junction transistors. Although much has been written about the voltage operational amplifier,1 especially where vacuum tubes are employed, it is hoped that this presentation of the subject will emphasize those properties of the network configuration which become important if transistors are to be used. A somewhat different approach to making the best use of transistors in the analogue computer type of circuits is to use currents instead of voltages as the dependent variables. This leads to what in some respects seems to be a more reasonable utilization of the natural properties of transistors than the obvious expedient of simply “transistorizing” existing circuits. One of the aims of this paper is to explore this possibility in a rather general way and to relate the principles and philosophy of the current operational amplifier to the more familiar voltage case. The analysis is based on the small signal operation of devices such as vacuum tubes and transistors which allows them to be replaced by the usual equivalent circuits. No attempt will be made to include practical circuit diagrams.