DIGITAL-IC MODELS FOR COMPUTER-AIDED DESIGN - 1. TTL NAND GATES.

Computer models can be generated for accurate simulation of digital integrated circuits; the ICs are treated as simple individual devices, rather than as a complex collection of transistors and diodes. Model complexity depends more on the quantity and type of external interface requirements than on the internal complexity of the device itself. There are two NAND gate models - one for a two-input device, and the other for a four-input device. Both gates are positive-logic integrated circuits. A two-input NAND gate can be adequately represented by its output signal levels and its delay characteristics. With this approach, there is no need for the wasteful classical method of modeling every transistor and diode junction. The electrical characteristics of the four-input gate can be approximated fairly accurately. The program description for the four-input gate model includes subprograms to assure that the simulated gate will conform to the desired truth table.