What is an Electronic Circuit?


An electronic circuit is a set of semiconductors and or passive electronic components connected with other with any electrically conductive medium, all connections comply with a defined schematic diagram. Schematic diagrams include all information about the connection and devices being used in the circuit. There are three types of electronic circuits first one is an Analog circuit second is a digital circuit and the third is a mixed analog and digital circuit. 

A practical electronic circuit has two things, the first is electronic components and the second is wiring. The wiring may be done on a printed circuit board (PCB), breadboard, and maybe flying wire connections on a plastic board. The most popular wiring method is the Printed circuit Board in which copper tracks are printed on an insulating sheet. Components are mounted with solder joints and connected through printed copper tracks. For Insulation sheet epoxy resin, fiberglass resin, like FR-4 or Backlite polymer is used. 

A breadboard is an array of small metal plugs on a plastic board. Where electronic components can be plugged-in and small jumper wires are used to make wiring connections. The breadboard is a flexible solution for initial circuit testing prototyping and demonstration purpose.

Analog Circuit

                               Circuits that are used to process or generate analog electrical signals are called an analog-circuit. Varying electrical quantity with continuous-time and magnitude is called Analog signal. Analog circuits consist of the following types of electronic components.

Passive Components and Transducer

Resistors, Capacitors, Inductors, Fuse, cells, batteries, and non-semiconductor transducers and sensors are passive electronic components. Almost all electronic circuits have some passive components. Resistors are used to limit current. Capacitors and inductors are electrical energy storage devices in form of electrostatic-field and magnetic-field respectively. Cells and batteries are used as the power source. Fuses are protection devices that protect the circuit from overcurrent and overvoltage. Normally passive fuses work as an overcurrent protection device, are consist of thin metal wire which melts upon more than a specific current. after this fuse act as an open circuit. sensors convert physical quantities to electrical signals. Like thermocouples convert temperature to millivolts signal, Hall sensors convert the magnetic field to an electrical signal. LDR changes its resistance upon a change in exposed light. Sensors are used to measure or estimate physical quantities by electronic circuits. Transducers convert physical energy to another form of energy. Like speaker converts electrical energy to sound wave. And the microphone converts sound waves to electrical signals. Motors, generators, and solar cells are transducers.

Diodes and Thyristors

A diode is a two-terminal (Anode and Cathode) device with a single PN junction. The diode works as a unidirectional device. Its means that electric current may pass through it only in one direction or forward bias, another direction or reverse bias its act as very high resistance and practically pass only very small leakage current. In forward-bias applied voltage must be greater than a certain level or diode forward voltage. Forward voltage is 0.7V for silicon diode and 0.3V for germanium general purpose diode. However special types of diodes’ forward voltage and other parameters may differ concerning their applications and formation. Normal diodes are formed by the general semiconductor epitaxial growth and diffusion process. Different types of diodes are available including Zener diode, varactor diode, Shockley diode, Schottky diode, PIN diode, Photodiode, LED, and Laser diodes. Circuitfeed.com will provide detailed info about diodes in further articles.

Thyristors

Thyristors are multilayered PN junction devices. These are called thyristors for their switching characteristics. SCR or silicon-controlled rectifier is the most common thyristor. SCR is a three-terminal device anode, cathode, and gate. SCR’s anode and cathode terminals behave like a latched switch which can be turn-on by a positive gate pulse. And once SCR is switched on it will latch even with no gate current. SCR can be turn-off by shorting anode and cathode for a while. Or cut-off anode current externally. Other thyristor common family members are SCS “Silicon Controlled Switch is like SCR with anode gate and cathode gate. And can be controlled by both gates, GTO is an abbreviation of gate turn-off Thyristor. It works the same as SCR but it can be turned OFF by gate Reverse pulse. Light-Activated SCR. These SCR can be turned-on upon exposure to light, And with a Gate terminal.

MOSFET-Controlled Thyristor or MCT. Above mentioned thyristor required the gate current to have switched ON. But MCT is an insulated gate and operates with voltage. TRIAC “Triode for Alternating Current” is a Bidirectional Thyristor.  DIAC is another AC thyristor that only switch-ON when appearing voltage across its terminals is greater than break-over voltage. 

Transistors

Transistors are semiconductor devices constructed with PN junctions in various forms. 

Bipolar Junction Transistor: – 

The most popular transistor type is Bipolar Junction Transistor or BJT. BJT is three terminals collector, Base, and emitter. BJT has two PN Junctions in NPN or PNP form. The base is the centre of both PN Junctions. BJT is a current-derived device. The basic current gain of BJT is equal to the Ratio between Collector current and Emitter-Base current. Which is normally 50 to 1000. 

Field Effect Transistor

Field Effect Transistor controls current by an electrostatic field. The electrostatic field is generated by an external voltage. Thus, FETs are voltage-controlled devices. There are many types of FET but the simplest is JFET. JFET or Junction FET has a single PN junction with three terminals Gate, Source, and Drain. The resistance between Source and drain increases with an increase in Gate-Source reverse voltage. Gate-Source reverse voltage increases the depletion layer which narrows the drain current path. When no voltage is applied between gate and source then JFET shows low Drain-Source resistance. This property is opposite to other FET and Transistors. JFET is available in form of N-Channel and P-Channel. Other types of FETs and transistors require input biasing to turn on. The second type is MOSFET Metal-Oxide-Semiconductor Field-Effect-Transistor. In MOSFET gate is insulated by a thin layer of silicon oxide. When the positive voltage is applied on gate-source terminals then Electrons take a place in the depletion region due to the electric field between gate and source. these electrons make a current path between drain and source. MOSFET also have further types by their structure. Like D-MOSFET or Depletion MOSFET, Enhanced mode MOSFET, and VMOSFET. MOSFET is available in both small-signal and high power. All power MOSFET exhibit very small turn-on resistance. This low resistance causes a very low power dissipation in high-power applications. So that MOSFETs are more commonly used in high power switching circuits than BJT.

IGBT or Isolated Gate Bipolar Transistor is an advanced shape of MOSFET that is designed to handle high voltage and current. But IGBT also drops nearly 1.2V across its collector and emitter. Which causes some power dissipation to be negligible in high voltage operation. But required a heat removing mechanism. 

Analog Integrated Circuits

A circuit wiring and its all components fabricated on one die are Integrated Circuits or IC. Nowadays ICs are manufactured with small-scale integration to very-very large-scale integration. Or we can say an IC enclosed with few components to billions of transistors and other electronic components. 

Op-Amp and analog ICs (regulators, PWM, function generator, oscillators, gate drivers)

Digital circuit

Digital circuits process digital signals and make logic gates combinations. The Digital circuit follows Boolean Logic rules. Digital circuit types are as described next

Combinational Logic Circuit

Outputs of the Combinational logic circuit are followed by immediate inputs and output is not bonded with any clocks or timing signals. Digital Multiplexer, Demultiplexer, binary to decimal, decimal to binary decoder, Adder, and subtracter are combinational logic circuit examples.

Sequential Logic Circuits

               A logic circuit that accepts and processes sequential inputs and generates sequential outputs. Sequential logic circuits can maintain logic states and process them with timing signals and clocks. So, outputs may depend on previous logic inputs and states. Sequential logic circuits make of flip-flops, registers, and latches with combinational logic circuits. Counters, Shift registers, RAM, ROM, and EEPROM are examples of sequential logic circuits.

Microprocessors and Microcontrollers

The microprocessor is the CPU or central processing unit of a computer. The microprocessor is a device that can perform arithmetic, logic, and control operations with routines of instructions. Microprocessor takes these instructions by data and address buses from memory interfaced with it. Address and data bus are used to interface memory and other peripherals. Microprocessors perform the logical, arithmetic operation in ALU (Arithmetic and Logic Unit) and send and receive data to I/O peripherals according to program or routine instructions. Instruction consists of operands and opcodes the opcode is the instruction that is executed by the microprocessor. The operand is memory location or data, or the numerical value used to execute that instruction. A routine or program is a sequence of instructions which is executed by a microprocessor step by step. So, the storage and execution of programs or software required memory. Non-volatile memory is used to store programs and volatile memory, or Random Access Memory is used to execute the program. RAM is directly interfaced memory. The program is always loaded first into RAM before execution. On the other hand, peripherals also required a peripheral controller which communicates with the microprocessor and peripherals. Keyboard, pointing devices, displays, and network adapters are common Peripherals. The microprocessor also required some control circuits for clock, power and date and time, etc. 

Microcontroller

Microprocessors need external RAM, ROM, CPU supervisory circuit, and peripheral controllers. These CPUs handle huge operating systems, Graphic displays, and large memory with an exceptional processing speed. A high-speed CPU with large memory and peripheral controllers was impossible to embed in one chip. But in small applications where very high speed, large ROM and EPROM are not required. Then processor, RAM, EPROM, and peripheral controllers can be integrated into one chip. This integrated chip is a microcontroller Unit or MCU. Microcontrollers offer small RAM and ROM with General Purpose I/O and special peripherals like UART, SPI, I2C, USB, CAN Bus, etc. Mostly these special Peripherals require no or few external components for operation. MCU offers a built-in clock generator, timers, RTC, and power controller. Some MCU also offers built-in ADC, PWM output, and analog comparators. 

PLD, CPLD, and FPGA or ASIC

Microprocessor and microcontroller execute instruction routine followed by sequence. So, the CPU core can handle only one instruction at a time. But if we require a reprogrammable unit that can perform multiple operations simultaneously. Then we have Field Programmable Logic Array shortly FPGA. FPGA consists of thousands of Reconfigurable Logic Blocks on a single silicon chip. These logic blocks perform the logic operation as configured in Hardware Description Language (HDL or Verilog HDL). Nowadays manufacturers offer FPGA with a microprocessor core in one chip to eliminate the need for an external MPU or MCU in an embedded system. ASIC or Application Specific Integrated Circuit, which is designed for a single application. So, it’s not programmable but in production is a low-cost method instead of using FPGA. The circuit is usually designed or compiled in HDL. Finally, a generated gate-level netlist with electrical parameters is sent to the manufacturer. Manufacturer gives back in IC form. These ICs are not reprogrammable as all gates and circuitry is fixed for only a specific application. CPLD or Complex Programmable Logic Device is like FPGA with fewer resources and non-volatile memory. CPLDs offer fewer resources with low power consumption and Low Cost also than FPGA. CPLDs offer up to several thousand logic elements while FPGA has several thousand to millions of logic elements. CPLDs use Look-up-table while FPGA uses Configurable Logic Blocks. The lower version of CPLD is PAL or programmable Array Logic which contains only a few hundred programmable logic elements and is limited to combinational logic circuits only. We can see PAL or GAL series ICs only in old circuits boards with through-hole technology.

Digital Sensors and hybrid digital circuits

Sensors and transducers generate analog output signals. These signals require some signal processing and quantization to make them useful for our application. Digital sensors convert and give us sensors reading in digital signals. Normally these sensors use Serial protocols like I2C, SPI, and one-wire. In the Digital sensor range, we can find the temperature, Humidity, pressure, Optical, magnetic, Position or displacement sensors, and many types of MEMs. Analog signals sampling and quantization are processed by Analog to Digital Converters or ADC. ADC converts analog signals into digital signals. Sometimes we require analog signal output following a certain digital signal value. For this purpose, a Digital analog converter circuit (DAC) is used. However, the Pulse width Modulation circuit also does the same thing but mostly in power applications. ADC, DAC, PWM, and MODEM for digital communication are hybrid digital circuit examples


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