Digital Electronics and Computer Organisation MCQs [set-2]

   
    26. Which type of gate can be used to add two bits?

            A. ex-or
            B. ex-nor
            C. ex-nand
            D. nor
    Answer: A
            

    27. Show from the truth table how an exclusive-OR gate can             be used to                   invert the data on one input if the other input is a          spe cial control function. 

A. using a as the control, when a = 0, x is the same as b. when a = 1, x is the same as b. 

B. using a as the control, when a = 0, x is the same as b. when a = 1, x is the inverse of b. 

C. using a as the control, when a = 0, x is the inverse of b. when a = 1, x is the same as b. 

D. using a as the control, when a = 0, x is the inverse of b. when a = 1, x is the inverse of b. Answer: B 

28. In a flash analog-to-digital converter, the output of each comparator is connected to an input of a ________. 

A. decoder 

B. priority encoder 

C. multiplexer 

D. demultiplexer 

Answer: B 

29. Which term applies to the maintaining of a given signal level until the next sampling? 

A. holding 

B. aliasing 

C. shannon frequency sampling 

D. "stair-stepping" 

Answer: A 

30. An op-amp has very ________. 

A. high voltage gain 

B. high input impedance

C. low output impedance 

D. all of the above 

Answer: D 

31. The dual-slope analog-to-digital converter finds extensive use in ________. 

A. digital voltmeters 

B. function generators 

C. frequency counters 

D. all of the above 

Answer: D 

32. The ADC0804 is an example of a ________. 

A. single-slope analog-to-digital converter 

B. dual-slope analog-to-digital converter 

C. digital-ramp analog-to-digital converter 

D. successive-approximation analog-to-digital converter 

Answer: D 

33. In a digital representation of voltages using an 8-bit binary code, how many values can be defined? 

A. 16 

B. 64 

C. 128 

D. 256 

Answer: D 

34. A 4-bit R/2R ladder digital-to-analog converter uses ________. A. one resistor value 

B. two resistor values 

C. three resistor values 

D. four resistor values 

Answer: B 

35. A binary-weighted-input digital-to-analog converter has a feedback resistor, Rf, of 12 k. If 50 A of current is through the resistor, voltage out of the circuit is ________. 

A. 0.6 v 

B. –0.6 v 

C. 0.1 v 

D. –0.1 v 

Answer: B 

 36. The resolution of a 6-bit DAC is ________. 

A. 63% 

B. 64% 

C. 15.9% 

D. 1.59% 

Answer: D 

37. How are unwanted frequencies removed prior to digital conversion? 

A. pre-filters 

B. digital signal processing 

C. sample-and-hold circuits 

D. all of the above 

Answer: A 

38. Which type of programming is typically used for digital signal processors? 

A. assembly language 

B. machine language 

C. c 

D. none of the above 

Answer: A 

 39. Which of the following best defines Nyquist frequency? 

A. the frequency of resonance for the filtering circuit 

B. the second harmonic 

C. the lower frequency limit of sampling 

D. the highest frequency component of a given analog signal Answer: D 

40. Which is not an A/D conversion error? 

A. differential nonlinearity

B. missing code 

C. incorrect code 

D. offset 

Answer: A 

41. Settling time is normally defined as the time it takes a DAC to settle within ________. 

A. 1/8 lsb of its final value when a change occurs in the input code 

B. 1/4 lsb of its final value when a change occurs in the input code 

C. 1/2 lsb of its final value when a change occurs in the input code 

D. 1 lsb of its final value when a change occurs in the input code

Answer: C 

42. Determine the output frequency for a frequency division circuit that contains 12 flip-flops with an input clock frequency of 20.48 MHz. 

A. 10.24 khz 

B. 5 khz 

C. 30.24 khz 

D. 15 khz 

Answer: B 

43. Which statement BEST describes the operation of a negative-edge-triggered D flip-flop? 

A. the logic level at the d input is transferred to q on ngt of clk. 

B. the q output is always identical to the clk input if the d input is high. 

C. the q output is always identical to the d input when clk = pgt. 

D. the q output is always identical to the d input. 

Answer: A

44. Propagation delay time, tPLH, is measured from the ________. 

A. triggering edge of the clock pulse to the low-to-high transition of the output 

B. triggering edge of the clock pulse to the high-to-low transition of the output 

C. preset input to the low-to-high transition of the output 

D. clear input to the high-to-low transition of the output 

Answer: A 

45. How is a J-K flip-flop made to toggle? 

A. j = 0, k = 0 

B. j = 1, k = 0 

C. j = 0, k = 1 

D. j = 1, k = 1 

Answer: D 

 46. How many flip-flops are in the 7475 IC? 

A. 1 

B. 2 

C. 4 

D. 8 

Answer: C 

47. How many flip-flops are required to produce a divide-by-128 device? 

A. 1 

B. 4 

C. 6 

D. 7 

Answer: D

 

48. The ________ circuit overcomes the problem of switching caused by jitter on the inputs. 

A. astable multivibrator

 B. monostable multivibrator 

C. bistable multivibrator 

D. schmitt trigger 

Answer: D 

49. Why would a delay gate be needed for a digital circuit? 

A. a delay gate is never needed. 

B. to provide for setup times 

C. to provide for hold times 

D. to provide for setup times and hold times 

Answer: D 

50. A Schmitt trigger has VT+ = 2.0 V and VT– = 1.2 V. What is the hysteresis voltage of the Schmitt trigger? A. 0.4 volt

B. 0.6 volt 

C. 0.8 volt 

D. 1.2 volts 

Answer: C