Question Bank For UNIT 4&5 with answers
Sub Name: ANALOG DEVICES AND CIRCUITS Department: MCT
Sub Code: MT17303 Year &Sec: II
PART – A
1. Explain the operation of basic sample and hold circuit.
A typical sample and hold circuit stores electric charge in a capacitor and contains at least one fast FET switch
and at least one operational amplifier. To sample the input signal the switch connects the capacitor to the
output of a buffer amplifier. The buffer amplifier charges or discharges the capacitor so that the voltage across
the capacitor is practically equal, or proportional to, input voltage. In hold mode the switch disconnects the
capacitor from the buffer. The capacitor is invariably discharged by its own leakage currents and useful load
currents, which makes the circuit inherently volatile, but the loss of voltage (voltage droop) within a specified
hold time remains within an acceptable error margin.
2. Give applications of a sample and hold circuit.
• Digital interfacing
• Analog to Digital converters
• Pulse Code Modulation systems
3. 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).
5. 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
[1]
, V0 = 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
6. List out the advantages of sample and hold circuits.
The advantages of sample and hold circuits are
• It reduces the cross talk in the multiplexer.
• In the case of multi channel ADCs, synchronization can be achieved by sampling signals from all
channels at the same time.
7. What are the sources of errors in DAC?
The sources of errors in DAC are
• Linearity error.
• Offset error.
• Gain error.
8. 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.
9. 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.
10. What are the types of ADC and DAC.
Types of ADC:
[2]
,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
11. Give the 2 advantages of SA type ADC.
i) The conversion time is equal to the n clock cycle period for n bit ADC. Thus the conversion time is less as
compared to dual slope and counter type ADC.
ii) Conversion time is constant & independent of the amplitude of i/p signal.
iii) Compact design compared to flash type ADC.
iv) Cheaper as compared to flash type ADC.
12. Define Monotonicity
A monotonic DAC is one whose analog output increases for an increase in digital input. If a DAC has to be
1
LSB
monotonic, the error should be less than 2 at each output level.
13. Give the applications Dual slope ADC.
➢ Dual slope ADC’s are particularly suitable for accurate measurement of slowly varying signals, such
as thermocouples and weighing scales.
➢ They are also used in the digital panel meters and Multimeters.
14. What is Voltage to Time converters?
The linear ramp technique is essentially a voltage to time converter. As the name of this technique implies, a
linear ramp is used to convert an analog d.c signal in to a front panel digital representation.
15. Give the advantages of integrating type ADC.
▪ This type of convertors do not need a sample and hold circuit at the input.
▪ It is highly accurate.
▪ Low cost.
[3]
, • It provides excellent noise rejection of ac signals whose periods are integral multiples of the
integration time T.
• It is immune to temperature caused variations in R1 & C1.
15. What is an isolation amplifier?
An isolation amplifier is an amplifier that offers an ohmic or electrical isolation between its input and
output terminals. Isolation amplifiers are often used when there is a very large common mode voltage
difference between the input and output sides of the device.
16. What is an optocoupler?
It is an electronic device it consists of one diode and transistor. Combined package of a LED and a photodiode.
It isolates the op-amp circuit from any high voltage load.
17. What is power amplifier?
The last stage or any output stage of any electronics system however has to supply current and sufficient power
to the load which may be a loudspeaker or servomotor. Such amplifiers are called power amplifier.
18. What are the limitations of IC-723 general purpose regulator?
The limitations of 723 regulators are,
a) No built in thermal protection.
b) It has no short circuit current limits.
19. What is a switched capacitor filter?
The switched capacitor filter requires no external reactive components, capacitors or inductors. The operation
of the filter is based on the ability of on – chip capacitors and metal oxide semiconductor (MOS) switches to
stimulate resistors. These on chip stimulating capacitor values can be closely matched to other capacitors on
IC. It yields an integrated filter.
20. What are the limitations of three terminal regulators?
a. Output voltage cannot be precisely adjusted.
b. Available only in certain output voltages and currents.
c. Obtaining greater current capability is more difficult than with other regulators.
21. Define the duty cycle in astable multivibrator using IC 555.
The duty cycle, the ratio of the time tc during which the output is high to the total time period T is given as
% duty cycle, D = tc / T * 100 = (RA + RB) / (RA + 2RB) * 100
From the above equation it is obvious that square wave (50 % duty cycle) output cannot be obtained unless
RA is made zero. However, there is a danger in shorting resistance RA to zero. With RA = 0 ohm,
[4]
Sub Name: ANALOG DEVICES AND CIRCUITS Department: MCT
Sub Code: MT17303 Year &Sec: II
PART – A
1. Explain the operation of basic sample and hold circuit.
A typical sample and hold circuit stores electric charge in a capacitor and contains at least one fast FET switch
and at least one operational amplifier. To sample the input signal the switch connects the capacitor to the
output of a buffer amplifier. The buffer amplifier charges or discharges the capacitor so that the voltage across
the capacitor is practically equal, or proportional to, input voltage. In hold mode the switch disconnects the
capacitor from the buffer. The capacitor is invariably discharged by its own leakage currents and useful load
currents, which makes the circuit inherently volatile, but the loss of voltage (voltage droop) within a specified
hold time remains within an acceptable error margin.
2. Give applications of a sample and hold circuit.
• Digital interfacing
• Analog to Digital converters
• Pulse Code Modulation systems
3. 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).
5. 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
[1]
, V0 = 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
6. List out the advantages of sample and hold circuits.
The advantages of sample and hold circuits are
• It reduces the cross talk in the multiplexer.
• In the case of multi channel ADCs, synchronization can be achieved by sampling signals from all
channels at the same time.
7. What are the sources of errors in DAC?
The sources of errors in DAC are
• Linearity error.
• Offset error.
• Gain error.
8. 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.
9. 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.
10. What are the types of ADC and DAC.
Types of ADC:
[2]
,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
11. Give the 2 advantages of SA type ADC.
i) The conversion time is equal to the n clock cycle period for n bit ADC. Thus the conversion time is less as
compared to dual slope and counter type ADC.
ii) Conversion time is constant & independent of the amplitude of i/p signal.
iii) Compact design compared to flash type ADC.
iv) Cheaper as compared to flash type ADC.
12. Define Monotonicity
A monotonic DAC is one whose analog output increases for an increase in digital input. If a DAC has to be
1
LSB
monotonic, the error should be less than 2 at each output level.
13. Give the applications Dual slope ADC.
➢ Dual slope ADC’s are particularly suitable for accurate measurement of slowly varying signals, such
as thermocouples and weighing scales.
➢ They are also used in the digital panel meters and Multimeters.
14. What is Voltage to Time converters?
The linear ramp technique is essentially a voltage to time converter. As the name of this technique implies, a
linear ramp is used to convert an analog d.c signal in to a front panel digital representation.
15. Give the advantages of integrating type ADC.
▪ This type of convertors do not need a sample and hold circuit at the input.
▪ It is highly accurate.
▪ Low cost.
[3]
, • It provides excellent noise rejection of ac signals whose periods are integral multiples of the
integration time T.
• It is immune to temperature caused variations in R1 & C1.
15. What is an isolation amplifier?
An isolation amplifier is an amplifier that offers an ohmic or electrical isolation between its input and
output terminals. Isolation amplifiers are often used when there is a very large common mode voltage
difference between the input and output sides of the device.
16. What is an optocoupler?
It is an electronic device it consists of one diode and transistor. Combined package of a LED and a photodiode.
It isolates the op-amp circuit from any high voltage load.
17. What is power amplifier?
The last stage or any output stage of any electronics system however has to supply current and sufficient power
to the load which may be a loudspeaker or servomotor. Such amplifiers are called power amplifier.
18. What are the limitations of IC-723 general purpose regulator?
The limitations of 723 regulators are,
a) No built in thermal protection.
b) It has no short circuit current limits.
19. What is a switched capacitor filter?
The switched capacitor filter requires no external reactive components, capacitors or inductors. The operation
of the filter is based on the ability of on – chip capacitors and metal oxide semiconductor (MOS) switches to
stimulate resistors. These on chip stimulating capacitor values can be closely matched to other capacitors on
IC. It yields an integrated filter.
20. What are the limitations of three terminal regulators?
a. Output voltage cannot be precisely adjusted.
b. Available only in certain output voltages and currents.
c. Obtaining greater current capability is more difficult than with other regulators.
21. Define the duty cycle in astable multivibrator using IC 555.
The duty cycle, the ratio of the time tc during which the output is high to the total time period T is given as
% duty cycle, D = tc / T * 100 = (RA + RB) / (RA + 2RB) * 100
From the above equation it is obvious that square wave (50 % duty cycle) output cannot be obtained unless
RA is made zero. However, there is a danger in shorting resistance RA to zero. With RA = 0 ohm,
[4]
