D2 Channel Bank: Multiplexing and Coding

This paper is concerned with the analog multiplexing and the coding processes in the D2 Channel Bank. Economies in a digital channel bank 1675 1676 THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1972 are mostly due to the ability to share complex equipment such as the coder among all of the channels. To permit such sharing to take place, it is necessary to time-division multiplex the message signals from all the channels. This is accomplished by the multiplexing circuits. Because of the fragile nature of pulse-amplitude-modulated signals, it is here that most of the degradations, other than quantizing noise, are introduced. Great care must be exercised in the electrical and mechanical design of the multiplexing and demultiplexing circuits. The bulk of this paper is devoted to coding. The presence of a coder is characteristic of digital channel banks, since it converts analog signals into digital form. The choice of the compression law will be discussed here. The method used to achieve the chosen compression law will be described. The speed and accuracy achieved by the D2 coder represented a significant technical advance in the art of analog-to-digital conversion. The success in developing and manufacturing this coder to the required speed and accuracy proved the basic soundness of the approach taken.