Improvements in or relating to transistor circuit arrangements for demodulating and amplifying signals

摘要

876,042. Transistor demodulator and amplifier circuits. PHILIPS ELECTRICAL INDUSTRIES Ltd. Nov. 28, 1957 [Dec. 1, 1956], No. 37118/57. Classes 40(5) and 40(6) In a circuit for demodulating an A.M. or F.M. signal and amplifying both the modulation and the D.C. automatic gain control components, the demodulator is connected through a D.C. path to a transistor amplifier, the output of which includes a transformer which supplies an amplified modulation output and which has sufficient resistance in its primary winding to provide thereacross an amplified direct current component representing the carrier amplitude, negative feedback at modulation frequency being provided between the transformer and input of the transistor. The Figure shows an I.F. output circuit coupled to a detector 6 connected through a load resistance 7 to a transistor amplifier 8. The collector of the transistor supplies modulation frequency output by way of a transformer 10, the primary winding of which has sufficient resistance to provide an amplified D.C. voltage at the collector for automatic gain control purposes. Negative feedback at signal frequencies is provided by a circuit 13, 14 or by a tertiary winding 17 connected in series either with the emitter circuit or the base circuit. The feedback prevents distortion due to the variation of the transistor characteristic as the signal amplitude varies and can be arranged to vary the input or output impedance of the amplifier. It is suggested that the amplifier could alternatively be operated in the common base or common collector configuration.