| 摘要 |
<p>PROBLEM TO BE SOLVED: To inexpensively set amplitude gain characteristic and frequency characteristic of a subscriber's line at high speed by a simple method by obtaining an attenuation constant and a phase constant of a subscriber's line and equalization correcting the amplitude attenuation characteristics and the frequency characteristics. SOLUTION: A digital phase synchronizing circuit 18 detects/phase compares an information pattern from an output of a low band pass filter 13, controls a frequency division ratio of a fixed frequency oscillator 180 output, receives a clock signal and maintains reproduction. An amplitude attenuation amount and a delay time value of a line are detected white increasing the clock signal inputted to an amplitude detection circuit 20 and a delay time detection circuit 21 from a transducer 10 as a reference, are inputted to an equalization correction amount calculation table 24, the kind of line is specified, an attenuation constant and a phase characteristics are obtained in a use frequency, and the amplitude attenuation characteristics and frequency characteristics of the line are comppehuded. Then, after a variable gain DC amplifier 20 is reset, a high band-pass frequency of a variable high band-pass filter 21 is made to change and is controlled, so that its output voltage value becomes equal to an input voltage of the variable gain DC amplifier 20.</p> |
