The basic building blocks in today's integrated circuits are silicon semiconductor devices-more specifically the MOS transistors. In this chapter we will discuss the functional operation of MOS transistor to highlight its importance in digital integrated circuit design. The inverter is truly the nucleus of digital designs. This important block we will discuss in second section. After addressing the design considerations of inverter we will extend this discussion to address the synthesis of digital gates such as NOR, NAND and XOR. The focus is on combinational logic or nonregenerative circuits i.e. the circuits having the property that at any point in time the output of circuit is related to its current input signals by some Boolean expression. Further, the chapter discusses a set of basic properties of digital circuits. These properties help to quantify the quality of a design from different perspective. The properties include propagation delay, power consumption, functionality etc. These properties are relevant at all levels of abstractions such as system, chip, module and gate. From digital system designers point of view the speed of digital circuit is expressed in terms of systems computational ability e.g. the number of instructions executed per second by a microprocessor, whereas when the designer focus only on circuit aspects the speed is expressed by the duration of the clock and the propagation delay.
Therefore, in this chapter we will also discuss about the delay estimation principles, the static and the dynamic power consumptions components.