Digital Circuit Implementation - Digital System Design - Lecture Slides, Slides of Digital Systems Design

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Digital Circuit Implementation

 Wafers and Chips

 Integrated circuit (IC) chips are manufactured on silicon wafers

 Transistors are placed on the wafers through achemical etching process

 Each wafer is cut into chips (dies)which are then packaged individually

 IC Cost

 Cost of an integrated circuit (IC) can be modeled with three equations

 Cost per die = (cost per wafer) / ((dies per wafer) * yield)  Yield = fraction of dies on a wafer that pass testing

 Dies per wafer  Ignores border of the circular wafer that cannot accommodatea rectangular die  (wafer area) / (die area)

 Yield = 1 / (1 + (defects per area * die area) / 2)  Based on many years of empirical observations^2

 Basic IC Chip Types

 Logic circuits may be implemented …   on single chip, orusing many chips interconnected on a printed circuit board

(PCB)

 Main types of IC chips are:   Standard chipsProgrammable Logic Devices (PLD)

 Custom chips

 7400 Series TTL Logic Chips

 The 7400 NAND Chip: pin layout

Vcc = +5V

Gnd 7400

14^00

129

(^25) (^1013)

(^36) (^811)

The equivalent logic layout

 7400 Series Implementation

 Implementing f = x VDD 1 x 2 + x 2 'x 3 using 7400 series ICs

x x x^123 f

 PLDs

 Programmable chips the designer  Can even be reprogrammed – functionality determined by

 Can handle more complex functions than standard chips (approx 100 million transistors per PLD)

   FPGA: Field Programmable Gate ArraysCPLD: Complex Programmable Logic DevicesPAL: Programmable Array Logic

 PLA: Programmable Logic Arrays

 These are used very extensively in industry Docsity.com

 Custom Chips

 Programmable chips have two major drawbacks:  Consume space due to large number of switches forprogrammability

 Slow(resistance/capacitance)  speed also limited by excessive switches

 Custom chips   Logic designer builds a custom chipManufactured by a special fabrication facility ($$$!)

 ASIC: Application Specific Integrated Circuit   Fast, smallExpensive! And takes time to build and manufacture

 Design Loop for Digital Hardware

 The basic design loop:

 Initial design takescreativity andexperience

 CAD tools are usedfor simulation and to work out details

Design concept

Successful design

Initial design

Simulation

Design correct?

Redesign

Yes^ No

 The Entire Development Process

 Design is only one part

 Verification and testingare also importantis called design verification – this

 Errors may not be uncovereduntil after the prototype is made

 Errors may not be uncovered until after “release”!  Pentium bug

Design specifications^ Required product Initial design Simulation Implement prototype^ Design correct?^ Redesign Meets specs?^ Testing Finished product

Minor errors?

Make corrections Yes^ No Yes^ No

Yes No

 CAD Tools

 There are a number of commonly used industry standard CAD tools  CAD = Computer Aided Design

 Altera, Cadence, Mentor Graphics, Synopsys, Synplicity,Xilinx  We have Altera products

 Tools are used for multiple purposes  Synthesis, timing simulation, functional simulation, layout

 Can even download the design onto a PCB

 CAD Tools vs Theory

 Why learn any theory if the CAD tools do the work?  Initial design must be provided by the designer

 Quality of final design is a function of the quality of the initialdesign

 Tools implement the theory  Designers need to understand how the tools work in order tobe effective in using them

 Tools have many options  Knowing which to select requires knowing what they do andhow they do it