31. 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.
32. 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.
33. 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.
34. 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.
35. 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.
36. In integrating type ADCs, the input/output voltage is proportional to
A. Input averaged over the integration period
B. Input averaged over the integration period
C. Sum of input voltage
D. Sum of input voltage
Answer: B
Since the integrating type ADC does not require a sample and hold circuit at the input. The change in input during conversion will not affect the output voltage and is proportional to the value of the input averaged over the integration period.
37. Which type of ADC is chosen for a noisy environment?
A. Successive approximation ADC
B. Dual slope
C. Charge balancing ADC
D. All of the mentioned
Answer: C
The main advantage of these converters is that it is possible to transmit frequency even in noisy environments or in an isolated form.
38. How to overcome the drawback of the charge balancing ADC?
A. By using a precision integrator
B. By using Voltage to frequency converter
C. By using a voltage comparator
D. By using a dual-slope converter
Answer: D
Charge balancing ADC depends upon RC product whose value cannot be easily maintained with temperature and time. This is eliminated using dual-slope ADC as it is independent of R, C, and T.
39. Which among the following has a long conversion time?
A. Servo converter
B. Dual ramp converter
C. Flash converter
D. None of the mentioned
Answer: B
The main disadvantage of dual-slope ADC is the long conversion time. For instance, if 2n-T=1/50 is used to reject line pick-up, the conversion time will be 20ms.
40. In which application dual slop converter is used.
A. Thermocouple
B. Digital panel meter
C. Weighting scale
D. All of the mentioned
Answer: B
Dual slope converters are particularly suitable for accurate measurement of slow varying signals hence it is used for Digital panel meter.
