JPS56102184A - Multifrequency signal receiver - Google Patents

Abstract

PURPOSE:To remove echo signals by controlling the switch on the input side with the AND output signal between the output of a variable threshold controlling circuit which detects the trailing edge of an input signal and the output generated during the period the out circuit of a multifrequency signal receiver is in operation. CONSTITUTION:Since a multifrequency signal inputted into terminal IN includes echo signals between gaps of digit signals, these echo signals are inputted into variable threshold controlling circuit 30 through switch 33, amplifier 1 and band elasing filter 2. Circuit 30 compares the maximum value of the input signal with the output of the rectifier which generates variable threshold signal whose value is lower than the maximum value and, when the variable threshold is higher, circuit 30 detects the trailing edge of input signal and enters it into AND gate 31. The output generated during the period the out circuit which actuates after confirming that the input signal is effective is operating is inputted into gate 31 and the output of the gate 31 is entered into delay switching circuit 32. Circuit 32 outputs signals only the period echo signals are continued to be outputted to control switch 33 by opening the switch so as to remove echo signals equivalently.