| 摘要 |
A coder/decoder in a PCM communications system, employs a common digital-to-analog converter. In a basic sampling interval the incoming PCM signal is decoded at a decision level on one side of the desired reconstruction level; then modified and again decoded at a different decision level on the other side of the desired level. The average of the two decoded signals then lies on the desired level giving a decoding characteristic having decision levels between those of the encoding characteristics. As used in a conventional PCM system, the two PCM samples differ by only one least significant bit. In a preferred embodiment, separate storage registers R1 R2 are used for encoding and decoding, plus a selector 262 for switching between the two registers during the decoding intervals. Thus, encoding may be effected during a substantial portion of the basic sampling cycle, being interrupted only to generate decoded samples. The invention is applicable to PCM systems generally, including compressed pulse code modulation systems. <IMAGE> |
