Abstract

A voltage-controlled oscillator (VCO) in Colpitts circuit configuration is demonstrated using a twisted-nematic (TN) liquid crystal (LC) cell as a capacitance that can be varied as a function of applied voltage. Oscillation frequencies in the range of kHz have been obtained for the combination of inductance and capacitances used in the circuit. A theoretical study for the whole circuit is proposed and experimentally validated. Applications of this circuit include, among others, modulation and demodulation frequency signal, phase locked-loops, and function generators.