# 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. Vo =KVFS(d12-1+d22-2+….dn2-n)
B. Vo =VFS/k(d12-1+d22-2+….dn2-n)
C. Vo =VFS(d12-1+d22-2+….dn2-n)
D. Vo =K(d12-1+d22-2+….dn2-n)

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

Vo =KVFS(d12-1+d22-2+….dn2-n) where, K -scaling factor, VFS-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

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. (VR/R )× (do/2 +d1/22 + ……dn/2n)
B. (VR/R )× (d1/21 +d2/22 + ……dn/2n)
C. (VR/R )× (d02/2 +d12/22 + ……dn2/2n)
D. None of the mentioned

The output current

Io= I1+I2+….In

Io= (VR/2R )×(d1) +(VR/22R)× (d2) ….+(VR/2nR )×(dn)

Io =(VR/R)× (d1/21 +d2/22 + ……dn/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 VFS
B. Selecting proper value of R
C. Selecting proper value of RF
D. All of the mentioned

The size of the steps depends on the value of RF, 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

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

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

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

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

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

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. Vo= -RF [(b2/8R) +(b1/4R) +(b0/2R)].
B. Vo= -RF [(b2/R) +(b1/2R) +(b0/4R)].
C. Vo= -RF [(b2/2R)+(b1/4R) +(b0/8R)].
D. Vo= -RF [(b0/4R)+(b1/2R) +(b2/R)].

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

Vo=-RF [(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

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

So, the output voltage

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

From the circuit

b3=5v,

b2=0v

b1=5v, bo=0v.

Vo= -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

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

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
D. All of the mentioned

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

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

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 VR = Vom cos2πft. Determine the output voltage?

A. Vo(t) = Vom sin(2πft+180o)
B. Vo(t) = Vom cos(2πft+180o)
C. Vo(t) = Vom tan(2πft+180o)
D. Vo(t) = Vom sec(2πft+180o)

Vo(t) = Vom cos2πft+180o. The 180ophase shift is added since the VR is connected to inverting input terminal and

Vom = 0v to (1-2-n)×Vim 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

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

Vo=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

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

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

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