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What is Electronic Circuits?


Electronic circuits are interconnected networks of electronic components designed to perform a specific function. Circuits are the fundamental building blocks of all electronic devices and systems. They process signals using a combination of active components like transistors, diodes, integrated circuits along with passive components such as resistors, capacitors and inductors powered by a voltage or current source. The combination and configuration of components determines the operation and purpose of the circuit. This article provides an introduction to the key concepts, fundamental analog and digital circuits, common applications and frequently asked questions about this broad field.

Electronic Components for Circuits

Electronic components can be categorized into two main groups – active components and passive components:

Active Components

  • Transistors – Semiconductor devices used for amplifying and switching signals
  • Integrated Circuits – Microchips integrating multiple transistors and components
  • Vacuum Tubes – Early amplifier device preceding transistors
  • Diodes – Allow current flow in only one direction

Passive Components

  • Resistors – Limit and resist current flow
  • Capacitors – Store electrical charge and filter signals
  • Inductors – Store and release electromagnetic energy
  • Transformers – Transfer electrical energy between two circuits

Selecting the right components and combining them properly allows implementing innumerable circuit functions.

Circuit Diagrams

Circuit diagrams use standardized symbols to describe the components and interconnections in a circuit. They serve as an engineering blueprint for constructing and analyzing circuits. Standardized schematic symbols represent each component type, with lines between them showing electrical nodes and branches.

Common electronic component symbols

Circuit diagrams provide a quick visual representation of the circuit function and topology. They allow simulating and optimizing the circuit before constructing it physically.

Analog and Digital Circuits

Electronic Choke Circuit
Electronic Choke Circuit

Electronic circuits can be categorized into two major classes – analog circuits and digital circuits:

Analog Circuits

  • Signals are continuous, typically voltage or current waveforms
  • Amplitude and frequency vary over time
  • Used for functions like amplification, filtering, modulation
  • Designed using principles of analog electronics

Typical analog circuit – an amplifier

Digital Circuits

  • Signals have discrete on-off or high-low logic levels
  • Represent numeric values, characters, logic states
  • Used for data processing, computing, logic, memory
  • Designed using gates, flip flops, microcontrollers

Example of a digital counter circuit

Both analog and digital circuits are essential building blocks of modern electronics and serve very different purposes.

Power Supplies for Electronic Circuits

All electronic circuits require power supplies to operate. Power supplies convert main AC voltage to the required low level AC or DC voltages to energize a circuit.

Common power supply types include:

  • AC-AC converters – Convert 120/220VAC mains down to lower AC to run heaters, motors, lights
  • AC-DC converters – Rectify and filter AC into a DC level like 5V or 12V for most electronic circuits.
  • DC-DC converters – Switch and convert a DC source to a different voltage level
  • Linear Regulators – Regulate the DC output voltage against load changes
  • Switch Mode Regulators – Efficient high frequency DC-DC conversion

Power supplies employ transformers, rectifiers, filters, linear and switching regulators to deliver stable, appropriate voltage and current levels. Well designed power systems are critical for proper functioning of electronic circuits.

Fundamental Analog Circuits

Analog circuits work with signals free to vary continuously in time. They are extensively used for interfacing with sensors, instrumentation, control systems and real world signals. Here are some fundamental analog circuit types:

Voltage Divider

A simple circuit producing an output voltage (Vout) that is a fraction of its input voltage (Vin). Composed of two resistors in series, with the voltage dropped across each resistor proportional to its resistance.

Used for measurement, sensing, monitoring, and voltage reduction.

Current Mirror

Mirrors the current flowing in one active circuit branch into a second branch by matching the V-I characteristics of two transistors. This forces the second branch current to match the reference current in the first branch.

Used extensively in integrated circuits to bias active components.

Voltage Amplifier

Uses transistors to amplify low level input signals to produce larger output signals while maintaining the original signal shape and frequency. The gain determines the amplifier voltage multiplication ratio.

Essential for boosting sensor signals, audio systems, instrumentation.

Active Filters

Use active components like op-amps combined with resistors and capacitors to produce various filter response shapes like low-pass, high-pass, bandpass, notch and all-pass.

Widely used for audio processing, control systems, radio communications and more.

These form the core analog functions integrated into more complex circuits and ICs.

Fundamental Digital Circuits

digital hardware design

Digital circuits operate on discrete signal levels representing binary 1s and 0s. They perform calculations, data processing, encoding and logic operations by combining basic building blocks. Common digital circuit blocks include:

Logic Gates

Process one or more binary inputs to produce a single binary output according to a Boolean logic function. Basic gates include AND, OR, NOT, NAND, NOR, XOR, XNOR. Combining gates enables complex logic functions.

Used throughout computer systems and embedded devices for data processing and control logic.


Bistable multivibrator circuits with two stable output states based on clock timing and input gates. Latch the current data input or maintain the previous value based on the clock. Types include D, JK, T.

Essential components for registers, counters, finite state machines and digital systems.


Use a control input to switch a common output between multiple input sources. The selected input connection is passed through to the output via high speed electronic switches.

Used extensively to reduce circuit interconnect complexity in large scale ICs and systems.

Analog to Digital Converters (ADCs)

Convert continuous analog signals like audio, video or sensor data into discrete digital values for processing. Common types include successive approximation, integrating, flash, and sigma-delta ADCs.

Essential for digital capture, analysis and storage of real-world analog signals.

Digital circuits underpin the incredible advances in modern computing, embedded systems and communications.

Printed Circuit Boards

Printed circuit boards (PCBs) provide the physical base for assembling electronic circuits and components. PCBs have conductive copper traces etched on an insulating substrate that interconnects the components mechanically and electrically. They provide the pathways for signals and power.

Assembled PCB with components

PCBs allow constructing multilayer circuits with much higher component densities versus point-to-point wiring. They are essential for all but the simplest electronic devices.

Major Applications of Electronic Circuits

Test Electronic Components on a Circuit Board
Test Electronic Components on a Circuit Board

Electronic circuits power functionality across every sphere of technology, industry, science, and daily life. Nearly all electronic devices and systems are enabled by integrated circuits and PCBs populated with discrete components.

Some major applications include:

  • Computing – Microprocessors, memory, data storage, interfaces in PCs, servers, embedded systems
  • Communications – Radio, cellular, WiFi, Bluetooth modules for transmitting/receiving data
  • Consumer Electronics – Audio, video, mobile, gaming, home appliances, IoT devices
  • Automotive – Engine control units, infotainment, diagnostics, safety systems
  • Aerospace/Defense – Avionics, radar, guidance systems, communications, tracking
  • Industrial – PLCs, instrumentation, process control systems, robotics
  • Medical – Patient monitors, imaging equipment, diagnostics, prosthetics

Electronics and circuits are integral to all modern technological capabilities we depend on across every industry and domain.

Circuit Design Process

Designing electronic circuits involves an iterative workflow and optimization:

1. Define Requirements

  • Define the application, inputs, outputs, modes, and performance specifications expected from the circuit.

2. Concept Generation

  • Research existing solutions, circuits, and ICs applicable to the requirements. Identify viable circuit architectures and blocks to provide desired functionality.

3. Circuit Simulation

  • Use SPICE or other analog/digital simulation tools to model the proposed circuit virtually. Simulate and validate expected behavior meets specs.

4. Schematic Capture

  • Draw up detailed circuit schematics with components, interconnects, and construction guidelines for PCB layout stages.

5. PCB Layout

  • Lay out PCB traces, vias, layers, and footprints for the circuit components following layout best practices.

6. Physical Prototyping

  • Have PCBs fabricated and populate components to build working circuit prototypes. Test with instruments.

7. Design Validation

  • Verify prototypes meet all input, output, and performance requirements originally defined. Repeat process until validated.

8. Productionization

  • Finalize manufacturable design that can be reproduced at scale based on feedback from prototypes.

Circuit design brings together a multidisciplinary skillset to translate application requirements into functioning electronic implementations.

Circuit Analysis Techniques

pcb Failure Analysis

Several analysis techniques are essential for understanding, simulating, and troubleshooting circuits:

Nodal Analysis

Analyzes circuits through examination of voltage levels at circuit nodes. Uses Kirchoff’s Current Law to analyze how currents sum at each node. Determining nodal voltages provides full circuit voltage and current solutions.

Mesh Analysis

Analyzes circuits via interconnected loops and branches called meshes. Applies Kirchoff’s Voltage Law around each mesh to determine voltages and currents. Simplifies analysis of complex interconnected circuits.

Thevenin / Norton Equivalent

Reduces complex active circuits down to a simple equivalent model composed of an ideal voltage source and series resistance (Thevenin) or current source and parallel resistance (Norton). Used to simplify analysis.

Frequency Response

Examines how circuits behave over a range of input signal frequencies. Bode plots characterize the gain, phase shift, and frequency limitations of different circuits like filters and amplifiers.

Sensitivity Analysis

Determines how variations in component values affect overall circuit performance. Used to estimate tolerances, tune component specifications, and optimize robustness.

Applying these techniques assists in ensuring circuits are properly designed and performing as intended.

Circuit Design Tools

Modern EDA tools assist in effective circuit design, simulation and PCB layout:

  • Multisim – Perform analog and digital circuit simulation with component libraries
  • OrCAD – Complete PCB design suite for schematic capture and layout
  • LTSpice – Powerful free analog circuit simulator from Analog Devices
  • TINA-TI – Integrated analog, digital, and embedded design tools
  • MATLAB – Math and modeling software with circuit add-ons
  • Altium – High end PCB design environment with integrated simulation
  • Cadence Orcad – Popular schematic and PCB design solution
  • Cadence Spectre – Advanced circuit simulator supporting analog, RF, and DSP
  • Keysight ADS – Leading RF integrated circuit and PCB design platform

Leveraging appropriate EDA tools shortens development cycles and reduces circuit prototyping iterations.

Circuit Construction Techniques

Constructing working circuit prototypes requires key skills:

  • Soldering – Hand soldering using proper techniques to join components on PCBs
  • Rework – Hot air soldering, solder wick for modifying problematic joints
  • Wire Crimping – Securely crimp connector terminals to wires
  • Cable Fabrication – Cut, strip, and terminate multi-wire cables
  • Component Lead Forming – Shape component leads to match PCB footprints
  • Compliance Testing – Validate safety, EMI and regulatory requirements
  • Enclosures – 3D print or machine mechanical housings, brackets

Learning PCB population, hand soldering, wiring, and general prototyping skills accelerates building functioning circuit prototypes.

Circuit Troubleshooting Techniques

Troubleshooting PCB
Troubleshooting PCB

Defects arise when constructing any electronic system. Structured troubleshooting techniques isolate root causes:

  • Visual Inspection – Check for device damage, loose connections, blown components
  • Power Verification – Confirm presence of correct voltages at each point
  • Signal Injection – Inject test signals and stimuli to verify traces and nodes
  • Continuity Testing – Use DMM to check PCB trace continuity and shorts
  • Component Checking – Employ DMM diode test, capacitor test to find faulty parts
  • Oscilloscope Probing – Observe signal waveforms to identify abnormalities
  • Split-Half Isolation – Divide circuit and test subsections separately
  • Circuit Simulation – Compare simulated vs actual performance for discrepancies

Applying these empirical debugging strategies efficiently identifies most circuit faults.

Circuit Design Examples

Below are a few examples of common electronic circuit designs:

Buck Converter

Steps down a higher DC voltage to a lower regulated DC output. Uses an inductor, capacitor, diode and switch control. Used extensively for DC power regulation.

Phase Locked Loop (PLL)

Generates precise clock signals synchronized to an external reference clock. Compares phase against a frequency controlled internal oscillator to match frequencies. Used in radio, clock recovery, frequency synthesis.

H-Bridge Motor Controller

Drives DC motors by providing bidirectional drive current through switched transistor pairs. Allows pulse width modulated (PWM) motor speed control.

Class D Audio Amplifier

Amplifies audio signals very efficiently by producing a pulse width modulated square wave instead of a proportional analog voltage. Used in audio equipment due to high efficiency.

These examples illustrate the wide range of functions realized through specialized circuit designs.


In summary, electronic circuits provide the underlying foundation across every electrical and electronic system. Combining active and passive components in infinite innovative configurations enables all modern technology capabilities. Circuit designers employ rigorous methodologies translating application requirements into functioning implementations. Leveraging fundamental analog and digital circuit principles, modern EDA tools, disciplined troubleshooting and prototyping best practices leads to developing novel, revolutionary solutions through electronic circuit innovations.

Frequently Asked Questions

What is the difference between analog and digital circuits?

Analog circuits work with continuous voltage or current waveforms while digital circuits operate using discrete binary voltage levels representing 1s and 0s. Analog deals with real-world signals while digital encodes data.

What education is required for circuit design?

Circuit designers typically have an electrical engineering or electronics engineering degree. Important subjects include analog/digital circuits, electronics, microcontrollers, signal processing, control systems, and PCB design.

What are the essential instruments needed for circuit design?

Key instruments include oscilloscopes, digital multimeters, function generators, power supplies, prototyping boards, and soldering equipment. Spectrum analyzers, network analyzers and logic analyzers used for advanced RF




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