In Part 1 of this book, we explained digital design and simulation at a higher level of abstraction such as gates, data flow, and behavior. However, in rare cases designers will choose to design the leaf-level modules, using transistors. Verilog provides the ability to design at a MOS-transistor level. Design at this level is becoming rare with the increasing complexity of circuits (millions of transistors) and with the availability of sophisticated CAD tools. Verilog HDL currently provides only digital design capability with logic values
z, and the drive strengths associated with them. There is no analog capability. Thus, in Verilog HDL, transistors are also known switches that either conduct or are open. ...