1. How many control lines are present in analog to digital converter in addition to reference voltage?
A. Three
B. Two
C. One
D. None of the mentioned
Answer: B
ADC usually has two additional control lines
1. Start input-tell ADC when to start conversion.
2. EOC- end of conversion.
2. Find out the integrating type of analog to the digital converter?
A. Flash-type converter
B. Tracking converter
C. Counter type converter
D. Dual slope ADC
Answer: D
Other than dual-slope ADC the rest belongs to direct type ADCs.
3. Which type of ADC follows the conversion technique of changing the analog input signal to a linear function of frequency?
A. Direct type ADC
B. Integrating type ADC
C. Both integrating and direct type ADC
D. None of the mentioned
Answer: B
Integrating type ADC performs conversion in an indirect manner by first changing the analog input signal to a linear function of time or frequency and then to a digital code.
4. Which A/D converter is considered to be simplest, fastest, and most expensive?
A. Servo converter
B. Counter type ADC
C. Flash type ADC
D. All of the mentioned
Answer: C
The simplest possible A/D converter is flash type converter and is expensive for a high degree of accuracy.
5. The flash type A/D converters are called as
A. Parallel non-inverting A/D converter
B. Parallel counter A/D converter
C. Parallel inverting A/D converter
D. Parallel comparator A/D converter
Answer: D
The flash type A/D converter is also called a parallel comparator A/D converter because the purpose of the circuit is to compare the analog input voltage with each node voltage.
6. What is the advantage of using a flash-type A/D converter?
A. High-speed conversion
B. Low-speed conversion
C. Nominal speed conversion
D. None of the mentioned
Answer: A
Flash type ADC has the advantage of high speed as the conversion takes place simultaneously rather than sequentially. The typical conversion time is 100nanosecond or less.
7. The number of comparators required for flash type A/D converter
A. Triples for each added bit
B. Reduce by half for each added bit
C. Double for each added bit
D. Doubles exponentially for each added bit
Answer: C
The number of comparators required almost doubles for each added bit. For example – 2 -bit ADC requires three comparators, 3 -bit ADC needs seven comparators, and a 4 -bit ADC requires fifteen comparators.
8. Drawback of counter type A/D converter
A. Counter clears automatically
B. More complex
C. High conversion time
D. Low speed
Answer: D
In counter type, ADC counter frequency is kept low enough to give sufficient time for DAC to settle and for the comparator to respond. So, low speed is the most serious drawback.
9. Calculate the conversion time of a 12-bit counter-type ADC with 1MHz clock frequency to convert a full-scale input?
A. 4.095 µs
B. 4.095ms
C. 4.095s
D. None of the mentioned
Answer: B
conversion time = 2n -1 clock periods
= (12n-1) = 4.095ms.
10. In a servo tracking A/D converter, the input voltage is greater than the DAC output signal at this condition
A. The counter counts up
B. The counter count down
C. The counter back and forth
D. None of the mentioned
Answer: A
In the servo converter, the circuit consists of an up/down counter with a comparator controlling the direction of the count. So, if the input voltage is greater than the DAC output signal, the output of the comparator goes high and the counter is caused to count up.
11. At what condition does the error occur in the servo tracking A/D Converter?
A. Slow change input
B. Rapid change in input
C. No change in input
D. All of the mentioned
Answer: B
As long as the analog input changes slowly, the tracking A/D converter will be within one LSB of the corrected value. When the input changes rapidly, the tracking A/D converter cannot keep up with change and error occurs.
12. How many clock pulses do a successive approximation converter require for obtaining a digital output.
A. Twelve
B. Six
C. Eight
D. None of the mentioned
Answer: D
The successive approximation technique uses a very efficient code search strategy to compute n-bit conversion in just the n-clock period.
13. At what condition the digital to analog conversion is made?
A. Va > Vd
B. Va ≤ Vd
C. Va ≥ Vd
D. Va ≠ Vd
Answer: B
When Vad, the output of the comparator becomes low and the AND gate is disabled. This stops the counting at that time and the digital output of the counter represents the analog input voltage.
14. If an input at Va is 1010, then find the correct conversion sequence for the given circuit.
A.
Input signal
SAR output at different stages
comparator output
1010
1000
1
1100
0
1010
1
1011
0
1010
B.
Input signal
SAR output at different stages
comparator output
1010
0001
0
0010
1
0011
0
1010
1
C.
Input signal
SAR output at different stages
comparator output
1010
1111
0
1011
0
1001
1
1010
1
D. None of the mentioned
Answer: A
The given circuit is a successive approximation register and it finds the required value of each bit by trial and error method. When the conversion start SAR set MSB d1=1 with other bits zero. So, the trial code is 1000. If Va(1010) is greater than DAC output (1000). Then MSB is left `1′ and the next lower significant bit is made `1′ and further tested.
15. The Integrating type converters are used in
A. Digital meter
B. Panel meter
C. Monitoring system
D. All of the mentioned
Answer: D
The Integrating type converters are used in applications such as digital meters, panel meters, and monitoring systems where the conversion accuracy is critical.
