Unit -1 IC Fabrication 1. Define an Integrated circuit. An integrated circuit(IC) is a miniature, low cost electronic circuit consisting of active and passive components fabricated together on a single crystal of silicon. The active components are transistors and diodes and passive components are resistors and capacitors. 2. What are the advantages of Integrated Circuits?

1. Miniaturization and hence increased equipment density 2. Cost reduction due to batch processing 3. Increased system reliability due to elimination of soldered joints 4. Improved functional performance 5. Matched devices 6. Increased operating speeds. 7. Reduction in power consumption

3. What are the limitations of Integrated circuits?

Faulty IC can’t be repaired, they have to be replaced by a new one.

Some components like transformers and inductors cannot be integrated into an IC.

High grade P-N-P assembly is not possible.

The IC will not work properly if wrongly handled or exposed to excessive heat.

It is difficult to achieve low temperature coefficient.

It is difficult to fabricate an IC with low noise.

It is not possible to fabricate capacitors that exceed a value of 30pF. Thus, high value capacitors are to be connected externally to the IC.

There is a large value of saturation resistance of transistors.

4. How Integrated circuits are classified? Based on application 1. Analog ICs 2. Digital ICs Based on fabrication Technology 1. Monolithic ICs 2. Hybrid ICs Based on the type of active device used 1. Bipolar ICS(uses BJT) It is further classified based on the Isolation technique being used—

i. PN junction isolation ii. Dielectric isolation

2. Unipolar device i. JFET ii. MOSFET

Based on device density refer QNo. 5

5. How are integrated circuits classified based on the device density? 1. Small scale integration (SSI)—3 to 30 gates/chip. 2. Medium scale integration (MSI)—30 to 300 gates/chip. 3. Large scale integration (LSI)—300 to 3,000 gates/chip. 4. Very large scale integration (VLSI)—more than 3,000 gates/chip. 5. Ultra large scale integration (ULSI) — 106 to 107 transistors / chip 6. Giant scale Integration (GSI) — greater than 107 transistors / chip

6. What are the basic processes involved in fabricating ICs using planar technology?

i. Silicon wafer (substrate) preparation ii. Epitaxial growth iii. Oxidation iv. Photolithography v. Diffusion vi. Ion implantation vii. Isolation technique viii. Metallization ix. Assembly processing & packaging

7. List out the steps used in the preparation of Si –wafers.

Crystal growth &doping

Ingot trimming & grinding

Ingot slicing

Wafer policing & etching

Wafer cleaning

8. Write the basic chemical reaction in the epitaxial growth process of pure silicon. The basic chemical reaction in the epitaxial growth process of pure silicon is the hydrogen reduction of silicon tetrachloride. 1200oC SiCl4+ 2H2<-----------> Si + 4 HCl 9. What are the two important properties of SiO2?

i. SiO2is an extremely hard protective coating & is unaffected by almost all reagents except by hydrochloric acid. Thus it stands against any contamination.

ii. By selective etching of SiO2, diffusion of impurities through carefully defined windows can be accomplished to fabricate various components.

10. Explain the process of oxidation. The silicon wafers are stacked up in a quartz boat & then inserted into quartz furnace tube. The Si wafers are raised to a high temperature in the range of 950 to 1150oC & at the same time, exposed to a gas containing O2or H2O or both.The chemical action is Si + 2H2O -----------> Si O2+ 2H2

11. What is meant by molecular beam epitaxy(MBE)? In the molecular beam epitaxy, Silicon along with dopants is evaporated.The evaporated species are transported at a relatively high velocity in a vacuum to the substrate. The relatively low vapour pressure of silicon & the dopants ensures condensation on a low temperature substrate.Usually, silicon MBE is performedunder ultra high vacuum (UHV) condition of 10-8 to 10 -10Torr.

12. What are the advantages of Molecular Beam Epitaxy( MBE )?

i. It is a low temperature process, useful for VLSI. This minimizes outdiffusion & auto-doping.

ii. It allows precise control of doping& permits complicated profiles to be generated. iii. Linear doping profile desirable for varactor diode in FM, can be obtained with MBE. iv. Wider choice of dopants can be used.

13. What are oxidation induced defects in semiconductor?

1. Stacking faults 2. Oxide isolation defects

Stacking faults: Structural defects in the silicon lattice are called oxidation induced stacking faults. The growth of stacking faults is a strong function of substrate orientation, conductivity type & defect nuclei present.The stacking faults formation can be suppressed by the addition of HCl. Oxide isolation defects: The stress along the edges of an oxidized area produce severe damage in the silicon. Such defects results in increased leakage in nearby devices.High temperatures (around 950oC ) will prevent stress induced defect formation. 14. What is bird’s beak? In local oxidation process, the oxidation of silicon proceeds slightly under the nitride as well. Also, a large mismatch in the thermal expansion co-efficient of Si3N4&Silicon results in damage to the semiconductor during local oxidation.This damage can be greatly reduced by growing a thin layer of SiO2prior to placement of the Si3N4 mask. Typically 100 to 200A ois used for this purpose. Unfortunately, this greatly enhances the penetration of oxide under the nitride masked regions, resulting in oxide configurations called bird’s beak. 15. What is lithography? Lithography is a process bywhich the pattern appearing on the mask is transferred to the wafer.It involves two steps: the first step requires applying a few drops of Photo resist to the surface of the wafer & the second step is spinning the surface to get an even coating of the photoresist across the surface of the wafer. 16. What are thedifferent types of lithography? What is optical lithography? The different types of lithography are:

1. Photolithography 2. Electron beam lithography 3. X-ray beam lithography 4. Ion beam lithography

Optical lithography: Optical lithography comprises the formation images with visible or UV radiation in a photoresist using contact, proximity or projection printing.

17.What are the two processes involved in photolithography? a) Making a photographic mask b) Photoetching The development of photographic mask involves the preparation of initial artwork and its reduction , decomposition of initial artwork or layout into several mask layers. Photoetchingis used for the removal of SiO2from desired regions sothat the desired impurities can be diffused. 18. Distinguish between dry etching & wet etching.

19. What is meant by reactive plasma etching? The term reactive plasma is meant to describe a discharge in which ionization & fragmentation of gases takesplace& produce chemically active plasma species, frequently oxidizers and reducing agents.Such plasmas are reactive both in the gas phase & with solid surfaces exposed to them.When these interactions are used to form volitile products so that material is removed or etching of material form surfaces that are not masked to form lithographic patterns, the technique is known as reactive plasma etching. 20.What are isotropic & anisotropic etching processes? Isotropic etching is a wet etching process which involves undercutting. Aisotropic etching is a dry etching process which provides straight walled patterns. 21.Define diffusion. The process of introducing impurities into selected regions of a silicon wafer is called diffusion. The rate atwhich various impurities diffuse into the silicon will be of the order of 1µm/hrat the temperature range of 900oC to 1100oC .The impurity atoms have the tendency to move from regions of higher concentrations to lower concentrations. 22.What is dielectric isolation? In dielectric isolation, a layer of solid dielectric such as SiO2or ruby completely surrounds each components thereby producing isolation , both electrical&physical. This isolating dielectric layer is thick enough so that its associated capacitance is negligible. Also, it is possible to fabricate both pnp & npn transistors within the same silicon substrate. 23.What are the advantages of ion implantation technique? 1. It is performed at low temperature. Therefore, previously diffused regions have a lesser tendency for lateral spreading. 2. In diffusion process, temperature has to be controlled over a large area inside the oven, where as in ion implantation process,accelerating potential & beam content are dielectrically controlled from outside.

24.What is metallization? The process of producing a thin metal film layer that will serve to make interconnection of the various components on the chip is called metallization. 25. Why aluminium is preferred for metallization?

It is a good conductor.

It is easy to deposit aluminium films using vacuum deposition.

It makes good mechanical bonds with silicon.

It forms a low resistance contact. 26. What is the significance of using buried layer? The heavily doped n region is sandwiched between the n-type epitaxial collector and p-type substrate. This buried n+ region provides a low resistivity current path from the active collector region to the collector current. In effect the n+ layer shunts the n layer of the collector region with respect to the flow of current thus effectively reducing the collector current. 27. What are the advantages of poly-silicon Gate MOSFET over aluminium gate? Polycrystalline silicon is conductive when doped with phosphorous and used as gate electrode instead of aluminium. This reduces VT to about 1 to 2 V. Such devices are called silicon gate MOS transistor. 28. Differentiate between thin film and thick film technology in IC fabrication.

Thin film resistors have a lower tolerance than the thick film resistors.

The capacitance of thin film resistors is lower than that of the thick film resistors.

The temperature coefficient of thin film resistors is much lower than that of the thick film resistors.

The production of thin film resistors is expensive than the production cost of the thick film resistors.

The process of manufacturing the thin film resistor is different from the manufacturing process of the thick film resistors.

29. Give the difference between monolithic IC and hybrid IC

Sl.No Monolithic Hybrid

1. The word ‘monolithic’ comes from the Greek words ‘monos’ and ‘lithos’ which means ‘single’ and ’stone’. As the name suggests, monolithic IC’s refer to a single stone or a single crystal. The single crystal refers to a single chip of silicon as the semiconductor material, on top of which all the active and passive components needed are interconnected.

The circuit is fabricated by interconnecting a number of individual chips. The active components are diffused transistors or diodes. The passive components may be group of diffused resistors or capacitors on a single chip, or they may be thin-film components. Interconnection between the individual chips is made by wiring process or a metallized pattern.

2. This is the best mode of manufacturing IC’ as they can be made identical, and produces high reliability.

multi-chip techniques are quite economical for small quantity production and are more often used as prototypes for monolithic ICs or for custom design.

3. They have been found applicable for IC’s used for AM receivers, TV circuits, computer circuits, voltage regulators,

Hybrids ICs are mostly used for high power audio amplifier applications from 5 Watts to more than 50 Watts.

amplifiers and so on.Low power applications.

4. Have some limitations Hybrid IC’s are also known to provide a better performance than monolithic IC’s.

5. The cost factor is also low and can be manufactured in bulk in very less time.

process is too expensive for mass production

30. State the limitations of Monolithic IC 1.Monolithic IC’s have low power rating. They cannot be used for low power applications as they cannot have a power rating of more than 1 watt. 2. The isolation between the components inside the IC is poor. 3. Components like inductor cannot be fabricated to the IC. 4. The passive components that are fabricated inside the IC will be if small value. For higher values they have to be connected externally to the IC pins. 5. It is difficult to make a circuit flexible for any kind of variation; a new set of masks is required. 31. What are the various methods used to fabricate integrated resistors?

1. Diffused resistor 2. Epitaxial resistor 3. Pinched resistor 4. Thin film resistor

32. What are the various methods used to fabricate integrated capacitors? 1. Junction capacitor 2. MOS and thin film capacitor 33. How monolithic diodes were fabricated? Transistors can be used asDiodes by floating the third terminal or by shorting it to the remaining two terminals. e.g. 1. Base emitter junction with collector shorted to base 2. Base emitter junction with collector open. 3. Base emitter junction with the collector shorted to emitter

34. What are the steps involved in the fabrication of monolithic transistor? 1. Epitaxial growth 2. Isolation diffusion 3. Base diffusion 4. Emitter diffusion 5. Aluminium metallization The starting material for the fabrication of a monolithic transistor is a lightly doped p-type substrate. 35. What is CMOS? CMOS means complementary MOSFET It is possible to fabricate the NMOS and PMOS enhancement devices on the same silicon chip. These devices are called complementary MOSFET.

Unit -2 Operational Amplifiers 1. Define an operational amplifier.

An operational amplifier is a multistage, direct-coupled, high gain amplifier consisting of one or more differential amplifiers. It can handle signals of wide frequency range (from dc to high frequency ac). By properly selecting the external components, it can be used to perform a variety of mathematical operations such as addition, subtraction, differentiation etc.

2. List out the ideal characteristics of OPAMP? 1. Open loop gain = infinite 2. Input impedance = infinite 3. Output impedance = low(zero) 4. Bandwidth = infinite 5. Zero offset, i.e.,Vo=0 when V1=V2=0. 6. Infinite CMRR 7. Infinite slew rate and 8. Characteristics do not drift with temperature.

3. Define Input bias current. Input bias current is the average of the currents that flow into the inverting and non-inverting terminals of an Op-amp IB = IB1+IB2 / 2 4. Define input offset current and input offset voltage. (i) Input offset current: The difference in magnitude between IB1 and IB2 is called input offset current IOS

IOS = IB1 - IB2 (ii) Input offset voltage: A small voltage applied to the input terminals to make the output voltage as zero when the two input terminals are grounded is called input offset voltage. 5.Define input offset current. State the reasons for the offset currents at the input of the op-amp.

The difference between the bias currents at the input terminals of the op-amp is called as input offset current. The input terminals conduct a small value of dc current to bias the input transistors. Since the input transistors cannot be made identical, there exists a difference in bias currents.

6. Define CMRR of an op-amp. The relative sensitivity of an op-amp to a difference signal as compared to a common – mode signal is called the common –mode rejection ratio. It is expressed in decibels. CMRR= Ad/Ac. 7. Define slew rate. The slew rate is defined as the maximum rate of change of output voltage caused by a step input voltage usually specified in V/micro sec.An ideal slew rate is infinite which means that op-amp’s output voltage should change instantaneously in response to input step voltage. 8. In practical op-amps, what is the effect of high frequency on its performance? The open-loop gain of op-amp decreases at higher frequencies due to the presence of parasitic capacitance. The closed-loop gain increases at higher frequencies and leads to instability.

9. What is the need for frequency compensation in practical op-amps? Frequency compensation is needed when large bandwidth and lower closed loop gain is desired. Frequency compensation is needed when large bandwidth and lower closed loop gain is desired. Compensating networks are used to control the phase shift and hence to improve the stability. 10. Mention the frequency compensation methods. (i) Dominant-pole compensation (ii) Pole-zero compensation. 11. What are the merits and demerits of Dominant-pole compensation?

o Noise immunity of the system is improved. o Open-loop bandwidth is reduced.

12. Why IC 741 is not used for high frequency applications? IC741 has a low slew rate because of the predominance of capacitance present in the circuit at higher frequencies. As frequency increases the output gets distorted due to limited slew rate. 13. What causes slew rate? There is a capacitor with-in or outside of an op-amp to prevent oscillation.It is this capacitor which prevents the output voltage from responding immediately to a fast changing input. 15. What are the different kinds of packages of IC741?

Metal can (TO) package

Dual-in-line package

Flat package or flat pack

16. What are the assumptions made from ideal op-amp characteristics?

The current drawn by either of the input terminals(non- inverting/inverting) is negligible.

The potential difference between the inverting & non-inverting input terminals is zero.

17. Mention some of the linear applications of op – amps: Adder, subtractor, voltage–to-current converter, current–to-voltage converters, instrumentation amplifier, analog computation,power amplifier, etc. are some of the linear op-amp circuits. 18. Mention some of the non – linear applications of op-amps:- Rectifier, peak detector, clipper, clamper, sample and hold circuit, log amplifier, anti–log amplifier, multiplier are some of the non – linear op-amp circuits. 19. What are the areas of application of non-linear op- amp circuits? Industrial instrumentation, Communication, Signal Processing 20. Define thermal drift. The bias current, offset current & offset voltage change with temperature. A circuit carefully nulled at 25oC may not remain so when the temperature raises to 35oC.This is called thermal drift. Often, offset current drift is expressed in nA/ oC and offset voltage drift in mV/ oC. 21.Define supply voltage rejection ratio(SVRR) The change in OPAMP’s input offset voltage due to variations in supply voltage is called the supply voltage rejection ratio. It is also called Power Supply Rejection Ratio(PSRR) or Power Supply Sensitivity (PSS).

22. What happens when the common terminal of V+ and V- sources is not grounded? If the common point of the two supplies is not grounded, twice the supply voltage will get applied and it may damage the op-amp. 23. Define unity gain band bandwidth of an op-amp? The frequency at which gain equals 1 is known as the unity gain bandwidth. It is the maximum frequency the OPAMP can be used for. Furthermore, the gain bandwidth product obtained from the open loop gain vs frequency curve is equal to the unity gain bandwidth of the OPAMP. 24. Draw the pin details of IC741

25. What are the basic requirements of the input stage of Op-amp?

1. High voltage gain. 2. High input impedance 3. Two input terminals. 4. Small input offset voltage. 5. Small input offset current. 6. High CMRR. 7. Low input bias current.

26. What are the basic requirements of the output stage of Op-amp?

1. Large output voltage swing capability. 2. Large output current swing capability. 3. Low output impedance. 4. Low quiescent power dissipation. 5. Short circuit protection

27. Define Differential gain. The gain with which differential amplifier amplifies the difference between two input signals, is called differential gain (Ad). Ad = V0 / Vd 28. Define Common Mode Gain. The gain with which differential amplifieramplifies thecommon mode signal to produce the output is called commonmode gain. AC = VO/ VC

29. Define Common Mode Signal. The average level of two input signals is called common mode signal (VC). VC = (V1 + V2) / 2

30. What are the features of Differential amplifier?

1. High differential voltage gain. 2. Low common mode gain. 3. High CMRR. 4. Two input terminals. 5. High input impedance. 6. Large band width. 7. Low output impedance. 8. Low offset voltages and currents.

31. What are the D.CCharacteristics of Op-amp?

1. Input Bias current. 2. Input offset current. 3. Input offset voltage. 4. Thermal Drift.

32. What are the A.C Characteristics of Op-amp? 1. Slew rate. 2. Frequency response. 3. Bandwidth 33. What are the four feedback configurations available for an op-amp? 1. Voltage seriesfeedback. 2. Voltage shunt feedback. 3. Current series feedback. 4. Current shunt feedback. 34. What are the advantages of negative feedback?

1. It reduces the gain and makes it controllable. 2. It reduces thepossibility of distortion. 3. It increases the bandwidth i.efrequency range. 4. It increases the input resistance ofthe op-amp. 5. It decreases the output resistance ofthe op amp. 6. It reduces the effects of temperature, power supplyon the gain of the circuit.

35. What are the classification of op-amp ICs based on temperature ranges.

1. Military temperature range: -55 oC to – 125 oC. 2. Industrial temperature range: - 20oC to + 85 oC. 3. Commercial temperature range: 0 o C to 70 oC.

36. What are the features of IC 741.

1. No frequency compensation required. 2. Short circuit protection provided. 3. Offset voltage null capability. 4. No latch up. 5. Large common mode anddifferential voltage range.

37. Define voltage follower. A circuit in which the output voltage follows the input voltage is called voltage follower circuit. Gain of the amplifier is unity. VO = V in

38. What are the advantages of voltage follower? 1. Very large input resistance, ofthe order of mega ohms.

2. Low output impedance, almost zero. Hence it can be used to connect highimpedance source to a low impedanceload as a buffer.

3. It has large band width. 4. The output follows the input exactly without phase shift.

39. What is meant by an integrator? Integrator or integrating amplifier is a circuit in which the output voltage wave form is the time integral of the input voltage waveform as given by

Vo = - 1

𝐶𝑅∫ 𝑉𝑖

𝑡

0 𝑑𝑡 + Vo(0)

40. Write theapplications of Practical Integrator.

1. In the analog computers. 2. In solving thedifferential equations. 3. In analog to digital converters. 4. In ramp generators. 5. Used in wave shaping circuits

41. What is meant bya differentiator? The circuit which produces the differentiation of the input voltage at its output is called differentiator. The circuit using active devices like op-amp is called active differentiator. The circuit can be obtained without using active devices like op amp, transistors is called passive differentiator.

Vo = -CR 𝑑𝑉𝑖

𝑑𝑡(for a inverting type differentiator.

42. Write theapplications ofPractical differentiator. 1. In the wave shaping circuits to detect the high frequency components in the input

signal. 2. As a rate- of-change detector in the FM demodulation.

43. What are the drawbacks of ideal integrator and how to overcome the same in practical circuit?

For dc operation, the ideal op-amp circuit feedback capacitor is an open circuit, so the op-amp output is likely to be saturated at either the +ve or –ve maximum voltage. The result of this is that, instead of being symmetrical above and below the ground level, the output wave form have a substantial dc offset and is very lively to be distorted.Resistor Rf must be included in parallel with feed-back capacitor behaves as inverting amplifier with a voltage gain of Rf / R1. The parallel combination of Rf and Cf behaves like an practical capacitor and dissipates power so the circuit is also called as lossy integrator. 44. What are the drawbacks of ideal differentiator and how to overcome the same in practical differentiator circuits? The voltage gain of the circuit is –Rf/XCI at very high frequencies the XC is very low and the gain is very high and it may lead to oscillations also it will load the input signal source because of low input impedance. To overcome the above two problems a series resistor R1 is included in the input circuit and a capacitor C2 is added in parallel with the feedbackresistor.

45. Compare Inverting and Non-inverting Amplifier

Sl.no Non-Inverting Amplifier Inverting amplifier

1. Basically a voltage Series Amplifier Voltage shunt feedback amplifier

2. Input impedance increases No change

3. Output impedance decreases Output resistance decrease

4. Gain is purely based on the external components and given by (1+Rf/R1)

Here also gain depends on the external components and given by –Rf/R1

5. Gain is always greater than one Gain can be decreased below 1

6. No inversion of polarity takes place Output is phase shifted by 180o

46. Draw the small signal and high frequency equitant circuit of op-amp.

47. What is the need for compensating network in op-amp? In order to attain > Larger bandwidth > Lower closed loop gain > Single break frequency > Central the phase shift and stability 48. What are the types of V/I converter. 1. Floating type. 2. Grounded type. 49. Write the applications of V-I Converter. 1. Low Voltage D.C Voltmeter. 2. Low Voltage A.C Voltmeter. 3. Zener diode tester 4. Diode tester and Match filter. 50. Write the applications of I-V Converter. 1. Photo diode detector. 2. Photo FET Detector. 51. Why integrators are preferred over differentiators in analog computers? Integrators are more linear than the differentiators and the integrators reduce the power consumption than the high pass filter. Gain of the integrator decreases with increasing frequency and hence signal to noise ratio of integrator is higher than that of differentiator.

52. Define Virtual ground property of an OP-AMP A virtual ground is a ground which acts like a ground. It may not have physical connection to ground. This property of an ideal op-amp indicates that the inverting and non-inverting terminals of op-amp are at the same potentials. The non-inverting input is grounded for the inverting amplifier circuit. This means that the inverting input of the op-amp is also at ground potential. 54. What is a V to C convertor? A trans-conductance amplifier (gm amplifier) puts out a current proportional to its input voltage. In networkanalysis, the trans-conductance amplifier is defined as a voltage controlled current source (VCCS). For direct current, trans-conductance is defined as follows:Iout/Vin

UNIT III - APPLICATIONS OF OP AMP 1. What is the need for an instrumentation amplifier?

In a number of industrial and consumer applications, the measurement of physical quantities is usually done with thehelp of transducers. The output of transducer has to be amplified So that it can drive the indicator or display system.This function is performed by an instrumentation amplifier.

2. What is meant by transducer?

A transducer is a device which converts one form of energy to another form of energy. Example thermocouple, it converts the heat energy into an electrical energy.

What is meant by instrumentation amplifier? The special amplifier which is used for such a low level amplification with high

CMRR, high input impedance to avoid loading, low power consumption and some other features is called an instrumentation amplifier. It is also called dataamplifier and isbasically adifference amplifier.

3. What are the applications of Instrumentation amplifier? 1. Temperature controller. 2. Light intensity meter. 3. Analog weight Scale. 4. Temperature indicator 4. What are the requirements of good instrumentation amplifier?

1. Finite, accurate, and stable gain. 2. Easier gain adjustment. 3. High Input impedance. 4. Low output impedance. 5. High CMRR. 6. Low power consumption. 7. Low thermal and time drifts. 8. High slew rate.

5. Define Log and Antilog amplifier.

When a PN junction is used in the feedback network of op-amp, the circuit exhibits log or antilog properties. Log amplifier:

The Log amplifier is a current to voltage converter with the transfer characteristics of Vo = Viln (If/ Ii)

Antilog Amplifier: Antilog amplifier is a decoding circuit which converts the logarithmically encoded signal back to original signal levels as given by VL = VR 10-KVi

6. What is a filter? A filter is a circuit that is designed to pass a specified band of frequencies while attenuating all the signals outside that band. It is a frequency selective circuit. 7. What are the different types of filters? Based on functions: Low pass filter, High pass filter, Band pass filter, Band reject filter Based on order of transfer function: first, second, third higher order filters. Based on configuration: Bessel, Chebychev, Butterworth filters.

8. State the advantages of active filters.

Active filters use Op-amp as active element and Resistors and capacitors as passive elements. (No Inductors were used)

They provide gain. (Signal attenuation can be avoided as in the case of passive filters) As the op-amp is used in non-inverting configuration, it offers high input impedance and

low output impedance (This will improve the load drive capacity and isolates the load frequency determining circuit.)

Large value of resistors can be used, thereby reducing the value capacitors size used in the circuit.

Note: Passive filters works good for high frequencies(radio range). But for audio range the inductors required become problematic, as the inductors becomes large,heavy and expensive.For low frequency application more no. of wires must be used which in turn adds to the series resistance degrading Inductors’ performance. 9. What is zero crossing detector? The basic inverting and non-inverting compactor act as a zero crossing detector provider that Vref is set to zero. This circuit is also called as sine wave to square wave generator. 10. What is a comparator? A comparator is a circuit which compares a signal voltage applied at one input of an op-amp with a known reference voltage at the other input. It is anopen loop op - amp with output ±Vsat. 11. What are the types of comparator? 1. Inverting comparator. 2. Non inverting comparator. 12. What arethe applications of comparator?

a. Zero crossing detectors b. Window detector c. Time marker signal generator d. Phase detector. e. Amplitude distribution analyzer f. Pulse time modulator

13. What is a peak detector? A peak detector is a series connection of a diode and a capacitor outputting a DC voltage equal to the peak value of the applied AC signal. 14. What is a window detector?

A device, usually consisting of a pair of voltage comparators, in which output indicates whether the measured signal is within the voltage range bounded by two different thresholds (an "upper" threshold and a "lower" threshold). 15. What is a Schmitt trigger? Schmitt trigger is a regenerative comparator. It converts sinusoidal input into asquare wave

output. The output of Schmitt trigger swings between upper and lower threshold voltages, which are the reference voltages of the inputwaveform.

16. Define the term hysteresis in Schmitt trigger? Hysteresis means that the output will switch when the input increases to one levelbut

will not switch backuntil the input falls below a different level. (Called a hysteresis loop) Output voltage switches to +max V whentheinput voltage decreases below the Lower Trigger Limit and the output switches to –Vmax when the input exceeds upper trigger limit. Comparator having this characteristic is called a Schmitt trigger.

17. What is a multivibrator? Multivibrators are a group of regenerative circuits that are used extensively in timing

applications. It is a waveshaping circuit which gives symmetric or asymmetric square output. It has two states stable or quasi- stable depending on thetype of multivibrator.

18. What do you mean by Monostable multivibrator?

Monostable multivibrator is one which generates a single pulse of specified duration in response to each externaltrigger signal. It has onlyone stable state. Application of a trigger causes a change to the quasi-stable state. An external trigger signal generated due to charging and dischargingof the capacitor produces the transition to the originalstable state. 19. What is an Astable multivibrator?

Astable multivibrator is a free running oscillator having two quasi-stable states. Thus, there are oscillations betweenthese two states and no external signal is required to produce the change in state. 20. What is a Bistablemultivibrator?

Bistable multivibrator is one that maintains a given output voltage level unless an external trigger is applied. Applicationof an external trigger signal causes a change of state, and this output level is maintained indefinitely until a secondtrigger is applied. Thus, it requires two external triggers before it returns to its initial state. 20. What are the requirements forproducing sustained oscillations in feedback circuits? For sustained oscillations, The total phase shift around the loop must be zero at the desired frequency of oscillation, fo. i.e. Aβ = 0 (or) 360o. At fo, the magnitude of the loop gain Aβ must be equal to unity. 21. Differentiate Schmitt trigger and comparator.

A Schmitt trigger is a comparator with a small amount of positive feedback applied to create a hysteresis for the input level. 22. How does the precision rectifier differ from the conventional rectifier?

These rectifiers are used to rectify very small voltages or currents for which the diode never gets forward biased in the conventional one. i.e. voltage or currents are always less than .7V which cannot be rectified by normal rectifiers. This rectifier doesn’t give any kind of drop in output since diodes are previously biased using op-amp. 23. Mention the classification of oscillators. According to the frequency determining networks, 1. RC oscillators 2. LC oscillators 3. Crystal oscillators

24. How can you obtain triangular wave using schmitt trigger? The output of Schmitt trigger when connected to integrator yields triangular output. 25. Wein bridge oscillator uses positive and negative feedback. Why? Negative feedback is used for stability gain positive feedback is used for oscillation. 26. What is the function of lead-lag network in Wein bridge oscillator? The function of lag lead network is to obtain the zero degree phase shift. 27. Why Schmitt trigger is called regenerative comparator? The reference voltages LTP andUTP are regenerated depending on the output voltages +Vsat and –Vsat. 28. List the advantages of phase shift oscillator. 1. The phase shift oscillator does not required conductance or transformers. 2. It is suitable for the low frequency range i.e., from a few hertz to several hundred KHz. The upper frequency is limited because the impedance of RC network may become so small that it loads the amplifier heavily. 3. The circuit is simple to design. 4. Produces sinusoidal output wave form. 29. Write the disadvantages of Phase shift oscillator. 1. It is necessary to change the C or R in all the three RC networks simultaneously for changing the frequency of oscillations. This is practically difficult. 2. It is not suitable for high frequencies. 30. Write the main drawback of LC oscillators. 1. The frequency stability is not very good. 2. They are too bulky and expensive and cannot be used to generate low frequencies. 31. Define Piezo electric effect. Certain crystal, when suitable wt, develop a potential difference between opposite faces, magnitude and polarity of which depends on pressure or tension applied to the other pair of perpendicular faces. This effect is called Piezo electric effect. 32. Write the advantages of Wein’s bridge oscillator. 1. By varying the two capacitorvalues simultaneously, by mounting them on thecommon shaft, different frequency ranges can be obtained. 2. It is useful audio frequency range i.e. 20 HZ to 100 HZ. 3. The perfect sine wave output is possible. 33. What is meant by clipper? The circuits which are used to clip off the unwanted portions of the input voltage above or below certain levels, so as to produce limited required output are called limiting circuits. As some part of input gets clipped off to produce output, these circuits are commonly called clipping circuits. 34. What is meant by clamper circuits? The circuits which are used to add a d.c.Levelas per the requirement, to thea.c. output are called as clamper circuits. Itis also called asd.c. restorer circuits.

35. What are the types of clipper circuits? 1. Positive clipper circuits- remove some positive partby comparing the input with ±Vrefto produce output. 2. Negative clipper circuits- remove some negative part by comparing the input with ±Vrefto produce output. 36. What are the types of clamper circuits? 1. Positive clamper circuits-The clamped d.c. level is positive. 2. Negative clamper circuits- Theclamped d.c. level is negative. 37. What is a sample and hold circuit? Where it is used? A sample and hold circuit is one which samples an input signal and holds on to its last sampled value until the input is sampled again. This circuit is mainly used in digital interfacing, analog to digital systems, and pulse code modulation systems. 38. Define sample period and hold period. The time during which the voltage across the capacitor in sample and hold circuit is equal to the input voltage is called sample period. The time period during which the voltage across the capacitor is held constant is called hold period. 39. State the advantages and applications of sample and hold circuits. A sample and hold circuit is one which samples an input signal and holds on to its last sampled value until the input is sampled again. This circuit is mainly used in digital interfacing, analog to digital systems, and pulse code modulation systems. 40. What are the types of ADC and DAC? Types of ADC: 1. Flash (comparator) type converter 2. Counter type converter 3. Tracking or servo converter 4. Successive approximation type converter Types of DAC: 1. Weighted resistor DAC 2. R-2R Ladder 3.Voltage mode R-2R ladder type 3. Inverted or current mode R-2R Ladder 41. Give the expression for output voltage of a voltage type D/A converter Vo= KVFS(b12-1+b2 2-2 +b3 2-3 +b4 2-4 +……..+ bn2-n) 42. Give the expression for the output voltage of a weighted resistor type DAC. Vo = IoRf = Rf/R VR(b1 2-1 + b2 2-2 + b3 2-3 + b4 2-4 +……..+ bn2-n) 43. Write the output voltage expression for a n bit R-2R ladder D/A converter Vo = (VR / 21 + VR / 22+ VR / 23+…………..+VR / 2n) 44. What are the advantages and disadvantages of R-2R ladder DAC. Advantages: a) Easier to build accurately as only two precision metal films are required. b) Number of bits can be expanded by adding more sections of same R/2R values.

Disadvantage: a) In this type of DAC, when there is a change in the input, changes the current flow in the resistor which causes more power dissipation which creates non-linearity in DAC. 45. List the broad classification of ADCs. 1. Direct type ADC. 2. Integrating type ADC. 46. List out the direct type ADCs.

1. Flash (comparator) type converter 2. Counter type converter 3. Tracking or servo converter 4. Successive approximation type converter.

47. List out some integrating type converters.

1. Charge balancing ADC. 2. Dual slope ADC.

48. What is the difference between direct ADC and integrating type ADC. a) The integrating type of ADC’s do not need a sample/Hold circuit at the input. b) It is possible to transmit frequency even in noisy environment or in an isolated form. 49. What is integrating type converter?

An ADC converter that perform conversion in an indirect manner by first changing the analog I /P signal to alinear function of time or frequency and then to a digital code is known as integrating type A/D converter. 50. Explain in brief the principle of operation of successive Approximation type ADC.

The circuit of successive approximation ADC consists of a successive approximation register (SAR), to find the requiredvalue of each bit by trial & error. With the arrival of START command, SAR sets the MSB bit to 1. The O/P is convertedinto an analog signal & it is compared with I/P signal. This O/P is low or high. This process continues until all bits are checked. 51. What are the main advantages ofintegrating type ADCs? i. The integrating type of ADC’s doesn’t need a sample/Hold circuit at the input. ii. It is possible to transmit frequency even in noisy environment or in an isolated 52. Define conversion time.

It is defined as the total time required converting an analog signal into its digital output. It depends on theconversion technique used & the propagation delay of circuit components. The conversiontime of a successive approximation type ADC is given by T(n+1) Where T---clock period Tc---conversion time n- no. of bits. 53. Define resolution of a data converter.

The resolution of a converter is the smallest change involtage whichmay beproduced atthe output or input of theconverter. Resolution (in volts) = VFS/2n-1=1 LSB increment. The resolution of an ADC is defined as the smallest change in analoginput for a one-bit change atthe output.

54. Explain in brief stability of a converter. The performanceof converter changes with temperature age and power supply variation.

So all the relevant parameterssuch as offset, gain, linearity error and monotonicity must be specified over the full temperature and power supply ranges to have better stability performances. 55. What is meant by linearity?

The linearity of an ADC/DAC is an important measure of its accuracy & tells us how close the converter output is to its ideal transfer characteristics. The linearity error is usually expressed as a fraction of LSB increment or percentage of fullscale voltage. A good converter exhibits a linearity error of less than ±½LSB. 56. Which is the fastest ADC give reasons? Flash type (or Simultaneous / Parallel converter) is the fastest A/ D converter because A/D conversion is simultaneously through a set of comparators. Conversion time only depends on the signal propagation time through various components and this delay is typically 100 nsec or less. 57. List the drawbacks of binary weighted resistor technique of D/A conversion. a) Wide range of resistor values needed b) Difficulty in achieving and maintaining accurate ratios over a wide range of variations 58. What are the advantage and disadvantages of flash type ADC? Flash type ADC is the fastest as well as the most expensive. The disadvantage is the number of comparators needed almost doubles for each added bit (For a n-bit convertor 2(n-1) comparators, 2n resistors are required). 59. The basic step of a 9 bit DAC is 10.3 mV. If 000000000 represents 0Volts, what is the

output for an input of 101101111? The output voltage for input of 101101111 is = 10.3 mV (1*28+0*27+1*26+1*25+0*24+1*23+1*22+1*21+1*20) = 10.3 * 10-3 * 367 = 3.78 V 60. Why does the dual slope ADC provide excellent noise rejection of AC signal whose

periods are integral multiples of the integration time? 61. Find the resolution of a 12 bit DAC converter. Resolution (volts) = VFS/(212-1) = I LSB increment VFS – Full scale voltage 62. Define start of conversion and end of conversion. Start of Conversion in ADC (SOC): This is the control signal for start of conversion which initiates A/D conversion process. End of Conversion in ADC (EOC): This is the control signal which is activated when the conversion is completed. 63. Define following performance parameters of D/A converters: a) Resolution The resolution of a converter is the smallest change in voltage which may be produced at the output or input of the converter. Resolution (in volts)= VFS/2n-1=1 LSB increment. The resolution of an ADC is defined as the smallest change in analog input for a one bit change at the output.

b) Accuracy Absolute accuracy: It is the maximum deviation between the actual converter output & the ideal converter output. Relative accuracy: It is the maximum deviation after gain & offset errors have been removed. The accuracy of a converter is also specified in form of LSB increments or % of full scale voltage. c) Monotonicity A monotonic DAC is one whose analog output increases for an increase in digital input. d) Conversion time It is defined as the total time required to convert an analog signal into its digital output. It depends on the conversion technique used & the propagation delay of circuit components. The conversion time of a successive approximation type ADC is given by T(n+1)where T---clock periodTc---conversion time and n----no. of bits

Unit IV Special ICs 1. List out the applications of 555 timer? a. Oscillator b. Pulse generator c. Ramp and square wave generator demodulator, mono-shot multivibrator. e. Burglar alarm f. Traffic light control. 2. Enlist the important features of 555 timer. 1. Versatile IC.Other than timing applications, it can be used for numerous other applications. 2. Highly stable device used to produce very accurate time delay or oscillation. 3. It can provide time delay ranging from μs to hours. 4. It can drive load upto 200mA. 5. It is compatible with both TTL and CMOS logic circuits. 6. It can be used with the supply voltage in the range of +5v to +18v

3. Define sink current and source current? Sink current: When the output is low, the load current that flows through the load connected between Vcc and o/p terminal is called sink current. Source current: When the output is high, the load current that flows through the load connected between ground and o/p terminal is called source current. 4. Define normally ON load and normally OFF load? Normally ON load: The load connected between VCC and output terminal. Normally OFF load: The load connected between output terminal and ground. 5. What is the use of reset pin of 555 timer?

This is an interrupt for the timing device when pin 4 is grounded, It resets the timer output to low level irrespective of the input conditions. 6. What is the purpose of control voltage pin (5) of 555 timer?

This pin is the inverting input terminal of upper comparator. This is reference level for the upper comparator with which threshold is compared. If reference level is other than 2/3 VCC, then external input is to be given to pin 5 which changes the threshold and trigger limits. Pulse width modulation is possible due to pin 5. 7. List out the major blocks of 555 timer functional diagram? The IC 555 timer combines the following elements. 1) A relaxation oscillator 2) RS flip-flop 3) Two comparators 4) Discharge transistor 8. Define duty cycle? It is defined as the ratio of on time to the total time of one cycle. D = Ton/Ttotal Ton – time for output is high Ttotal– total time of one cycle.

9. Write the expression for pulse width of 555 timer in monostable mode? Pulse width W = 1.1 RC seconds R – resistor in ohms, C – capacitor in farads 10. Write the expression for total time period of 555 timer in astable mode? T = 0.693 (RA + 2 RB) C seconds 11. What is the frequency of oscillation of free running mode of 555 timer? F = 1.44/ (RA + 2 RB) CHz 12. List out the applications of 555 timer in astable mode.

FSK generator

Pulse position modulation

Schmitt trigger 13. Why invariably a suitable value of capacitor is connected to pin 5 of 555 timer

applications? To bypass the unwanted ripples and noise present in the dc supply voltage, thereby the DC threshold limits can be accurately maintained. If pin 5 is not used it is usually grounded through a 0.01μF capacitor.

14. List out the applications of 555 timer in monostable mode. a. missing pulse detector b. Linear ramp generator c. Frequency divider d. Pulse width modulation. 15. What is a voltage controlled oscillator?

A Voltage-Controlled Oscillator (VCO) is a circuit that provides a varying output signal (typically of square-wave or triangular-wave form) whose frequency can be adjusted over a range controlled by a dc voltage. An example of a VCO is the 566 IC unit, which contains circuitry to generate both square wave and triangular-wave signals whose frequency is set by an external resistor and capacitor and then varied by an applied dc voltage. 16. What is free running frequency of VCO?

A free-running or center-operating frequencyof, can be calculated from Eq.

With the following practical circuit value restrictions:

R1should be within the range

VCshould be within range

f oshould be below 1MHz

V+should range between 10 V and 24 V.

17. Define voltage to frequency conversion factor of VCO. Voltage to Frequency conversion factor is defined as, Kv= ∆fo / ∆Vc = 8fo /Vcc where, ∆Vc is the change in modulation voltage required to produce a corresponding frequency shift ∆fo 18. What are the desirable properties of VCO

Linearity in voltage to frequency conversion

Frequency stability against temperature changes and drift characteristics

High operating frequency and wide tracking range of frequencies

High modulating sensitivity K0 and ease of tuning 19. State two applications of VCO.

1. It is used in converting the low frequency signals such as EEG and EKG into audio frequency range.

2. The audio frequency signals can be transmitted over telephone lines for diagnostic purpose or can be recorded on magnetic tapes

20. Define PLL. The phase locked loop or PLL, an important building block of linear system is a closed loop frequency feedback system, whose output frequency and phase are in lock with the frequency and phase of the input signal. It can detect the phases of two signals and reduce the difference in the presence of a phase difference. 21. List out the blocks of PLL. a. Phase detector/comparator b. Low pass filter c. Error amplifier d. Voltage controlled oscillator 22. List the important characteristics of PLL.

1. Lock-in range. 2. Capture range 3. Pull-in time

23. Define Tracking or lock-in range of a PLL. When the frequency of the input to the PLL system is changed, the output frequency changes to follow (or track) the input frequency. However, for each PLL there is an upper and lower frequency limit beyond which fo will not track fi. The range of frequencies between these limits is known as the lock-in range. 2Δ fL = ± KΦKvA π / 2 24. Define the following terms related to PLL, a) Capture range The range of frequencies over which the PLL can acquire lock with an input signal is called the capture range. Itis expressed as a percentage of the VCO free running frequency. b) Lock range The range of frequencies over which the PLL can maintain lock with the incoming signal is called the lock-in range or tracking range. It is expressed as a percentage of the VCO free running frequency.

25. Write the expression of a) capture range Capture range = ∆f c = [∆fL / (2*π*R*C)] 1/2

b) lock range

Lock in range ∆f L = ± 7.8 fo/ V fo is free running frequency 26. What is the pull in time of PLL

The total time taken by the PLL to establish lock is called pull in time. This depends on the initial phase and frequency difference between two signals as well as on the overall loop gain and loop filter characteristics.

27. List the applications of IC 565 PLL

1. Frequency multiplication 2. Frequency division 3. AM Detection 4. FM Detection 5. FSK modulation/demodulation 6. Frequency synthesizing

28. Mention the applications of analog multiplier.

1. Frequency doubling 2. Measurement of real power 3. Detecting phase angle difference between two signals of equal frequency 4. Multiplying two signals 5. Dividing one signal by another 6. Taking square root of a signal 7. Squaring a signal

29. When does a frequency doubler works as an ideal circuit? The multiplication of two sine waves of the same frequency, but of possibly different amplitudes and phase allows doubling a frequency using an analog multiplier.

Ux = Vxsinωt Uy = Vysinωt

Vo= VxVy

𝑉𝑟𝑒𝑓sinω2t =

VxVy

𝑉𝑟𝑒𝑓(1-

cos ω2t

2 )

The output thus contains a dc term and a negative cosine term of double frequency. The dc term can be easily removed by using a 1μF coupling capacitor between load and the output terminal. 30. What are one, two and four quadrant multipliers?

1. One Quadrant multiplier: if both the inputs are positive, the IC is said be in one quadrant multiplier.

2. Two quadrant multiplier: Two quadrant multipliers is one in which if one input is held positive and the other is allowed to swing both positive and negative.

3. If both the inputs may be either positive and or negative, the IC is called for Quadrant multiplier.

31. In what way VCO is different from other oscillators. The VCO is a free running multivibrator and operates a set of frequency fo called free running frequency. This free running frequency is determined by an external timing capacitor and an external resistor. It can also be shifted to either side by applying a dc control voltage VC to an appropriate terminal of the IC. 32. Which is greater “capture range” or “Lock in range”?

The lock in range is greater than the capture range because the error voltage generated is the average value but for maximum capture range needs maximum value of error voltage. The capture range also depends on the low pass filter characteristics.

33. List the problems of switch type phase detector (analog phase detector).

1. The output voltage Vo is proportional to the input signal amplitude Vs. This is undesirable since it makes phase detector gain and loop gain dependent on the input signal amplitude.

2. The output is proportional to cosφ and not proportional to φ,making it non-linear.

34. What are the uses of capacitor in the PLL circuit? 1. The low pass filter not only removes the high frequency components and noise but also

controls the dynamic characteristics of PLL. 2. The charge on the capacitor gives short time memory to PLL.

35. Define phase transfer conversion coefficient of PLL. The conversion ratio Kd of phase detector is given by Kd = Vcc/π 36. Briefly write on frequency synthesizers. A frequency synthesizer is an electronic system for generating any of a range of frequencies from a single fixed time base or oscillator. They are found in many modern devices, including radio receivers, mobile telephones, radiotelephones, walkie-talkies, CB radios, satellite receivers, GPS systems, etc. A frequency synthesizer can combine frequency multiplication, frequency division, and frequency mixing (the frequency mixing process generates sum and difference frequencies) operations to produce the desired output signal.

Unit V Application ICs

1. Define voltage regulators and give the types?

A voltage regulator is an electronic circuit that provides a stable dc voltage independent of the load current, temperature, and ac line voltage variations. The classification of voltage regulators:

Series / Linear regulators Fixed type voltage regulators Adjustable type voltage regulators

Switching regulators. 2. List the important parts of regulated Power supply ICs Reference voltage circuit Error amplifier Series pass transistor Feedback network

3. What are the limitations of linear voltage regulators?

1. The step-down transformer used in the power supply circuit is bulky and it is the most expensive component of the circuit.

2. Large values of filter capacitors are required to eliminate ripples, due to the line frequency (50 Hz) of operation.

3. The efficiency of series regulator is normally less than 50%. 4. The input voltage must be more than the required output regulated voltage. 5. The difference between the input and output voltage drops across the linear pass

transistor and dissipates power. 4. Define (i) Line Regulation (ii) Load regulation

Line regulation Line regulation is defined as the change in output voltage for a change in line supply voltage when the load current and temperature remain constant. It is given by

Line regulation = 𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑜𝑢𝑡𝑝𝑢𝑡 𝑣𝑜𝑙𝑡𝑎𝑔𝑒

𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑖𝑛𝑝𝑢𝑡 𝑣𝑜𝑙𝑡𝑎𝑔𝑒

Load Regulation

Load regulation is defined as the change in output voltage for a change in load current. it is

expressed in millivolts or as a percentage of the output voltage.

Load regulation = (𝑉 𝑛𝑜 𝑙𝑜𝑎𝑑 − 𝑉 𝑓𝑢𝑙𝑙 𝑙𝑜𝑎𝑑)

𝑉 𝑛𝑜 𝑙𝑜𝑎𝑑

5. Define ripple rejection

Ripple rejection is defined as the ratio of peak-to peak input ripple voltage ΔVo (unreg) to the peak to peak output ripple voltage ΔVo (reg). It is typically 60dB or more for the commonly used voltage regulators. 6. List the features of LM78XX fixed voltage regulators

3 terminal positive voltage regulator with seven voltage options High Output Current - typically 1.5A Short circuit current limit - 750mA at 5v

Internal thermal overload protection Low quiescent current - 6mA Max input voltage = 35v Minimum Input Voltage = Vout + 2.5

7. Draw the circuit of IC78XX used as a current source

IL= (VR/ R )+ IQ 8. What are the features of IC 79XX

Same as that of 78XX series except that 79XX series are negative regulators They are available in same seven voltage options with two extra voltage options,-

2V and -5.2V

9. What are the disadvantages of linear voltage regulators? 1. It has low efficiency as it is constantly in conduction 2. Internal power consumption is high 3. It has no short circuit protection 4. If the input is more compared to the rated output the excess voltage is dropped

across the regulator. 10. Name few voltage protection circuits used for voltage regulators

1. Current limit Protection 2. Current fold back 3. Current boosting

11. What do you mean by linear voltage regulators? Series or linear regulator uses a power transistor connected in series between the unregulated

dc input and the load and it conducts in the linear region .The output voltage is controlled by the continuous voltage drop taking place across the series pass transistor. 12. Define switched voltage regulators?

Switching regulators are those which operate the power transistor as a high frequency on/off switch, so that the power transistor does not conduct current continuously. This gives improved efficiency over series regulators. 13. What are the advantages of adjustable voltage regulators over the fixed voltage

regulators? i) Improved line and load regulation by a factor of 10 or more. ii) Because of the improved overload protection, greater load current can be drawn. iii) Improved reliability.

14. Define dropout voltage of a fixed voltage regulator?

It is the minimum voltage that must exist between input and output terminals. For most of regulators, it is 2 to 3 volts. 15. Draw the pin details of IC723.

16. What is the principle of switched mode power supplies?

The switched mode power supplies rely on pulse width modulation to control the average value of the output voltage. If the duty cycle of wave form is varied the output voltage changes proportionally. Power 17. What are the advantages of switch mode power supplies?

Advantages 1. Efficiency is high because of less heat dissipation. 2. As the transformer size is very small, it will have a compact unit. 3. Decrease in cost 4. Protection against excessive output voltage by quick acting guard circuits. 5. Reduced harmonic feedback into the main supply. 6. Generation low and medium voltage supply is easy.

18. Why current boosting is done in 723 regulators?

The maximum current that 723 IC regulator can provide is 140mA. For many applications it is not sufficient. Hence a boost transistor Q1 is added to voltage regulator. The load current thus is Increased. Iload = β pass transistorx Io(723)

19. State the need for protection diodes in voltage regulators based on LM 317 regulator. The 317 regulators have no protection. If the load demands move current eg. Under short circuit condition, the IC tries to provide it at a constant output voltage getting hotter all the time. This may ultimately burn the IC.

20. List the features of LM380 1. It has a wide operating supply voltage range from 5v to 20v. 2. It operates with low quiescent power drain 3. Voltage gain of 34 dB can be achived. 4. It can deliver high peak current of 1.3 A maximum. 5. It has a unique, ground referenced or ac coupled input stage. 6. High input impedance of the order of 150 KΩ is made available. 7. It has low distortion (total harmonic distortion of 0.2) 8. The quiescent output voltage at one half of the supply voltage is possible. 9. The standard dual in line packages(8 – pin and 14 – pin) are available. 10. It can operate at temperature of 0oC to 70oC. 11. A band widh of 100KHz typically at an output power of 2W and load of 8Ω is

possible. 21. What are the applications of LM380?

Audio power amplifier High gain audio amplifier Intercom system Bridge amplifier

22. Draw the pin details and Symbol LM380

23. What are the advantages of adjustable voltage regulators? improved system performance improved overload protection improved system reliability Example: LM317

24. Give the output expression for the LM317.

25. List the features of IC723

The device can be set to work as both positive and negative voltage regulators with an output voltage ranging from 2 V to 37 V,

Output current levels upto 150 m A.

The maximum supply voltage is 40 V, and

The line and load regulations are each specified as 0.01%.

26. What are the internal functional blocks of IC723. It consists of a voltage reference source (Pin 6), an error amplifier with its inverting input on pin 4 and non-inverting input on pin 5, a series pass transistor (pins 10 and 11), and a current limiting transistor on pins 2 and 3.

27. What is the purpose of having input and output capacitors in three terminal IC

regulators? A capacitor connected between the input terminal and ground cancels the inductive

effects due to long distribution leads. The output capacitor improves the transient response.

28. What is meant by current limiting? Current limiting refers to the ability of a regulator to prevent the load current from increasing above a preset value. 29. What are the advantages of IC voltage regulators?

IC voltage regulators were inexpensive, versatile, provides current /voltage boosting, internal short circuit current limiting, thermal shutdown, floating operation for high voltage applications. 30. How IC regulators are classified?

There are basically two kinds of IC voltage regulators: 1. Multi-pin type, e.g. LM723C 2. 3-pin type, e.g. 78/79XX Multi-pin regulators are less popular but they provide the greatest flexibility and produce the highest quality voltage regulation. 3-pin types make regulator circuit design simple.

Types of IC voltage regulators: Fixed output voltage regulators: positive fixed output regulator(78XX series) and

negative fixed output regulator(79XX series) Adjustable output voltage regulators: positive (LM317) and negative(LM337) Switching regulators: motorola ‘s MC1723

31. What are the various performance parameters of voltage regulators?

Line or input regulation: defined as a change in output voltage for a change in input voltage

Load regulation: defined as the change in output voltage for a change in load current. Temperature stability or average temperature coefficient of output voltage (TCVO):

defined as the change in output voltage per unit change in temperature and expressed in millivolts per degree Celsius.

Ripple rejection: is the measure of regulator‘s ability to reject ripple voltages.it is usually expressed in decibels.

Quiescent current Iq : current that flows into the regulator and does not include current drawn by load or internal resistor networks.

The smaller the value of these performance parameters, the better the regulator.what

32. List out the features of LM8038

Low frequency drift with temperature(-250ppm/C)

Simultaneous sine, square, and triangular wave outputs

Low distortion – 1%(sine wave output)

High linearity – 0.1%(Triangular wave output)

Wide operating frequency range –0.001Hz to 300KHz

Variable duty cycle -2% to 98%

High level outputs – TTL to 28V

Easy to use – just a handful of external components required

33. Draw the pin details of IC 8038

34. How to vary the frequency and duty cycle of output in IC8038

The timing resistors connected to pin 4 and 5 as well the timing capacitor connected to pin 10 decides the frequency of the output waveform. If R1 = R2 then the duty cycle is 50%.

The frequency of the output wave form can be calculated by using the formula

F = 0.33/ RC (it R1 = R2)