A ferroelectric amplifier

Abstract

“Ferroelectric” refers to a class of nonlinear dielectrics characterized by a charge vs. voltage relationship exhibiting hysteresis and dielectric saturation. A capacitor made from barium-strontium titanate ceramic, a ferroelectric material, was used as the capacitive element in a single tuned circuit to which a high frequency current was applied. A low frequency signal to be amplified was applied to the capacitor, causing its capacitance to vary. The resulting amplitude-modulated high frequency voltage was applied to a detector circuit to recover the signal frequency. An analysis of this circuit shows what must be done to achieve maximum amplification. A circuit such as described was constructed and power gains of about 60 were obtained. When the signal was removed and the output of the amplifier fed back to the input, sustained oscillations of low frequency were obtained, with only the high frequency current source applied. The frequency of oscillation could be varied continuously over a wide range.