| 摘要 |
PURPOSE:To obtain desired impedance characteristics with high accuracy by providing plural simple analog transfer functions, selecting a proper value among them and making an auxiliary connection for use. CONSTITUTION:The terminal impedance obtained by viewing a BS circuit 2 from a two-line subscriber (a) is a function of both the transmission characteristics of a loop consisting of a digital processing part 4, a D/A converter 10, and a four-line reception-side analog part (c) including a four-line transmission-side analog part (b), an A/D converter 3, and a programmable digital filter 9 and the transfer characteristics of an analog auxiliary transfer function circuit 12. For the purpose, a function circuit 12 where the most effective circuit constant among circuit constants Z1-Z3 is selected to approximate to respective impedance values is connected to match the impedance to subscriber line impedance values which are difference by countries, and the coefficient of the filter 9 is found by various function approximating methods according to the circuit constant, thereby obtaining impedance approximating to a desired value.
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