ULTRASONIC WAVE RECEIVING SIGNAL AMPLIFYING CIRCUIT AND GAIN CONTROL SYSTEM THEREOF

摘要

PURPOSE:To set a gain stepwise, finely and selectively, by adding a reference signal to a variable gain amplifying circuit during a receiving stop period and comparing the output thereof with an objective value to control the gain. CONSTITUTION:In the stop period during the repeating cycle of an ultrasonic wave receiving signal, a reference signal is preliminarily generated from a reference signal generator 22 to be inputted to the terminal 21c of an amplifier 20 and amplifying output is sent out to the (-) phase input of an error amplifier 24. Further, a gain setting signal is sent out to the (+) phase input of said amplifier 24 while the DC voltage level formed by a calibration voltage generating circuit 27 and a gain operator 26 is set as an objective value. A feedback control loop system is controlled by these two inputs and the mu-factor of the amplifier 20 is set to the gain corresponding to the objective value and this gain is kept in the next measuring period.