Digital circuits building blocks

The main distinguishing feature of semicustom ASICs, compared to full custom ones, is that the basic circuit building blocks, whether analog or digital, are already designed and proven to work. These basic circuits typically reside in libraries within a CAD system. The users simply select from the library the components needed, place them on their circuits, and interconnect them. Circuit simulation is also done at a much higher level than SPICE, and the designer is, therefore, not required to be familiar with either semiconductor or device physics. 

In this chapter, we will give the simulation user the tools to use these building blocks in order to perform more complex functions. We will also attempt to aid the engineer in recognizing the potential pitfalls of both breadboard digital circuits and simulated digital circuits. 

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