Chapter 0 deSiGn conCepTs EKT 221 / 4 DIGITAL ELECTRONICS II

Block Diagram of Combinational Circuit

Design Topics Modern digital design Techniques & tools for complex circuits & systems design Some important concepts CAD tools, HDL, logic synthesis, design hierarchy, top-down design

Design Hierarchy Approach to design complex digital system E.g VLSI circuits “Divide & Conquer” approach Break up circuit into smaller pieces / blocks Interconnect the blocks to form complete circuit

Approach  “Hierarchical design” Resulting symbols & schematics  “hierarchy” Steps in blocks division  “hierarchy levels”

Example : 9 – input odd function

Design Hierarchy Concepts 1. Reduces complexity of schematic diagram 2. Reuse of blocks One block is used multiple times Cascaded “Functional blocks”

Diagrams Representing Hierarchy

Top – down Design Describe circuit function by text, including constraints on cost, performance & reliability Divide circuit into hierarchy levels

Bottom – up Design Used to design certain portions of big design Starts with design of functional blocks So that functional blocks can be reused multiple times

Computer Aided Design (CAD) Schematic capture tools Drawing of blocks & interconnections at all hierarchy levels Libraries of graphic symbols Ready – made primitives & functional blocks design

Libraries in Max Plus II Prim Basic Fbs Mf Mega_lpm Edif Own libs from self-created symbols

CAD Logic simulator To verify behavior & timing of each hierarchy blocks / complete circuit Apply a set of inputs to determine the outputs

Hardware Description Language Important to design complex circuits Similar to other programming languages Describe hardware structures & behavior

Power of HDL Used to represent Schematic information Boolean equations Truth tables Can use hierarchical design approach High – level description can be partitioned into lower – level descriptions

Logic synthesis An HDL description written at an intermediate level called Register Transfer Language (RTL) It can be converted into interconnection of primitive components that forms the circuit HDLs are portable across CAD design tools

HDL Languages VHDL Very High – Speed ICs Developed by DoD, US IEEE standard Verilog HDL IEEE standard AHDL

The End