# IOT Questions and Answers – Analog to Digital Converter

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This set of IOT Assessment Questions and Answers focuses on “Analog to Digital Converter”.

1. Quantization is the method used for conversion?
a) True
b) False

Explanation: The conversion involves quantization of the input, as it necessarily introduces a small amount of error. Furthermore, instead of continuously performing the conversion, an ADC does the conversion periodically, sampling the input.

2. ENOB stands for_________
a) Effective number of bits
b) Effective number of bytes
c) Efficient number of bits
d) Efficient number of bytes

Explanation: The dynamic range of an ADC is often summarized in terms of its effective number of bits(ENOB), the number of bits of each measure it returns that are on average not noise. An ideal ADC has an ENOB equal to its resolution.

3. Perfect resolution is possible when?
a) sampling rate greater than thrice the bandwidth of the signal
b) sampling rate greater than twice the bandwidth of the signal
c) sampling rate less than twice the bandwidth of the signal
d) sampling rate less than thrice the bandwidth of the signal

Explanation: If an ADC operates at the sampling rate greater than twice the bandwidth of the signal, then perfect resolution is possible given an ideal ADC and neglecting quantization error.

4. Resolution is expressed in __________
a) Bytes
b) Bits
c) Word
d) Nibble

Explanation: The values are usually stored electronically in binary form, so the resolution is usually expressed in bits.

5. The discrete levels available are_________
a) Sides
b) Edges
c) Levels
d) Bytes

Explanation: The number of discrete values available, or levels, is assumed to be power of two.
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6. Resolution is expressed in terms of_________
a) Milli volts
b) Ampere
c) Milli ampere
d) Volts

Explanation: Resolution can also be defined electrically, and expressed in volts. The minimum change in voltage required to guarantee a change in the output code level is called least significant bit.

7. The rate of new values is called the sampling rate or sampling frequency.
a) True
b) False

Explanation: The analog signal is continuous in time and it is necessary to convert this to a flow of digital values. It is therefore required to define the rate at which new digital values are sampled from the analog signal. The rate of new values is called the sampling rate or sampling frequency of the converter.

8. How many common ways are there for implementing an ADC?
a) 2 ways
b) 5 ways
c) 8 ways
d) 10 ways

Explanation: The most common ways for implementing ADC are direct conversion, successive approximation, ramp compare, Wilkinson, integrating, delta encoded, pipelined, sigma delta, time interleaved, intermediate FM stage, other types.

9. Other name for data conversion is ________
b) Wilkinson
c) Sigma delta
d) Ramp compare

Explanation: A direct conversion ADC or flash ADC has a bank of comparators sampling the input signal in parallel, each firing for their decoded voltage range.

10. Which ADC narrows the range?
b) Wilkinson
c) Sigma delta
d) Successive approximation

Explanation: A successive approximation ADC uses a comparator to successively narrow a range that contains the input voltage.

11. Clock jitters is caused by __________
a) Sampling rate
b) Spectrum
c) Phase noise
d) Sampling frequency

Explanation: Clock jitter is caused by phase noise. Phase noise is the frequency domain representation of rapid, short term, random fluctuations in the phase of a waveform, caused by time domain instabilities.

12. The analog signal is __________ in __________
a) Continuous, frequency
b) Continuous, time
c) Discrete, frequency
d) Discrete, time

Explanation: The analog signal is continuous in time and it is necessary to convert this to a flow of digital values.

13. Sample and hold circuit is a _______ circuit.
a) Analog device
b) Digital device
c) Both analog and digital
d) Neither analog nor digital

Explanation: In electronics, a sample and hold (also known as sample and follow) circuit is an analog device that samples (captures, takes) the voltage of a continuously varying analog signal and holds (locks, freezes) its value at a constant level for a specified minimum period of time.

14. Nyquist rate is defined as ___________
a) twice the lowest frequency
b) thrice the highest frequency
c) twice the highest frequency
d) thrice the lowest frequency

Explanation: Nyqist rate, defined as twice the highest frequency of interest, then all frequencies in the signal can be reconstructed.

15. To avoid aliasing we use a __________ filter.
a) Digital filter
b) Aliasing filter
c) Analog filter
d) Anti-aliasing filter

Explanation: To avoid aliasing, the input to an ADC must be low pass filtered to remove frequencies above half the sampling rate. This filter is called an anti-aliasing filter.

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