D4 Digital Channel Bank Family: Custom-Integrated Circuits for DigitalTerminals

Custom-integrated circuits offer significant cost savings for system applications. These savings are achieved by using fewer printed-circuit boards, connectors, and less hand wiring, thereby leaving fewer components to test and assemble and requiring less physical space. This article describes three types of custom-integrated circuits: (1) Custom metal-oxide-semiconductor (MOS) very large-scale integration (VLSI), (2) bipolar gate array, and (3) custom-analog complementary bipolar 2791 integrated circuit (CBIC) combined with analog-digital buried injector logic (BIL) bipolar. The technology for the digital terminals described in this article was determined by the following considerations, MOS technology offers the advantages of a high packing density for a large number of gates. In addition, the complementary MOS (CMOS) option permits chip power dissipation to be very low. Bipolar gate arrays are especially attractive for the use of minimum work force when gate counts are fewer than 1000 and when the volume is low. Both MOS polycells and bipolar gate array layouts permit quick turnaround for design changes. The CBIC is the best means for realizing high-performance analog functions. The CBIC-BIL combination allows digital logic to be put on the same chip with the analog functions, thereby achieving high packing densities. Whatever the technology choice, the effective support of the system organizations by the device organization has led to a rapid growth of custom large-scale integration (LSI) in the Bell System.