Digital System
Digital Signal Representation
• High Precision – Higher number of bits required 2
Digital Signal Representation
• Binary digit represents – logic HIGH or logic LOW
• In an electronic system – logic HIGH is 1, logic LOW is 0 or vice-versa
• 1 bit represents – 2 states
• 2 bits represents – 4 states – {00,01,10,11}
• n bits represents – 2n states
• 210 = 1024 ~ 1K bits
• 220 = 10,48,576 ~ 1M bits
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Analog and Digital Systems
• Analog systems process analog signals which can take any value within a
range
• Microphone, Analog meter display
• Digital systems process digital signals which can take only a limited
number of values between two values
• Flip-flops, Shift registers, Digital display
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Advantage and Disadvantages of Digital Systems
• High accuracy (+)
• Programmability (+)
• Maintainability (+)
• Design Automation (+)
• Area, Power, Performance (-)
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Introduction
• Rise in functionality increase design complexity
• So, post design steps are automated using Computer Aided Design (CAD)
tools
• However, even designs using automated CAD tools may have bugs
• Due to extremely large size of the design space it is not possible to verify
correctness of the design under all possible situations
• Techniques that can verify, without exercising exhaustive input-output
combinations, that the design meets all the input specifications - formal
verification
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Introduction
• Manufacturing defect could arise due to decrease in the inter-component distance
• All the chips need to be physically tested by giving input signals from a pattern generator
and comparing responses using a logic analyzer - testing.
• In the process of manufacturing a VLSI IC there are three broad steps
• Design
• Verification
• Test
• Categorization of the IC’s can be done based on the functionality
• Analog, Digital or Mixed-signal
• Analog IC
• Ex: Current mirrors, Voltage followers, filters, OPAMPs etc. work by processing continuous signals.
• They perform functions like amplification, active filtering, demodulation etc.
• Digital IC
• Ex: logic gates, flip-flops, multiplexers, and other circuits which work using binary mathematics to process
"one" and "zero" signals.
• Mixed Signal IC
• Ex: Analog to Digital Converter (ADC)
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Introduction
• Automation algorithms and CAD tools are mainly available for digital ICs
• Digital circuits comprise millions of components and transformation of design
specifications to silicon implementation can be accomplished using logical procedures
• Most of the analog circuits comprise less than hundred devices and its design
is like an “art” which is best performed by designers with “aid” of some CAD
tools
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Introduction
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Introduction
Design Abstraction Levels
SYSTEM
MODULE
+
GATE
CIRCUIT
DEVICE
G
S D
n+ n+
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Introduction
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Introduction
Top-down design - Design complex circuits in a simple way
Architecture
Components
Gates
Transistors
Layout
IC
F=AB+C
Bottom-up analysis – Analyze simple components in a complex way
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Introduction
• Functionality of electronics equipment and gadgets has increased but
their physical size has come down drastically
• Due to the rapid advances in integration technologies - millions of
transistors in a single Integrated Circuit (IC) or chip.
• Small Scale Integration (SSI) - integration with 10's of transistors
• Medium Scale Integration (MSI) - integration with 100's of transistors
• Large Scale Integration (LSI) - integration with 1000's of transistors
• Very Large Scale Integration (VLSI) - integration with 1000's of transistors
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