Design of Broad Band I.F. Amplifiers

Abstract

This paper deals with the design of broad band I.F. amplifiers with single tuned circuits in t stages. It is found that the figures of merit (Qn) of the individual circuits should be related to the Q of a reference circuit according to: Q/Qn=sin [(2m+1)π/2t]·ω0ω0n, m=0,1,2,…(t−1). Then by proper tuning either an oscillatory or a monotonic response may be obtained. The relative band width BW/f0 and the gain tolerance d0 within the band determines the value of Q. The minimum number of stages for a given minimum attentuation in the cut-off region depends only on the gain tolerance and on the desired kind of response. Gain maxima (attenuation minima) appear at frequency deviations Δfnmin from middle band frequency f0 given by: 2Δfnmin/BW=cos [(2m+1)π/2t]. Their location depends only on the number of stages. The resonance deviations Δf0n of the tuned circuits are proportional to Δfnmin with a proportionality factor F dependent on t and d0. The circuit impedances are calculated from a prescribed gain or from the maximum attainable gain. A formula for the maximum gain band width product is derived. The result is extended to double tuned stages. A practical example is given.