ADE UNIT-I.pptx

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1. ANALOG & DIGITAL ELECTRONICS by Kumar Saliganti Assistant Professor (C) [email protected] Department of Electrical and Electronics Engineering JNTUH University College of Engineering Manthani

2. S YLLABUS : I : Diodes and Applications II : BJTs IV : FETs and Digital Circuits III : Combinational Logic Circuits UNIT - UNIT – UNIT – UNIT – UNIT – V : Sequential Logic Circuits

3. P .K I RAN K UMAR, E C E D E P A R T M E N T 3 Circ u its and Integra t ed Elect r on i c s : Ana l og and D i gital S ystems, 2/ e , J ac c ob M i llman, C h ris t os Hal k ias and Chethan D. Parik h , T a t a McGraw-Hill Education , India, 2010. Digital De s ig n , 5 /e, Morr i s Mano and M i c h a e l D. Cilette, Pearson, 2011 TEXTBOOKS:

4. UNIT - I : DIODES AND APPLICATIONS Diodes and Applications: Junction diode characteristics: Open circuited p-n junction, p-n junction as a rectifier, V-I characteristics, effect of temperature, diode resistance, diffusion capacitance, diode switching times, breakdown diodes, Tunnel diodes, photo diode, LED. Diode Applications: Clipping circuits, Comparators, Half wave rectifier, Full wave rectifier, Rectifier with capacitor filter .

5. A Diode is the simplest two-terminal electronic device. It allows current to flow only in one direction and blocks the current that flows in the opposite direction. The two terminals of the diode are called as anode (+) and cathode (-) . DIODE A K Symbol of a Diode

6. The name diode is derived from “ Di–Ode ” which means a device that has two electrodes. Di – means Two (2) Ode – m e a ns El e ctro d es Diode: “Di – Ode”

7. Formation of a Diode If a P -type and an N -t y pe m at e ri a l are broug h t clo s e t o e a ch other, both of them join to form a junction . As shown in the figure below.

8. P-type material has holes as the majority carriers and an N-type material has electrons as the majority carriers . As opposite charges attract, few holes in P-type tend to go to N-side , whereas few electrons in N-type tend to go to P- side . As both of them travel towards the junction, holes and electrons recombine with each other to neutralize and forms ions . Now, in this junction, there exists a region where the positive and negative ions are formed, called as PN junction or junction barrier

9. Diode’s Three Operation Regions In order to understand the operation of a diode, it is necessary to study its three operation regions: equilibrium, reverse bias, and forward bias.

10. The formation of negative ions on P-side and positive ions on N-side results in the formation of a narrow charged region on either side of the PN junction. This region is now free from movable charge carriers.

11. The ions present here have been stationary and maintain a region of space between them without any charge carriers. As this region acts as a barrier between P and N type materials, this is also called as Barrier junction . This has another name called as Depletion region meaning it depletes both the regions.

12. Types of Diode

13. The PN junction diode is a two terminal device, which is formed when one side of the PN junction diode is made with p-type and doped with the N-type material. Forward & Reverse Biased

14. Current-Voltage Relationship Forward Bias: current exponentially increases. Reverse Bias: low leakage current equal to ~I o Ability of pn junction to pass current in only one direction is known as “ rectifying ” behavior. PN Junction: I-V Characteristics

15. In the forward bias , it's shifts to 2.5mV per °C In the reverse biased condition because the reverse saturation current of a silicon diode doubles for every 10°C rose in temperature Effects of Temperature on V-I Characteristics

16. Diode resistance Static Resistance or (DC resistance) Forward Resistance R f Reverse Resistance R r Dynamic Resistance or (AC resistance) Forward Resistance r f Reverse Resistance r r

17. Diode resistance ΔV/ΔI is called ac ( dynamic ) resistance of the diode because we consider small change in voltage We would not want to calculate ac resistance between V=0.55V and V=0.65V rd= ΔV/ΔI ohms The dc resistance of a diode is found by dividing the dc voltage across it by dc current through it. DC resistance also called the static resistance. Rd=V/I ohms Diode is nonlinear in both the dc & the ac sense, that is, both its dc & ac resistance change over a wide range.

18. AC & DC Resistance V (V) I (mA) 0 0.1 0.2 0.3 0.4 0.5 0.6 40 10 20 30 Δ I ΔV r D = ΔV / ΔI AC Resistance DC Resistance R D = V / I r D = V T / I

19. Diode capacitance Transition capacitance (C T ) The change of capacitance at the depletion region can be defined as the change in electric charge per change in voltage. C T = dQ / dV C = ε A / W Where, C T = Transition capacitance dQ = Change in electric charge dV = Change in voltage The transition capacitance can be mathematically written as,

20. , Diffusion capacitance or Storage capacitance (C D ) CD is due to the storage of minority carriers in a forward biased diode It will dominate in the device only during high frequency operation C D >C T

21. S witching characteristics of pn junction diode The sudden change from forward to reverse and from reverse to forward bias, affects the circuit. The time taken to respond to such sudden changes is the important criterion to define the effectiveness of an electrical switch. The time taken before the diode recovers its steady state is called as Recovery Time .(t rr ) The time interval taken by the diode to switch from reverse biased state to forward biased state is called as Forward Recovery Time. The time interval taken by the diode to switch from forward biased state to reverse biased state is called as Reverse Recovery Time. Storage time − The time period for which the diode remains in the conduction state even in the reverse biased state, is called as Storage time . Transition time − The time elapsed in returning back to the state of non- conduction, i.e. steady state reverse bias, is called Transition time .

22. Reverse recovery time (trr)= Storage time(Ts)+Transition time (Tt)

23. Ideal vs practical diode

24. Block diagram of a Power Supply

25. R ectif i e r s Rectifier is a device which convert AC voltage in to pulsating DC A rectifier utilizes unidirectional conducting device Ex :P-N junction diodes

26. T ype s Depending up on the period of conduction Half wave rectifier Full wave rectifier Depending up on the connection procedure Bridge rectifier

27. Half wave Rectifier The process of removing one-half the input signal to establish a dc level is called half-wave rectification . In Half wave rectification, the rectifier conducts current during positive half cycle of input ac signal only. Negative half cycle is suppressed.

28. Full Wave Rectifier and a centre tap Circuit has two diodes D1 , D2 transformer. During positive half cycle Diode D1 conducts and during negative half cycle Diode D2 conducts. It can be seen that current through load RL is in the same direction for both cycle.

29. Full Wave Bridge Rectifier Need for centre tapped PT is eliminated. Consists of 4 diodes instead of 2.

30. Full Wave Bridge Rectifier During period t=0 to t=T/2 D2 and D3 are conducting while D1 and D4 are in the “off” state.

31. During period t=T/2 to t=T D1 and D4 are conducting while D2 and D3 are in the “off” state.

32. Fil t ers A capacitor is added in parallel with the load resistor of a half-wave rectifier to form a simple filter circuit. At first there is no charge across the capacitor During the 1 st quarter positive cycle, diode is forward biased , and C charges up. V C = V O = V S - V  . As V S falls back towards zero, and into the negative cycle, the capacitor discharges through the resistor R. The diode is reversed biased ( turned off) If the RC time constant is large, the voltage across the capacitor discharges exponentially.

33. Fil t ers During the next positive cycle of the input voltage, there is a point at which the input voltage is greater than the capacitor voltage, diode turns back on . The diode remains on until the input reaches its peak value and the capacitor voltage is completely recharged.

34. Quarter cycle; capacitor charges up Capacitor discharges through R since diode becomes off Input voltage is greater than the capacitor voltage; recharge before discharging again V C = V m e – t / RC NOTE: V m is the peak value of the capacitor voltage = V P - V  Since the capacitor filters out a large portion of the sinusoidal signal, it is called a filter capacitor . V p V m

35. P .K I RAN K UMAR, E C E D E P A R T M E N T 35 Figure: Half-wave rectifier with smoothing capacitor. Ripple Voltage, and Diode Current V r = ripple voltage V r = V M – V M e -T’/RC where T’ = time of the capacitor to discharge to its lowest value V r = V M ( 1 – e -T’/RC ) Expand the exponential in series, V r = ( V M T’) / RC T’ Tp

36. If the ripple is very small, we can approximate T’ = T p which is the period of the input signal Hence for half wave rectifier V r = ( V M T p ) / RC For full wave rectifier V r = ( V M 0.5T p ) / RC

37. DIODE CLIPPERS Clipping circuits basically limit the amplitude of the input signal either below or above certain voltage level. They are referred to as Voltage limiters, Amplitude selectors or Slicers. A clipping circuit is one, in which a small section of input waveform is missing or cut or truncated at the out put section. Clipping circuits are classified based on the position of Diode . 1.Series Diode Clipper 2.Shunt Diode Clipper

38. Series Diode clippers

39. Shunt diode clippers

40. 40 I n ele c t ro n ic s , a c om p ar a tor i s a d e v i ce that c o m p are s two voltages or currents and outputs a digital signal indicating which is larger. It has two analog input terminals V+ and V- and one binary digital output . Series diode clipper with bias

41. P.KIRAN KUMAR,ECE DEPARTMENT 41

42. Slicer ( Clipping at two independent levels )

43. Diode equivalent circuits / models:

44. Applications There are many applications in which diode switching circuits are used, such as −

45. Breakdown Mechanisms in a diode When reverse voltage increases beyond certain value, large diode current flows, this is called breakdown of diode, and corresponding voltage is called reverse breakdown voltage of diode. There are two distinct mechanisms due to which the break down may occur in the diode, these are: Avalanche breakdown Zener break down

46. Breakdown Mechanisms in a diode Avalanche Breakdown: The avalanche breakdown occurs in lightly doped diodes. The multiplication factor due to the avalanche effect is given by 1 n V M    1   V   BD  Where M is carrier multiplication factor n-type silicon n=4 and For p-type n=2 V is applied reverse voltage V BD is reverse breakdown voltage

47. Breakdown Mechanisms in a diode Zener Breakdown The zener breakdown occurs in heavily doped diodes. For heavily doped diodes, the depletion region width is small. Under reverse bias conditions, the electric field across the depletion layer is very intense. Breaking of covalent bonds due to intense electric field across the narrow depletion region and generating large number of electrons is called Zener effect. These generated electrons constitute a very large current and the mechanism is called Zener breakdown. The diodes having reverse breakdown voltage less than 5v shows the Zener mechanism of breakdown.

48. Zener Diode Zener diode is a heavily doped diode, and is designed with adequate power dissipation capabilities to operate in the reverse breakdown region. The operation of the zener diode is same as that of ordinary PN diode under forward biased condition. In reverse biased condition, the diode carries reverse saturation current, till the reverse voltage applied is less than the reverse breakdown voltage. When the reverse voltage exceeds the reverse breakdown voltage, the current through it changes drastically but the voltage across it remains almost constant such a break down region is a normal operating region for a zener diode. The symbol of zener diode is

49. Zener Diode The dynamic resistance of a zener diode is defined as the reciprocal of the slope of the reverse characteristics in zener region. r z   V z  I z = 1 / s l o p e of re v e r s e characteristics in zener region The dynamic resistance is very small, it is of he order of few tens of ohms.

50. Equivalent circuit of Zener diode

51. Applications of zener diode The various applications of zener diode are, As a voltage regulating element in voltage regulators. In various protecting circuits. In zener limiters i.e., clipping circuits which are used to clip off the unwanted portion of the voltage waveform.

52. Tunnel diode If the concentration of impurity atoms is greatly increased, say 1 part in 10 3 the device characteristics are completely changed. The new diode was announced in 1958 by Leo Esaki. This diode is called ‘Tunnel diode’ or ‘Esaki diode’. The barrier potential VB is related with the width of the depletion region with the following equation. From the above equation the width of the barrier varies inversely as the square root of impurity concentration. As the depletion width decreases there is a large probability that an electron will penetrate through the barrier. This quantum mechanical behavior is referred to as tunneling and hence these high impurity density pn-junction devices are called Tunnel diodes. B q N A V  .  ² 2  q N A 2V B  .   ² 

53. Tunnel diode Energy band structure of heavily doped pn-junction diode under open circuited conditions

54. The volt-ampere characteristics Under applied reverse bias

55. The volt-ampere characteristics Under applied Forward bias

56. The volt-ampere characteristics Under applied reverse bias

57. Tunnel diode The tunnel diode symbol and small-signal model are Applications of Tunnel diode: It is used as a very high speed switch, since tunneling takes place at the speed of light. It is used as a high frequency oscillator.

58. Photodiode The photodiode is a device that operates in reverse diode. The photodiode has a small transparent window that allows light to strike one surface of the pn-junction, keeping the remaining sides unilluminated. The symbol of photodiode is

59. The volt-ampere characteristics of photodiode

60. Photodiode Advantages of Photo diodes: It can be used as variable-resistance device. Highly sensitive to the light. The speed of operation is very high. Disadvantages of Photo diodes: The dark current is temperature dependent. Applications of photodiode: Photodiodes are commonly used in alarm systems and counting systems. Used in demodulators. Used in encoders. Used in light detectors. Used in optical communication systems.

61. Light Emitting Diode (LED) The LED is an optical diode which emits light when forward biased, by a phenomenon called electroluminescence. The LEDs use the materials like Gallium Arsenide (GaAs), Gallium Arsenide Phospide (GaAsP) or Gallium Phospide (GaP). These are the mixtures of elements Ga,As,P. The symbol of LED is

62. LED Working Principle When an LED is forward biased, the electrons and holes move towards the junction and recombination takes place. As a result of recombination, the electrons lying in the conduction bands of n-region fall into the holes lying in the valance band of p-region. The difference of energy between the conduction band and the valance band is radiated in the form of light energy. The energy released in the form of light depends on the energy corresponding to the forbidden gap. This determines the wavelength of the emitted light. The wavelength determines the color of the light and also determines whether the light is visible or invisible (infrared).

63. LED Working Principle The color of the emitted light depends on the type of material used. Gallium Arsenide (GaAs) --- Infrared radiation (invisible) Gallium Phospide (GaP) --- Red or Green Gallium Arsenide Phospide (GaAsP) --- Red or Yellow. The brightness of the emitted light is directly proportional to the forward bias current.

64. Output characteristics of LED Process of electro luminescence Typical output characteristics for LED

65. Light Emitting Diode (LED) Advantages of LEDs: LEDs are small in size. LEDs are fast operating devices. LEDs are light in weight. LEDs are available in various colors. The LEDs have long life. The LEDs are cheap and readily available. LEDs are easy to interface with various other electronic circuits. Disadvantages of LEDs: Needs large power for the operation. The characteristics are affected by the temperature.

66. Light Emitting Diode (LED) Applications of LEDs: The LEDs are used in all kinds of visual displays i.e., seven segment displays and alpha numeric displays. Such displays are commonly used in multimeter, calculator, watches etc. LEDs are also used in optical devices such as optocouplers. They are also used in burglar alarm systems.