Basic semiconductor electronics pdf

The one coulomb of charge difference between the two points is the voltage polarity. The item which provides a path for the electrons to flow is called a conductor. If it points from a more negative to a more VR R positive potential, then the numerical value receives a minus sign, -6V. Such alternating currents are produced by generators and other such voltage sources whose polarities alternate between a positive direction and a negative direction rather than being fixed in a constant direction as with DC sources.

By convention, alternating currents are called AC currents and alternating voltages are called AC voltages. The most common AC source is the commercial AC power system that supplies energy to your home. The variation of an AC voltage or an AC current over time is called a waveform. Since these waveforms vary with time, AC supplies are designated by lowercase letters v t for voltage, and i t for current instead of uppercase letters V and I for DC values. Note that the subscript t represents time.

There are many different types and shapes of waveforms but the most fundamental is the sine wave also called sinusoid. The sine wave or Sinusoidal waveforms are sinusoidal AC waveform is the voltage and current waveform shape at the wall produced by rotating a coil socket outlets in your home. One complete variation between the same points on the waveform is referred to as a cycle. Since the waveform repeats itself at regular intervals over time, it is called a periodic waveform.

S, Form Factor and Crest Factor can be use with any type of periodic waveform including Triangular, Square, Sawtoothed or any other irregular or complex voltage or current waveform shape. For a pure sinusoidal waveform the effective or R. The RMS value for a sinusoidal waveform is always greater than its Average value. The sine wave function is periodic in time. This means that the instantaneous value at time t will be exactly the same at a later time.

The time taken by the alternating waveform to complete one full cycle is known as its time period An Alternating Current also called wavelength in radio , denoted by T seconds. AC waveform is defined as one which changes The number of cycles per second of a waveform is defined as its frequency. T The advantage of using alternating voltages and currents for electronic power supplies is that they can be raised and lowered with the help of a device called a transformer. In DC circuits, raising and lowering voltages is not so easy because transformers cannot be used with direct current.

There are also square waves, asymmetrical triangle, rectangular and complex waveforms. Complex waveforms generally consist of base fundamental waveform plus various harmonics superimposed on top.

The exact appearance of a complex waveform will depend on the frequencies, magnitudes, and phase relationships of the voltage waves superimposed upon the fundamental wave. Note that the terms wave and waveform do not refer to the same thing as a wave is a varying voltage or current, but a waveform is a graphical representation of such a varying voltage or current.

Resistance, R of a circuit is its ability to resist or prevent the flow of current electron flow through itself making it necessary to apply a greater voltage to the electrical circuit to cause the current to flow again. Resistance opposes current flow. The amount of resistance a circuit element has determines whether the element is a "good conductor" with low resistance, or a "bad conductor" insulator with high resistance or somewhere in between.

Low resistance, for example one ohm or less implies that the circuit is a good conductor made from materials with lots of free electrons in its valence shell. Examples of good conductors are generally metals such as copper, Resistance is the opposition aluminium, gold, silver or non-metals such as carbon, mercury and some to current flowing around acids and salts. The unit of resistance is the High resistance, one mega-ohm or more implies the circuit is a bad Ohm conductor of electricity made from insulating materials with no free electrons, or tightly grouped electrons in its valence shell.

Examples of insulators include glass, porcelain, rubber, pvc polyvinyl chloride plastics, mineral oils and dry wood or paper, etc. Copper Cable Insulator Conductor 2. A conductor is said to have a resistance of one ohm when one volt causes one ampere of current to flow through it.

Length of Material: The resistance of a material is directly proportional to its length. The longer the material the more resistance it has. Cross-sectional Area: The resistance of a material is indirectly proportional to its width. The wider or thicker the material is the less resistance it has allowing more free electrons to flow.

Type of Material: The type of material affects the amount of free electrons able to flow through it. A material which is a conductor has less resistance while a material which is an insulator has more resistance. Temperature: The temperature of the material affects its resistance. Some materials such as thermocouples and thermistors are design to change their resistance with temperature.

The resistor is the simplest passive element used in Electrical and Electronic circuits that is they contain no source of power or amplification but only attenuate or reduce the voltage or current signal passing through them. A resistor can either be fixed or variable. Most resistors are of the fixed type, meaning their resistance remains constant. Variable resistors, called potentiometers or rheostats can be either linear or logarithmic types having an adjustable resistance value from zero ohms to their maximum resistance.

Georg Ohm found that, at a constant temperature, the electrical current flowing through a fixed linear resistance is directly proportional to the voltage applied across it, and also inversely proportional to the resistance. This relationship between the Voltage, Current and Resistance forms the bases of Ohms Law and is shown below. Ohms Law is used extensively in electronics formulas and calculations so it is "very important to understand and accurately remember these formulas".

Linear resistors have a constant resistance for all values of positive or negative voltages and currents. This linear relationship gives a current-voltage I-V characteristic of a straight line. One watt of power is equal to the work done in one second by one volt of potential difference in moving one coulomb of charge around a circuit.

If more heat is generated by the resistor than can be dissipated, the resistor will overheat and become damaged. Resistor power rating is specified in watts.

When calculating the power in resistors or resistances, the main equation to use whenever there is current flowing in 2 the resistance is I R. The physical size of a resistor is no indication of its resistance as a small resistor can have a very low or a very high resistance value. A resistors physical size, however, does give some indication of its power rating. Whenever current flows Generally speaking the larger their physical size the higher its wattage rating.

When resistors with electrical power in Watts higher wattage ratings are required, wirewound resistors fitted to metal heatsinks are generally used to dissipate the excessive heat. When selecting the appropriate resistor for a circuit, always try to select a resistor with a higher wattage rating than the actual calculated power dissipation for safety reasons as resistors that conduct lots of current can become very hot.

These coloured painted bands produce a system of identification generally known as a Resistors Colour Code.

These coloured bands are usually printed towards one end of the resistors body to indicate the first digit with the colours being read from left to right. In the four-band system, the first band closest to the edge represents the first digit of the resistance value, the second band is the second digit, the third band is the decimal multiplier, which tells us how many zeros to add after the first two digits and the fourth band is the tolerance giving Digit, Digit, Multiplier, Tolerance.

The five-band system displays the coloured bands the same as for the four-band, except for an additional third coloured band to represent a third significant digit giving, Digit, Digit, Digit, Multiplier, Tolerance. The five-band system is used for high precision resistors with low tolerance. These resistive networks have an equivalent resistance which is a combination of the individual resistors. It makes no matter what the combination or complexity of the resistor network is, all resistors obey the same basic rules defined by Ohm's Law above.

Since all the current flowing through the first resistor has no other way to go it must also pass through the second resistor and the third and so on. Resistors in series have a Common Current flowing through them as the current that flows through one resistor must also flow through the others as it can only take one path.

Unlike the previous series circuit, in a parallel resistor network the current can take more than one path. Since there are multiple paths for the supply current to flow through, the current is not the same at all points in a parallel circuit. However, the voltage drop across all of the resistors in a parallel resistive network is the same. Then, Resistors in Parallel have a Common Voltage across them and this is true for all parallel connected elements. This method of calculation can be used for calculating any number of individual resistances connected together within a single parallel network.

If however, there are only two individual resistors in parallel then a much simpler and quicker formula can be used to find the total resistance value, and this is given as: 2.

The capacitor is a component which has the ability or "capacity" to store energy in the form of an electrical charge producing a potential difference across its plates. Capacitors consists of two or more parallel conductive metal or foil plates which are not connected or touching each other, but are electrically separated either by air or by some form of insulating material such as paper, mica, ceramic or plastic and which is commonly called the capacitors Dielectric.

When a sufficient amount of charge, Q measured in units of coulombs have been transferred from the source voltage to the capacitors plates, the voltage across the plates, Vc will be equal to the source voltage, Vs and the flow of electrons will cease. The voltage developed across the capacitors plates is not instantaneous but The material used to builds up slowly at a rate that depends on the capacitance value of the plates, separates the plates of a the greater the capacitance, the slower the rate of change of voltage in the capacitor from each other plates.

A capacitance of one farad, F, represents a charging current of one ampere when there is a voltage, V increase or decrease at a rate of of one volt per second. Capacitance, C is always positive and has no negative units. However, the Farad is a very large unit of measurement to use on its own so sub-multiples of the Farad are generally used such as micro-farads, nano-farads and pico-farads, for example.

Also like resistors, there are also variable types of capacitors which allow us to vary their capacitance value for use in radio or "frequency tuning" type circuits. The various types of capacitors include, disc and tubular ceramics made from aluminium oxide or titanium oxide, silvered mica, metallised film made using strips of waxed or oiled paper and aluminium foil, or with plastic dielectrics such as polyethylene, mylar, polypropylene, polycarbonate, and polyester, and finally large electrolytic capacitors in the form of Aluminum Electrolytic Capacitors and Tantalum Electrolytic Capacitors either polarised or non-polarised.

Variable capacitors change value due to the variation in the overlapping area of the plates, or by varying the spacing between parallel plates.

Air dielectric is used for the larger capacitance values. Trimmers and smaller variable types use very thin mica or plastic sheets as the dielectric between the plates. The key advantage of the photocoupler is the electrical isolation between two circuits.

It is employed to couple circuits whose voltage level may differ by several thousand volts. Also determine the values of K in Eq. Read from Fig. Solution Light intensity in fc 3. Explain what is depletion region in a PN-junction diode?

What is reverse saturation current in a diode? Does it exist in both reverse-biased and forward-biased diodes. What is threshold voltage of a diode? What is its value for Si and Gi diodes? Write the diode conduction equation. Explain the meaning of each symbol. Draw the circuit equivalent of a forward-biased diode. Explain the operation of a zener diode and draw its circuit equivalent. A zener diode acts as a voltage regulator. Explain the meaning of the statement. Draw the circuit of a bridge rectifier.

What is the input and output waveform? Write the expression of dc voltage of half-wave and full-wave rectifiers. What is the ripple factor of a diode rectifier? Derive its expression for a full-wave rectifier. Will the ripple factor be more or less than this value for a half-wave rectifier?

What is the conversion efficiency of a rectifier circuit? Will the value be more or less than this in a half-wave rectifier? For the diode circuit of Fig.

For the diode OR gate logic of Fig. For the diode AND logic of Fig. In the zener diode circuit of Fig. Calculate the values of Vz, RS and power rating of the zener. For the circuit with zener diode Fig. VL RL. If the source voltage VS varies from 20 V to 30 V, find the maximum and minimum current in the diode? For the diode bridge of Fig. Sketch vo. Find Vo dc and PIV of each diode. For the diode network of Fig. A CT transformer full-wave rectifier has ac voltage of each half-secondary of 20 V rms.

The resistance of each half is 1 W. The load resistance is Determine Vdc and Idc of the load. A bridge rectifier has four identical diodes of forward resistance of 5 W each.

It is supplied from a transformer with output voltage of 20 V rms and secondary winding resistance of 10 W. Calculate the a dc output voltage at a dc load current of mA b rms value of output voltage at a dc load current of mA c rms value of the ac component of the voltage in part b. For the circuit of Fig. Draw the output voltage of Fig. In Fig. The cut in knee voltage of a germanium diode is a 0. Junction breakdown of a PN-junction diode occurs a with forward bias b with reverse bias c because of improper design d All of these 3.

A zener diode a is useful as an amplifier b has a negative resistance c has a high forward voltage d has a sharp breakdown at low reverse voltage 4.

Which of the following diodes is best suited as a switching diode for very high frequencies? The ripple factor of a half-wave rectifier is a 0. Which of the following is a type of clipping circuit? Level shifter circuits are also known as a clipper circuits b clamper circuits c diodes d transistors 9. In a zener diode, the value of Izm, if power dissipation rating is mW and zener voltage rating is 6. Basically, a transistor is a combination of two back-to-back diodes, provided crystal continuity is maintained.

Addition of another layer results in a three-layer two junctions device which has npn or pnp form and is called a transistor. Such a transistor is known as Bipolar Junction Transistor BJT which acts as a current-controlled device with the output current being controlled by the input current, such that the input-current waveform is replicated at the output.

This mode of operation of a BJT finds wide applications in high-speed digital electronics. In a pnp transistor, a thin N-type layer is sandwiched between two P-type layers, while in an npn transistor, a thin layer of P-type is sandwiched between two N-type layers. A transistor is like two diodes.

The type of transistor can be recognised from the direction of arrow of E emitter , Fig. These constitute the emitter current IE. This is why the base width is kept very small. Recombination rate is small as electron concentration is very light in the base. To replenish the recombining electrons, a small electron current IB flows out of the base. Note that direction of IB is that of conventional current.

Basic Electronics 3. This current flow can be ignored [not shown in the figure]. Carrier flow in an npn transistor is shown in Fig. At the CB junction, there is a depletion region as the CB junction is reversed biased, while there is no such region at the EB junction as it is forward biased. As VCB increases, the depletion region, and so effective base width, reduces. This base-width modulation is known as early effect. This phenomenon is known as punch through. The EB diode is forward biased and the CB diode is reverse biased.

It can, therefore, be modelled as two diodes shown in Fig. This will result in equations already presented. For circuit operations, we require two terminals for input as well as output. So, one terminal of the transistor is grounded. Common base 2. Common emitter 3. Common collector To describe the behaviour of any configuration, two characteristics are required.

Unless otherwise mentioned the transistor is npn. A typical characteristic to scale is presented Fig. It is found that it is practically independent of VCB.

It can be approximated as a diode characteristic. Typical output or collector characteristics are drawn in Fig. The characteristics can be divided into three regions. All the carriers that are injected into the emitter are swept away through the base to the collector. This is easily seen from Fig. This is the linear region in which amplifying action of the circuit takes place.

The input current is transferred by the transistor to output. Voltage amplification will result from low driving-point resistance 10 — W [see Fig. The configuration is not used for amplification but serves certain special purposes. Its circuit is drawn in Fig. The collector characteristics are drawn in Fig. These are related by b. The middle of this region is linear w.

IB and VCE. From Eq. The b: bdc and bac lie in the middle region of Fig. We observe here that b is the common-emitter forward-current gain. This causes, the output to be in phase with input signal. It offers a high input resistance and low output resistance. It is, therefore, employed for impedance matching. In this configuration, aR factor will exist which shows the amplification of input at output.

As shown in Fig. The frequency range has now been extended to 50 kHz, which are employed in high-frequency applications like induction heating and ultrasonic cleaning. Its four layers are arranged as pnpn shown in Fig.

The outer layers are connected to terminals to form anode positive terminal and cathode negative terminal. The P-layer closer to the cathode is connected to the gate terminal. The SCR symbol is drawn in Fig. It is similar to that of a diode, the difference being the indication of the gate terminal.

If a positive pulse is applied at the gate, such that a current of magnitude equal to more than IG turn-on flows into the gate, the processes in the device cause it to go into conduction. The forward current anode to cathode is offered a resistance as low as 0.

However, because of regenerative action, removing the gate current does not cause the device to turn off. The dynamic reverse resistance of an SCR is as high as kW or more. The middle n and p layers can be imagined to be subdivided into two halves, as shown by the dotted line.

The corresponding two-transistor equivalent circuit is drawn in Fig. This circuit will now be used to explain the action of the gate pulse IG. This in turn, increases IB2 causing a regenerative action to set in this is indeed a positive internal feedback. The result is that the SCR is turned on, that is, the switch between the anode E1 and cathode E2 is closed turn-on.

The current IA must be limited by the external circuit, say a series resistance between the source and E1.

The turn-on time of an SCR is typically 0. The turn-off mechanism is called commutation and it can be achieved in two ways explained below. Natural Commutation When the source that feeds the current to anode of SCR is such that it naturally passes through zero, the SCR turns off at the current zero. This is the case when the SCR is fed from the ac source.

In this situation, the commutation is also known as line commutation. Forced Commutation In this method of commutation, the current through the SCR is forced to become zero by passing a current through it in opposite direction from an independent circuit.

One basic turn-off circuit which illustrates the principle is drawn in Fig. A transistor and dc battery source in series are connected to the SCR. To turn off the SCR, a positive IB pulse of magnitude large enough to drive the transistor into saturation is applied at the transistor base. The transistor acts almost like a short circuit. This causes flow of very large Ioff through the SCR in the opposite direction to its conduction current. The total SCR current reduces to zero in a very short time causing it to turn off.

The transistor has to withstand a large current but for a very short time. Various voltages and currents which provide important information for SCR applications are described below. As is seen from Fig. Holding current IH is the value of the current below which SCR switches from conduction state to forward blocking regions of specified conditions. Forward and reverse blocking regions are those regions in which the SCR is open circuited and no current flows from anode to cathode.

Reverse breakdown voltage corresponds to Zener or avalanche region of a diode. As for applications in power and drives, these form the subject matter of a separate course for which several excellent books are available.

We shall give here a single application for illustrative purpose. This action is the same as that of a diode. On application of alternating voltage, it causes rectified ac to flow but it needs to be triggerd for each positive half cycle of ac.

It then produces constant dc average value current through load and dc voltage across load. Adjusting the triggering time on positive half cycle of ac voltage would yield variable dc output. This method is known as phase control. A variable-resistance phase-control circuit is provided in Fig. As R1 is reduced, IG rises to turn-on value at a particular angle time of vi.

If R1 is adjusted for firing at a [see Fig. So the operation of this circuit is known as half-wave, variable-resistance phase control. It may be noted that a diode is provided in the firing circuit to prevent the flow of reverse gate current.

The characteristics of the device, presented in Fig. This possibility of an on condition in either direction can be used to its fullest advantage in ac applications. Note that neither terminal is referred to as the cathode. Instead, there is an anode 1 or electrode 1 and an anode 2 or electrode 2. When the anode 1 is positive with respect to the anode 2, the semiconductor layers of particular interest are p1n2p2 and n3.

For the anode 2 to be positive with respect to the anode 1, the applicable layers are p2n2p1 and n1. In other words, for either direction, the gate current can control the action of the device in a manner very similar to that demonstrated for an SCR. Note the holding current in each direction not present in the characteristics of the DIAC. The graphical symbol for the device and the distribution of the semiconductor layers are provided in Fig.

For each possible direction of conduction, there is a combination of semiconductor layers whose state will be controlled by the signal applied to the gate terminal.

A UJT is a three-terminal device basic construction shown in Fig. Two base contacts are made at each end of one side of the slab, while an aluminium rod is fused on the other side to form a single pn-junction, and hence the name unijunction. The rod is located closer to the base terminal 2 which is made positive with respect to the base terminal 1 by VBB.

The symbol and biasing of a UJT is shown in Fig. The circuit equivalent to the UJT is drawn in Fig. Here the input diode represents the pn-junction operation; RB2 is a fixed resistance and RB1 is a variable resistance, which reduces with increase in emitter current IE.

This ratio h is controlled by the location of the aluminium rod Fig. As VE crosses VP, the emitter fires and holes are injected into the slab from the P-type aluminium rod. This causes increase in the hole content of the N-type slab with consequent increase in the number of free electrons in it, and so, increased conductivity. Thus, VE drops off while IE increases. The device is designed with large base and collector regions as compared with ordinary BJTs with photosensitive material being used for base.

Figure 3. The symbol of npn phototransistor and physical phototransistor are shown in Fig. The lines pointing towards the base represent the light input to base for the required voltage generation.

The metal casing is usually used to improve the exposure of base of transistor to light. The biasing circuit and output characteristics of phototransistor are shown in Fig. At the initial stage, when no exposure of light is there, a minute reverse saturation current flows owing to the presence of minority charge carriers.

When exposed to light, transistor starts conducting through reverse biasing. The response of transistor is different for different intensities of light.

The number of free electrons generated in each material is proportional to the intensity of incident light. The material used for construction of phototransistor includes silicon, germanium with non-identical material like gallium arsenide on either side of p-n junction. The different applications of phototransistor include optocoupling, switching and controlling, optical isolation, optical sensor, etc.

This process is called biasing the BJT. The biasing locates an operating point, also called quiescent point Q , on the characteristics, about which signal-caused variation takes place [ac input causing ac output suitably modified amplified ]; dc biasing and ac analysing can be carried out separately results superimposed if necessary.

In order to isolate the ac signals from dc sources, isolating capacitors are used, which act as short circuits for ac signals. From the signal point of view, these are coupling capacitors. We shall now proceed to analyse and design the dc biasing which determines the location of the Q-point appropriately. KVL equation for BE loop. VCC - 0. Along VCE axis. It intersects the characteristics for IBQ at the operating point Q.

If IB is increased, the Q-point moves up along the load line. The fixed bias cannot counter the thermal effect on the BJT characteristics. Correspondingly, the Q-point moves up on the load line. The circuit also shows coupling capacitors Cc which are open circuit for dc.

The emitter includes voltage drop RE IE, which acts as negative feedback to stabilize the bias Q-point. So there is no significant shift in Q-point, which has been stabilised by inclusion of RE. It can be shown by exact analysis that the sensitivity of the Q-point to changes in b is quite small by proper design of circuit parameters.

If b changes, the level of IBQ will change because of the negative feedback effect of RE but the collector characteristics also change accordingly. Voltage feedback bias is somewhat better than emitter self-bias because of additional voltage feedback. But the voltage-divider bias is the best of all the schemes of BJT bias and is universally adopted.

Remark: In order that emitter resistance RE does not affect the ac performance, it should be shunted by a capacitor called bypass capacitor. Determine IC and IB. Solution From Fig. Solution a We find from Fig. Solution a The operating point is located at Q in Fig. ICBO 0. Solution Assume active mode. Solution 18 - 0.

Solution 20 - 0. Solution a and b Q-point is located on Fig. Review Questions 1. Comment on the doping levels of the three components of a BJT.

Why is the base layer of a BJT made very thin compared to emitter and collector layer? What are the three regions of operation of a BJT. Explain with help of CE configuration collector characteristics. In the three regions of operation how are the BJT junctions biased? Define a of a BJT. Define b of a BJT. How are a and b related? Distinguish between adc and aac 9. Distinguish between bdc and bac. What is reverse saturation current in a BJT? How can this be observed independently?

Draw the symbols for pnp and npn BJT. What distinguishes one from the other? What is meant by biasing a transistor? What is self-bias? How does it help in stabilising the Q-point? Draw the circuit of a voltage-divider bias.

What is voltage feedback bias? Draw the circuit. Is this type of bias almost independent of b? What is meant by b insensitive bias? Problems 1. What is the value of IC? Does it depend on VCB in the active region. From the collector characteristics of Fig. Calculate adc and the corresponding IE. Check from the value of VCB if it is so. Hint: CB junction should be reverse biased. For the fixed-bias configuration of Fig. For the emitter-stabilised bias circuit of Fig.

For the voltage-divider bias circuit of Fig. For the voltage feedback network of Fig. Multiple-Choice Questions 1. Current gain of BJT in common base is a a b b c g d none of these 2.

An SCR device has a four layers b three layers c two layers d one layer 3. When the collector junction in transistors is biased in the reverse direction and the emitter junction in forward directions, the transistor is said to be in the a cut-off region b saturation region c active region d none of these 6. Which of the following acts like a diode and two transistors? Early effect in BJT refers to a avalanche breakdown b zener breakdown c base narrowing d none of these 8.

In a BJT, largest current flows a in the base b in the emitter c in the base and emitter d in the collector 9. These differ from BJTs in two respects. Basic Electronics 4. It is embedded on both sides with P-type material as shown in Fig. The two p-type materials are joined together through ohmic contacts and connected to the terminal gate G. The N and P materials form PN-junctions on the two sides of the channel. The top and bottom of the N-channel make ohmic contact with the Drain D and source S terminals, respectively.

Around both the PN-junctions there is the depletion region like in a diode. The reverse biasing reduces towards the S terminal because of voltage drop in the channel from D to S.

As a result, the depletion region widens at the D-end of the channel. The width of depletion region reduces along the channel towards the S-end. The depletion region is therefore non-uniform as shown in Fig. The initial behaviour of the channel is that of voltage-controlled resistor.

This negative VGS reverse biases both the junctions uniformly, reducing the channel width throughout. This is over and above the effect of VDS. The complete characteristics typical are drawn in Fig. ID mA Locus of pinch-off values. It is further observed that the slope decreases as VGS increases.

That is why JFET is a voltage- controlled device in which input voltage controls the output current. The current flow is due to the movement of these holes. It carries two n-type silicon terminals positioned on both sides and connected to the gate G terminal. The drain and source leads are connected to both sides of p-type channel.

When VGS is zero, the current due to holes as majority carriers flows freely. When positive voltage is applied to the gate terminal, the drain source current starts decreasing till it reaches its cutoff and transistor enters into OFF state. For zero voltage at the gate, the drain current attains its maximum value. Saturation Region This is the fully operational region and maximum current flows during this region.

During this region transistor is in ON state. Breakdown Region It is the region when the voltage supplied to the source exceeds the required voltage.

The transistor loses its ability to resist current and breaks down. During this the current flows from source to drain. What is the nature of their relationship? Small signal modeling analysis is done by replacing all signal sources with their ideal internal resistance, leaving the ac voltages and currents in the circuit.

Small signal models are different for low and high frequencies. Though the resistance of input terminal is very high but gate source voltage affects the value of drain current which is represented by voltage controlled current source gm , VGS with value proportional to gate source voltage. The output resistance or the drain resistance is represented by rd. Drain resistance may have a typical value from kW. From Fig. Due to internal capacitances, the feedback exits between the input and output terminals.

With increase in frequency, Fig. Find mid-band ac gain, output and input impedance. Its thermal stability and other general features makes it suitable for IC design fabrication because of smaller silicon-chip area. On a p-type substrate, an n-channel is formed which is connected to D and S terminals through heavily doped n-regions. The N-channel is insulated from the gate G terminal by an SiO2 layer, which extends over the complete device. The holes recombine with electrons being repelled by the gate, thereby reducing the concentration of electrons in the channel as shown in Fig.

The result is reduction in saturation current ID sat. The drain characteristics and transfer characteristics are similar to those of JFET, as shown in Fig. Depletion mode and enhancement mode are both shown in Fig. In its ON state, the current carrier holes move through the channel. The pinch-off voltage VP will be positive; see Fig. When the voltage between the gate and source terminal is zero then depletion type MOSFET p-channel is in ON state and current flows form source to drain.

When voltage applied to gate terminal is increased, the drain to source path becomes more resistive. If the voltage at gate terminal is made higher than that required, the transistor completely shuts off. Only the P-substrate as shown in Fig.

When negative voltage is applied to the gate terminal then the channel becomes conductive and reaches ON state.

The positive gate pushes the holes in the region underneath the gate into the P-substrates, while the minority electrons are attracted more into the regions just below the SiO2 layer. The result is the formation of an N-channel as shown in Fig.

The channel begins to conduct with positive VDS applied. There is a thin layer depleted of holes at the contact of N-channel and P-substrate. VGD reduces from 6 V to 3 V. This is brought out in the drain characteristics of Fig. The expression 4.

A typical plot is drawn in Fig. VT is also available there. Output is taken from the drain across suitable impedance and source is the common terminal, which is grounded as shown in Fig. This is the most useful and commonly used connection for voltage amplification. As in case of small signal models the capacitances are ignored, but at high frequency, the internal Fig.

The JFET implementation of the common-source amplifier is similar to common-emitter amplifier. C1 and C2 are the coupling capacitors that provide the ac grounds to the input signals and used to couple the input voltage to output voltage. CS is the bypass capacitor. This external coupling and bypass capacitors are large enough that we can model them as short circuits for high frequencies.

Common-source configuration is very important and is widely used. This configuration provides good impedance, good voltage gain and moderate output impedance. Equivalent circuit of common-source amplifier is drawn by capacitors with short circuits and by reducing the dc supply to zero. It hardly yields any gain and is not used in practice. This connection is shown in Fig. It has special applications and is known as source- follower as the output signal has the same phase as the input signal.

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As a result, the latest findings, research and discoveries can be quickly disseminated. This workshop provides all participating research groups with an excellent platform for interaction and collaboration with other members of their respective scientific community. Many eminent scientists from various national and international organizations are actively participating with their latest research works and also equally supporting this mega event by joining the various organizing committees.

This classic book has set the standard for advanced study and reference in the semiconductor device field. Now completely updated and reorganized to reflect the tremendous advances in device concepts and performance, this Third Edition remains the most detailed and exhaustive single source of information on the most important semiconductor devices. It gives readers immediate access to detailed descriptions of the underlying physics and performance characteristics of all major bipolar, field-effect, microwave, photonic, and sensor devices.

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