Accurate Linear Bidirectional Diode Gates

In a computer developed at the Columbia University Electronics Research Laboratories, it was necessary to design a network having the following properties: Its transfer function should be determined by an audio-frequency square-wave control voltage, the transfer function should be unity for one polarity of the square wave and zero for the other polarity, and the inaccuracies should be less than 0.1 per cent. This paper describes two-diode, four-diode, and six-diode types of bridge switches which were investigated to meet the above need. For each type a discussion is given of the important parameters of the system such as control voltage amplitudes, magnitude of gain, constancy of gain versus signal amplitude, leakage through the back resistances of the diodes, effects of unbalances in the system, and others. A brief review is given of triode and pentode gates. A discussion is also given of the considerations arising from the use of series, parallel, and series-parallel combinations of switches. Some actual circuits are described which meet the original specifications. An experimental method for checking the linearity is given.