초록 ▼

A gain of a variable gain amplifier circuit is controlled by applying a signal of a predetermined voltage level to the variable gain amplifier circuit during an idle period of an ultrasonic receiving signal, deriving an output from the variable gain amplifier circuit, comparing it with a voltage lev

A gain of a variable gain amplifier circuit is controlled by applying a signal of a predetermined voltage level to the variable gain amplifier circuit during an idle period of an ultrasonic receiving signal, deriving an output from the variable gain amplifier circuit, comparing it with a voltage level obtained as an aimed value by a gain regulator or other control circuit of an ultrasonic signal amplifier circuit including the variable gain amplifier circuit and producing a gain control signal according to a difference resulting from the comparison to control the gain to the aimed value until the difference becomes zero. The gain of the variable gain amplifier circuit set in the idle period is maintained during a measurement period of a subsequent receiving signal so that the latter is amplified with the maintained gain. Thus, a stepwise and selective gain setting corresponding to the aimed value can be obtained by controlling the gain of the variable gain amplifier according to the aimed value.

대표청구항 ▼

An amplifier circuit for an ultrasonic receiving signal comprising a variable gain amplifying circuit for amplifying an ultrasonic receiving signal, said variable gain amplifying circuit having a gain variable according to a gain control signal, a reference signal generator for supplying a reference

An amplifier circuit for an ultrasonic receiving signal comprising a variable gain amplifying circuit for amplifying an ultrasonic receiving signal, said variable gain amplifying circuit having a gain variable according to a gain control signal, a reference signal generator for supplying a reference signal to said variable gain amplifying circuit during an idle period in which there is no said receiving signal, an aimed value generator for generating an aimed value corresponding to a gain set and a control circuit responsive to a difference between said aimed value and a value of said reference signal amplified by said variable gain amplifying circuit during said idle period to generate said gain control signal corresponding to said aimed value and holding it for at least a time in which said receiving signal exists.