A New Type of Selective Circuit and Some Applications

This paper describes the use of the inverse feed-back principle to obtain sharply selective circuits. Important advantages of such circuits are (1) inductances are not necessary, (2) "tuning" may be changed by merely varying resistances, (3) ready adaptability for use at very low frequencies, (4) "tuning" may be varied over wide ranges of frequency while maintaining a selectivity curve which is a constant percentage function of the tuned frequency, (5) the possibility of using a single set of frequency-determining elements for "tuning" several amplifying stages, and (6) the general simplicity of construction and operation when compared with many other types of equipment designed to produce equivalent results. Many uses for a circuit of this type immediately suggest themselves. Two important applications are described, including a novel type of analyzer and an oscillator having extremely good wave form.