Transistor 70-Mc IF amplifier

A 70-Mc IF amplifier using seven diffused-base germanium transistors is described. The insertion gain is 90 db, with bandwidth greater than 15 mc, flat to within ±0.3 db. The +12-dbm output is stabilized against change in input level or temperature by 35 db of AGC and the noise figure is 5 db. A digital computer was used as a tool in the circuit design. A rough first approximation to the desired design was made on the basis of the measured transistor parameters neglecting feedback and frequency effects. The changes necessary were then determined experimentally, and the computer was used to verify the goodness of the design and to determine the sensitivity of the adjustable parameters. The four-terminal-network parameters of the transistors in the common-emitter connection were measured at frequencies and operating points of interest with the aid of coaxial jigs. These parameters, together with circuit-element values, were put into a computer program based on a cascade of one-stage circuits. Modified parameters can be calculated from these if the transistor is to be used in a connection other than common-emitter. The computer then calculated the desired circuit characteristics. Good agreement has been obtained with experimental results.