phys225 lecture 20 -...
TRANSCRIPT
Last lecture
• Power Supplies and Voltage Regulation
• Critical “components” of any circuit– Must be stable and reliable
• Batteries are stable, but require replacement
• Power supplies– AC into DC with a rectifier and Zener diode
– Use an IC for better stability• LM78XX/LM79XX (XX=voltage out)
• LM317/LM337 for an adjustable supply
– Switching supplies are efficient, but noisy
Digital Electronics
• Most widespread electronics in the world
• Appears in nearly every device– Phones
– Cars
– Televisions
– Etc.
• Large scale deployment of digital electronics has changed the world– Roughly 1018 equivalent components exist
Digital Electronics
• Digital Electronics represents information (0, 1) with only two discrete values.
• Ideally “no voltage” (e.g., 0v) represents a 0 and “full source voltage” (e.g., 5v) represents a 1
• Realistically “low voltage” (e.g., <1v) represents a 0 and “high voltage” (e.g., >4v) represents a 1
• We achieve these discrete values by using switches.
• We use transistor switches, which operates at high speed, electronically, a small in size.
Analog versus Digital
• Analog systems process time-varying signals thatcan take on any value across a continuous rangeof voltages (in electrical/electronics systems).
• Digital systems process time-varying signals that can take on only one of two discrete values of voltages (in electrical/electronics systems).
– Discrete values are called 1 and 0 (ON and OFF, HIGHand LOW, TRUE and FALSE, etc.)
Representing Information Electronically
• “Analog electronics” deals with non-discrete values
– Any value of the potential
– Any current
– etc.
– Represents what we want to measure in the Universe
• “Digital electronics” deals with discrete values
– Compact representation of analog information
– How high can you count on your hands?
Benefits of Digital over Analog
• Reproducibility
• Not effected by noise means quality
• Ease of design
• Data protection
• Programmable
• Speed
• Economy
Digital Revolution
• Digital systems started back in 1940s.
• Digital systems cover all areas of life:
– still pictures
– digital video
– digital audio
– telephone
– traffic lights
– Animation
Gates
• The most basic digital devices are called gates.
• Gates got their name from their function ofallowing or blocking (gating) the flow of digitalinformation.
• A gate has one or more inputs and produces anoutput depending on the input(s).
• A gate is called a combinational circuit.
• Three most important gates are: AND, OR, NOT
Digital Logic• Binary system -- 0 & 1, LOW & HIGH,
negated and asserted.
• Basic building blocks -- AND, OR, NOT
Digital Abstraction
• It is difficult to make ideal switches means aswitch is completely ON or completely OFF.
• So, we impose some rules that allow analogbehavior to be ignored in most cases, so circuitscan be modeled as if they really did process 0sand 1s, known as digital abstraction.
• Digital abstraction allows us to associate a noisemargin with each logic values (0 and 1).
Logic levels• Undefined region
is inherent
digital, not analog
• Switching threshold varies with voltage, temp
need “noise margin”
• Logic voltage levels decreasing with new processors.
5 , 3.3 , 2.5 , 1.8 V
Flip-flops
• A device that stores either a 0 or 1.
• Stored value can be changed only at certaintimes determined by a clock input.
• New value depend on the current state and it’scontrol inputs
• A digital circuit that contains filp-flops is called asequential circuit
Integrated Circuits
• A collection of one or more gates fabricated on asingle silicon chip is called an integrated circuit(IC).
• ICs were classified by size:– SSI - small scale integration - 1~20 gates
– MSI - medium scale integration - 20~200 gates
– LSI - large scale integration - 200~200,000 gates
– VLSI - very large scale integration - over 1Mtransistors
• Count has grown exponentially– Roughly doubles every 24 months
Programmable Logic Devices
• PLDs allow the function to be programmed intothem after they are manufactured.
• Complex PLDs (CPLD) are a collection of PLDs onthe same chip.
• Another programmable logic chip is FPGA - field-programmable gate arrays.
Application Specific ICs (ASICs)
• Chips designed for a particular application arecalled semicustom ICs or application-specific ICs(ASICs).
• ASICs generally reduce the total component andmanufacturing cost of a product by reducing chipcount, physical size, and power consumption,and they often provide higher performance.
• But costly if not produced in bulk.
Printed-Circuit Boards
• An IC is normally mounted on a printed-circuitboard (PCB) that connects it to other ICs in asystem.
• Individual wire connection or traces can be asnarrow as 4 mils with 4 mils spacing (one-thousandth of an inch)
• Now a days, most of the components use surfacemount technology.
• They are normally layered.
Software Aspects of Digital Design
• Today software tools are an essential part of digital design.
• Software tools improve productivity, correctness and quality of designs
• Software tools are:
– Schematic entry
– HDL (Hardware Description Language) Editors
– Simulators - to verify the behaviour of the design
– Synthesis tools - circuit design
– Timing analyzers and verifiers
Digital Design Levels
• the lowest level of design is device physics and ICmanufacturing processes.
• design at the transistor level
• level of functional building blocks
• level of logic design using HDLs
• computer design and overall system design.
Different Design Levels
Consider a simple design example:
Build a multiplexer with two data inputs A and B, acontrol input S, and an output Z.
Switch model for the example multiplexer
Designing at the transistor level
• Transistor-levelcircuit diagrams
• Gate symbols (for simple elements)
Assembly Language
• Low level programming– Microcontrollers
– Microprocessors
– Programmable devices
• One level higher than “machine code”– Difficult for a human to read
– Uses simple mnemonics for instructions• MOV for move to a location
• An “assembler” is used to convert AL to machine code