Analog vs Digital Systems

Analog and Digital Systems

• Analog quantities are common in nature and handle higher power than digital systems.
• Digital systems efficiently transmit data.
• They assign discrete values to data points.
• Two voltage levels include high and low.
• A bit is a single binary digit (1 or 0).
• Digital electronics represents information digitally.
• Digital logic uses limited codes.
• Analog information can be converted to digital.
• Storage, processing, and transmission of digital information is easy.
• Binary digits 1 and 0 represent data.

Advantages of Digital Systems

• Alphanumeric information can be viewed.
• They are less susceptible to electrical interference (noise).
• Cheap ICs can be used, minimizing external components.
• Data storage is indefinite.
• Data is used for calculations.
• Compatible logic families design is possible.
• Systems can be programmed.

Digital Waveforms

• Digital waveforms are a series of pulses.
• Positive-going pulse: Shifts from LOW to HIGH logic level and back.
• Negative-going pulse: Shifts from HIGH to LOW logic level and back.
• Pulses include rise time, fall time and amplitude.
• DC offset is a constant voltage shifting the pulse's peak.
• Pulse Width: Active pulse time.
• The active high signal exhibits activity when voltage is high.
• The active low signal exhibits activity when voltage is low.
• Digital waveforms graphically denote logic levels over time, also known as PULSE WAVEFORM.
• Positive Pulse: Shifts from low voltage at 0 to peak value at 1.
• Negative Pulse: Shifts from high voltage at 0 to peak value at 1.
• Duty cycle is the percentage of active pulses in a period.
• The most common waveforms are square wave.
• Square waves have a 50% duty cycle.
• The period is the time interval for a pulse to repeat.
• Frequency is the rate of pulse repetition.
• Periodic pulse waveforms consist of repeating pulses in a fixed interval (period).
• Clocks serve as basic timing signals.
• Timing Diagrams denote the relationship between digital waveforms.
• Examples include logic analyzers.
• Amplitude (A), pulse width (tw), and duty cycle support repetitive pulse waveforms.
• Data transmission can be serial or parallel.

Basic Logic Functions

• AND: Output is true if all inputs are true.
• OR: Output is true if one or more inputs are true.
• NOT: Output is the opposite of the input.

Basic System Functions

• AND, OR, NOT elements create logic functions.
• Counting functions represent the number of input pulses.
• Shift registers store and move data with each clock pulse.

Digital System Hierarchy

• Levels of a digital system include systems, functional units, gates and flip-flops, electronic circuits and components.

The Evolution of Electronic Digital Devices

• Gates evolved from constructed vacuum tubes and discrete passive components.
• Transistors replaced vacuum tubes.
• Integrated gate circuits (ICs) consist of transistors and passive components.
• IC's are also called chips

Levels of Integrated Circuits

• SSI circuits have few gates per chip, and all gate terminals are at chip pins.
• MSI circuits feature interconnected gates and flip-flops on a chip.
• SSI and MSI circuits are standard chips.
• LSI/VLSI circuits feature millions of interconnected transistors.
• Modern VLSI chips can contain hundreds of millions of transistors.

Types of VLSI Chips

• Programmable Logic Devices
• ROM's PLA's and PAL's
• Complex PLD's (CPLD)
• Field Programmable Gate Arrays (FPGA's)
• Custom or Semi-custom chips
• Applications-Specific Integrated Circuits (ASICs)

PLD

• PLDs consist of arrays of "and" and "or" gates, serving as alternatives to fixed function devices.
• PALs combine and and fixed OR arrays.
• FPGAs are programmed after manufacture and consist of logic elements.
• CPLDs are high-density PLDs with macro cells interconnected by a Global Routing Pool, offering high speed.
• VHDL (VHSIC Hardware Description Language) is used to model systems.

Hardware Description Languages (HDL)

• VHDL is a hardware description language (HDL).
• Verilog is a hardware description language (HDL) used to model electronic systems.
• AHDL, ABEL, and CUPL are examples of IC Programming languages.

IC Packaging

• Dual In-Line Package (DIP) is a type of IC packaging.
• Surface Mount Technology (SMT) is a type of IC packaging.
• Other IC packaging methods include Small Outline IC (SOIC).
• Plastic Leaded Chip Carrier (PLCC) is a type of IC packaging.
• Leadless Ceramic Chip Carrier (LCCC) is a type of IC packaging.
• Flat Pack (FP) is a type of IC packaging.
• Shrink Small-Outline Package (SSOP) is a type of IC packaging.
• Thin Shrink Small-Outline Package (TSSOP) is a type of IC packaging.

Logic Analyzer

• Logic Analyzers display data in tabular form.

Terms

• Analog values are continuous.
• Digital values are discrete.
• Binary uses 1 and 0 as digits.
• A Bit is either 1 or 0.
• Pulses are swift shifts from one level to another.
• Clocks provide synchronization signals.
• Gates perform AND, OR, and NOT.
• AND has a high output when all inputs are HIGH
• OR has a high output when one or more inputs are HIGH
• Fixed-function logic cannot be altered.
• Programmable logic performs set functions.

Numbering Systems

• Number systems are based on both a unit and a base value.
• The radix is referenced as the base of the numbering system.
• The most significant bit (MSB) holds the highest weight.
• The least significant bit (LSB) holds the lowest weight

Types of Number Systems

• The decimal system radix/base is ten with digits 0-9.
• The binary system radix/base is two with digits 0-1.
• Binary is useful in digital information representation.
• The octal system radix/base is eight with digits 0-7.
• The hexadecimal system radix/base is sixteen with digits 0-9 and A-F.
• Hexadecimal express binary information in a shorter notation.
• Binary Codes represent alphanumeric characters.

More Terms

• Bit time the duration of a bit in a digital waveform.
• Timing waveform represents a graph of a digital waveform.
• Data presents a group of pieces of information.
• Serial data is transmitted one bit at a time.
• Parallel data is transmitted at the same time.
• A byte is 8 bits.
• A word is a large data group.
• Word size presents the width of one data set
• A nibble, also known as a half-byte, has four bits.

Data Formatting

• Binary Coded Decimal (BCD), also named 8421 codes has a 4-bit binary number.
• BCD is used in arithmetic progression where valid digits range from 0000 to 1001.
• Excess-3 code encodes decimal digits with 4 bits; Valid digits are 0011 to 1100
• Gray code changes one bit between consecutive codes.
• Alphanumeric Binary Codes transmit written information via a computer.
• EBCDIC: extended binary coded decimal information code is an 8-bit binary code comprising of 256 characters.
• ASCII: American standard code for information interchange uses 7-bit binary, where 128 characters can use a parity bit in data transmission.
• Binary Signed Numbers present the MSB sign bit (0=positive, 1=negative).
• Binary logic involves variables (two values) , logic operators and logic gates (implementing logic functions).
• Boolean Algebra presents a mathematical system for specifying/transforming logic functions.

Binary Logic and Gates

• Binary variables: one of two values.
• Logical operators: operate on binary values and binary variables.
• Logic Gates: implement logic functions.
• Boolean Algebra: mathematical system for specifying and transforming logic functions.
• Binary variables can evaluate as True/False, Yes/No, and On/Off.
• Variable identifiers include: A, B, y, z and RESET, START_IT and ADD1
• Logical operators can operate using AND, OR, and NOT commands.
• AND is denoted by a dot (.).
• OR. is denoted by a plus (+).
• NOT. is denoted by an overbar (¯).
• Truth Table - listing of all combinations of values.

Topic 4: Logic Gates

• Transistors are electronic switches that regulate current pathways.
• A NOT function is also defined as an inverter.
• AND Function defines boolean multiplication.
• OR functions define boolean addition.
• NAND function presents inverted boolean multiplication.
• NOR function presents inverted boolean addition..
• XOR function presents inequality.
• XNOR function presents equality.

Integrated Circuits

• 7404 - hex NOT gate
• 7408 - quad AND gate
• 7432- quad OR gate
• 7400- quad NAND gate
• 7402-quad NOR gate
• 7486- quad XOR gate
• 4266 - quad XNOR gate
• Gate Delay - Delay between input and output

Boolean Algebra

• Boolean Algebra was introduced By George Boole in 1854..
• Switching Algebra Developed by Claude Elwood Shannon in 1938 consists of two-valued Boolean Algebra.
• All these where formalised by Edward Vermilye

Boolean Laws

• Law of Identity: A = A
• Commutative Law: AB=BA
• Associative Law: A+(B C) =ABC
• Idempotent Law: A+(B+C) = A+B+C
• Double Negative Law/Involution: A . A = A
• Complementary Law/Inverse AA = 0
• Law of Intersection: A +1=1
• Law of Union: A+1=A

Duality

• Duality interchanging addition(+) multiplying(), swapping O's and 1's.
• E.g. F = (A + C) B+0 translates to dual F = (AC) + B1 = AC+B
• In order of operation of the expressions; Parenthesis then NOT before either AND, OR.
• Remember De Morgan's Theorem.
• Comparison for equality with Minterms (AND terms) in relation to of Products (SOP).
• If the variable is "l" this means we denote it as “Not Complemented”.
• the variable is "0" it means we denote it as “Not Complemented”.