Electronics Essentials

Cheatsheet Content

UNIT 2: Transistors & MOSFETs 1. Define Transistor & Types (NPN & PNP) A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It's one of the basic building blocks of modern electronics. Bipolar Junction Transistor (BJT): Current-controlled device. NPN Transistor: Two N-type regions separated by a P-type region. Current flows from collector to emitter. Symbol: Emitter has an arrow pointing out . PNP Transistor: Two P-type regions separated by an N-type region. Current flows from emitter to collector. Symbol: Emitter has an arrow pointing in . Field-Effect Transistor (FET): Voltage-controlled device. MOSFET is a type of FET. 2. BJT as a Switch and CE Amplifier BJT as a Switch: Operated in cutoff (OFF) and saturation (ON) regions. Cutoff Region: Both junctions reverse-biased. $I_C \approx 0$. Output voltage high. Saturation Region: Both junctions forward-biased. $I_C$ max. Output voltage low. BJT as a Common Emitter (CE) Amplifier: Operated in the active region. Input signal applied to base, output taken from collector. High voltage gain, current gain, and power gain. Output is $180^\circ$ out of phase with input. Voltage Gain: $A_v = -g_m R_C \approx -\frac{R_C}{r_e'}$ 3. Input & Output Characteristics of BJT in CE Configuration Input Characteristics ($I_B$ vs $V_{BE}$): Similar to a forward-biased diode. Shows how base current changes with base-emitter voltage. Output Characteristics ($I_C$ vs $V_{CE}$ for various $I_B$): Cutoff Region: $I_C \approx 0$ (below $I_B=0$ curve). Active Region: $I_C = \beta I_B$. Current source behavior. Linear amplification. Saturation Region: $V_{CE}$ small, $I_C$ limited by collector resistor. 4. Construction & Operation of MOSFET (Enhancement-type) N-channel MOSFET (NMOS): Construction: P-substrate, N+ source/drain, gate insulated by SiO2. Operation: Positive $V_{GS}$ creates an N-channel inversion layer in the P-substrate, allowing current flow between source and drain. P-channel MOSFET (PMOS): Construction: N-substrate, P+ source/drain, gate insulated by SiO2. Operation: Negative $V_{GS}$ creates a P-channel inversion layer in the N-substrate, allowing current flow between source and drain. 5. Drain Characteristics of MOSFET (E-MOSFET) ($I_D$ vs $V_{DS}$ for various $V_{GS}$) Cutoff Region: $V_{GS} Triode (Linear) Region: $V_{DS} Saturation Region: $V_{DS} \geq (V_{GS} - V_{th})$. MOSFET acts like a current source. $I_D$ is relatively constant, largely independent of $V_{DS}$. $I_D = K(V_{GS} - V_{th})^2$ (approx.) 6. Single Stage CE Amplifier Circuit & Components A common emitter amplifier typically includes: BJT: Active device for amplification. Biasing Resistors ($R_1, R_2, R_C, R_E$): Set the DC operating point (Q-point) for stable amplification. Coupling Capacitors ($C_1, C_2$): Block DC, allow AC signal to pass. Isolate DC biasing from input/output. Bypass Capacitor ($C_E$): Bypasses $R_E$ for AC signals, increasing AC voltage gain without affecting DC stability. Input Signal Source ($V_{in}$): AC signal to be amplified. Output Load ($R_L$): Where the amplified signal is delivered. 7. Compare BJT and MOSFET Feature BJT (Bipolar Junction Transistor) MOSFET (Metal-Oxide-Semiconductor FET) Control Current-controlled device (Base current) Voltage-controlled device (Gate voltage) Input Impedance Low (due to forward-biased BE junction) Very high (insulated gate) Noise Generally higher Generally lower Thermal Runaway Prone to thermal runaway Less prone, negative temperature coefficient Switching Speed Slower due to minority carrier storage Faster, no minority carrier storage Size Larger for same power rating Smaller for same power rating (good for ICs) Applications Analog amplifiers, high current switches Digital circuits, power switching, high-frequency apps UNIT 3: Digital Electronics 1. Microcontroller vs Microprocessor Microprocessor: CPU on a single chip. Requires external RAM, ROM, I/O ports to form a functional system. Focuses on computation. Microcontroller: A complete computer system on a single chip, including CPU, RAM, ROM, I/O ports, timers, etc. Designed for embedded control applications. 2. De Morgan's Theorem (Sum & Product) Theorem 1 (AND-to-NOR): The complement of a product is equal to the sum of the complements. $\overline{A \cdot B} = \overline{A} + \overline{B}$ Theorem 2 (OR-to-NAND): The complement of a sum is equal to the product of the complements. $\overline{A + B} = \overline{A} \cdot \overline{B}$ 3. Universal Logic Gates (NAND & NOR) NAND and NOR gates are called universal gates because any other logic gate (AND, OR, NOT, XOR, XNOR) can be implemented using only NAND gates or only NOR gates. NOT using NAND: $\overline{A} = \overline{A \cdot A}$ AND using NAND: $A \cdot B = \overline{\overline{A \cdot B}}$ OR using NAND: $A + B = \overline{\overline{A} \cdot \overline{B}}$ (Similar derivations exist for NOR gates). 4. Basic Logic Gates & Truth Tables NOT Gate (Inverter): $Y = \overline{A}$ A Y 0 1 1 0 AND Gate: $Y = A \cdot B$ A B Y 0 0 0 0 1 0 1 0 0 1 1 1 OR Gate: $Y = A + B$ A B Y 0 0 0 0 1 1 1 0 1 1 1 1 NAND Gate: $Y = \overline{A \cdot B}$ A B Y 0 0 1 0 1 1 1 0 1 1 1 0 NOR Gate: $Y = \overline{A + B}$ A B Y 0 0 1 0 1 0 1 0 0 1 1 0 XOR Gate (Exclusive OR): $Y = A \oplus B = \overline{A}B + A\overline{B}$ A B Y 0 0 0 0 1 1 1 0 1 1 1 0 XNOR Gate (Exclusive NOR): $Y = \overline{A \oplus B} = AB + \overline{A}\overline{B}$ A B Y 0 0 1 0 1 0 1 0 0 1 1 1 5. Half Adder and Full Adder Half Adder: Adds two single-bit binary numbers ($A, B$). Produces a Sum ($S$) and a Carry ($C_{out}$). $S = A \oplus B$ $C_{out} = A \cdot B$ Full Adder: Adds three single-bit binary numbers ($A, B, C_{in}$). Produces a Sum ($S$) and a Carry ($C_{out}$). Used for multi-bit addition. $S = (A \oplus B) \oplus C_{in}$ $C_{out} = (A \cdot B) + (C_{in} \cdot (A \oplus B))$ 6. Flip-Flops (SR, JK, T, D) Flip-flops are 1-bit memory elements that store binary data. They are edge-triggered sequential logic circuits. SR Flip-Flop: (Set-Reset) S R Q$_{n+1}$ Comment 0 0 Q$_n$ No Change 0 1 0 Reset 1 0 1 Set 1 1 Invalid Undefined state JK Flip-Flop: (J-K) - resolves SR's invalid state. J K Q$_{n+1}$ Comment 0 0 Q$_n$ No Change 0 1 0 Reset 1 0 1 Set 1 1 $\overline{Q_n}$ Toggle T Flip-Flop: (Toggle) - derived from JK by connecting J and K. T Q$_{n+1}$ Comment 0 Q$_n$ No Change 1 $\overline{Q_n}$ Toggle D Flip-Flop: (Data or Delay) - stores the input bit. D Q$_{n+1}$ Comment 0 0 Reset 1 1 Set 8. Numbering Systems & Complements Binary (Base 2): Digits 0, 1. $(1011)_2 = 1 \cdot 2^3 + 0 \cdot 2^2 + 1 \cdot 2^1 + 1 \cdot 2^0 = (8+0+2+1)_{10} = (11)_{10}$ Octal (Base 8): Digits 0-7. $(27)_8 = 2 \cdot 8^1 + 7 \cdot 8^0 = (16+7)_{10} = (23)_{10}$ Decimal (Base 10): Digits 0-9. Hexadecimal (Base 16): Digits 0-9, A-F (A=10, F=15). $(1A)_{16} = 1 \cdot 16^1 + 10 \cdot 16^0 = (16+10)_{10} = (26)_{10}$ 1's Complement: Invert all bits (0 to 1, 1 to 0). 2's Complement: 1's complement + 1. Used for representing negative numbers and performing subtraction using addition. Example (4-bit): $(0101)_2 = 5_{10}$. 1's complement: $(1010)_2$ 2's complement: $(1010)_2 + 1 = (1011)_2 = -5_{10}$ Binary Addition: $0+0=0$ $0+1=1$ $1+0=1$ $1+1=10$ (Sum=0, Carry=1) Binary Subtraction (using 2's complement): $A - B = A + (\text{2's complement of } B)$. Discard any final carry out. UNIT 4: Operational Amplifiers & Measurement 1. Functional Block Diagram of Operational Amplifier (Op-Amp) An Op-Amp is a high-gain, differential amplifier. Its block diagram typically includes: Input Stage (Differential Amplifier): High input impedance, amplifies the difference between two inputs ($V_+$ and $V_-$). Intermediate Stage (Voltage Amplifier): Provides additional voltage gain. Level Shifting Stage: Shifts the DC level of the signal. Output Stage (Power Amplifier): Low output impedance, provides current drive capability, typically push-pull configuration. 2. Ideal vs. Practical Parameters of Op-Amp Parameter Ideal Op-Amp Practical Op-Amp Input Impedance ($Z_{in}$) $\infty$ Very high ($M\Omega$ to $G\Omega$) Output Impedance ($Z_{out}$) $0$ Very low ($\Omega$ to $100\Omega$) Open-Loop Voltage Gain ($A_{OL}$) $\infty$ Very high ($10^5$ to $10^6$) Bandwidth (BW) $\infty$ Finite (from DC up to MHz) Offset Voltage ($V_{OS}$) $0$ Small ($mV$ range) Input Bias Current ($I_B$) $0$ Small ($nA$ to $pA$) CMRR (Common Mode Rejection Ratio) $\infty$ High (80-120 dB) Slew Rate (SR) $\infty$ Finite ($V/\mu s$) 3. Op-Amp Parameters & Values a. CMRR (Common Mode Rejection Ratio): Ability to reject common-mode signals. $CMRR = \frac{A_{DM}}{A_{CM}}$ (Differential Mode Gain / Common Mode Gain) Ideal: $\infty$. Practical: 80-120 dB. b. PSRR (Power Supply Rejection Ratio): Ability to reject variations in power supply voltage. Ideal: $\infty$. Practical: 60-100 dB. c. Slew Rate (SR): Maximum rate of change of output voltage. $SR = \frac{dV_{out}}{dt}_{max}$ Ideal: $\infty$. Practical: $0.5 V/\mu s$ to $1000 V/\mu s$ (e.g., 741 Op-Amp is $0.5 V/\mu s$). d. Input Bias Current ($I_B$): Average of the currents flowing into the inverting and non-inverting input terminals. $I_B = \frac{I_{B+} + I_{B-}}{2}$ Ideal: $0$. Practical: $nA$ to $pA$ (e.g., 741 Op-Amp is $80 nA$). e. Input Offset Voltage ($V_{OS}$): The differential input voltage required to make the output voltage zero. Ideal: $0$. Practical: $mV$ range (e.g., 741 Op-Amp is $2 mV$). 4. Op-Amp as Inverting & Non-Inverting Amplifier Inverting Amplifier: Input applied to inverting terminal, non-inverting grounded. Voltage Gain: $A_v = -\frac{R_f}{R_{in}}$ Output is $180^\circ$ out of phase with input. Non-Inverting Amplifier: Input applied to non-inverting terminal, feedback to inverting terminal. Voltage Gain: $A_v = 1 + \frac{R_f}{R_{in}}$ Output is in phase with input. 5. Digital Multimeter, Function Generator, DC Power Supply, Digital Storage Oscilloscope (DSO) Digital Multimeter (DMM): Block Diagram: Input attenuator, AC/DC converter, Analog-to-Digital Converter (ADC), digital display. Function: Measures voltage (AC/DC), current (AC/DC), resistance, capacitance, frequency, etc. Displays readings digitally. Function Generator: Block Diagram: Oscillator, wave shaper (for sine, square, triangle), attenuator, output amplifier. Function: Generates various waveforms (sine, square, triangle, pulse) at adjustable frequencies, amplitudes, and offsets. Used for testing circuits. DC Power Supply: Block Diagram: Transformer, rectifier, filter, voltage regulator. Function: Converts AC mains voltage to a stable, regulated DC voltage to power electronic circuits. Digital Storage Oscilloscope (DSO): Block Diagram: Input attenuator, vertical amplifier, ADC, memory, microprocessor, display, time base generator. Function: Captures, stores, and displays waveforms as a function of time. Allows for detailed analysis of signal characteristics (amplitude, frequency, phase, rise/fall times, etc.). 6. Analog Ammeter & Analog Voltmeter Analog Ammeter: Principle: Based on PMMC (Permanent Magnet Moving Coil) galvanometer. Current flowing through a coil in a magnetic field produces a deflecting torque. Construction: Low resistance shunt connected in parallel with a galvanometer coil to extend current range. Function: Measures current in a circuit. Must be connected in series. Analog Voltmeter: Principle: Also based on PMMC galvanometer. Voltage across a high resistance produces a small current through the coil. Construction: High resistance multiplier connected in series with a galvanometer coil to extend voltage range. Function: Measures voltage across two points in a circuit. Must be connected in parallel. UNIT 5: Communication & Sensors 1. Operation of Communication System (Block Diagram) A basic communication system consists of: Information Source: Generates the message (e.g., voice, data). Transducer (Input): Converts non-electrical message into electrical signal (e.g., microphone). Transmitter: Processes the electrical signal for efficient transmission (e.g., modulation, amplification). Channel: Medium through which the signal travels (e.g., air, cable, fiber optic). Receiver: Processes the received signal to recover the original information (e.g., demodulation, amplification, filtering). Transducer (Output): Converts electrical signal back to original message format (e.g., speaker). Destination: The ultimate recipient of the message. 2. GSM Architecture and IOT-based Data Acquisition & Automation System GSM Architecture (Global System for Mobile Communications): Components: Mobile Station (MS): User equipment (mobile phone). Base Station Subsystem (BSS): Manages radio links (Base Transceiver Station - BTS, Base Station Controller - BSC). Network Switching Subsystem (NSS): Handles call setup, routing, mobility management (Mobile Switching Center - MSC, Home Location Register - HLR, Visitor Location Register - VLR, Authentication Center - AuC, Equipment Identity Register - EIR). Operation and Support Subsystem (OSS): Manages the network. IoT-based Data Acquisition & Automation System: Components: Sensors/Actuators: Collect data (temp, pressure) or perform actions (turn light on/off). Gateway: Connects sensors to the internet, potentially performs local data processing. Connectivity: Network protocols (Wi-Fi, Bluetooth, Zigbee, cellular). Cloud Platform: Stores, processes, and analyzes data from devices. Provides services like analytics, machine learning, and visualization. Applications/User Interface: Allows users to monitor data, control devices, and configure automation rules. 3. Sensor Definition, Classification & Types (Active/Passive) A sensor is a device that detects and responds to some type of input from the physical environment (e.g., light, heat, motion, pressure), and converts it into an electrical signal. Classification by Output: Analog, Digital. Classification by Energy Source: Active Sensors: Require an external power source to operate. They emit energy to sense and then detect the change in the energy return. Examples: Radar (emits radio waves), Ultrasonic sensors (emits sound waves), Strain gauge (requires excitation voltage). Passive Sensors: Generate their own electrical signal in response to a physical stimulus without requiring an external power source. They detect naturally occurring energy. Examples: Thermocouple (generates voltage due to temperature difference), Photodiode (generates current from light), PIR sensor (detects IR radiation). 4. Selection Criteria of Sensor or Transducer Accuracy: Closeness of measured value to true value. Precision/Repeatability: Consistency of measurements under same conditions. Resolution: Smallest change in input that produces a detectable output change. Sensitivity: Ratio of change in output to change in input. Range: Minimum and maximum values the sensor can measure. Linearity: How well the output curve approximates a straight line. Response Time: Time taken for the output to reach a certain percentage of its final value. Hysteresis: Difference in output for the same input when approached from different directions. Stability: Ability to maintain performance over time and environmental changes. Environmental Conditions: Operating temperature, humidity, vibration, etc. Cost: Purchase and implementation cost. Size and Weight: Physical dimensions. 5. LVDT (Linear Variable Differential Transformer) Construction: A primary coil and two secondary coils wound on a cylindrical former. A ferromagnetic core moves axially within the coils. Operation: The primary coil is excited by an AC voltage. The core's position determines how much magnetic flux links with each secondary coil, inducing different voltages. The differential output voltage is proportional to the core's displacement. Advantages: High accuracy, excellent linearity, infinite resolution, frictionless, robust. Disadvantages: AC excitation required, sensitive to stray magnetic fields, relatively large size. Applications: Displacement measurement, position sensing, machine tool position feedback, material testing. 6. RTD (Resistance Temperature Detector) Construction: A resistive element (e.g., platinum wire, film) whose resistance changes predictably with temperature. Working Principle: The resistance of metals increases with temperature. By measuring the resistance, the temperature can be determined. $R_T = R_0(1 + \alpha T)$ (approx. for small range) where $R_T$ is resistance at temperature $T$, $R_0$ at $0^\circ C$, $\alpha$ is temperature coefficient. Advantages: High accuracy, excellent stability, good linearity over a wide range. Disadvantages: Slower response time than thermocouples, requires excitation current (active device), self-heating errors possible. Applications: Industrial temperature control, precision temperature measurement in laboratories, HVAC systems. 7. Thermocouple Construction: Two dissimilar metal wires joined at one end (measuring junction) and connected to a reference junction. Working Principle (Seebeck Effect): A temperature difference between the two junctions of dissimilar metals creates a voltage (thermoelectric EMF). This voltage is proportional to the temperature difference. Advantages: Wide temperature range, robust, fast response time, inexpensive, self-powered (passive device). Disadvantages: Lower accuracy than RTDs, requires reference junction compensation, non-linear output. Applications: High-temperature measurement in furnaces, exhaust gas temperature, industrial process control. 8. Strain Gauge Working Principle: Based on the piezoresistive effect. When a conductive material (foil or wire) is stretched or compressed, its resistance changes. $R = \rho \frac{L}{A}$ When stretched, L increases, A decreases, leading to increased R. Gauge Factor $GF = \frac{\Delta R/R}{\Delta L/L}$ Operation: Bonded to the surface where strain is to be measured. Typically used in a Wheatstone bridge circuit to convert resistance change into a measurable voltage. Applications: Stress and strain analysis, load cells, pressure transducers, torque sensors. 9. Biosensor Operation: Combines a biological recognition element (e.g., enzyme, antibody, DNA) with a transducer. The biological element interacts specifically with the analyte, and this interaction is converted into a measurable electrical signal by the transducer. Components: Bioreceptor: Recognizes the target analyte. Transducer: Converts the biological event into a measurable signal. Signal Processor & Display: Amplifies and displays the output. Application: Glucose monitoring (blood glucose meters), pregnancy tests, pathogen detection, environmental monitoring for pollutants. 10. Electromagnetic Spectrum & Application The electromagnetic spectrum is the range of all types of EM radiation. Radiation is energy that travels and spreads out as it goes – the visible light that comes from a lamp in your house and the radio waves that come from a radio station are two types of electromagnetic radiation. It spans from long wavelength, low frequency radio waves to short wavelength, high frequency gamma rays. Radio Waves: Longest wavelengths. Applications: Radio communication, broadcasting, MRI, remote controls, wireless networks (Wi-Fi, Bluetooth). Microwaves: Shorter than radio waves. Applications: Microwave ovens, radar, satellite communication, mobile phones (cellular). Infrared (IR): Heat radiation. Applications: Thermal imaging, night vision, remote controls, fiber optic communication, heating lamps. Visible Light: The portion detectable by the human eye. Applications: Illumination, photography, optical fibers, lasers. Ultraviolet (UV): Shorter than visible light. Applications: Sterilization, tanning beds, water purification, forensic analysis. X-rays: High energy, penetrate soft tissues. Applications: Medical imaging (radiography), security scanners, crystallography. Gamma Rays: Highest energy, shortest wavelength. Applications: Cancer treatment (radiotherapy), sterilization of medical equipment and food, astronomy.