GB846003A - Improvements relating to amplifier circuits employing transistors - Google Patents

Abstract

846,003. R. F. couplings; transistor amplifier circuits. TELEFUNKEN G.m.b.H. Nov. 8, 1956 [Nov. 9, 1955], No. 34159/56. Classes 40(6) and 40(7). The circuit coupling a ferrite rod or other aerial to a transistor, or coupling a first transistor to a succeeding one, is arranged so that the input and transistor are substantially power matched at all points in a frequency band. According to the invention the tuned aerial circuit or other tuned input is transformer coupled to the transistor and a coupling capacitor is introduced providing voltage or current coupling between the primary and secondary sides of the transformer. As shown in the figure the transformer is wound on the ferrite rod aerial F and has a primary L and secondary S. The aerial is tuned over a frequency band by variable capacitor Cl which is in series with coupling capacitor C k . The latter is common to both the primary and secondary circuits of the transformer and provides current coupling between them. The voltage across it decreases as the frequency increases and, the winding S providing a voltage of the same polarity, a power match is maintained to the transistor, the input resistance of which decreases with increase of frequency. If a voltage coupling capacitor is to be provided the junction between the windings L and S is connected directly to earth and the coupling capacitor inserted between their other ends. Instead of a ferrite rod F a coupling transformer connected to an external aerial may be used as indicated by the dotted outline.