A voltage-controlled resistor for a linear voltage-controlled oscillator

To realize a linear voltage-controlled oscillator (VCO), a voltage-controlled resistor (VCR) whose reciprocal resistance is linear with respect to the control voltage V-c was fabricated and tested. The VCR was composed of an analog multiplier (AM) and an operational amplifier (OA). The static effective resistance R-e of the VCR varied as R-e(-1) = R-1(1 + alpha V-c), where R is the feedback resistance used in the VCR and a the scale factor of the AM. As for the dynamic characteristics, the reciprocal of the effective resistance of the VCR was not linear with respect to V-c at high frequencies or for low control voltages, which resulted from an equivalent reactance of the VCR caused by the time lag at both the AM and the OA. Experimental testing of the Wien bridge oscillator with the VCRs showed that the oscillation was stable and that the frequency of oscillation varied linearly with V-c. (C) 1997 Scripta Technica, Inc.