Digital Electronics-Interfacing to the Analog World

Digital Electronics-Interfacing to the Analog World
31. What is the major advantage of the R/2R ladder D/A converter as compared to a binary-weighted D/A converter?
  • It has fewer parts for the same number of inputs.
  • It is much easier to analyze its operation.
  • It uses only two different resistor values
  • The virtual ground is eliminated and the circuit is therefore easier to understand and troubleshoot.
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32. What is the main disadvantage of the stairstep-ramp A/D converter?
  • The counter must count up from zero at the beginning of each conversion sequence, and the conversion time will vary depending on the input voltage.
  • It requires a counter.
  • It requires a precision clock in order for the conversion to be reliable.
  • All of the above
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33. What is the purpose of a sample-and-hold circuit?
  • To keep temporary memory
  • To hold a voltage constant so an ADC has time to produce an output
  • To hold a voltage constant so a DAC has time to produce an output
  • To hold data after a multiplexer has selected an output
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34. What is the linearity of a D/A converter?
  • It is the reciprocal of the number of discrete steps in the D/A output.
  • It is the comparison between the actual output of the converter and its expected output.
  • It is the converter's ability to resolve between forward and reverse steps when sequenced over its entire range of inputs.
  • It is the deviation between the ideal straight-line output and the actual output of the converter.
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35. What is the disadvantage to using a counter-ramp type ADC?
  • complex circuit
  • high cost
  • very slow
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36. What is the maximum conversion time for a counter-ramp ADC with 8-bit resolution and a clock frequency of 20 kHz?
  • 12.8 ms
  • 6.4 ms
  • 0.05 ms
  • 0.4 ms
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37. A test system using the GPIB is being used to monitor a potentially dangerous crash test from a distance of 200 feet. The engineer decides to have you fabricate a special cable, rather than order one, since all the materials are on hand and the tests are already behind schedule. When the tests are run, the test system is erratic and the data is almost useless. What has gone wrong?
  • The engineer is probably not using the correct data format for the specific instruments being used to collect the data.
  • The GPIB cable is too long; a bus extender should be used.
  • The cable should be shielded and properly grounded.
  • The tests themselves probably produced extraneous signals that confused the instruments, resulting in unusable data.
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38. A certain digital-to-analog converter has a step size of 0.25 V and a full-scale output of 7.75 V. Determine the percent of resolution and the number of input binary bits.
  • 31%, 4 bits
  • 3.23%, 4 bits
  • 31%, 5 bits
  • 3.23%, 5 bits
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39. A simultaneous A/D converter is also known as a(n) ________ A/D converter.
  • flash
  • synchronous
  • comparator
  • asynchronous
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40. The primary disadvantage of the simultaneous A/D converter is:
  • that it requires the input voltage to be applied to the inputs simultaneously
  • the long conversion time required
  • the large number of output lines required to simultaneously decode the input voltage
  • the large number of comparators required to represent a reasonable sized binary number
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