Comparison of Simple Design Methods for Voltage Controllable Resistance

This paper compares several ways of electronic resistance control for tunable applications (filters, oscillators, amplifiers, etc.). Simulation (PSpice) and experimental tests of basic J-FET transistor-based adjustable resistor, optocoupler as well as more advanced active solutions using active devices (variable gain amplifiers, voltage-mode multiplier) are performed in order to see available linear range, readjustability range and expected frequency features.