LOGARITHMIC AMPLIFYING CIRCUIT

PURPOSE:To obtain an output of a logarithmic amplifier, by dividing an intermediate frequency part into preamplifier groups and post-amplifier groups, extracting the output of an amplifier of each stage of each amplifier group with the same phase to be added with common load resistance of each group and then to obtain a DC output after wave detection and then by having a DC addition of the DC output. CONSTITUTION:The input/output phase difference is compensated by a capacitor, etc. for each amplifier of preamplifier groups 4-7, and the phase difference between an input signal 1 and the output of the amplifier 7 is minimized. Then the output of each amplifier is applied to the input resistance of an adder 12-1 with division of resistance. The wave detection of envelope curve is given to the output of the adder 12-1 by a wave detector 14-1. Thus an output is obtained for the 1st logarithmic amplifier with a wide dynamic range and synthesization of logarithmic characteristics of each amplifier. Each amplifier of post-amplifier groups 8-11 is processed in a way exactly same as the above-mentioned preamplifier groups to obtain the 2nd logarithmic amplifier output of a wide dynamic range through a wave detector 14-2. The DC outputs given from detectors 14-1 and 14-2 are synthesized by an adder 15 to obtain a logarithmic amplifier output 3 having a wide dynamic range.