Voltage-controlled oscillator using an emitter-coupled differential pair

A voltage-controlled oscillator using the antisymmetric transfer characteristics of an emitter-coupled differential pair of transistors is presented. Variation of the differential bias condition of this pair changes the average slope of Its transconductance parameter, thereby changing the frequency of the near harmonic mode of oscillation in a system which has been shown to produce van-der-Pol-type oscillations with passive parameter control only. Over a sufficiently wide range of frequency the distortion of this oscillation is reasonably low. A simple slope/differential-voltage relation is proposed to calculate the frequencies by computer solution of the general relation, as well as by approximate solution by using the method of small parameters. Experimental results are also presented for comparison.