Broadband Codecs for an Experimental 224 Mb/s PCM Terminal

The design of the coding and decoding complexes of the PCM terminals discussed by Mayo 1 will be covered herein. The term "codec" will he used to denote the coder (analog to digital converter), the decoder (digital to analog converter), and all of the associated circuits, such as sample and hold, parallel (o serial converted, Gray to binary translator, resampler, and framing and timing circuits. This definition specifically excludes the multiplexing and demultiplexing portions of the terminal covered in the paper by Witt. 2 Before the detailed circuit designs are examined, it will be profitable to delineate the two approaches taken to the realization of the encoder. In both coder approaches ideal uniform quantization was sought. The additional quantizing noise advantage attendant to nonuniform quantization was left for future development. When this project was undertaken only the beam coding tube 3 appeared (o satisfy the need for high performance mastergroup and TV 1887 1900 T H E B E L L SYSTEM TECHNICAL JOURNAL, N O V E M B E R 19(15