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)].
Answer: C
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)].
11. 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
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.
12. 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.
13. 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.
14. 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.
15. 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.
16. 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.
17. 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)
Answer: B
The output voltage is
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.
18. 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.
19. 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
The output voltage produced when the input binary number is 1110001010 is
