Integrated Circuits (IC) and Scale of Integration

Integrated Circuit (IC)

• ICs are used in both linear and digital devices.
• Operational amplifiers use digital ICs, like audio amplifier ICs.
• Flat pack is a popular IC package.
• The SiO2 layer in an IC acts as an insulating layer.
• Digital IC processes handle both digital and linear signals.
• ICs are extremely small and made of silicon.
• Monolithic ICs are most commonly used.

Scale of Integration

• Small Scale Integration (SSI): 1 to 20 components
• Medium Scale Integration (MSI): 20 to 100 components
• Large Scale Integration (LSI): 100 to 1,000 components
• Very Large Scale Integration (VLSI): 1,000 to 10,000 components
• Super Large Scale Integration (SLSI) / Ultra Large Scale Integration (ULSI): 10,000 to 100,000 components
• SSI stands for small scale integration.
• ICs in computers are digital.
• ICs consist of transistors, diodes, resistors, and capacitors.
• Active components in ICs: transistors, FETs (diodes)
• Passive components in ICs: resistors, capacitors, inductors
• It's not possible to fabricate inductors and transformers on a semiconductor chip surface due to space requirements.

Types of ICs

• Monolithic
• Thin film
• Thick film
• Hybrid

Advantages of ICs

• High reliability
• Extremely small size
• Lesser weight and spare requirement
• Low power requirement
• Ability to operate at extreme temperatures
• Low cost

Disadvantages of ICs

• Cannot be repaired
• Not possible to produce high power
• Lack of flexibility
• Additional cooling required for electronic components
• Not possible to fabricate inductors and transformers on the surface of a semiconductor chip

Diodes

• TTL operating voltage is 3V
• CMOS operating voltage is 18V
• Types of diodes include: P-N junction, Zener, signal, LED, Varistor, Varactor, photodiodes, tunnel, PIN, and Schottky diodes.

P-N Junction Diode

• P-type and N-type regions are referred to as anode and cathode, respectively.
• The arrow head indicates the conventional direction of current flow when forward biased.
• P-N junction diodes offer low resistance and high current when forward biased, and high resistance in reverse bias.
• P-N Junction diodes are mostly used in rectifiers, converting AC to DC.

LED (Light Emitting Diode)

• The intensity of radiated light is directly proportional to the forward current of the LED.
• Forward voltage rating: 1V to 3V
• Current rating: 20mA to 100mA
• Uses include power indicators, seven-segment displays, and general-purpose indicators.
• The voltage drop across a conducting LED is approximately 1.7V.
• Advantages: low voltage, longer life, fast on-off switching.
• Disadvantage: low reverse current
• Round type LEDs are most popular, with a size of 3mm-5mm (0.2 inch) and a viewing angle of 20 to 40 degrees.
• Rectangular type LEDs are 5mm x 2mm with a viewing angle increased to around 100 degrees.

Zener Diode

• Operates in reverse bias.
• Zener breakdown occurs in the junction with heavy doping and a narrow depletion layer.
• The field is strong enough to break or rupture covalent bonds by electron-hole pairs.
• Avalanche breakdown occurs in a lightly doped junction with a wide depletion layer where the electric field isn't strong enough.
• With reverse bias, only leakage current flows through the diode.
• A Zener diode is used for voltage regulation.

Signal Diode

• Used in radio signal processing.
• Passes small current, usually up to 100 milliamps.

LED Diode (Light Emitting Diode)

• Forward biased.
• Used in liquid crystal display screens, pocket calculators, lights, and frequency counters.
• In forward bias, electrons cross the junction, fall into holes, and radiate energy as heat.
• Light-emitting diodes dissipate energy by light.
• LEDs do not emit light when reverse biased.
• Gallium-red
• Arsenic-green
• Phosphorus-yellow
• LEDs emitting blue light are available, but red is common.

Varistor

• Variable resistor.
• Not exactly a semiconductor diode.
• Applies voltage and causes very little current flow.
• High resistance at low voltage, low resistance at high voltage.

Varactor Diode

• Reverse bias.
• A semiconductor with variable voltage, also vari-cap or volt-cap.
• Reverse biased junction.
• Capacitance is in proportion to 1/VR.
• In forward bias, the depletion zone decreases, creating low resistance and high current.
• In reverse bias, the depletion layer size increases, leading to high resistance and low current.

Tunnel Diode

• Forward bias
• Very thin depletion layer.
• Heavy doping, reduces the width of the depletion layer.
• Heavy doping reduces reverse breakdown voltage and produces negative resistance.
• Used in oscillators and switches.

Schottky Diode

• Forward bias.
• Is also called hot carrier diode.
• Used as a rectifier in signal frequency applications.
• A metal-semiconductor junction diode with no depletion layer, using metals like gold, silver, platinum, tungsten, etc.
• Electrons plunge into the metal with very large energy and are called hot carriers.
• Can switch off faster than a bipolar diode and are used in clipping and clamping.

PIN Diode

• Forward bias.
• Usual P-type and N-type regions are sandwiched between an intrinsic layer or I-layer of pure silicon.
• The intrinsic layer offers relatively high resistance.

Photodiode

• Reverse bias.
• Light contains electromagnetic energy carried by photons.
• The amount of energy depends on the frequency of the photon.
• Light striking the photodiode causes a current to flow in the circuit.

Transistor

• A bipolar junction device.
• Has two junctions and three regions: emitter, base, collector.
• Has two depletion layers.

Transistor Regions

• Emitter: Heavily doped, supplies majority carriers (electrons or holes) to the base.
• Base: Very lightly doped, very thin (10⁻⁶ m) compared to the emitter or collector.
• Collector: Moderately doped, large in size because it has to dissipate much greater power.

Transistor Bias and Current Flow

• The arrow head is always at the emitter and indicates the conventional direction of current flow.
• Emitter-base is forward biased, leading to decreased resistance and increased current.
• Base-collector is reverse biased, resulting in increased resistance and decreased current.

Current Amplification Factor in Base (α)

• α = ΔIC / ΔIE
• Input = ΔVBE
• Output = ΔVCE

Current Amplification in Emitter (β)

• β = ΔIC / ΔIB
• VCB = constant
• Y = ΔVBE / ΔIB

Collector Amplification (γ)

• γ = ΔIE / ΔIB
• YO = ΔVCE / ΔIC

Transistor Signal Transfer

• Transistors transfer signals from low resistance to high resistance.

Characteristics

• CB (Common Base)
  • Low input
  • Very high output
  • Less than 1 voltage gain
  • High application frequency
  • 0 degree phase shift
• CE (Common Emitter)
  • Low input
  • High output
  • High curent gain
  • Audio Frequency
  • 180 degree phase shift
• CC (Common Collector)
  • Very high input
  • Low output
  • High current and voltage gain, less than 1
  • Impedance matching application
  • 0 degree phase shift

Transistor Classes

• Class A: Output current flows for a full cycle of input signal (360 degrees), efficiency is 50%.
• Class B: Output current flows for half cycle of input signal (180 degrees), efficiency is 78.5%.
• Class C: Output current flows for less than half cycle of input signals (120-150 degrees), efficiency is 85-90%.

Transistor Junctions

• Base-Emitter RB, Base-Collector RB = Cut-off Region
• Base-Emitter FB, Base-Collector FB = Saturated Region
• Base-Emitter FB, Base-Collector RB = Active Region

Transistor Types

• PNP Transistor: Collector and base are negative with respect to the emitter; the collector is more negative than the base.
• NPN Transistor: Collector and base are positive with respect to the emitter; the collector is more positive than the base.
• Transistors can be used for switching or amplification.

Printed Circuit Board (PCB) Basics

• PCBs are also called "printed wiring boards" or "printed wiring cards."
• A PCB is constructed from a thin sheet of non-conductive material, often just 1/16 inch (1.5 mm) thick.
• Two common materials used in PCBs: resin-impregnated paper and epoxy resin-impregnated fiberglass cloth.
• Copper foil is bonded to the surface of the board in a heat press operation.
• Conductive paths are called traces and are created with copper foil on one side, with components on the opposite side.
• PCBs can be single-sided or multi-layered with copper circuit traces.
• PCBs can be joined electrically by what looks like a hollow rivet called a via.
• Solder is the metal that makes the electrical connection between the PCB surface and electronic components.
• A PCB is like a layer cake or lasagna.

PCB Layers

• Silkscreen markings
• Solder mask
• Copper traces
• Substrate (FR4)

FR4 Base Material

• The base material or substrate is usually fiberglass.
• This solid core gives the PCB its rigidity and thickness.
• Common thickness for spark fun products is 1.6 mm (0.063").
• Lilypad boards and Anidino pro micro boards use 0.8 mm thick board.
• Cheaper PCBs and perf boards may be made with materials such as epoxies or phenolics, but are less expensive.

Copper Foil

• The next layer is thin copper foil, laminated to the board with heat and adhesive.
• In common double-sided PCBs, copper is applied to both sides.
• In low-cost PCBs, copper is only on one side.
• "Double-sided" or "2-layer" refers to the number of copper layers in the board.
• This can be as few as one layer or many (16 or morelayers).
• Copper thickness varies and is specified by weight in ounces per square foot.
• Most PCBs have 1 ounce of copper per square foot but some high-power PCBs may use 2 or 3 ounces.
• Each ounce per square foot translates to about 35 micrometers, or 1.4 thousandths of an inch of cu.

Solder Mask

• A layer on top of the copper foil
• This layer gives the PCB its green (or spark fun red) color
• Solder mask is commonly green in color but any color is possible
• Red solder masks are used for most sparkfun boards, while white is used for the IOIO board and purple for the lilypad boards

Silkscreen

• The white silkscreen layer is on top of the solder mask layer
• White silkscreen adds letters, numbers, and symbols to the PCB that are allow for easy assembly and indications for Human being to better understand
• Silkscreen is commonly white but any color can be used, Black, gray, Red, and even yellow silkscreen colors are widely avaliable
• It is uncommon to see more than one color on a single board

PCB Terminology

• Annular ring: ring of copper around a plate through hole in a PCB.
• DRC (Design Rule Check): check to ensure the design does not contain errors, such as incorrectly touching traces, traces which are too skinny or drill holes which are too small.
• Drill hit: design where a hole should be drilled.
• Finger: exposed metal pads along the edge of a board, used to create connection between two circuit boards

More PCB Terminology

• Mouse bites: A set of drill holes that are close together.
• Panel: A larger circuit board consisting of smaller boards which will be broken off before use.
• Paste stencil: A thin, metal (or sometimes plastic) stencil that lies over the board.
• Pick and place: The machine or process by which components are placed on a circuit board.
• Plane: A continuous block of copper on a circuit board.
• Plated through-hole: A connection point through a hole or compartment.
• POGO PIN: A spring-loaded contact which is used to make a temporary connection for testing/programming purposes.
• Reflow: Melting solder to create joints between pads and component leads.
• Silkscreen: Letters, numbers and symbols on a circuit board and usually only one color is available.
• Slot: a hole in a board which is not round and may or may not be plated.

Additional PCB Notes

• PCBs and complete assemblies may vary according to the circuit requirements and specifications.
• Base material is insulating.
• Base material is made up of layers of phenolic resin-impregnated paper or epoxy resin-impregnated fiberglass cloth.
• Thickness of base material depends on strength and stiffness requirements of the finished board.
• Base material is normally stored at a low temperature in a 'B'-stage state.
• The most commonly used conducting material is copper foil with at least 99.5% purity.
• Electrical tests are performed on each batch of boards.
• Circuit printing is carried out using either an etching or additive process.
• Flux must be used to prevent oxidation.
• Silver is particularly suitable for power switching.
• Gold provides a durable, low-resistance, corrosion-resistant finish with longer service life.
• Organic coatings are applied to the surface to protect them from oxidation and contamination.
• Printed wiring circuits are plated with tin/lead for solderability, and nickel/gold for durability.
• Rhodium is the hardest material for coating film in PCBs.
• Palladium is the cheapest material for plating.