PCM CODING AND DECODING DEVICE CONTAINING TWO-WIRE/FOUR-WIRE CONVERSION FUNCTION

摘要

PURPOSE:To attain the compensation of delay with high accuracy and to obtain a satisfactory return loss by controlling the signal delay at a circuit part having a short sampling cycle. CONSTITUTION:The PCM signal supplied from a four-wire type input line 115 is converted into a linear PCM signal by an expander 112 and then into a digital signal by a digital filter 110. This digital signal is partially demodulated into an analog signal via a digital filter 108, an over-sample type D/A converter 107 and a post filter 106. This analog signal is partially sent to a two-wire type line 206 serving as a subscriber line via a termination impedance 205. While the analog signal C sent from a subscriber line 206 is converted into a digital signal by an over-sample type A/D converter 102 via an amplifier 203 and a pre-filter 101 and applied to a subtractor 113 via a digital filter 103. The output of the subtractor 113 is applied to a digital filter 104 with only the signal component given from the line 206 and then converted into a linear PCM signal. This PCM signal is converted into a nonlinear PCM signal by a compressor 105 and sent to a four- wire type output line 114.