Transistorized low-noise i.f. amplifier of large bandwidth


1,045,374. Transistor amplifying circuits. INTERNATIONAL STANDARD ELECTRIC CORPORATION. May 21, 1965 [May 23, 1964], No.21597/65. Heading H3T. A transistor I.F. amplifier is provided with negative feedback over two stages, whereby the input impedance is so modified as to obtain a matching to the preceding mixer which minimizes noise; i.e. the amplified input impedance is rendered substantially smaller or larger than the output impedance of the mixer. The amplifier comprises two transistors T1, T2 of opposite conductivity types in common emitter connection, direct-coupled over inductor L2 and shunt resistor R4. Each transistor is neutralized by means of an inductor L1, 3, respectively, connected between collector and base. Capacitor C5 and resistor R8 in the emitter circuit determine the local feedback around transistor T2 and the upper cut-off frequency and phase characteristic of the amplifier. Overall negative feedback determining the amplifier input impedance is provided by resistors Z, R3, 5 and capacitor C3, in which Z includes the load resistance.




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