GB1245708A - Inverter - Google Patents

Abstract

1,245,708. Capacitive amplifiers. CESKOSLOVENSKA AKADEMIE VED. 8 Oct., 1969 [9 Oct., 1968], No. 49374/69. Heading H3B. [Also in Division H2] Relatively low D.C. voltages Em (e.g. from measuring circuits) are converted into A.C. voltages E 2K by an inverter comprising a ferroelectric disc 10 (Fig. 1), e.g. a single crystal of triglycinesulphate, in thermally autostable mode of operation and which forms a mechanical resonator when excited piezo-electrically by an A.C. voltage E 1 from a generator 2 applied between an annular excitation electrode 12 and an electrode 11. A pick-up region 103 is maintained by heat transfer from the exciting region 102 which is heated by the dielectric losses, at the temperature of the phase transition of the ferroelectric disc (Curie temp.), and is contacted by a pick-up electrode 13 and the electrode 11. In this thermal region the piezoelectric coefficient d of the pick-up region 103 depends upon the D.C. voltage Em applied between electrodes 11 and 13. With constant excitation voltage E 1 therefore, the pick-up piezo-electric output A.C. voltage E 2K magnitude is directly proportional to the magnitude of voltage Em and has a frequency equal to the 2nd harmonic of the excitation frequency. The "working point" of the disc 10 is set by an adjustable D.C. bias from a source 7. The inverter output E 2 K is amplified by an amplifier 4. The excitation frequency is adjusted to correspond to a critical frequency # 0 whereat shifts of the resonance peaks of mechanical vibration and hence of the output voltage E 2 K, in dependence upon temperature, are minimum (Fig. 2, not shown). Specification 1,049,613 is referred to.