Electronics and Instrumentation by lanyuehua


									                                   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

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

                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
andoscillator applications. The 555 can be used to provide time delays, as an oscillator, and as a flip-flop
element. Derivatives provide up to four timing circuits in one package.

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
types. As of 2003, it was estimated that 1 billion units are manufactured every year.

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

Depending on the manufacturer, the standard 555 package includes 25 transistors, 2 diodes and
15 resistors on a silicon chip installed in an 8-pin mini dual-in-line package (DIP-8). Variants available
include the 556 (a 14-pin DIP combining two 555s on one chip), and the two 558 & 559s (both a 16-pin
DIP combining four slightly modified 555s with DIS & THR connected internally, and TR is falling edge
sensitive instead of level sensitive). There is no 557.

The NE555 parts were commercial temperature range, 0 °C to +70 °C, and the SE555 part number
designated the military temperature range, −55 °C to +125 °C. These were available in both high-
reliability metal can (T package) and inexpensive epoxy plastic (V package) packages. Thus the full part
numbers were NE555V, NE555T, SE555V, and SE555T. It has been hypothesized that the 555 got its
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
variation in power supply voltage might interfere with other parts of a circuit or influence its threshold

                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
an electronic power supply that incorporates a switching regulator in order to be highly efficient in the
conversion of electrical power. Like other types of power supplies, an SMPS transfers power from a
source like the electrical power grid to a load (such as apersonal computer) while
converting voltage and current characteristics. An SMPS is usually employed to efficiently provide a
regulated output voltage, typically at a level different from the input voltage.

Unlike a linear power supply, the pass transistor of a switching mode supply continually switches between
low-dissipation, full-on and full-off states, and spends very little time in the high dissipation transitions
(which minimizes wasted energy). Ideally, a switched-mode power supply dissipates no power. Voltage
regulation is achieved by varying the ratio of on-to-off time. In contrast, a linear power supply regulates
the output voltage by continually dissipating power in the pass transistor. This higher power conversion
efficiency is an important advantage of a switched-mode power supply. Switched-mode power supplies
may also be substantially smaller and lighter than a linear supply due to the smaller transformer size and

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
cause electrical noise problems if not carefully suppressed, and simple designs may have a poor power

                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
circuits. The 78xx family is commonly used in electronic circuits requiring a regulated power supply due to
their ease-of-use and low cost. For ICs within the family, the xx is replaced with two digits, indicating the
output voltage (for example, the 7805 has a 5 volt output, while the 7812 produces 12 volts). The 78xx
line are positive voltage regulators: they produce a voltage that is positive relative to a common ground.
There is a related line of 79xx devices which are complementary negative voltage regulators. 78xx and
79xx ICs can be used in combination to provide positive and negative supply voltages in the same circuit.

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
    power, making them easy to use, as well as economical and efficient uses of space. Other voltage
    regulators may require additional components to set the output voltage level, or to assist in the
    regulation process. Some other designs (such as a switched-mode power supply) may need
    substantial engineering expertise to implement.
   78xx series ICs have built-in protection against a circuit drawing too much power. They have
    protection against overheating and short-circuits, making them quite robust in most applications. In
    some cases, the current-limiting features of the 78xx devices can provide protection not only for the
    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
amplifier particularly suitable for use in measurement and test equipment. Additional characteristics
include very low DC offset, low drift, low noise, very high open-loop gain, very high common-mode
rejection ratio, and very high input impedances. Instrumentation amplifiers are used where
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
    inputs and ground to shunt away some of the negative feedback; however, the single resistor
     between the two inverting inputs is a much more elegant method: it increases the differential-mode
    gain of the buffer pair while leaving the common-mode gain equal to 1. This increases the common-
    mode rejection ratio (CMRR) of the circuit and also enables the buffers to handle much larger
    common-mode signals without clipping than would be the case if they were separate and had the
    same gain. Another benefit of the method is that it boosts the gain using a single resistor rather than
    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.

                 Answer any THREE questions from Section B. Each question carries 10 marks.
                                  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
a differential input and, usually, a single-ended output. An op-amp produces an output voltage that is
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.

Op-amps are among the most widely used electronic devices today, being used in a vast array of
consumer, industrial, and scientific devices. Many standard IC op-amps cost only a few cents in moderate
production volume; however some integrated or hybrid operational amplifiers with special performance
                                                          [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.

The op-amp is one type of differential amplifier. Other types of differential amplifier include the fully
differential amplifier (similar to the op-amp, but with two outputs), the instrumentation amplifier (usually
built from three op-amps), the isolation amplifier (similar to the instrumentation amplifier, but with
tolerance to common-mode voltages that would destroy an ordinary op-amp), and negative feedback
amplifier (usually built from one or more op-amps and a resistive feedback network).

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

Ans. A bandgap voltage reference is a temperature independent voltage reference circuit widely used
in integrated circuits, usually with an output voltage around 1.25 V, close to the theoretical 1.22
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
inputs to produce a rate-responsive pacemaker using parameters such as the QT interval, pO2 -
pCO2 (dissolved oxygen or carbon dioxide levels) in the arterial-venous system, physical activity as
determined by an accelerometer, body temperature, ATP levels, adrenaline, etc. Instead of producing a
static, predetermined heart rate, or intermittent control, such a pacemaker, a 'Dynamic Pacemaker', could
compensate for both actual respiratory loading and potentially anticipated respiratory loading. The first
dynamic pacemaker was invented by Dr. Anthony Rickards of the National Health Hospital, London, UK,
         [citation needed]
in 1982.

Dynamic pacemaking technology could also be applied to future artificial hearts. Advances in transitional
tissue welding would support this and other artificial organ/joint/tissue replacement efforts. Stem cells
may or may not be of interest to transitional tissue welding.

Many advancements have been made to improve the control of the pacemaker once implanted. Many of
these have been made possible by the transition to microprocessor controlled pacemakers. Pacemakers
that control not only the ventricles but the atria as well have become common. Pacemakers that control
both the atria and ventricles are called dual-chamber pacemakers. Although these dual-chamber models
are usually more expensive, timing the contractions of the atria to precede that of the ventricles improves
the pumping efficiency of the heart and can be useful in congestive heart failure.
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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