Digital to Analog and Analog to Digital Converters Interview Questions and Answers:

1. Why conversion of an analog signal into an equivalent digital signal is essential?

Ans. Because most sensors have analog output while much data processing is accomplished with digital computers, analog-to­-digital conversion is essential.

2. What is digital-to-analog conversion?

Ans. Basically, D/A conversion is the process of taking a value represented in digital code (such as simply binary or BCD) and converting it into a voltage or current which is proportional to the digital value.

3. What is A/D conversion?

Ans. The A/D conversion is the process of converting an analog input voltage into an equivalent digital signal.

4. Why an A/D converter is usually considered as an encoder?

Ans. A/D converter is usually considered as an encoder as it is used for encoding analog signals for entry into digital system.

5. Mention the various types of analog to digital converters in the increasing order of speed of Operation.

Ans. A/D converters in the increasing order of speed of operation is given as dual slope type, successive approximation type, paral­lel-comparator type.

6. Arrange the following A/D converter in order of increasing speed of operation. (i) Successive approximation (ii) Dual slope (iii) Flash (iv) Single slope.

Ans. A/D converters in order of increasing speed of operation are: Dual slope, single slope, successive approximation and flash type.

7. Give the advantages and disadvantages of an integrating type A to D converters under the following heads: (i) speed of operation (ii) change in R-C values (iii) presence of periodic noise (iv) offset voltage of the op-amp.

Ans.

• Speed of operation — Slow.
• Change in R-C values — The accuracy of this converter is independent of R-C values or any change in them.
• Presence of periodic noise — This converter is very less sensitive to periodic noise.
• Offset voltage of op-amp — Accuracy depends upon the offset values, therefore, the reference voltage should be precise.

8. What are the advantages of integrating type A/D converters over the non-integrating type?

Ans. The integrating type ADC has the following advantages:

• It is relatively simple and inexpensive.
• Conversion accuracies obtainable are very good.
• Capacitors and resistors need not have high precision.
• Errors due to propagation delay times are eliminated.
• Accuracy depends only on the stability of the reference voltage V_REF.
• The comparator offset voltage and current are automatically compensated as the input signals cross zero voltage twice.

9. What is resolution for a DAC?

Ans. Resolution of a DAC defines the smallest increment in the voltage that can be discerned. Resolution is primarily a function of the number of bits in the digital input signal i.e. the smallest increment output voltage is determined by the LSB.

10. What is the maximum conversion time for successive approximation ADC?

Ans. The maximum conversion time for successive approximation type ADC is nT_c where n is the number of bits and T_c is the time period of one clock pulse.