Digital to Analog Converters Questions and Answers

Q: An 8-bit DAC is used to control a linear valve with a 0 to 5 volt signal. The valve is fully open if the signal is 5 volts and closed if signal is 0 volt. An approximate resolution of the DAC in terms of volts and percentage of valve opening will be :

The resolution is about 0.02 V and 0.4%.An 8-bit DAC has \(2^{8} = 256\) levels, so its 0-5 V range is divided into 255 steps:\[ \begin{aligned} \Delta V &= \frac{5}{255} \approx 0.0196\ \text{V} \approx 0.02\ \text{V} \\ \% &= \frac{1}{255} \times 100 \approx 0.39\% \end{aligned} \]Since the valve opening is linear in the voltage, one step moves it about 0.4% of its full travel. 4% and 10% are ten or more times too coarse for 8 bits, and 0.01 V would need about 9 bits.

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Directions : Q. Nos. 21 to 30 : The following items consist of two statements, one labelled the “Assertion (A)” and the other labelled the “Reason (R)”. You are to examine these two statements carefully and decide if the Assertion (A) and the Reason (R) are individually true and if so, whether the Reason is a correct explanation of the Assertion. Select your answers to these items using the codes given below and mark your answer accordingly.

Assertion (A) : R-2R ladder type D/A converter has a higher speed of conversion than a weighted resistance D/A converter.

Reason (R) : R-2R ladder type D/A converter uses a smaller number of components than the weighted resistance D/A converter.

A.Both (A) and (R) are true and (R) is the correct explanation of (A).
B.Both (A) and (R) are true, but (R) is not correct explanation of (A).
C.(A) is true, but (R) is false.
D.(A) is false, but (R) is true.

Exam Year(s)

UGC NET - 2012,

Answer: C

The keyed answer is (A) true and (R) false. An R-2R ladder D/A converter is faster than a weighted-resistor converter, because it needs only two resistor values and so avoids the very large resistance ratios that slow the weighted network, which makes (A) true. But for n bits the ladder needs 2n resistors against n for the weighted-resistor network, so it does not use a smaller number of components, and (R) is false. Options that call (R) true, or (A) false, are therefore wrong, and option C is the keyed one.

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An 8-bit DAC is used to control a linear valve with a 0 to 5 volt signal. The valve is fully open if the signal is 5 volts and closed if signal is 0 volt. An approximate resolution of the DAC in terms of volts and percentage of valve opening will be :

A.0.02 V and 0.4%
B.0.01 V and 10%
C.0.1 V and 10%
D.0.02 V and 4%

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: A

The resolution is about 0.02 V and 0.4%.

An 8-bit DAC has \(2^{8} = 256\) levels, so its 0-5 V range is divided into 255 steps:

\[ \begin{aligned} \Delta V &= \frac{5}{255} \approx 0.0196\ \text{V} \approx 0.02\ \text{V} \\ \% &= \frac{1}{255} \times 100 \approx 0.39\% \end{aligned} \]

Since the valve opening is linear in the voltage, one step moves it about 0.4% of its full travel. 4% and 10% are ten or more times too coarse for 8 bits, and 0.01 V would need about 9 bits.

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Digital to Analog Converters Questions and Answers

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