Characteristics of broadband parametric amplifiers using filter networks

Abstract

The paper gives a derivation of the relation between the bandwidth and the gain of a single diode parametric amplifier using filter networks at both signal and idling frequencies. Approximate algebraic expressions are obtained and compared with computed characteristics. The effects of small variations in component values are computed in an attempt to estimate the probable permissible tolerances for diode parameters and circuit elements. The phase- and group-delay characteristics are also computed, and the latter is shown to be of the order of twice the inverse of 2π times the amplifier bandwidth.The noise contribution due to the parametric action is shown to be a function of the signal frequency gain and the signal/idling frequency ratio. Because this relationship is such that the noise contribution falls with decreasing gain, the effective bandwidth of a low-noise receiver using a parametric amplifier as the first stage may be substantially greater than the normal bandwidth defined by a reduction of 3dB in the gain.Reported practical results are briefly examined in the light of the theory.