GB1036106A - Improvements in transistor modulator circuits - Google Patents

Abstract

1,036,106. Transistor amplifying circuits; pulse modulator circuits. BAILEY METERS & CONTROLS Ltd. Aug. 28, 1962 [Aug. 29, 1961], No. 31102/61. Headings H3T and H4L. In a transistor modulator circuit comprising a transistor which is rendered periodically conducting and non-conducting by means of an alternating voltage applied across its basecollector electrode pair, the variation with temperature of the " offset " voltage existing in the emitter-collector path of the transistor when the latter is driven into conduction is minimized by limiting the collector-base voltage applied thereto by means of a diode network connected between the source of alternating voltage and the base of the transistor. As shown in Fig. 1 the base 6 of an overdriven amplifying transistor 5 is connected to A.C. supply 1 which latter supply is in addition rectified and smoothed over diode 2 and resistor-capacitor network 4, 3 to provide a collector bias for the transistor 5. The square wave voltage produced at the collector of transistor 5 at the frequency of the supply is fed to the base collector electrode pair of a modulator transistor 10, the base voltage of this transistor being limited to between zero and approximately one volt negative by means of diodes 11, 12. In this way the " offset " voltage appearing in the emitter-collector path of the transistor 10 is reduced to a value of approximately 1 mV. which is temperature dependent only to a small degree. In a second embodiment, Fig. 2 (not shown), the diode 12 of Fig. 1 is replaced by a Zener diode which together with a potential dividing network limits the negative excursions of the square wave form applied to the base of the chopper transistor.