What are the Advantages of Integrated Circuits (ICs)?

Advantages of Integrated Circuits:

The major advantages of integrated circuits over those made by interconnecting discrete components are as follows:

1. Extremely small size – Thousands times smaller than discrete circuits. It is because of fabrication of various circuit elements in a single chip of semiconductor material.
2. Very small weight owing to miniaturised circuit.
3. Very low cost because of simultaneous production of hundreds of similar circuits on a small semiconductor wafer. Owing to mass production of an IC costs as much as an individual transistor.
4. More reliable because of elimination of soldered joints and need for fewer interconnections.
5. Lower power consumption because of their smaller size.
6. Easy replacement as it is more economical to replace them than to repair them.
7. Increased operating speed because of absence of parasitic capacitance effect.
8. Close matching of components and temperature coefficients because of bulk production in batches.
9. Improved functional performance as more complex circuits can be fabricated for achieving better characteristics.
10. Greater ability of operating at extreme temperatures.
11. Suitable for small signal operation because of no chance of stray electrical pickup as various components of an INC are located very close to each other on a silicon wafer.
12. No component project above the chip surface in an INC as all the components are formed within the chip.

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What are the limitations of integrated circuits?

The integrated circuits have few limitations also, as listed below:

1. In an IC the various components are part of a small semi-conductor and the individual component or components cannot be removed, replaced, therefore, if any component in an IC fails, the whole IC has replaced by the new one. 
2. Limited power rating as it is not possible to manufacture high power greater than 10 Watt) ICs.
3. Need of connecting inductors and transformers exterior to the conductor chip as it is not possible to fabricate inductors and transform on the semi-conductor chip surface. 
4. Operations at low voltage as ICs function at fairly low voltage.
5. Quite delicate in handling as these cannot withstand rough handling or excessive heat. 
6. Need of connecting capacitor exterior to the semi-conductor chip as it is neither convenient nor economical to fabricate capacitances exceeding 30pF. Therefore, for higher values of capacitance, discrete components, exterior to IC chip are connected. 
7. High grade P-N-P assembly is not possible.
8. Low temperature coefficient is difficult to be achieved.
9. Difficult to fabricate an IC with low noise.
10. Large value of saturation resistance of transistors.
11. Voltage dependence of resistors and capacitors.
12. The diffusion processes and other related procedures used in the fabrication process are not good enough to permit a precise control of the parameter values for the circuit elements. However, control of the ratios is at a sufficiently acceptable level. 

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What is Schmitt trigger? How it works? Where is it used?

Schmitt trigger:

Schmitt trigger is an electronic circuit with positive feedback which holds the output level till the input signal to the comparator is higher than the threshold. It converts a sinusoidal or any analog signal to digital signal. It exhibits hysteresis by which the output transition from high to low and low to high will occur at different thresholds.

Invention:

The Schmitt trigger was invented by American scientist Otto H. Schmitt in 1934. By that time, Otto Schmitt was a student. In the year 1937, he published his invention in his doctoral. The name he gave was "thermionic trigger".

Schmitt Trigger Types:

The two different Schmitt trigger types are:

1. Non-inverting type, in which the input and output are both high / both low at the same time (no phase shift).
2. Inverting type, in which there is 180° phase shift between input and output.

Symbols:

There are basically two symbols for the Schmitt Trigger. The symbol is a triangle with an input and an output, just like the one used for the non-inverting buffers. Inside there is the hysteresis symbol. Depending on the type of Schmitt Trigger, inverting or non-inverting (standard), the hysteresis curve sign differs.

Figure 1: Logic Symbols of Schimitt Trigger.

Operations of Schimitt Trigger:

The Schmitt Trigger is a type of comparator with two different threshold voltage levels. Whenever the input voltage goes over the High Threshold Level, the output of the comparator is switched HIGH (if is a standard ST) or LOW (if is an inverting ST). The output will remain in this state, as long as the input voltage is above the second threshold level, the Low Threshold Level. When the input voltage goes below this level, the output of the Schmitt Trigger will switch.

The HIGH and LOW output voltages are actually the POSITIVE and NEGATIVE power supply voltages of the comparator. The comparator needs to have positive and negative power supply (like + and -) to operate as a Schmitt Trigger normally. The following drawing shows how a Schmitt Trigger would react to an AC voltage input:

Figure 2: Basic operation of a Schimitt Trigger.

The orange line is the AC input. The horizontal RED line indicates the High Threshold Level, while the BLUE horizontal line indicates the Low Threshold Level. The green line is the output of the Schmitt Trigger. When the input voltage level goes above the High Threshold Level, then the output of the ST goes High. When the input voltage level goes below the Low Threshold Level, then the output of the ST goes Low. This is the basic operation of a Schmitt Trigger.

Figure 3: The most simple Schmitt Trigger circuit is implemented with a comparator with a positive feedback.

Applications of Schimitt Trigger:  

• Squaring circuit (where a noisy signal requires squaring up).
• Sine-to-Square comparator 
• Amplitude comparator 
• Level detector
• Oscillator i.e. bistable multivibrator, relaxation oscillator etc. 

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Write a short note on AC-to-DC Converter.

Figure (a): AC–DC converter. 

AC-to-DC Converter:

Transformers are commonly used in the process of converting AC to low-voltage direct current (DC) used by electronic devices such as computers. The standard voltage available in North America is 120 V AC, 60 Hz. Computers, however, operate on 5 and 12 V DC. In  Figure (a), the transformer steps the AC down to a lower AC voltage. Thebridge rectifier, consisting of four diodes, converts this AC into a pulsating DC. This DCis smoothed out by capacitors. In some systems, a voltage regulator is used to remove all remaining fluctuations in the voltage, resulting in a steady DC voltage.  

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What are the Linear Variable Differential Transformers (LVDT)? Describe some applications of LVDT.

Linear Variable Differential Transformers (LVDT):

The linear variable differential transformer (LVDT) is a displacement sensor, which consists of a transformer with a single primary coil and two identical secondary coils connected in a seriesopposing manner.  An LVDT is operated based on the mutual inductance concept.

Some applications of LVDT include the following:

1. Weighing systems: LVDTs can be used to measure spring deformation in weighing systems. The measured displacement can be used to calculate the applied force based on the characteristics of the spring.  
2. Displacement sensing: An LVDT may be mounted externally in parallel with the cylinder, thus making the core assembly free to move with the piston rod, and allowing measurement of the displacement of a piston. 
3. Bill detector in ATMs: Using an LVDT, ATMs can detect the number of bills inserted. When bills pass, a motion signal is transferred to the LVDT core element and then a changing output signal is generated. As the bills pass between the rollers, the voltages vary according to the thickness of the bills.     

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What are the Accelerometers? Describe some applications of Accelerometers.

Accelerometers:

Accelerometers (acceleration sensors) are used to measure acceleration, vibration, and mechanical shock. Acceleration is the time rate of change of velocity with respect to a reference system. Acceleration is a vector quantity, and is closely related to velocity and displacement.

Some applications of accelerometers include the following:

1. Sport watches: When runners wear sport watches, their acceleration and speed can be determined by watches that contain accelerometers. 
2. Digital cameras: Some digital cameras contain accelerometers to determine the orientation of the photo being taken. 
3. Rockets: Accelerometers are used in rocket design to maintain the rocket’s stability. 
4. Vehicles: Accelerometers are used widely in vehicles to measure motion of the vehicle. A typical application is that accelerometers can help decide whether air bags should be deployed.

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What are the temperature sensors? Describe some applications of temperature sensors.

Temperature Sensors:

Temperature sensors measure the temperature, which is one of the most frequently measured physical quantities. Thermocouples, resistance temperature devices (RTDs), thermistors, and infrared thermometers represent different types of temperature sensors. The most common types of temperature sensors are thermocouples and RTDs. Thermistors are part of the RTD family. 

Some applications of temperature sensors include the following:

1. Air conditioning: Temperature sensors are used to measure the temperature of the air to control air conditioners. 
2. Heating systems: Temperature sensors are used to control heating systems to maintain the temperature in a room. 
3. Cooling systems in computers: When a personal computer is running for a long time, the motherboard generates a great deal of heat. Using the temperature sensor to sense the temperature inside the computer’s case, the computer can automatically turn on the fan to reduce system temperature. It may also shut down the computer when high temperatures are detected.  
4. Food transport and storage: Temperature sensors are used to make sure food does not exceed safe temperatures to minimize harmful bacterial growth.     

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What is pressure sensor? Describe some applications of pressure sensors.

Pressure sensor:

A pressure sensor is defined as a device that responds to the pressure applied to its sensing surface and converts the pressure to a measurable signal. The most common family of force and pressure sensors is made up of those based on strain gauges and piezoelectric sensors.

Some applications of pressure sensors are listed below:

1. Fuel pressure: Pressure sensors are used to measure fuel pressure during fuel pumping.  
2. Fluid flow: Pressure sensors are used to measure the differential pressure across an orifice. For example, intake airflow or engine coolant flow is measured in this way.  
3. Air pressure: An aneroid barometer (a kind of pressure sensor) is used to measure the air pressure outside an aircraft.  
4. Tire pressure: Pressure sensors are used to monitor the pressure in vehicle tires. 
5. Blood pressure: A small sensor is penetrated into blood vessels to measure blood  pressure. 
6. Altitude sensing: The relationship between changes in pressure relative to altitude is used to measure the altitude in aircraft, rockets, satellites, and weather balloons.     

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What is a differential amplifier? Why use differential amplifiers?

Differential Amplifier:

A differential amplifier is the combination of inverting and non inverting amplifier. The amplifier, which is used to amplify the voltage difference between two inputs-lines, neither of which is grounded, is called differential amplifier. This reduces the amount of noise injected into the amplifier, because any noise appearing simultaneously on both the input terminals as the amplifying circuitry rejects it being a common mode signal.

Figure- Differential Amplifier

Uses of Differential Amplifier:

• Volume Control
• Automatic Gain Control (AGC)
• Amplitude Modulation
• Signal Amplification
• Controlling of Motors & Servo Motors
• Input Stage Emitter Coupled Logic
• Switch

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What is optical fiber cable? What are the advantages of optical fiber cable?

Optical fiber cable:

An optical fiber cable is a cable containing one or more optical fibers that are used to carry light. The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed. Different types of cable are used for different applications, for example long distance telecommunication, or providing a high-speed data connection between different parts of a building.

Figure: Optical Fiber Cable.

Advantages of optical fiber cable:

• High Bandwidth Over Long Distances - Fiber optics have a large capacity to carry high speed signals over longer distances without repeaters than other types of cables. The information carrying capacity increases with frequency. This, however, doesn't mean that optical fiber has infinite bandwidth, but it's certainly greater than coaxial cables. 
• Less signal degradation - The loss of signal in optical fiber is less than in copper wire. 
• Data Security - Optical fibers are difficult to tap. As they do not radiate electromagnetic energy, emissions cannot be intercepted. As physically tapping the fiber takes great skill to do undetected, fiber is the most secure medium available for carrying sensitive data.  
• Safety - Since the fiber is a dielectric, it does not present a spark hazard. 
• Ease Of Installation - Increasing transmission capacity of wire cables generally makes them thicker and more rigid. Such thick cables can be difficult to install in existing buildings where they must go through walls and cable ducts. Fiber cables are easier to install since they are smaller and more flexible. They can also run along the same routes as electric cables without picking up excessive noise. 
• Light, flexible and cheap - Optical fiber cable can be used in corrosive environments and is light, flexible and cheap. 
• Non-flammable - Because no electricity is passed through optical fibers, there is no fire hazard.

Read More: What are the various kind of cables used for transmission?

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Compare JFET’s and MOSFET’s.

Comparison of JFET’s and MOSFET’s:

JFETs and MOSFETs are quite similar in their operating principles and in their electrical characteristics. However, they differ in some aspects, as detailed below :

JFETs vs MOSFETs
How it operates	JFETs	MOSFETs
	Voltage controlled	Voltage controlled.
Gain (Transconductance)	Low transconductance (gain)	Low transconductance (gain)
Input Impedance	JFETs are depletion type transistors only.	MOSFETs can be depletion type or enhancement type.
Input Impedance	JFETs offer less input impedance than MOSFETs. JFETs typically offer about 109 Ω of impedance.	MOSFETs offer greater input impedance. MOSFETs typically offer about 1014Ω of impedance, sometimes greater.
Cost	JFETs are somewhat cheaper to manufacture than MOSFETs. They have a less sophisticated manufacturing process.	MOSFETs are slightly more expensive to manufacture than JFETs.
Susceptibility to Damage	JFETs are less susceptible to damage from ESD because they have greater input capacitance than MOSFETs.	MOSFETs are more susceptible to damage from ESD because the metal oxide insulator that insulates the gate from the drain-source channel lowers the capacitance of the gate. This makes high voltage more able to break through and destroy the transistor.
Popularity	JFETs are less popular than MOSFETs.	MOSFETs are more popular and widely used today than JFETs.

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What is the Role of Capacitor in AC and DC Circuit?

Role of Capacitor in AC Circuits: 

In an AC circuit, capacitor reverses its charges as the current alternates and produces a lagging voltage (in other words, capacitor provides leading current in AC circuits and networks) 

Role and Performance of Capacitor in DC Circuit: 

In a DC Circuit, the capacitor once charged with the applied voltage acts as an open switch.

Rule of Capacitor in AC and DC Circuit

What is the Role of Capacitor in AC and DC Circuit?

Let’s explain in detail, but we will go back to the basics of capacitor first to discuss the matter.

What is Capacitor?

The capacitor is a two terminal electrical device used to store electrical energy in the form of electric field between the two plates. It is also known as a condenser and the SI unit of its capacitance measure is Farad “F”, where Farad is a large unit of capacitance, so they are using microfarads (µF) or nanofarads (nF) nowadays.

How Capacitor Works?

Working and Construction of a capacitor:

Whenever voltage is applied across its terminals, (Also known as charging of a capacitor) current start to flow and continue to travel until the voltage across both the negative and positive (Anode and Cathode) plates become equal to the voltage of the source (Applied Voltage). These two plates are separated by a dielectric material (such as mice, paper, glass, etc. which are insulators), which is used to increase the capacitance of the capacitor.

When we connect a charged capacitor across a small load, it starts to supply the voltage (Stored energy) to that load until the capacitor fully discharges.

Capacitor comes in different shapes and their value is measured in farad (F). Capacitors are used in both AC and DC systems (We will discuss it below).

Capacitance (C):

Capacitance is the amount of electric charge moved in the condenser (Capacitor), when one volt power source is attached across its terminal.

Mathematically,                 

Capacitance Equation:

C=Q/V

Where,

       C=Capacitance in Farads (F)

       Q=Electrical Charge in Coulombs

       V=Voltage in Volts

We will not go in detail because our basic purpose of this discussion is to explain the role and application/uses of capacitors in AC and DC systems. To understand this basic concept, we have to understand the basic types of capacitor related to our topic (as there are many types of capacitor and we will discuss capacitor types latter in another post because it is not related to the question).

Polar and Non-Polar Capacitor:

Non Polar Capacitor: (Used in both AC and DC Systems)

The Non Polar capacitors can be used in both AC and DC systems. They can be connected to the power supply in any direction and their capacitance does not effect by the reversal of polarity.

Polar Capacitor: (Only used in DC Circuits and Systems)

This type of capacitor is sensitive about their polarity and can be only used in DC systems and networks. Polar Capacitors don’t work in the AC system, because of the reversal of polarity after each half cycle in AC supply.

Types of Capacitors: Polar and Non Polar Capacitors with Symbols

Role of Capacitors in AC Circuits and System:

The capacitor has lots of applications in AC systems and we will discuss few uses of capacitor in AC networks below:

Transformer less power supply:

Capacitors are used in transformer less power supplies. In such circuits, the capacitor is connected in series with the load because we know that the capacitor and inductor in pure form does not consume power. They just take power in one cycle and deliver it back in the other cycle to the load. In this case, it is used to reduce the voltage with less power wastage.

Split phase induction motors:

The capacitors are also used in induction motor to split a single phase supply into a two phase supply to produce a revolving magnetic field in the rotor to catch that field. This type of capacitor is mostly used in household water pumps, Fans, air conditioner and many devices which need at least two phases to work.

Power Factor Correction and Improvement:

There are lots of advantages of power factor improvement. In a three phase power systems, capacitor bank is used to supply reactive power to the load and hence improve the power factor of the system. Capacitor bank is installed after a precise calculation. Basically, it delivers the reactive power which was previously traveled from the power system, hence it reduces the losses and improves the efficiency of the system.

Role of Capacitors in DC Circuits and system:

Power conditioning:

In DC systems, capacitor is used as a filter (mostly). Its most common use is converting AC to DC power supply in rectification (such as bridge rectifier). When AC power is converted into fluctuating (with ripples i.e. not a steady state with the help of rectifier circuits) DC power (Pulsating DC) in order to smooth and filter out these ripples and fluctuation, DC Polar capacitor is used. Its value is calculated precisely and depends on the system voltage and the demand load current.

Decoupling Capacitor:

Decoupling capacitor is used, where we have to decouple the two electronics circuits. In other words, the noise generated by one circuit is grounded by decoupling capacitor and it does not affect the performance of other circuit.

Coupling Capacitor:

As we know that Capacitor blocks DC and allows AC to flow through it (we will discuss it in the next session that how does it happens). So it is used to separate AC and DC signals (also used in the filter circuits for the same purpose). Its value is calculated in such a way that its reactance is minimized on the basis of frequency, which we want to pass through it. Coupling Capacitor is also used in filters (ripple remover circuits like RC filters) to separate AC and DC signal and removes the ripples from pulsating DC supply voltage to convert it into pure AC voltage after rectification.

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Draw the block diagram of a mobile communication system.

block diagram of a mobile communication system

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Write down some common applications of Diodes.

Some common applications of Diodes: 

1. Power supply applications
2. AM (amplitude modulation) detectors
3. Back-EMF path
4. Clamping or DC restoration
5. Clipper or limiter
6. Non-linear circuits
7. Logic circuits

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Discuss about Electronic Logic Gates.

Introduction:

          A logic gate is an idealized or physical device implementing a Boolean function, that is, it performs a logical operation on one or more logic inputs and produces a single logic output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and unlimited fan-out, or it may refer to a non-ideal physical device (see Ideal and real op-amps for comparison).

Logic gates are primarily implemented using diodes or transistors acting as electronic switches, but can also be constructed using electromagnetic relays (relay logic), fluidic logic, pneumatic logic, optics, molecules, or even mechanical elements. With amplification, logic gates can be cascaded in the same way that Boolean functions can be composed, allowing the construction of a physical model of all of Boolean logic, and therefore, all of the algorithms and mathematics that can be described with Boolean logic.

Logic circuits include such devices as multiplexers, registers, arithmetic logic units (ALUs), and computer memory, all the way up through complete microprocessors, which may contain more than 100 million gates. In practice, the gates are made from field-effect transistors (FETs), particularly MOSFETs (metal-oxide-semiconductor field-effect transistors).

Logic Gate:

Logic Gates perform basic logical functions and are the fundamental building blocks of digital integrated circuits. These are process signals which represent true or false. Normally the positive supply voltage +Vs represents true and 0V (Zero) represents false. Other terms which are used for the true and false states are shown in the table on the right. It is best to be familiar with them all.

Gates are identified by their function: NOT, AND, NAND, OR, NOR, EX-OR and EX-NOR. Capital letters are normally used to make it clear that the term refers to a logic gate.

Logic states
True	False
1	0
High	Low
+Vs	0V
On	Off

Note that logic gates are not always required because simple logic functions can be performed with switches or diodes:
• Switches in series (AND function)
• Switches in parallel (OR function)
• Combining IC outputs with diodes (OR function)

Logic Gate Symbols:

There are two series of symbols for logic gates:
1. Traditional Symbols &
2. IEC (International Electrotechnical Commission) Symbols.

The Traditional Symbols have distinctive shapes making them easy to recognize so they are widely used in industry and education.

The IEC (International Electrotechnical Commission) symbols are rectangles with a symbol inside to show the gate function. They are rarely used despite their official status, but you may need to know them for an examination.

Inputs and Outputs:

Gates have two or more inputs, except a NOT gate which has only one input. All gates have only one output. Usually the letters A, B, C and so on are used to label inputs, and Q is used to label the output. On this page the inputs are shown on the left and the output on the right.

The Inverting Circle (o):

Some gate symbols have a circle on their output which means that their function includes inverting of the output. It is equivalent to feeding the output through a NOT gate. For example the NAND (Not AND) gate symbol shown on the right is the same as an AND gate symbol but with the addition of an inverting circle on the output.

Truth Tables:

A truth table is a good way to show the function of a logic gate. It shows the output states for every possible combination of input states. The symbols 0 (false) and 1 (true) are usually used in truth tables. The example truth table bellow shows the inputs and output of an AND gate.

Input A	Input B	Output Q
0	0	0
0	1	0
1	0	0
1	1	1

There are summary truth tables below showing the output states for all types of 2-input and 3-input gates. These can be helpful if you are trying to select a suitable gate.

NOT Gate (inverter):

The output Q is true when the input A is NOT true, the output is the inverse of the
input: Q = NOT A

A NOT gate can only have one input. A NOT gate is also called an inverter.

(a) Traditional NOT Gate (Inverter) symbol

(b) International Electrotechnical

Commission NOT Gate (Inverter) symbol

Truth Table

Input A	Output Q
0	1
1	0

AND Gate:

The output Q is true or high if input A AND input B are both true or high:
Q = A AND B
or, Q = A.B

An AND gate can have two or more inputs. A dot (.) is used to show the AND operation i.e. A.B.
Keep in mind that this dot is sometimes omitted i.e. AB

(a) Traditional AND gate Symbol

(b) IEC AND gate Symbol

AND gate Truth Table

Input A	Input B	Output Q
0	0	0
0	1	0
1	0	0
1	1	1

OR Gate:

The output Q is true if input A OR input B is true (or both of them are true):
Q = A OR B
or, Q = A+B
An OR gate can have two or more inputs, its output is true if at least one input is true.

(a) Traditional (ANSI) OR Gate Symbol

(b) IEC OR Gate Symbol

OR Gate Truth Table

Input A	Input B	Output Q
0	0	0
0	1	1
1	0	1
1	1	1

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