Unit 2 (Transistor - Trans - resistor).pptx

Transistor

1. BY B. GOPINATH AP/EEE, CKEC UNIT 2: Transistor

2. 1. Introduction 2.Objectives 3.Transistor 4.Transistor history 5.Transistor construction 6.Comparison of transistor connection 7.Transistor biasing 8.Transistor types Bipolar Junction Transistor (BJT) Unipolar Junction Transistor (UJT) Field Effect Transistor (FET) Construction, working, and characteristic of various types of transistors Application of various types of transistor Some useful links C o ntent

3. Objectives After studying this unit, you should be able to- 1.Evolution of transistor 2.Importance of transistor 3.Definition & transistor types 4.Transistor symbol & operation Get knowledge about various types of transistors; UJT, BJT, FET, MOS FET, CMOSFET Understand construction, working, and characteristic of various types of transistors Comparison of transistor connection Comparison of various types of transistors Application of various types of transistor Some useful links

4. Transistor: Introduction Beside diodes, the most popular semiconductor devices is transistors. Transistors are often said to be the most significant invention of the 20 th Century. If cells are the building blocks of life, transistors are the building blocks of the digital revolution. Without transistors, the technological wonders you use every day -- cell phones, computers, cars -- would be vastly different, if they existed at all. Transistors are more complex and can be used in many ways. Most important feature: can amplify signals and as switch. Amplification can make weak signal strong (make sounds louder and signal levels greater), in general, provide function called Gain.

5. In the mid 1940’s a team of scientists working for Bell Telephone Labs in Murray Hill, New Jersey, were working to discover a device to replace the then present vacuum tube technology. Vacuum tubes were the only technology available at the time to amplify signals or serve as switching devices in electronics. The problem was that they were expensive, consumed a lot of power, gave off too much heat, and were unreliable, causing a great deal of maintenance. The scientists that were responsible for the 1947 invention of the transistor were: John Bardeen, Walter Brattain, and William Shockley. Bardeen, with a Ph.D. in mathematics and physics from Princeton University, was a specialist in the electron conducting properties of semiconductors. Brattain, Ph.D., was an expert in the nature of the atomic structure of solids at their surface level and solid-state physics. Shockley, Ph.D., was the director of transistor research for Bell Labs. Their original patent name for the transistor was: “Semiconductor amplifier; Three-electrode circuit element utilizing semi conductive materials.” In 1956, the group was awarded the Noble Prize in Physics for their invention of the transistor. In 1977, John Bardeen was awarded the Presidential Medal of Freedom. Transistor History

6. In 1947, John Bardeen and Walter Brattain devised - the first "point contact" transistor. The first transistor Transistor is an electronic device made of three layers of semiconductor material that can act as an insulator and a conductor. The three layered transistor is also known as the bipolar junction transistor. Transistor Definition

7. A tra n sis t o r h as t h ree dop ed re g i on s. For both types, the base is a narrow region sandwiched between the larger collector and emitter regions. The emitter region is heavily doped and its job is to emit carriers into the base. T h e b a se r e g i o n is v e r y t h in a n d l i g h t l y doped. Most of the current carriers injected into the base pass on to the collector. The collector region is moderately doped and is the largest of all three regions. Transistor Structure

8. BJT is bipolar because both holes (+) and electrons (-) will take part in the current flow through the device N-type regions contains free electrons (negative carriers) P-type regions contains free holes (positive carriers) 2 types of BJT NPN transistor P NP tr a n s i s t o r The transistor regions are: Emitter (E) – send the carriers into the base region and then on to the collector Base (B) – acts as control region. It can allow none,some or many carriers to flow Collector (C) – collects the carriers Transistor Construction

9. NPN Transistor Structure The collector is lightly doped. The base is thin and is lightly doped. The emitter is heavily doped.

10. The base-emitter (BE) junction is forward biased The base-collector (BC) junction is reverse biased. Transistor biasing I E =I B +I C T r an s istor T ypes

11. The transistor is a three-layer semiconductor device consisting of either two n- and one ptype layers of material or two p- and one ntype layers of material. The former is called an npn transistor, while the latter is called a pnp transistor So, there are two types of BJT i) pnp transistor ii) npn transistor Bipolar Junction Transistors In each transistor following points to be noted i) There are two junction, so transistor can be considered as two diode connected back to back. There are three terminals. The middle section is thin than other. Transistor symbol

12. Transistor has three section of doped semiconductor. The section one side is called “emitter” and the opposite side is called “collector”. The middle section is called “base”. Emitter: The section of one side that supplies carriers is called emitter. Emitter is always forward biased wr to base so it can supply carrier. For “npn transistor” emitter supply holes to its junction. For “pnp transistor” emitter supply electrons to its junction. Collector: The section on the other side that collects carrier is called collector. The collector is always reversed biased wrt to base. For “npn transistor” collector receives holes to its junction. For “pnp transistor” collector receives electrons to its junction. Base: The middle section which forms two pn junction between emitter and collector is called Base.

13. Transistor Operation 1) Working of npn transistor: Forward bias Is applied to emitter base junction and reverse bias is applied to collector base junction. The forward bias in the emitter-base junction causes electrons to move toward base. This constitute emitter current, I E As this electrons flow toward p-type base, they try to recombine with holes. As base is lightly doped only few electrons recombine with holes within the base. These recombined electrons constitute small base current. The remainder electrons crosses base and constitute collector current. I E =I B +I C

14. UOU, Haldwani 2) Working of pnp transistor: . Forward bias is applied to emitter base junction and reverse bias is applied to collector base junction. The forward bias in the emitter-base junction causes holes to move toward base. This constitute emitter current, I E As this holes flow toward n-type base, they try to recombine with electrons. As base is lightly doped only few holes recombine with electrons within the base. These recombined holes constitute small base current. The remainder holes crosses base and constitute collector current. Transistor Operation

15. Transistor Symbols Transistor Operating Modes Active Mode Base- Emitter junction is forward and Base-Collector junction is reverse biased. Saturation Mode Base- Emitter junction is forward and Base-Collector junction is forward biased. Cut-off Mode Both junctions are reverse biased.

16. Transistor can be connected in a circuit in following three ways- Common Base Common Emitter Common Collector Transistor Connection Common Base Connection The common-base terminology is derived from the fact that the base is common to both the input and output sides of the configuration. First Figure shows common base npn configuration and second figure shows common base pnp configuration.

17. Current amplification factor (α) : The ratio of change in collector current to the change in emitter current at constant V CB is known as current amplification factor, Practical value of is less than unity, but in the range of 0.9 to 0.99 Expression for Collector Current Total emitter current does not reach the collector terminal, because a small portion of it constitute base current. So, Also, collector diode is reverse biased, so very few minority carrier passes the collector-base junction which actually constitute leakage current. So, collector current constitute of portion of emitter current αI E and leakage current I CBO . I E =I B +I C I C =αI E +I CBO

18. Characteristics of common base configuration Input Characteristics V BE vs I E characteristics is called input characteristics. I E increases rapidly with V BE . It means input resistance is very small. I E almost independent of V CB . Output Characteristics V Bc vs I c characteristics is called output characteristics. IC varies linearly with V Bc ,only when V Bc is very small. As, VBc increases, I c becomes constant.

19. Input Resistance: The ratio of change in emitter-base voltage to the change in emitter current is called Input Resistance. Input and Output Resistance of common base configuration Output Resistance: The ratio of change in collector-base voltage to the change in collector current is called Output Resistance.

20. Common Emitter Connection The common-emitter terminology is derived from the fact that the emitter is common to both the input and output sides of the configuration. First Figure shows common emitter npn configuration and second figure shows common emitter pnp configuration. Base Current amplification factor ( β) : In common emitter connection input current is base current and output current is collector current. The ratio of change in collector current to the β change in base current is known as base current amplification factor,

21. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Normally only 5% of emitter current flows to base, so amplification factor is greater than 20. Usually this range varies from 20 to 500. Relation Between α and β Expression for collector current

22. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Characteristics of common emitter configuration V BE vs I B characteristics is called input characteristics. I B increases rapidly with V BE . It means input resistance is very small. I E almost independent of V CE . I B is of the range of micro amps. Input Characteristics Output Characteristics V CE vs I c characteristics is called output characteristics. I C varies linearly with V CE ,only when V CE is very small. As, V CE increases, I C becomes constant.

23. D r . M ee n a k s h i Ra n a De UOU, Haldwani Input Resistance: The ratio of change in emitter-base voltage to the change in base current is called Input Resistance. Input and Output Resistance of common emitter configuration ptt- Physics Output Resistance: The ratio of change in collector-emitter voltage to the change in collector current is called Output Resistance.

24. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani The common-collector terminology is derived from the fact that the collector is common to both the input and output sides of the configuration. Common Collector Configuration First Figure shows common collector npn configuration and second figure shows common collector pnp configuration. Current amplification factor (γ): In common emitter connection input current is base current and output current is emitter current. The ratio of change in emitter current to the change in base current is known as current amplification factor in common collector configuration.

25. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Relation between γ and α Expression for collector current

26. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Comparison of Transistor Connection

27. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani When used as an electronic switch, the transistor is normally operated alternately in cut-off and saturation regions. Transistor applications Transistor as a switch

28. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Due to the small changes in base current the collector current will mimic the input with greater amplitude. Transistor as amplifier Figure shows CE amplifier for npn transistor Battery V BB is connected with base in-order to make base forward biased, regardless of input ac polarity. Output is taken across Load R

29. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani During positive half cycle input ac will keep the emitter base junction more forward biased. So, more carrier will be emitted by emitter, this huge current will flow through load and we will find output amplified signal. During negative half cycle input ac will keep the emitter-base junction less forward biased. So, less carrier will be emitted by emitter. Hence collector current decreases. This results in decreased output voltage (In opposite direction).

30. D r . M ee n a k s h i Ra n a Deptt- Physics Transistor Load line analysis UOU, Haldwani Consider common emitter npn transistor circuit shown in figure. There is no input signal. Apply KVL in the output circuit

31. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Operating Point It is called operating point because variation of I C takes place about this point. It is also called quiescent point or Q-point.

32. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Field Effect Transistor Field effect Transistor is a semiconductor device which depends for its operation on the control of current by an electric field FET has several advantages over BJT Current flow is due to majority carriers only Immune to radiation 3.High input resistance 4.Less noisy than BJT 5.No offset voltages at zero drain current 6.High thermal stability JFET Symbol

33. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Classification of FET Based on the construction JFETS are of two types 1.N Channel FET 2 .P C h a nn e l FET

34. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Construction of N Channel FET S o u r c e : T h e s o u r c e is t h e ter m i n a l t h r ou g h which majority carriers enter the Silicon Bar D r a i n : T e r m i n a l t h r ou g h w h ich m a j o ri t y carriers leave the bar G a t e : c on tr o ls Dr a in c u rr e n t a n d is a l w a y s reverse biased The operation of FET can be compared to the water flow through a flexible pipe When one end is pressed the cross sectional area decreases hence water flow decreases In a FET drain is similar to outlet. Principle: To control the drain current FET makes use of channel formed in by Space charge region between Gate and the bar. By increasing the reverse bias the width of space charge region decreases. As a result the channel Resistance increases The Drain current decreases Operation of FET

35. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani As we increase the reverse bias on gate (VGS) The channel width decreases Gate is reverse biased by battery 2 The Bias voltage at which drain current becomes zero is known as pinch off voltage Working of FET Working of n channel FET and p channel FET

36. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani When Voltage is applied between source and Drain majority carriers move through the channel between depletion region. The value of Drain current is maximum when no external voltage is applied between gate and source. When gate to source reverse bias increases the depletion region widens and channel width decreases hence Drain current decreases. Hence Drain current decreases. When gate to source voltage is increased further The channel completely closes. This is called pinch off region. This reduces Drain current to zero. The Gate to source voltage at which the Drain current is zero is called “ Pinch off Voltage” Working of FET

37. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Electrical behavior is described in terms of the parameters of the Device. They are obtained from the characteristics. Important Parameters for FET are 1.DC Drain resistance 2.AC drain Resistance 3.Transconductance JFET Parameters Difference between N channel FET and P channel FET

38. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani DC Drain resistance : Defined as ratio of Drain to source Voltage V DS to Drain current I D . Also called static or Ohmic Resistance Mathematically JFET Parameters AC Drain resistance: Defined as the resistance between Drain to source when JFET is operating in Pinch off Region or saturation Region 2. Mathematically Transconductance (gm): It is given by the ratio of small change in drain current to the Corresponding change in the Gate to source Voltage V GS . Also known as Forward Transmittance Mathematically

39. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Difference between FET and BJT

40. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Drain Characteristics Drain characteristics show the relation between the drain to source voltage and V DS and drain current I D. At the Drain to source Voltage corresponding to point B Channel width reduces to a minimum value and is known as pinch off Drain current I D is given by The device gets damaged due to avalanche Breakdown mechanism.

41. D r . M ee n a k s h i Ra n a Deptt- Physics FET A p p li c a ti o n s UOU, Haldwani Phase shift oscillators: The high input impedance of FET is especially valuable in phase shift oscillator to minimize the loading effect. In voltmeters : The high input impedance of FET is useful in voltmeters to act as an input stage. As a buffer amplifier which isolates the preceding stage from the following stage. FET has low noise operation. So it is used in RF amplifiers in FM tuners and communication equipment. FET has low input capacitance, so it is used in cascade amplifiers in measuring and test equipment. Since FET is a voltage controlled device, it is used as a voltage variable resistor in operational amplifiers and tone controls. FET has low inner modulation distortion. So it is used in mixer circuits in FM and TV receivers, and communication equipment. Since it is low-frequency drifts, it is used in oscillator circuits. DISADVANTAGES OF FET OVER BJT FETs have a drawback of smaller gain bandwidth product compared to BJT. The high input impedance, low output impedance and low noise level make FET for superior of the bipolar transistor.

42. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Classification of MOSFETs Metal oxide semiconductor field effect transistor (MOSFET) MOSFET is an important semiconductor device and is widely used in many circuit application. The input impedance of a MOSFET is much more than that if a FET because of very small leakage current. MOSFETs has much greater commercial Importance than JFET. The MOSFET can be used in any of the circuits covered for the FET. Therefore all the equations apply equally well to the MOSFET and FET in amplifier connections. MOSFETs uses a metal gate electrode (instead of p-n junction in JFET), separated from the semi conductor by an Insulating thin layer SiO 2 to modulate the resistance of the conduction channel.

43. D r . M ee n a k s h i Ra n a Deptt- Physics Metal oxide semiconductor field effect transistor (MOSFET) UOU, Haldwan • i It is also called as insulated gate FET (IGFET) MOSFETs operates both in the depletion mode as well as an the enhancement mode Circuit symbols of MOSFET Differences between MOSFET and FET There is only a single p-region. This is called substrate. A thin layer of metal oxide is deposited over the left side of the channel. A metallic gate is deposited over the oxide layer. As silicon dioxide is an insulator, therefore a gate is insulated from the channel. For this reason MOSFET is some times called insulated gate FET.

44. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani P c h a nn e l E nh a n c e m e n t M O SFET symbols Enhancement MOSFET A p - c h a nn e l M OS FET c on sists o f l i g h t l y doped n-substrate into which two heavily doped p + regions act as the source and the drain. A th in la y e r o f S iO2 is g r o w n o v e r th e surface of the entire assembly. P c h a nn e l E nh a n c e m e n t M O SFET

45. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Construction of P channel Enhancement MOSFET Holes are cut into this SiO2 l ayer for making contact with p+ source and drain regions. On the SiO 2 layer, a metal (aluminum) layer is overlaid covering the entire channel region from source to drain. This aluminum layer constitutes the gate. The area of MOSFET is typically 5 square mills or less. This area is extremely small being only about 5% of the area required for a bipolar junction transistor. A parallel plate capacitor is formed with the metal areas of the gate and the semiconductor channel acting as the electrodes of the capacitor. The oxide layer acts as the dielectric between the electrodes.

46. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani The substrate will be connected to the common terminal i.e., to the ground terminal. A n e g a t i v e po te n t i a l w i l l b e a pp l i e d to t h e g a t e . This results in the formation of an electric field normal the SiO 2 . This electric field originates from the induced positive charges on the semiconductor side on the lower surface of the SiO2 layer. The induced positive charge become minority carriers in the n-type of substrate. Working P channel Enhancement MOSFET

47. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani n channel Enhancement MOSFET It consists of a lightly doped p type substrate in to which two heavily doped n type material are diffused. The surface is coated with a layer of silicon dioxide (SiO 2 ). Holes are cut through the SiO 2 to make contact with n-type blocks. Metal (Al) is deposited through the Holes to form drain and source terminals. The surface area between drain and source a metal plate is deposited from which gate terminal is taken out. Working of n channel Enhancement MOSFET

48. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Gate is insulated from the body of FET so it is called insulated gate FET(IGFET). Structurally there exits no channel between source and drain so MOSFET some times called as N-channel enhancement type Because a thin layer of P-type substrate touching the metal oxide film provides channel for electrons and hence acts like N-type material. Drain is made positive with respect to the source and no potential is applied to the gate as shown in figure. The two n-blocks and p-type substrate form back to back pn junctions connected by the Resistance of the p-type material. Both the junctions cannot be forwarded at the Same time so small drain current order of few nano amperes flows. W or k i n g

49. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani So MOSFET is cut off when gate source voltage is zero. That is why it is called normally- OFF MOSFET. The gate is made positive with respect to source substrate as shown in figure. A channel of electrons (n channel) is formed in between the source and drain regions. Behaves as a capacitor with gate metal acting as one electrode, upper surface of the substrate as other electrode and sio2 layer as dielectric medium. When positive voltage is applied to gate the capacitor begin to charge. Consequently positive charges appears on the gate and negative charges appears in the substrate between the drain and source. The n-channel thus formed is called induced n-channel or n-type inversion layer. As V GS increases, no. electrons in the channel increases, I D increases. The minimum gate source voltage which produces then induced n-channel is called threshold voltage V GS (th).when V GS < VGS (th), I D =0. Drain current starts only VGS >VGS (th). For a given value of VDS as VGS is increased , more and more electrons accumulate under the gate and ID increases. So the conductivity of the channel is enhanced by the positive bias on the gate, the device is known as enhancement mode MOSFET. The n-channel MOSFET can never operate with a negative gate voltage. W or k i n g

50. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Drain characteristics It is observed that the drain current has been enhanced on application of negative gate voltage. T h is is t h e r ea s on f o r ca l l i n g it a s e nh a n ceme n t MOSFET. By increasing the gate potential, pinch off voltage and drain currents are increased. The curves are similar to drain characteristics of JFET.

51. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Depletion type MOSFET Circuit symbols of n channel depletion type MOSFET Depletion MOSFET may be fabricated from the basic MOSFET structure. An n-type channel is obtained by diffusion between n+ type source and drain in an n-channel MOSFET. In depletion MOSFET a lightly doped n-type channel has been introduced between to heavily doped source& drain blocks,. Construction of n channel depletion type MOSFET

52. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Circuit symbols of p channel depletion type MOSFET Construction of p channel depletion type MOSFET Depletion MOSFET may be fabricated from the basic MOSFET structure. An p-type channel is obtained by diffusion between p+ type source and drain in an p channel MOSFET. In p-channel depletion MOSFETs are made by using n- type substrate and diffusing a lightly doped p-type channel between two heavily doped P-type source & drain blocks

53. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Working Negative gate operation of a depletion MOSFET is called Its depletion mode Operation When Vgs =0 electrons can flow freely from source to drain through the conducting channel. since a channel exists between drain & source, I d flows even when Vgs=0. It is also known as normally –ON MOSFET. When negative voltage is applied to the gate as shown in Fig positive charges are induced in the channel by capacitor action. The induced positive charges make the channel less conductive and drain current decreases as V GS is made more negative. With negative voltage a depletion MOSFET behave like JFET. When positive voltage is applied to the gate free electrons are Induced channel. This enhances the conductivity of the channel so increasing amount of current between terminals Since the action of negative voltage on gate is to deplete the channel of free n-type charge carriers so named as depletion MOSFET.

54. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Drain Characteristics of depletion MOSFET When the gate source voltage is zero considerable drain current flows. When the gate is applied with negative voltage, positive charge are induced in the n channel through the SiO 2 layer of the gate capacitor.

55. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani The conduction in n channel FET is due to electrons i.e., the majority carriers. Therefore the induced positive charges make the n-channel less conductive. The drain current therefore gets reduced with increase in the gate bias voltage The distribution of charges in the channel results in depletion of majority carriers. That is why this type of FET is called depletion MOSFET. The voltage drop due to the drain current causes the channel region nearer to the drain to be more depleted than the region due to the source. The depletion MOSFET can also be operated in enhancement mode simply by applying a positive voltage to the gate Drain Characteristics of depletion MOSFET

56. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Comparison of MOSFET and JFET The insulated gate in MOSFET s result in much greater input impedance than that of JFET Inter electrode capacitance are independent of bia voltage and these capacitances are smaller incase of MOSFETs than JEFT. It is easier to fabricate MOSFET than JFET. MOSFET has no gate diode. This makes it possible to operate with +ve or –ve gate voltages Advantages of MOSFET Over JFET

57. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Because of higher input resistance ,the enhancement type MOS devices have been used as micro-resistor in integrated micro-circuits. For electrometer circuits where exceptionally low currents are to be measured MOSFETs are most nearly ideal. MOSFET s are very small in size .which make them suitable for highly complex digital arrays. MOSFET is used for switching and amplifying electronics signals in the electronic devices. It is used as an inverter. It can be used in digital circuit. MOSFET can be used as a high frequency amplifier. It can be used as a passive element e.g. resistor, capacitor and inductor. It can be used in brushless DC motor drive. It can be used in electronic DC relay. It is used in switch mode power supply (SMPS). Application of MOSFETs

58. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani COMPLEMENTARY MOSFET(CMOS) CONSTUCTION OF COMPLEMENTARY MOSFET(CMOS) In this device two MOSFETs that are complementary to each other are used The drains of both the MOSFETs are combined and single terminal is taken. Similarly the gates of both the transistors are combined and a single gate terminal is taken out. Here the input is applied at the input terminal v i .

59. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Working principle of CMOSFET When v i is high i.e., equal to –V DD then Q 1 is turned ON and Q 2 is turned OFF. The output V O is zero. Similarly when the input voltage V i is low i.e., equal to 0v, the Q 2 turned ON and Q 1 turned OFF. So the output voltage V o lies at –V dd level i.e., high. Thus the CMOSFET in this configuration works as an Inverter. The key advantage of using CMOS design is this extremely low power consumption usually of the order of 50 mv

60. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani The UJT as the name implies, is characterized by a single pn junction. It exhibits negative resistance characteristic that makes it useful in oscillator circuits. With only one p-n junction, the device is really a form of diode because two base terminal are taken from one section of the diode this device is also called double-based diode The emitter is heavily doped the n-region, is lightly doped for this reason the resistance between the base terminals is very high (5to10 kohms) when emitter lead is open. Uni Junction Transistor (UJT) Circuit Symbol Device

61. D r . M ee n a k s h i Ra n a Deptt- Physics Equivalent circuit of UJT UOU, Haldwani The PN junction behaves like a diode The lightly doped silicon bar has high resistance can be represented by two resistors connected in series R B1 and R B2 . The Resistance offered by N-type bar between Base-1 and Emitter is referred as R B1 . The Resistance offered by N-type bar between Base-2 and Emitter is referred as R B2 . b a r is k no w n a s B a se T h e R e sist a n c e o f N - t y p e spreading resistance RBB. R BB = R B1 + R B2 Intrinsic stand of ratio The intrinsic stand-off ratio is denoted by η. η = R B1 /(R B1 + R B2 ) The intrinsic stand-off ratio is the property of a UJT is always less than unity. Typical range of η is lies between 0.5 to 0.8.

62. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Applications of UJT Phase control. Relaxation oscillator. Timing circuits. Switching Pulse generation. Sine wave generator. Voltage or current regulator supplies. A stable triggering voltage i.e., a fixed fraction of applied inter base voltage VBB A v e ry l o w v a l u e o f tr i gg e ri n g c u rr e n t. A h i g h pu lse c u rr e n t ca p a b i l i t y . A n e g a ti v e r e si s tan c e c h a r ac te r istic. Low cost. Features of UJT

63. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani Transistors, How do they work ? https://www.youtube.com/watch?v=7ukDKVHnac4 Bipolar Junction Transistor (BJT) https://www.youtube.com/watch?v=dTx9VKV0hjo https://www.youtube.com/watch?v=d2lmY-AMs24 Field Effect Transistor (FET) https://www.youtube.com/watch?v=PMOaS967Yus https://www.youtube.com/watch?v=Q0nhtmYT6uA MOSFET https://www.youtube.com/watch?v=g30xTHas3aU https://nptel.ac.in/courses/117101105/

64. D r . M ee n a k s h i Ra n a Deptt- Physics UOU, Haldwani