Digital to Analog (DAC) Techniques MCQ [Free PDF] - Objective Question Answer for Digital to Analog (DAC) Techniques Quiz

1. Express the output voltage of digital to analog converter?

A. V_o =KV_FS(d₁2^-1+d₂2^-2+….d_n2^-n)
B. V_o =V_FS/k(d₁2^-1+d₂2^-2+….d_n2^-n)
C. V_o =V_FS(d₁2^-1+d₂2^-2+….d_n2^-n)
D. V_o =K(d₁2^-1+d₂2^-2+….d_n2^-n)

Answer: A

The input is an n-bit binary word D and is combined with the reference voltage V_R to give an analog output signal. Mathematically it is described as

V_o =KV_FS(d₁2^-1+d₂2^-2+….d_n2^-n) where, K -scaling factor, V_FS-full scale output voltage.

2. Why the switches used in weighted resistor DAC are of single pole double throw (SPDT) type?

A. To connect the resistance to reference voltage
B. To connect the resistance to ground
C. To connect the resistance to either reference voltage or ground
D. To connect the resistance to the output

Answer: C

SPDT is electronic switches controlled by a binary word. If the binary input to a switch is 1, it connects the resistance to the reference voltage and if the input is 0, the switch connects the resistor to the ground.

3. Determine the output current for an n-bit weighted resistor DAC?

A. (V_R/R )× (d_o/2 +d₁/2² + ……d_n/2ⁿ)
B. (V_R/R )× (d₁/2¹ +d₂/2² + ……d_n/2ⁿ)
C. (V_R/R )× (d₀²/2 +d₁²/2² + ……d_n²/2ⁿ)
D. None of the mentioned

Answer: B

The output current

I_o= I₁+I₂+….I_n

I_o= (V_R/2R )×(d₁) +(V_R/2²R)× (d₂) ….+(V_R/2ⁿR )×(d_n)

I_o =(V_R/R)× (d₁/2¹ +d₂/2² + ……d_n/2ⁿ).

4. In a D-A converter with a binary-weighted resistor, the desired step size can be obtained by

A. Selecting proper value of V_FS
B. Selecting proper value of R
C. Selecting proper value of R_F
D. All of the mentioned

Answer: C

The size of the steps depends on the value of R_F, provided that the maximum output voltage does not exceed the saturation level of an op-amp.

5. Determine the Full-scale output in an 8-bit DAC for the 0-15v range?

A. Full-scale output=15.1v
B. Full scale output=15.2v
C. Full scale output=14.5v
D. Full scale output=14.94v

Answer: D

Full scale output = (Full scale voltage -LSB.

= [15v-(15v/2⁸)]

= (15v-0.0586) = 14.94v.

6. Pick out the incorrect statement “In a 3-bit weighted resistor DAC”

A. Although the op-amp is connected in inverting mode, it can also be connected in non-inverting mode
B. The op-amp simply works as a current to voltage converter
C. The polarity of the reference voltage is chosen in accordance with the input voltage
D. None of the mentioned

Answer: C

The polarity of the reference voltage is in accordance with the type of switch used. For example, in TTL switches, the reference voltage should be +5v and the output will be negative.

7. What is the disadvantage of binary-weighted type DAC?

A. Require a wide range of resistors
B. High operating frequency
C. High power consumption
D. Slow switching

Answer: A

For a better resolution of output, the input binary word length has to be increased. As the number of bits increases, the range of resistance values increases.

8. The smallest resistor in a 12-bit weighted resistor DAC is 2.5kΩ, what will be the largest resistor value?

A. 40.96MΩ
B. 10.24MΩ
C. 61.44 MΩ
D. 18.43MΩ

Answer: B

The largest resistor value for 12-bit DAC= 2ⁿ×R = 2¹²×2.5kΩ = 4096×2.5kΩ =10.24MΩ.

9. CMOS inverter is used as SPDT switch in resistor DAC and is connected to the op-amp line. Find the output of CMOS, if the input applied is 1

A. Resistance is connected to ground
B. Resistance is connected to the input line
C. Resistance is connected to the bit line
D. None of the mentioned

Answer: B

When Qbar =1, it makes transistor Q₁-ON and Q₂-OFF. The output of the CMOS inverter is 0v, connecting the resistance R₁ to the ground.

10. How to overcome the limitation of binary-weighted resistor type DAC?

A. Using R-2R ladder type DAC
B. Multiplying DACs
C. Using monolithic DAC
D. Using hybrid DAC

Answer: A

Usage wide range of resistors is the limitation of binary-weighted resistor type DAC, this can be avoided by using R-2R ladder type DAC Where only two values of the resistor are required.

11. Find output voltage equation for 3 bit DAC converter with R and 2R resistor?

A. V_o= -R_F [(b₂/8R) +(b₁/4R) +(b₀/2R)].
B. V_o= -R_F [(b₂/R) +(b₁/2R) +(b₀/4R)].
C. V_o= -R_F [(b₂/2R)+(b₁/4R) +(b₀/8R)].
D. V_o= -R_F [(b₀/4R)+(b₁/2R) +(b₂/R)].

Answer: C

The output voltage corresponding to all possible combinations of binary input in a 3-bit R-2R DAC is given as

V_o=-R_F [(b₂/2R) +(b₁/4R) +(b₀/8R)].

12. For the given circuit find the output voltage?

A. -5.625v
B. -3.50v
C. -4.375v
D. -3.125v

Answer: D

The given circuit is a 4-bit R-2R DAC.

So, the output voltage

V_o=-R_F [(b₃/2R) +(b₂/4R) +(b₁/8R)+(b₀/16R)]

From the circuit

b₃=5v,

b₂=0v

b₁=5v, b_o=0v.

V_o= -20kΩ[(5/2×20kΩ)+0+(5/8×20kΩ)+0]= -3.125v.

13. Which type of switches are not preferable for a simple weighted resistor DAC?

A. Bipolar Transistor
B. Voltage switches
C. MOSFET
D. All of the mentioned

Answer: A

Bipolar transistor does not perform well as voltage switches and MOSFET, due to the inherent offset voltage when in saturation.

14. The inverted R-2R ladder can also be operated in

A. Inverted mode
B. Current Mode
C. Voltage mode
D. Non-inverted mode

Answer: B

The inverted mode R-2R ladder circuit works on the principle of summing current. Therefore, it is said to operate in the current mode.

15. Which of the following circuit is considered to be linear?

A. Weighted Resistor type DAC
B. R-2R ladder type DAC
C. Inverter R-2R ladder DAC
D. All of the mentioned

Answer: C

Current remains constant in each branch of the ladder in inverted R-2R ladder DAC. So, the constant current implies constant voltage. The ladder mode voltage remains constant even when the input data changes. So, inverter R-2R ladder DAC is considered to be linear.

16. Multiplying DAC uses

A. Varying reference voltage
B. Varying input voltage
C. Constant reference voltage
D. Constant input voltage

Answer: A

A digital to analog converter which uses a varying reference voltage is called a multiplying D-A converter.

17. Calculate the value of LSB and MSB of a 12-bit DAC for 10v?

A. LSB =7.8mv, MSB =5v
B. LSB =9.3mv, MSB =5v
C. LSB =14.3mv, MSB =5v
D. LSB =2.4mv, MSB =5v

Answer: D

LSB=1/2ⁿ=1/2¹²=1/4096.

For 10v range, LSB =10v/4096=2.4mv

MSB = (1/2)×full scale =(1/2)×10v =5v.

18. A multiplying DAC is given a reference voltage V_R = V_om cos2πft. Determine the output voltage?

A. V_o(t) = V_om sin(2πft+180^o)
B. V_o(t) = V_om cos(2πft+180^o)
C. V_o(t) = V_om tan(2πft+180^o)
D. V_o(t) = V_om sec(2πft+180^o)

Answer: B

V_o(t) = V_om cos2πft+180^o. The 180^ophase shift is added since the V_R is connected to inverting input terminal and

V_om = 0v to (1-2^-n)×V_im depends on the input code.

19. Multiplying digital to analog converters are used in

A. All of the mentioned
B. Digitally programmable filter
C. Digitally programmable oscillator
D. Digitally controlled audio attenuator

Answer: D

In multiplying DAC, the output voltage is a fraction of the voltage representing the input digital code and the attenuator setting can be controlled by digital logic.

20. A 10-bit D/A converter has an output range from 0-9v. Calculate the output voltage produced when the input binary number is 1110001010.

A. ±7.96v
B. -7.96v
C. 7.96v
D. None of the mentioned

Answer: C

V_o=9v[(1×1/2)+ (1×1/2²) +(1×1/2³)+(0×1/2⁴)+(0×1/2⁵)+ (0×1/2⁶)+(1×1/2⁷)+(0×1/2⁸)+(1×1/2⁹)+( 0×1/2¹⁰)].

=9v×(0.5+0.25+0+0.125+7.8125×10^-3+1.95 ×10^-3) =9v×0.8547 =7.96v.

21. The basic step of an 8-bit DAC is 12.4mv.If the binary input 00000000 represents 0v. Determine the output, if the input is 101101111?

A. 1.36v
B. 2.27v
C. 5.45v
D. None of the mentioned

Answer: B

The output voltage for input 10110111 = 12.4mv ×[(1×2⁷)+(0×2⁶) + (1×2⁵) + (1×2⁴) + (0×2³)+ (1×2²) +(1×2¹)+ (1×2⁰)] = 12.4 × (128 + 32 + 16 + 4 + 2 + 1)

=12.4mv × 183 = 2.27v.

22. How many control lines are present in analog to digital converter in addition to reference voltage?

A. Three
B. Two
C. One
D. None of the mentioned

Answer: B

ADC usually has two additional control lines
1. Start input-tell ADC when to start conversion.
2. EOC- end of conversion.

23. Find out the integrating type of analog to the digital converter?

A. Flash-type converter
B. Tracking converter
C. Counter type converter
D. Dual slope ADC

Answer: D

Other than dual-slope ADC the rest belongs to direct type ADCs.

24. Which type of ADC follows the conversion technique of changing the analog input signal to a linear function of frequency?

A. Direct type ADC
B. Integrating type ADC
C. Both integrating and direct type ADC
D. None of the mentioned

Answer: B

Integrating type ADC performs conversion in an indirect manner by first changing the analog input signal to a linear function of time or frequency and then to a digital code.

Related Posts