This set of Avionics Interview Questions and Answers for Experienced people focuses on “Data Conversion – 3”.
1. Which of the following is not an advantage of undersampling?
a) Slower ADC
b) Less power
c) Fast microprocessors
d) Low memory capacity
Explanation: Since in undersampling the time period between samples is sufficiently large, this allows slower processors to be used for ADC. This also allows low memory capacity for storage and less power consumption.
2. Pick the odd one out?
a) R-2R converters
b) String converters
c) Weighted current source converters
d) Flash conversion
Explanation: R-2R, string and weighted current source converters are Digital to analog conversion methods whereas flash conversion is an analog to digital conversion method. Flash converter uses a voltage ladder along with a comparator to compare the reference voltage with the input voltages.
3. Which of the following does not belong to R-2R converter?
a) Reference regulators
b) Resistor network
c) Electronic switches
d) Input amplifiers
Explanation: The R-2R Digital to analog converter consists of four major parts. They are Reference regulators, Resistor network, Electronic switches, and output amplifiers. An output amplifier is used to scale the output voltage of the signal to any desired level.
4. What is the resolution of a sting DAC if the reference voltage is 10V and the number of input bits is 3?
Explanation: Resolution = reference voltage / 2N = 10/23 = 1.25V.
5. What is the alias produced when a signal of 15 MHz is sampled at a rate of 28 MHz?
Explanation: Frequency of alias signal = fa = fs – fm = 28-15 = 13MHz.
6. Settling time is the time taken to convert one binary data into analog.
Explanation: Settling time is the amount of time it takes for the output voltage of a DAC, after a change in binary input, to stabilize to within a specific voltage range. The output is thus not an accurate representation of the binary input; it is not usable until it settles down.
7. What is the maximum operation frequency that can be used if the settling time is 100ns?
Explanation: Operational frequency = 1 / (100 x 10-9)= 10MHz. Operational frequencies higher than this would produce errors.
8. During the sample mode the sample and hold circuit passes the analog signal unchanged.
Explanation: During its sampling mode, a sample-and-hold (S/H) circuit accepts the analog signal and passes it unchanged. In the hold mode, the amplifier remembers a particular voltage level at the instant of sampling.
9. Which of the following is the fastest type of ADC?
a) Successive approximation conversion
b) Flash conversion
c) Delta encoded conversion
d) Pipelined conversion
Explanation: The flash converter produces an output as fast as the comparators can switch and the signals can be translated to binary levels by the logic circuits. Comparator switching and logic propagation delays are extremely short. Thus, flash converters are the fastest type of A/D converter.
10. Find the resolution of an ADC which uses 14 bit numbers and have a voltage range of -6V to +6V?
11. What is the dynamic range of a 12 bit converter?
Explanation: 20 log( 212-1) = 20 log (4096-1) = 20 log (4095) = 72.24dB.
Sanfoundry Global Education & Learning Series – Avionics.
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