А.P. Alimov – Research Scientist, MESC AF «N.E. Zhukovsky and Y.A. Gagarin Air Force Academy» (Voronezh)
B.F. Zmij – Dr.Sc. (Eng.), Professor, MESC AF «N.E. Zhukovsky and Y.A. Gagarin Air Force Academy» (Voronezh)
Currently, construction of 1,5 to 60 MHz RF amplifiers is generally performed using connection of fourth-order passive coupled circuit band-pass filter and low-noise wideband amplifier. These circuits feature insufficiently wide dynamic range by virtue of high noise floor. As a solution of the problem to reduce the noise floor, there was proposed new layout for fourth-order RF band-pass amplifier.
The work objective is to improve dynamic range of RF amplifiers through the noise floor decrease.
The work objective was achieved via signal enhancement within passive amplifier component, reduction in gain value of integrated-circuit amplifier and sensitivity value minimization of transfer function to wideband amplifier parameter deviation. With this, the following was to be solved: approximation problem of the preset amplitude-frequency response characteristic level with the required variations in operating frequency band; problem for implementation of optimum ARLC-circuits.
Approximation of the required amplitude-frequency response characteristics was performed within normalized frequency domain based on making use of Chebyshev proximity criterion and modified Remez algorithm. In this connection, polynomial approximants for various frequency coverage degrees and ratio were obtained.
RF amplifiers were implemented based on: utilization of topological method for synthesis of linear four-terminal networks; definition of optimality criterion in terms of sensitivity function product of transfer function to divergence of integrated-circuit amplifier parameters and gain value; introduction of negative feedback from the amplifier output to the input of passive circuit component. Minimization of the criterion being introduced was performed within the component parameter space. As the result, there were obtained optimum design ratios for circuit element parameters to provide the required amplitude-frequency response characteristic and minimal noise floor in the operating frequency band.
The developed technique for synthesis of RF selective amplifiers allows at least 10-fold noise floor reduction with increase in dynamic range of a selective amplifier by 20 dB.
Frequency range of selective amplifiers on operational amplifiers is limited not only by circuit element parameters (physical realizability of nominal values) but by integrated-circuit amplifier performance (gain-band width product). The proposed amplifiers require lower amplification factor than in typical circuits that provides frequency range expansion.