Microchips come in various shapes and with various sizes. What they all have in common is that their outer appearance doesn’t reveal what’s inside. Looking at a cutaway diagram of a typical monolithic microchip in a Quad Flat Package (QFP), tiny structures become visible. Every package of a microchip accomodates an active device – the IC chip or IC die – the silicon centerpiece with countless circuits in it. The IC die is permanently attached to the package via a thin film of adhesive. Tiny bond wires connect the IC die with the lead wires of the IC package. The package itself protects the highly sensitive IC die from environmental attack, dissipates heat, and provides power and signal connections.
The complexity within an integrated circuit that has millions or even billions of transistors is incredibly high. It is therefore impossible to look onto an IC chip through a microscope and to comprehend the range of functions the particular chip offers. The only conceivable way to understand integrated circuits is to focus on individual levels of abstraction and to understand the underlying electronical principles of that level before looking at another level.
Thinking in levels of abstraction greatly improves the understanding and readability of even complex digital systems. The following chapter starts at the level with the smallest units – transistors – which has the lowest complexity, and gradually abstracts to higher levels. Every new level of abstraction can be seen as a short summary of the previous level, often using short symbols that save space and carry more information. In this way, a total of six levels of abstraction will be described by using simple analogies and illustrations to break down the complexity.