Two Marks Questions with Answers

Two Marks Questions with Answers

 

Q.1 What is a function of reset pin 4 in 555 timer ?

Ans. : This is an interrupt to the timing device. When pin 4 is grounded, it stops the working of device and makes it off. Thus, pin 4 provides on/off feature to the IC 555. This reset input overrides all other functions within the timer when it is momentarily grounded.

 

Q.2 Draw the functional diagram of 555 timer.

(Refer section 4.1.1)

 

Q.3 List any four applications of analog multipliers.

Ans. : 1. In communication it is used in amplitude modulation, phase modulation, frequency modulation, phase detection, suppressed carrier modulation etc.

2. In instrumentation and control used to measure velocity, acceleration, instantaneous power, automatic gain control, etc.

3. For voltage controlled attenuators and for voltage controlled amplification.

4. It is used for voltage divider, true r.m.s calculation, rectifier phase shift detection etc.

5. It is used for frequency converters, frequency doubling and frequency shifting etc.

6. It is used for squaring and square root calculations.

 

Q.4 What are the different stages of operation in a PLL ?

(Refer section 4.3)

 

Q.5 Enlist the important features of 555 timer circuit.

Ans. :          

1. The 555 is a monolithic timer device which can be used to produce accurate and highly stable time delays or oscillation. It can be used to produce time delays ranging from few microseconds to several hours.

2. It has two basic operating modes : Monostable and astable

3. It is available in three packages : 8-pin metalcan, 8-pin mini DIP or a 14-pin DIP. A 14-pin package is IC 556 which consists of two 555 timers.

4. The NE 555 (Signetics) can operate with a supply voltage in the range of 4.5 V to 18 V and is capable of sourcing and sinking output currents of 200 mA. Its CMOS version (TLC 555) can operate over a supply range of 2 V to 18 V and has output current sinking and sourcing capabilities of 100 mA and 10 mA, respectively.

5. It has a very high temperature stability, as it is designed to operate in the temperature range of - 55° to 125 °C.

6. Its output is capatible with TTL, CMOS and Op-Amp circuits.

 

Q.6 List the applications of NE 565.

(Refer section 4.5) 

 

Q.7 List any four applications of 555 timer in astable mode of operation.

Ans. :

1. Square wave generator

2. Voltage controlled oscillator

3. FSK generator     

4. Flasher circuit.

 

Q.8 What is the function of pin 5, control voltage input of 555 timer ?

Ans. : If external input applied to pin 5 is alternating then the reference level for comparator 1 keeps on changing above and below 2/3 V_CC. Due to this, the variable pulse width output is possible. This is called pulse width modulation, which is possible due to pin 5.

 

Q.9 List any four applications of 555 timer in monostable mode of operation.

Ans. :

1. Frequency divider 2. Pulse width modulation 3. Linear ramp generator

4. Pulse position modulation 5. Missing pulse detector  6. Timer for relays

 

Q.10 Draw the circuit of 555 timer connected as monostable multivibrator.

(Refer section 4.1.2)

 

Q.11 Draw the circuit of 555 timer connected as astable multivibrator.

(Refer section 4.1.3)

 

Q.12 Give the expression for the pulse width when 555 timer is used in monostable mode.

Ans. : The expression for the pulse width when 555 timer is used in monostable mode is, W = 1.1 RC

 

Q.13 Give the expression for the time period and duty cycle when 555 timer is used in astable mode.

Ans. : The expression for the time period and duty cycle when 555 timer is used in astable mode is,

T = 0.693 (R_A + 2 R_B) C          and %D = (R_A + R_B) / (R_A + R_B) × 100

 

Q.14 Compare the two modes of operation of 555 timer.

(Refer section 4.1.4)

 

Q.15 What is one quadrant, two quadrant and four quadrant multipliers ?

Dec.-03, 04, 11

Ans. : In one quadrant multiplier the polarities of both the inputs must always be positive. In two quadrant multiplier the one input must be held positive and other is allowed to swing in both positive and negative. While in four quadrant multiplier both the inputs are allowed to swing in both positive and negative directions.

 

Q.16 List the performance parameters of multiplier.

Ans. : 1. Accuracy 2. Linearity 3. Bandwidth 4. Feed through voltage

5. Zero trim 6. Scale factor 7. 1 % absolute error bandwidth  8. Quadrant 

 

Q.17 State the two multiplier ICs.

Ans. : 1. AD 533 and 2. AD 534.

 

Q.18 List the features of AD 533.

(Refer section 4.8.2.1)

 

Q.19 Mention the applications of AD 533.

Ans. : i) Function generator ii) Peak detection iii) RMS computation iv) Phase detection v) Automatic gain control vi) Square and square root extractor

 

Q.20 List the features of AD 534.

(Refer section 4.S.2.2)

 

Q.21 Mention the applications of AD 534.

Ans. : i) Multiplier ii) Divider iii) High quality analog signal processing  iv) Square and square root extractor v) Differential ratio and percentage computation vi) Algebraic and trigonometric function synthesis vii) Accurate voltage controlled oscillators and filters.

 

Q.22 Draw the circuit diagram of a squaring circuit using multiplier.

(Refer section 4.8.2.2)

 

Q.23 Explain how a frequency doubler can be realized using analog multiplier.

(Refer section 4.8.2.4)

 

Q.24 How phase angle detection is carried out by multiplier ?

(Refer section 4.S.2.5)

 

Q.25 Draw the pin diagram of 1C 555 timer.

(Refer section 4.1)

 

Q.26 What is an analog multiplier ? State its applications.

Ans. : An analog multipliter is a circuit which produces an output voltage or curent which is the scaled product of two voltages or currents. It is versatile functional device which can be used to perform various functions like product and division of two signals, squaring of a signal, frequency doubling and shifting, phase angle detection etc.

 

Q.27 Explain the function of trigger, pin 2 in 1C 555 timer.

Ans. : The pin 2 in IC 555 timer is trigger. The inverting input of comparator 2 is brought out as trigger. It is compared with [1/3 Vcc] and when it is below this level, the output of the comparator 2 goes high which is given to reset input of R-S flip-flop. Thus high ouput of comparator 2 resets the flip-flop.

 

Q.28 What are the applications of timer IC 555.

Ans. : The timer IC 555 is designed mainly to produce accurate and stable RC defined time periods. It is mainly used as monostable multivibrator, astable multivibrator or as a Schmitt trigger. The monostable multivibrator using 555 has many applications such as pulse width modulation, linear ramp generator, frequency divider, missing pulse detector etc. The astable multivibrator using 555 has many applications such as square wave generator, voltage controlled oscillator, FSK generator etc. 

 

Q.29 Define PLL.

Ans. : A phase locked loop is basically a closed loop system designed to lock the output frequency and phase to the frequency and phase of an input signal. It is commonly abbreviated as PLL.

 

Q.30 What is a voltage controlled oscillator ?

OR

Why VCO is called voltage to frequency converter ?

Ans. : A Voltage Controlled Oscillator (VCO) is an oscillator circuit in which the frequency of oscillations can be controlled by an externally applied voltage. The VCO provides the linear relationship between the applied voltage and the oscillation frequency. As voltage controls the frequency, it is called voltage controlled oscillator.

 

Q.31 How VCO different from oscillators ?

Ans. : An oscillator is circuit that generates the frequency output of fixed frequency. On the other hand, a Voltage Controlled Oscillator (VCO) is an oscillator circuit in which the frequency of oscillations can be controlled by an externally applied voltage.

 

Q.32 Why VCO is called voltage to frequency converter ?

Ans. : The VCO provides the linear relationship between the applied voltage and the output frequency, hence it is also called voltage to frequency converter.

 

Q.33 List the features of 1C 566 VCO.

(Refer section 4.2.3)

 

Q.34 Draw the block diagram of NE 566 voltage controlled oscillator.

(Refer section 4.2.1)

 

Q.35 With reference to a VCO, define voltage to frequency conversion factor K_v

Dec.-04,10

Ans. : The voltage to frequency conversion factor is denoted as K_v and defined as,

K_v = Δf_o / ΔV_C

Here ΔV_C is the change in control voltage producing corresponding change of Δf_o in the frequency.

 

Q.36 Give the applications of VCO.

(Refer section 4.2.5)

Q.37 Draw the block diagram of a PLL.

(Refer section 4.3)

 

Q.38 Define : Lock range.

Ans. : The range of frequencies over which the PLL can maintain lock with the incoming signal is called the lock range or tracking range of the PLL.

 

Q.39 Define capture range of a PLL.

Ans. : The range of frequencies over which the PLL can acquire lock with an input signal is called the capture range. 

 

Q.40 Draw the relation between the capture ranges and lock range in a PLL.

(Refer section 4.3)

 

Q.41 Give the relation between the capture ranges and lock range in a PLL.

Ans. : The relation between the capture ranges and lock range in a PLL is given by

where f_c : Capture range and f_L: Lock range

 

Q.42 What is pull-in time ?

Ans. : From the application of the input signal, the total time taken by the PLL to establish a lock is called pull-in time.

 

Q.43 Which parameter decides the pull-in time.

Ans. : 1. Initial phase and frequency difference between the two signals.

2. Overall loop gain.

3. Bandwidth of the low pass filter.

 

Q.44 State the problems associated with switch type phase detector.

Ans. : The problems associated with switch type phase detector are :

1. The error voltage V_e is proportional to the input signal amplitude V_s. This is undesirable since it makes phase detector gain and the loop gain dependent on the input signal amplitude.

2. The output is proportional to cos 0 instead of only 0. This makes it non-linear.

 

Q.45 State why the phase detector output in a PLL should be followed by a low pass filter.

Ans. : The output of phase detector is applied to low pass filter to remove high frequency noise from the dc voltage. The output of low pass filter without high frequency noise is often referred to as error voltage or control voltage for VCO.

 

Q.46 What is modulation ?

Ans. : The process of modifying the amplitude, frequency or phase of the original signal according to the amplitude of other signal is called modulation.

 

Q.47 Name two applications of PLL.

Ans. : PLL is used in

a. Frequency multiplier b. Frequency synthesizer          c. FM demodulator

d. FSK demodulator      e. AM detection    f. Frequency translation

 

Q.48 Draw the block diagrammatic representation of a frequeny multiplier using PLL ?

Ans. : Refer Fig. 4.5.1. 

 

Q.49 What is a frequency synthesizer ?

Ans. : The frequency synthesizer is a circuit that can produce a precise series of frequencies derived from a stable crystal controlled oscillator.

 

Q.50 Draw the circuit of AM detector using PLL.

(Refer section 4.5.5)

 

Q.51 A PLL frequency multiplier has an input frequency of f and a decade counter is included in the loop. What will be the frequency of the PLL ?

Ans. : The frequency of the PLL will be 10 f.

 

Q.52 What is companding ?

Ans. : The term companding is a combination of the words compressing and expanding. In a wireless system with companding, the audio signal is compressed in the transmitter and expanded in the receiver.

 

Q.53 Explain the necessity of companding ?

Ans. : The purpose of the companding process is to preserve the signal to noise ratio of the original signal and to avoid non-linear distortion of the signal when input amplitude is large. Companding is also effective in reducing buzz, hiss and low-level audio tones caused by mild interference. Companding improves the useful range of wireless systems.

 

Q.54 Determine the output pulse width of the monostable amplifier using 555 timer if R = 10 kΩ and C = 0.01 µF.

Ans.: Pulse width = 1.1 RC = 1.1 × 10 × 10³ × 0.01 × 10^-6 = 0.11 ms

 

Q.55 In an astable multivibrator using 555 timer R1 = 6.8 kΩ, R_B = 3.3 kΩ, C = 0.1 μF. Calculate the free running frequency.

Dec.-12

Ans. :

 

Q.56 List the applications of analog multipliers.

(Refer section 4.8.1)

 

Q.57 Why invariably a suitable value of capacitor is connected to the pin 5 of 555 Timer applications ?

May-14

Ans. : To bypass the noise and ripple from the supply, a capacitor is connected between pin 5 and ground.

 

Q.58 What are the advantages of variable transconductance technique ?

Ans. :

i) Simple to integrate into monolithic chip.

ii) Provides very good accuracy.

iii) Very cheap hence economical.

iv) Provides four quadrant operation. 

v) It provides high speed of operation which is 2 to 3 times more than the logarithmic method.

vi) Reduced error at least by 10 times.

vii) The bandwidth of 10 MHz and higher are available.

 

Q.59 In the monostable multivibrator of below figure circuit R₁ = 100 kΩ and the time delay T = 100 ms. Calculate the value C₁.

Dec.-15

Ans :

Q.60 What is analog multiplier IC ? Where it is used ?

Ans. : The analog multiplier IC is an integrated circuit whose output voltage at any instant is proportional to the product of the instantaneous values of two individual input voltages. Its important applications are multiplication, division, squaring, square rooting, modulation, peak detection etc.