M.
KUMARASAMY COLLEGE OF ENGINEERING
(Autonomous)
DEPARTMENT OF ECE
II YEAR / IV SEMESTER
ANALOG INTEGRATED CIRCUITS
UNIT III – OP-AMP ANDITS APPLICATIONS
POSSIBLE TWO MARKS:
1. Mention the advantages of integrated circuits.
i) Miniaturization and hence increased equipment density.
ii) Cost reduction due to batch processing.
iii) Increased system reliability due to the elimination of soldered joints
iv) Improved functional performance.
v) Matched devices.
vi) Increased operating speeds.
vii) Reduction in power consumption.
2. 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 can not be
rectified by normal rectifiers.
This rectifier doesn’t give any kind of drop in output since diodes are previously biased using op-
amp.
3. What is comparator? Give some applications of Comparator.
The comparator is a circuit which compares a signal voltage applied at one of the input terminals
of the op amp with a known reference voltage applied at the other terminal & produces the saturation
voltage either high or low, depending on which input is higher.
Applications of Comparator:
a.Zero crossing detector b. Window detector
c.Time marker generator d. Phase detector
4. 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)
5. Define an operational amplifier.
An operational amplifier is a direct-coupled, high gain amplifier consisting of one or more
differential amplifier. By properly selecting the external components, it can be used to perform a variety
of mathematical operation.
6. Mention the characteristics of an ideal op-amp.
o Open loop voltage gain is infinity.
o Input impedance is infinity.
o Output impedance is zero.
o Bandwidth is infinity.
o Zero offset.
7. Define 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.
8. 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
9. Define slew rate.
The slew rate is defined as the maximum rate of change of output voltage caused by a step input
voltage. An ideal slew rate is infinite which means that opamp’s output voltage should change
instantaneously in response to input step voltage.
10. Define P.S.R.R of an op-amp.
Power Supply Rejection Ratio (PSRR) is the ability of an amplifier to maintain its output voltage
as its DC power-supply voltage is varied.
PSRR = (change in Vcc)/(change in Vout)
11. Define Input bias current of an op-amp.
Input bias current IB is the average of the currents that flow into the inverting and non-inverting
input terminals of the op-amp.
i.e. IB = (IB1+IB2)/2
12. Define Input offset current of an op-amp.
The algebraic difference between the current into the inverting and non-inverting terminals is
referred to as input offset current Iio. Mathematically it is represented as
Iio = |IB - IB | Where I B+is the current into the non-inverting input terminals. IB- is the current
into the inverting input terminals.
13. 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
athigher frequencies. As frequency increases the output gets distorted due to limited slew rate.
14. Define 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.
15. What are the applications of current sources?
Transistor current sources are widely used in analog ICs both as biasing elements and as load
devices for amplifier stages.
16. Justify the reasons for using current sources in integrated circuits.
(i) Superior insensitivity of circuit performance to power supply variations and temperature.
(ii) More economical than resistors in terms of die area required providing bias currents of small
value.
(iii) When used as load element, the high incremental resistances of current source results in high
voltage gain at low supply voltages.
17. What is the advantage of widlar current source over constant current source?
Using constant current source output current of small magnitude(micro amp range) is not attain
able due to the limitations in chip area.Widlar current source is useful for obtaining small output currents.
Sensitivity of widlar current source is less compared to constant current source.
18. Mention the advantages of Wilson current source.
(i) Provides high output resistance.
(ii) Offers low sensitivity to transistor base currents.
19. Why open loop OP-AMP configurations are not used in linear applications?(may/june
2010)
The open loop gain of the op-amp is not a constant and it varies with changing the temperature
and variations in power supply. Also the bandwidth of the open loop op-amp is negligibly small. For thi
reasons open loop OP-AMP configurations are not used in linear applications.
20. What causes slew rate? (DEC 09)
There is a capacitor with-in or outside of an op-amp to prevent oscillation. The capacitor which
prevents the output voltage from responding immediately to a fast changing input.
21. Mention some of the linear applications of op – amps. (DEC 09)
Adder, subtractor,
Voltage –to current converter,
current –to- voltage converters,
Instrumentation amplifier
power amplifier
22. Mention some of the non – linear applications of op-amps.
Rectifier, peak detector,
clipper, clamper,
sample and hold circuit,
log amplifier, anti –log amplifier
23. 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 the help 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.
24. List the features of instrumentation amplifier:
1. High gain accuracy
2.High CMRR
3.High gain stability with low temperature co-efficient
4.Low dc offset
5.Low output impedance
25. Define Logarithmic and antilogarithmic amplifier. (MAY 2010)
When a logarithmic PN junction is used in the feedback network of op-amp, the circuit exhibits
log or antilog response. The logarithmic amplifier is a current to voltage converter with the transfer
characteristics v0=vi In(If/Ii) Antilog amplifier is a decoding circuit which converts the logarithmically
encoded signal back to the original signal levels as given by v1=vR10-kvi
26. Differentiate Schmitt trigger and comparator
1. It compares the input signal with references voltage then yields the output voltage
2. It need not consist of feedback
3. comparator output need not to be square wave
4. It operates between two reference points namely UTP<P.
5. It employs positive feedback 6. Its output is square wave.
27. List the applications of Log amplifiers
1. Analog computation may require functions such as lnx, log x, sin hx etc. These functions can
be performed by log amplifiers
2. Log amplifier can perform direct dB display on digital voltmeter and spectrum analyzer
3. Log amplifier can be used to compress the dynamic range of a signal
28. What are the limitations of the basic differentiator circuit?
1. At high frequency, a differentiator may become unstable and break into oscillations
2. The input impedance decreases with increase in frequency , thereby 0making the circuit
sensitive to high frequency noise.
29. Write down the condition for good differentiation.
1. For good differentiation, the time period of the input signal must be greater than or equal to Rf
C1
2.T > R f C1 Where, Rf is the feedback resistance
3. Cf is the input capacitance
30. What is a comparator? What are the applications of comparator? (MAY 2010)
A comparator is a circuit which compares a signal voltage applied at one input of an opamp with
a known reference voltage at the other input. It is an open loop op - amp with output + Vsat
Applications:
1. Zero crossing detectors
2. Window detector
3. Time marker generator
4. Phase detector
POSSIBLE 16 MARKS:
1. For a typical µA741 op-amp, the parameters are given as ICQ=15 µA and
Cc=35 pF. The peak value of the input voltage is 12 Determine the slew rate
and maximum possible frequency of the input voltage that can be applied to
get undistorted output.(8)
2. Design a practical integrator circuit with a dc gain of 10,to integrate a square
wave of 10 kHz. (8)
3. Design a practical differentiator circuit that will differentiate an input signal
with the fmax=150 Hz. (8)
4. Design a first order low pass filter at a cut off frequency of 15.9 kHz with a
pass band gain of 1.5. (8)
5. Sketch the Wilson current source and give detailed note about it.(8)
6. Using suitable diagram and necessary equations, explain the concept of
Widlar current source used in op‐amp circuit. (8)
7. Use appropriate block diagram, explain the general stages of an Op‐Amp
IC.(8)
8. Define and explain slew rate. Derive its equation. Also explain method
adapted to improving slew rate.(16)
9. Explain the operation of Instrumentation amplifier with suitable diagram. (16)
10.Sketch the Integrator circuit and explain the working principle in detail. (8)
11.Design an OP‐AMP based first order active low pass filter. (8) (apply)
12.Sketch the differentiator circuit and explain the working principle in detail. (8)
13.Derive the expression for log computation using opamp and explain necessary
circuit diagram. (8)
14.With neat diagram explain the operation of Schmitt trigger.(8)
15.Conclude that how antilog computations are performed using IC‐741 explain
using circuits and necessary equations. (8)
16.With neat sketch explain the working of Full wave Precision Rectifier in
detail.(8)
17.Using appropriate equations discuss about the working of Half wave Precision
Rectifier. (8
18.Explain how an op-amp can be used as comparator? (8)(apply)
19.Explain in briefly about open loop and closed loop configurations of an
opamp.(8)
20.Explain the DC and AC characteristics of an op-amp in detail.(16)
M.KUMARASAMY COLLEGE OF ENGINEERING
(Autonomous)
DEPARTMENT OF ECE
II YEAR / IV SEMESTER
ANALOG INTEGRATED CIRCUITS
UNIT IV – TIMER, PLL, ANALOG TO DIGITAL AND DIGITAL TO ANALOG
CONVERTERS
POSSIBLE TWO MARKS:
1. List out the blocks of PLL.
a. Phase detector/comparator
b. Low pass filter
c. Error amplifier
d. Voltage controlled oscillator
2. What are the three stages through which PLL operates?
1. Free running
2.Capture
3.Locked/ tracking
3. Define lock-in range of a PLL.
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.
4. Define capture range of PLL.
The range of frequencies over which the PLL can acquire lock with an input signal is called the
capture range. It is expressed as a percentage of the VCO free running frequency.
5. Define Pull-in time.
The total time taken by the PLL to establish lock is called pull-in time. It depends on the initial
phase and frequency difference between the two signals as well as on the overall loop gain and loop filter
characteristics.
6. Define voltage to frequency conversion factor of VCO.
Voltage to Frequency conversion factor is defined as,
Kv= Δfo / ΔVc = 8fo /Vcc
where, ΔVc is the modulation voltage required to produce the frequency shift Δfo
7. What is a voltage controlled oscillator?
Voltage controlled oscillator is a free running multivibrator operating at a set frequency called the
free running frequency. This frequency can be shifted to either side by applying a dc control voltage and
the frequency deviation is proportional to the dc control voltage.
8. List out the applications of PLL.
a. Frequency multiplication/division
b. Frequency translation c. AM detection
d. FM demodulation
e. FSK demodulation.
9. 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.
10. 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
4. What is 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).
11. 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
12. Find the resolution of a 12 bit DAC converter.
Resolution (volts) = VFS/(212-1) = I LSB increment
VFS – Full scale voltage
13. 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.
14. 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.
15. 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. Inverted R-2R Ladder
16. Define Resolution of D/A converters.
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.
17. b) Define Accuracy of D/A converters.
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.
18. Define monotonicity of D/A converters
A monotonic DAC is one whose analog output increases for an increase in digital input.
19. Define conversion time of D/A converters
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 period
Tc---conversion time n----no. of bits
20. Explain in brief the principle of operation of successive Approximation ADC.
The circuit of successive approximation ADC consists of a successive approximation register
(SAR), to find the required value of each bit by trial & error. With the arrival of START command, SAR
sets the MSB bit to 1. The O/P is converted into 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.
Multivibrators are a group of regenerative circuits that are used extensively in timing
applications. It is a wave shaping circuit which gives symmetric or asymmetric square output. It has two
states either stable or quasi- stable depending on the type of multivibrator.
21. What do you mean by monostable multivibrator & astable multivibrator?
Monostable multivibrator is one which generates a single pulse of specified duration in response
to each external trigger signal. It has only one stable state. Application of a trigger causes a change to the
quasi-stable state. An external trigger signal generated due to charging and discharging of the capacitor
produces the transition to the original stable state.
Astable multivibrator is a free running oscillator having two quasi-stable states. Thus, there is
oscillations between these two states and no external signal are required to produce the change in state
22. List the applications of 555 timer in monostable mode & Astable mode of operation:
Monostable:
Missing pulse detector Linear ramp generator Frequency divider
Pulse width modulation.
Astable:
FSK generator
Pulse Position Modular.
23. Which is the fastest ADC and why?
This type of ADC are fastest because it it is performed through a set of comparator.
24. What is 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).
25. Define 555 IC & its Pin diagram ?
The 555 timer is an integrated circuit specifically designed to perform signal generation and
timing functions.
POSSIBLE 16 MARKS:
1. How would you describe the block diagram of monolithic PLL IC565 and derive the
expression for Lock range and capture range. (16)
2. Illustrate the operation of VCO with neat block diagram. Also derive an expression for f0.
(16)
3. Design a monostable multivibrator for a pulse width of 10 ms by using IC555.(8)
4. A 555 timer is configured to run in astable mode with RA=4KΩ, RB=4KΩ and C=
0.01µF.Determine the frequency of output and duty cycle. (8)
5. Design a Astable multivibrator to generate the output signal with frequency of 1kHz and
the duty cycle of 75%.(8)
6. What is 555 timer? Explain the working of 555 timer as Monostable Multivibrator
Also derive an expression for the frequency of oscillation with relevant waveforms. (16)
7. Explain with neat sketch, the working of IC555 as an astable multivibrator. Also derive
the expression for frequency of oscillation and duty cycle. (16)
8. Explain the operation of a 4 bit R-2Rtype DAC and derive the expression for the output
voltage.(8)
9. Explain the working of binary weighted resistor type DAC with neat sketch.(8)
10. Draw and explain the functional diagram of the successive approximation type ADC. (8)
11. Explain the function of sample and hold circuit with neat sketch. (8)
12. Explain the performance parameters of DAC in detail.(8)
13. Categorize the different sources of error in DAC. (8)
