| 摘要 |
PURPOSE:To remarkably improve the frequency characteristic of a reception signal by using an equalizer circuit discriminating the line characteristic based on a level of plural tone signals received from a center equipment and compensating the characteristic of line. CONSTITUTION:A programmable gain amplifier 22 amplifies a reception signal outputted from a network controller 21 and its output signal is fed to a tone signal detection section 23. The detection section 23 selects the frequency of an input signal and detects whether or not a frequency signal reaches a prescribed level or over and its detection signal DT is fed to a communication control section 19. A reception signal outputted from the controller 21 is fed to a common terminal 24c of a changeover switch 24 and switching terminals 24a1-24a3 are connected to input terminals of the equalizers 25-27. The equalizers 25-27 compensate the frequency characteristic of the reception signal and each frequency characteristic is different from each other. For example, the equalizer 26 has a larger compensation gain at a higher frequency band than the equalizer 25 and the equalizer 27 has a larger compensation gain at a higher frequency band than the equalizer 26.
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