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Instrumentation Device Components

Semester 2nd

Chapter 2

Active Components for Instrumentation

Prof Z D Mehta Prof U P Soni

Instrumentation and Control department Govt Polytechnic Ahmedabad

Prof. Z. D. Mehta , Prof. U.P.Soni, GOVT.POLYTECHNIC AHMEDABAD Page 2

Q-1. Classification of 2/3/4 layer semiconductor devices.

Two-layer devices:

1. PN junction diode 2.Zener diode 3.Varactor diode

4. Varistor diode 5. Photo diode 6. Light emitting diode (LED)

7. Schottky diode 8. Shockley diode 9.PIN diode

10.IMPATT diode 11.Tunnel diode 12.Crystal diode

13. Gunn diode 14.Laser diode 15.Thermal diode

16. Power diode

Three-layer devices:

1. Bipolar transistor: NPN, PNP

2. Junction field effect transistor:

Depletion: n-channel, p-channel

Enhancement: NMOS, PMOS, CMOS

3. Power transistor

4. Darlington transistor

Four-layer devices:

1. RCT, SCS

Multi layer devices:

1. SCR 2. TRIAC 3. SBS

4. UJT 5. IGBT 6. GTO

Prof. Z. D. Mehta , Prof. U.P.Soni, GOVT.POLYTECHNIC AHMEDABAD Page 3

Q-2 Explain working and characteristics of P-N junction diode.

A diode is one of the simplest semiconductor devices, which has the characteristic of passing current in one direction only. However, unlike a resistor, a diode does not behave linearly with respect to the applied voltage as the diode has an exponential I-V relationship and therefore we cannot described its operation by simply using an equation such as Ohm's law.

If a suitable positive voltage (forward bias) is applied between the two ends of the PN junction, it can supply free electrons and holes with the extra energy they require to cross the junction as the width of the depletion layer around the PN junction is decreased. By applying a negative voltage (reverse bias) results in the free charges being pulled away from the junction resulting in the depletion layer width being increased. This has the effect of increasing or decreasing the effective resistance of the junction itself allowing or blocking current flow through the diode.

Then the depletion layer widens with an increase in the application of a reverse voltage and narrows with an increase in the application of a forward voltage. This is due to the differences in the electrical properties on the two sides of the PN junction resulting in physical changes taking place. One of the results produces rectification as seen in the PN junction diodes static I-V (current-voltage) characteristics. Rectification is shown by an asymmetrical current flow when the polarity of bias voltage is altered as shown below.

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Prof. Z. D. Mehta , Prof. U.P.Soni, GOVT.POLYTECHNIC AHMEDABAD Page 5

APPLICATIONS OF P-N JUNCTION DIODES Can be used as rectifier in DC Power Supplies. In Demodulation or Detector Circuits. In clamping networks used as DC Restorers. In clipping circuits used for waveform generation. As switches in digital logic circuits.

ZENER DIODE:

A Zener diode is a diode which allows current to flow in the forward direction in the same manner as an ideal diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, "zener knee voltage" or "zener voltage" or "avalanche point".

Zener diode it is nothing but a simple diode connecting in reverse bias. It is mainly a special property of the diode rather than any special type of equipment. Clearance Zener invented this property of the diode that’s why it is named after him. The main principle of this special property is that there is a breakdown in the circuit if the voltage applied across a reversely biased it does not allow the current to flow across it. Now as the voltage across the diode is increased, the temperature increases and the crystal ions vibrate with greater amplitude and all these leads to the breakdown of the depletion layer(i.e, the layer at the junction of p – type and n – type). And when the applied voltage exceeds an specific amount zener breakdown takes place.

Zener Diode is nothing but a single diode connected in a reverse bias, we have already stated that. A diode connected in reverse bias positive in a circuit is shown below A diode

Prof. Z. D. Mehta , Prof. U.P.Soni, GOVT.POLYTECHNIC AHMEDABAD Page 6

A diode connected in reverse bias .The circuit symbol of Zener diode is also shown below. For convenience and understanding, it is used normally symbol of zener diode.

Now, discussing about the diode circuits we should look through the graphical representation of the operation of the Zener diode. Normally it is called the V-I characteristics of a general p– n junction diode.

V-I characteristics of the Zener diode

Application of Zener Diode

It can be used as a Voltage regulator.

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It can be used as a Over Voltage Protector. It can be used as a Voltage reference. Zener diode can be used as a Voltage Clamper.

3. VARACTOR DIODE:

A junction diode which acts as a variable capacitor under changing reverse bias is known as avaractor diode.

Varactor diode Applications: It is used in variable resonant tank LC circuit. Here C part is varied using varactor diode. • AFC(Automatic Frequency Control) where in varactor diode is used to set LO signal. • Varactor is used as frequency modulator. • It is used as frequency multiplier in microwave receiver LO. • It is used as RF phase shifter.

4. PHOTO DIODE:

Photodiode symbol: The photodiode symbol shows the basic format for a diode. However the photodiode symbol also shows the light in the form of arrows striking the diode junction - the arrows are in the opposite direct to that of a light emitting diode where they emanate from the device.

Photodiode symbol used for circuit schematics

Application :

Prof. Z. D. Mehta , Prof. U.P.Soni, GOVT.POLYTECHNIC AHMEDABAD Page 8

• In the cameras for sensing the light intensity

• In the fiber optic receiver

• In the light intensity meter

• An optocoupler/optoisolator using LED & photodiode

5. LED:

A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting. Appearing as practical electronic components in 1962,[5] early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet, and infrared wavelengths, with very high brightness.

Application :

• In the optocoupler • In the infrared remote control • As indicators in various electronic circuits • In seven segment display & Alphanemaric Display • In the traffic signals • In the DVD players

6. Shockley diode: Named after its inventor, a Shockley diode is a PNPN device having two terminals as shown

in Fig.7.24 (i). This device acts as a switch and consists of four alternate P-type and N-type layers in a single crystal. The various layers are labelled as P1, N1, P2 and N2 for identification. Since a P-region adjacent to an N-region may be considered a junction diode, the Shockley diode is equivalent to three junction diodes connected in series as shown in Fig. 7.24 (ii).The symbol of Shockley diode is shown in Fig.

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Application:

7. VARISTOR DIODE: A varistor is a voltage dependent resistor (VDR). The resistance of a varistor is variable

and depends on the voltage applied. The word is composed of parts of the words “variable resistor”. Their resistance decreases when the voltage increases. In case of excessive voltage increases, their resistance drops dramatically. This behavior makes them suitable to protect circuits during voltage surges. Causes of a surge can include lightning strikes and electrostatic discharges. The most common type of VDR is the metal oxide varistor or MOV.

Varistors are nonlinear two-element semiconductors that drop in resistance as voltage increases. Voltage dependent resistors are often used as surge suppressors for sensitive circuits.

Varistor symbol: The following symbol is used for a varistor. It is depicted as a variable resistor which is dependent on voltage, U.

Application : • Telephone and other communication line protection • Radio communication equipment transient suppression • Surge protector power strips • Cable TV system surge protectors • Power supply protection • Microprocessor protection • Electronics equipment protection

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• Low voltage board level protection • Transient voltage surge suppressor (TVSS) • Car electronics protection • Industrial high energy AC protection

8. PIN diode:

A PIN diode is a diode with a wide, lightly doped 'near' intrinsic semiconductor region between a p-type semiconductor and an n-type semiconductor region. The p-type and n-type regions are typically heavily doped because they are used for ohmic contacts

PIN Diode Applications: 1. Rf Switches: Pin diode is used for both signal and component selection. For example pin

diodes acts as range-switch inductors in low phase noise oscillators. 2. Attenuators: it is used as bridge and shunt resistance in bridge-T attenuator. 3. Photo Detectors: it detects x-ray and gamma ray photons.

9. IMPATT diode:

An IMPATT diode (Impact ionization Avalanche Transit-Time) is a form of high-power diode used in high-frequency electronics and microwave devices. They are typically made with silicon carbide owing to their high breakdown fields.

Typically the device is used in a number of applications including:

• Alarms • Radar • Detectors using RF technology 10. TUNNEL DIODE:

A tunnel diode or Esaki diode is a type of semiconductor diode that is capable of very fast operation.

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Application :

• As a high frequency oscillator • In the digital networks • As a high speed switch • As microwave Amplifiers • Oscillatory circuits. • Microwave circuits. • Resistant to nuclear radiation.

11. Crystal Diode:

This is also known as Cat’s whisker which is a type of point contact diode. Its operation depends on the pressure of contact between semiconductor crystal and point. In this a metal wire is present which is pressed against the semiconductor crystal. In this the semiconductor crystal acts as cathode and metal wire acts as anode. These diodes are obsolete in nature. Mainly used in microwave receivers and detectors. Crystal Diode Applications:

1. Crystal diode rectifier 2. Crystal diode detector 3. Crystal radio receiver

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12. Gunn Diode:

Gunn diode is fabricated with n-type semiconductor material only. The depletion region of two N-type materials is very thin. When voltage increases in the circuit the current also increases. After certain level of voltage the current will exponentially decrease thus this exhibits the negative differential resistance. It has two electrodes with Gallium Arsenide and Indium Phosphide due to these it has negative differential resistance. It is also termed as transferred electron device. It produces micro wave RF signals so it is mainly used in Microwave RF devices. It can also use as an amplifier. The symbol of Gunn diode is shown below:

Gunn diode Applications:

o Used as Gunn oscillators to generate frequencies ranging from 100mW 5GHz to 1W 35GHz outputs. These Gunn oscillators are used for radio communications, military and commercial radar sources.

o Used as efficient microwave generators with a frequency range of up to hundreds of GHz. o Used for remote vibration detectors and rotational speed measuring tachometers. o Used as a microwave current generator (Pulsed Gunn diode generator). o Used in microwave transmitters to generate microwave radio waves at very low powers. o Used as fast controlling components in microelectronics such as for the modulation of

semiconductor injection lasers. o Some other applications include door opening sensors, process control devices, barrier operation,

pedestrian safety systems, linear distance indicators, level sensors, moisture content measurement and intruder alarms.

13.LASER DIODE:

A laser diode is an electrically pumped semiconductor laser in which the active medium is formed by a p-n junction of a semiconductor diode similar to that found in a light-emitting diode. The laser diode is distinct from the optically pumped semiconductor laser, in which, while also semiconductor based, the medium is pumped by a light beam rather than electric current.

Prof. Z. D. Mehta , Prof. U.P.Soni, GOVT.POLYTECHNIC AHMEDABAD Page 13

Laser diode Applications:

Diode lasers have proven their value in many fields of application:

• Pumping of solid-state and fiber lasers • Material processing (welding of plastic materials, soldering and annealing of metals) • Medical equipment (hair removal, surgery, dentistry and ophthalmology) • Lighting • Measuring equipment • Printing industry • Science and research

14. DIAC:

A diac is a two-terminal, three layer bidirectional device which can be switched from its OFFstate to ON state for either polarity of applied voltage.

Application : • light dimming • heat control and • universal motor speed control.

BIPOLAR TRANSISTOR:

A Bipolar Junction Transistor (a.k.a. a BJT or Bipolar Transistor) is an active semiconductor device formed by two P-N junctions whose function is amplification of an electric current.

Bipolar transistors are made from 3 sections of semiconductor material (alternating P-type and N-type), with 2 resulting P-N junctions. Schematically, a bipolar transistor can be thought of in this fashion:

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NPN Transistor: Symbol:

The construction and terminal voltages for a Bipolar NPN Transistor are shown above. The voltage between the Base and Emitter ( VBE ), is positive at the Base and negative at the Emitter because for an NPN transistor, the Base terminal is always positive with respect to the Emitter. Also the Collector supply voltage is positive with respect to the Emitter ( VCE ). So for a bipolar NPN transistor to conduct the Collector is always more positive with respect to both the Base and the Emitter.

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Construction: 1. The area of collector layer is largest. So it can dissipate heat quickly. 2. Area of base layer is smallest and it is very thin layer. 3. Area of emitter layer is medium. 4. Collector layer is moderately doped. So it has medium number of charges (electrons). 5. Base layer is lightly doped. So it has a very few number of charges (holes). 6. Emitter layer is heavily doped. So it has largest number of charges (electrons). 7. There are two junctions in this transistor – junction J-1 and junction J-2. 8. The junction between collector layer and base layer is called as collector-base junction

or c-b junction. 9. The junction between base layer and emitter layer is called as base-emitter junction

or b-e junction. 10. The two junctions have almost same potential barrier voltage of 0.6V to 0.7V, just like in a

diode.

Working Principle:

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JFETs (Junction Field Effect Transistors) What is a JFET? A JFET, or junction gate field-effect transistor, is a type of field-effect transistor. A JFET can be used as a voltage-controlled resistance or as an electronically-controlled switch. A p-type JFET consists of a channel of semiconductor material containing a large amount of positive charge carriers or holes, whereas an n-type JFET consists of a channel of semiconductor material containing a large amount of negative charge carriers or holes. At each end of the JFET, ohmic contacts form the source and drain. Electric charge flows through the channel between the source and drain. Electric current can be impeded or switched off by applying a reverse bias voltage to a gate.

FET stands for "Field Effect Transistor" it is a three terminal uni polar solid state device in which current is control by an electric field.

Source:-

It is the terminal through which majority carriers are entered in the bar, so it is called Source.

Drain:-

It is the terminal through which the majority carriers leads the bar, so it is called the drain terminal.

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Gate:-

These are two terminals which are internally connected with each other and heavily doped regions which form two PN-Junctions.

Applications for JFETs:

JFETs can be used for several applications including: • High Input Impedance Amplifier • Low-Noise Amplifier • Differential Amplifier • Constant Current Source • Analog Switch or Gate • Voltage Controlled Resistor

The MOSFET – Metal Oxide FET

Application of MOSFET

MOSFET have wide application in field of electronics some of these applications are given below.

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1. As input amplifier in oscilloscope, electronic volt meter, and other measuring and testing equipment because they have high input resistance.

2. It is used In logic circuits for fast switching. 3. It is also used in TV receiver. 4. It is used in computer circuits. 5. In high frequency amplifiers.

DARLINGTON TRANSISTOR:

In electronics, the Darlington transistor (often called a Darlington pair) is a compound structure consisting of two bipolar transistors (either integrated or separated devices) connected in such a way that the current amplified by the first transistor is amplified further by the second one. This configuration gives a much higher common/emitter current gain than each transistor taken separately and, in the case of integrated devices, can take less space than two individual transistors because they can use a shared collector. Integrated Darlington pairs come packaged singly in transistor-like packages or as an array of devices (usually eight) in an integrated circuit.

Circuit diagram of a Darlington pair using NPN transistors

In electronics, a transistor is a semiconductor device commonly used to amplify or switch electronic signals. A transistor is made of a solid piece of a semiconductor material, with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals. Because the controlled (output) power can be much larger than the controlling (input) power, the transistor provides amplification of a signal. The transistor is the fundamental building block of modern electronic devices, and is used in radio, telephone, computer and other electronic systems. Some transistors are packaged individually but most are found in integrated circuits.

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A transistor is basically two diodes with impurity built into the depletion to both diodes. A power transistor is just this transistor built to carry more power and dissipate more power as opposed to a tiny transistor.

Applications of Darlington Transistor

This transistor is used in various applications where a high gain is required at a low frequency. Some applications are

• Power Regulators • Audio Amplifier o/p stages • Controlling of motors • Display drivers • Controlling of Solenoid • Light and touch sensors.

There are different types of transistors available in different packages. All these types of transistors can

be checked using DMM or AMM. But for this you need to understand their pin configuration first. You

know that a transistor has three terminals: collector, base and emitter and these three terminals

generally in the same sequence for their pin configuration. That is if you hold the transistor such that its

terminals are pointing upward and the printed code number on its body is facing you, then the right

terminal is collector, left is emitter and the middle terminal is the base. However, some of the special

transistors like RF and some power transistors may have different pin configuration.

Terminal Testing of Given Semiconductor Device as Follows:

How to test a transistor using Digital Multimeter ?

If you have read the above topic, it is simple now, to test a

transistor, and find out whether it is OK or FAULTY. Now refer

the first diagram given below.

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It shows that the base is in the middle. For a large

variety of transistors, the base is generally at the

middle. So assuming this, we shall now see how to

check it.

Connect the black probe to base and red

probe to either collector or emitter. If the meter gives deflection, then the transistor is NPN;

if not then transistor may be either faulty or it may be PNP.

Now connect red probe to base and black probe to either collector or emitter. If the meter

gives deflection, then transistor is PNP. If the meter does not give any deflection then

transistor is faulty.

Note that the ohmmeter shows deflection only from base–to–emitter and base–to–collector

or vice versa. In all such conditions, the transistor is GOOD.

Note that if you get deflection between emitter–to–collector, then the transistor is FAULTY.

See the following figure for more details…

What is the conclusion?

Prof. Z. D. Mehta , Prof. U.P.Soni, GOVT.POLYTECHNIC AHMEDABAD Page 22

If you are getting deflection in both directions i.e. from base-emitter and base-collector, but nowhere else, it means that the transistor is OK. If you getting deflection, as above, in OK condition, keeping RED probe to base, then the transistor is NPN transistor. If you are getting deflection, as above, in OK condition, keeping BLACK probe to base, then the transistor is PNP transistor.