Integrated circuits (ICs) are classified according to their levels of complexity: small-scale integration (SSI), medium-scale integration (MSI), large-scale integration (LSI) and very large-scale integration (VLSI). They are also classified according to the technology employed for their fabrication (bipolar, N metal oxide semiconductor (NMOS), complementary metal oxide semiconductor (CMOS), etc.). The design of integrated circuits needs to be addressed at the SSI, MSI, LSI, and VLSI levels. Digital SSI and MSI typically consist of gates and combinations of gates. Design of digital SSI and MSI is presented in Sec. 6.3, and consists largely of the design of standard gates. These standard gates are designed to have large noise margins, large fan out, and large load current capability, in order to maximize their versatility.