Electronics and Instrumentation

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					                                   Electronics and Instrumentation

Duration -3 Hrs                                                                   Max Marks: 70


1. Answer any EIGHT questions from Section A. Each question carries 5 marks.

2. Answer any THREE questions from Section B. Each question carries 10 marks.

                                                 Section A


                1. Draw and explain the functional diagram of a 555 timer IC.

Ans. The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation

Introduced in 1971 by Signetics, the 555 is still in widespread use, thanks to its ease of use, low price and
good stability, and is now made by many companies in the original bipolar and also in low-power CMOS

The IC was designed in 1971 by Hans R. Camenzind under contract to Signetics, which was later
acquired by Philips.

sensitive instead of level sensitive). There is no 557.

name from the three 5 kΩ resistors used within, but Hans Camenzind has stated that the number was
Low-power versions of the 555 are also available, such as the 7555 and CMOS TLC555. The 7555 is
designed to cause less supply glitching than the classic 555 and the manufacturer claims that it usually
does not require a "control" capacitor and in many cases does not require a decoupling capacitor on the
power supply. Such a practice should nevertheless be avoided, because noise produced by the timer or

                2. What is the principle of working of Switch Mode Power Supply? Discuss its
                     advantages and disadvantages.

Ans. A switched-mode power supply (switching-mode power supply, SMPS, or simplyswitcher) is
source like the electrical power grid to a load (such as apersonal computer) while

Unlike a linear power supply, the pass transistor of a switching mode supply continually switches between
(which minimizes wasted energy). Ideally, a switched-mode power supply dissipates no power. Voltage

Switching regulators are used as replacements for the linear regulators when higher efficiency, smaller
size or lighter weight are required. They are, however, more complicated, their switching currents can

                3. Explain briefly positive fixed voltage regulator. What voltage options are
                     available in 78xx and 79xx voltage regulators?

Ans. he 78xx (sometimes LM78xx) is a family of self-contained fixed linear voltage regulator integrated

78xx ICs have three terminals and are commonly found in the TO220 form factor, although smaller
surface-mount and larger TO3 packages are available. These devices support an input voltage anywhere
from a couple of volts over the intended output voltage, up to a maximum of 35 or 40 volts, and typically
provide 1 or 1.5 amperes of current (though smaller or larger packages may have a lower or higher
current rating).


   78xx series ICs do not require additional components to provide a constant, regulated source of
    regulation process. Some other designs (such as a switched-mode power supply) may need
    substantial engineering expertise to implement.
    78xx itself, but also for other parts of the circuit.
78xx ICs are easy to use and handle but these cannot give a altering voltage required so Lm317 series of
ICs are available to obtain a voltage output from 1.25 volts to 37 volts.

                4. Draw the block diagram of CRO and explain the purpose of each blocks.

   Ans. Cro is an American animated television series produced by the Children's Television
    Workshopand Film Roman. It debuted on September 18, 1993 as part of the Saturday morning line-
    up forfall 1993 on ABC. Cro did not do well with the viewers. The show had an educational theme in
    accordance with FCC-mandated educational/instructional requirements, introducing basic concepts
    of physics, mechanical engineering, and technology. The premise of using woolly mammoths as a
    teaching tool for the principles of technology was inspired by David Macaulay'sThe Way Things
    Work; Macaulay is credited as writer on the show. The last new episode aired on October 22, 1994.
    The show was released on video (VHS) in a total of nine volumes. Cro was a fully evolved 11-year-
    old Cro-Magnon boy. Cro lives with the Neanderthals and is the smartest one, which was the reason
    most of the characters hated him.
   Jim Cummings as Ogg: The big show-off of the Neanderthals, Ogg was the leader and bossed
    everyone around. He gets into arguments with Nandy and once forced Bobb out of the tribe, causing
    everyone to leave Ogg all alone (with the exception of Gogg, the others came back to him because
    they thought he felt lonely). Ogg's phrases include: "In cases like this, only one thing to say:
    <something>" and "We gonna die," which is often used by other Neanderthals; Gogg said it once and
    Nandy said it too, but Ogg told her that it was his line. According to "Play It Again, Cro...Not!" Ogg
    claims to have a brilliant singing voice
   Frank Welker as Gogg: Gogg is the sensitive one in the tribe. He sticks up for Bobb and mostly
    translates for him, even though Nandy and Ogg do occasionally. It was disclosed in "Play It Again,
                                               [4]                                                     [5]
    Cro...Not!" that Gogg could play his armpit which Phil decided to use for his band's wind section.
   Frank Welker as Bobb: Bobb is the Neanderthal on the lowest rank in the evolutionary scale,
    meaning he is still an ape-like creature. He does not speak like the rest of the Neanderthals, but
    makes monkey-like noises which Gogg and Nandy then translate. When Bobb was younger, he was
    in a different tribe made up of apes that looked like him. The tribe took a nap and Bobb woke up to
    find the whole tribe had vanished without a trace, creating a fear of loneliness. In "Play It Again,
    Cro...Not!" Bobb is revealed to be a master nose flute player, which impresses everyone.

                 5. Why signal conditioning in necessary in an instrumentation systems?
                 6. Describe in detail the instrumentation amplifier.

Ans. An instrumentation (or instrumentational) amplifier is a type ofdifferential amplifier that has been
outfitted with input buffers, which eliminate the need for input impedance matching and thus make the
great accuracy andstability of the circuit both short- and long-term are required.

Although the instrumentation amplifier is usually shown schematically identical to a standard op-amp, the
electronic instrumentation amp is almost always internally composed of 3 op-amps. These are arranged
so that there is one op-amp to buffer each input (+,−), and one to produce the desired output with
adequate impedance matching for the function.

The most commonly used instrumentation amplifier circuit is shown in the figure. The gain of the circuit is

    The rightmost amplifier, along with the resistors labelled     and       is just the standard differential
    amplifier circuit, with gain =         and differential input resistance = 2·    . The two amplifiers on
    the left are the buffers. With       removed (open circuited), they are simple unity gain buffers; the
    circuit will work in that state, with gain simply equal to        and high input impedance because
    of the buffers. The buffer gain could be increased by putting resistors between the buffer inverting
    mode rejection ratio (CMRR) of the circuit and also enables the buffers to handle much larger
    a pair, thus avoiding a resistor-matching problem (although the two     s need to be matched), and
    very conveniently allowing the gain of the circuit to be changed by changing the value of a single
    resistor. A set of switch-selectable resistors or even a potentiometer can be used for           ,
    providing easy changes to the gain of the circuit, without the complexity of having to switch matched
    pairs of resistors.

                 7. Explain with the help of a neat block diagram the working principle of digital
                 8. Discuss the successive approximation A/D converter and list out the merits of
                     the same.
                 9. What is X-Y recorder? How do you distinguish it from X-t (or) Y-t recorder?
                 10. Explain with a suitable circuit diagram the working of a X-Y recorder.

                                  Section B

                 11. What are the applications of Operational amplifiers?

Ans. An operational amplifier ("op-amp") is a DC-coupled high-gain electronic voltageamplifier with
typically hundreds of thousands times larger than the voltage difference between its input terminals.

Operational amplifiers are important building blocks for a wide range of electronic circuits. They had their
origins in analog computers where they were used in many linear, non-linear and frequency-dependent
circuits. Their popularity in circuit design largely stems from the fact that characteristics of the final op-
amp circuits withnegative feedback (such as their gain) are set by external components with little
dependence on temperature changes and manufacturing variations in the op-amp itself.

                                                          [citation needed]
specifications may cost over $100 US in small quantities.                   Op-amps may be packaged as
components, or used as elements of more complex integrated circuits.


                 12. What is voltage reference? Why is it needed?

Ans. A bandgap voltage reference is a temperature independent voltage reference circuit widely used
eV bandgap of silicon at 0 K. This circuit concept was first published by David Hilbiber in 1964. Bob
       [2]            [3]           [4]
Widlar, Paul Brokaw and others followed up with other commercially successful versions. The
voltage difference between two p-n junctions (e.g. diodes), operated at different current densities, is used
to generate a proportional to absolute temperature (PTAT) current in a first resistor. This current is used
to generate a voltage in a second resistor. This voltage in turn is added to the voltage of one of the
junctions (or a third one, in some implementations). The voltage across a diode operated at constant
current, or here with a PTAT current, is complementary toabsolute temperature (CTAT—reduces with
increasing temperature), with approx. −2 mV/K. If the ratio between the first and second resistor is chosen
properly, the first order effects of the temperature dependency of the diode and the PTAT current will
cancel out. The resulting voltage is about 1.2–1.3 V, depending on the particular technology and circuit
design, and is close to the theoretical 1.22 eV bandgap of silicon at 0 K. The remaining voltage change
over the operating temperature of typical integrated circuits is on the order of a few millivolts. This
temperature dependency has a typical parabolic behavior.

Because the output voltage is by definition fixed around 1.25 V for typical bandgap reference circuits, the
minimum operating voltage is about 1.4 V, as in a CMOS circuit at least one drain-source voltage of
a FET (field effect transistor) has to be added. Therefore, recent work concentrates on finding alternative
solutions, in which for example currents are summed instead of voltages, resulting in a lower theoretical
limit for the operating voltage (Banba, 1999).

Note that sometimes confusion arises when using the abbreviation CTAT, where the "C" is incorrectly
taken to mean "constant" rather than "complementary". To avoid this confusion, although not in
widespread use, the term constant with temperature (CWT) is sometimes used.

                13. Show the representation of IC voltage regulator.
                14. What are the major components of CRT?

Ans. A major step forward in pacemaker function has been to attempt to mimic nature by utilizing various
dynamic pacemaker was invented by Dr. Anthony Rickards of the National Health Hospital, London, UK,
         [citation needed]
in 1982.

may or may not be of interest to transitional tissue welding.

15. How can a Q-meter be used for measurement of stray capacitance?
16. What are the basic components of digital systems?

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