QUESTIONS ON ADC DAC

1. What Is an ADC (Analog-to-Digital Converter)?

An analog-to-digital converter (also known as an ADC or an A/D converter) is an electronic circuit that measures a real-world signal (such as temperature, pressure, acceleration, and speed) and converts it to a digital representation of the signal.

2. What Is a DAC (Digital-to-Analog Converter)?

A digital-to-analog converter (also known as a DAC or a D/A converter) is an electronic circuit that converts a digital representation of a quantity into a discrete analog value. The input to the DAC is typically a digital binary code. This code, along with a known reference voltage, results in a voltage or current at the DAC's output. 

3. How Does a Flash ADC Work?

A flash ADC is also called a "parallel encoder." The key advantage of this architecture is very fast conversion times. The main disadvantage is high power consumption. A flash ADC is suited for very-high-speed, low-resolution applications. 

4. What is resolution of ADC?

Resolution of converter is defined as the change in output voltage per one LSB change in input.

Resolution=Vfs/2^n-1

5. Howmany comparators are require to construct a 3-bit flash type ADC?

In general for a n bit ADC we require a minimum of 2^n-1 comparators, for a 3-bit comparator we require minimum of 7 comparators.

6. What is meant by conversion delay in ADC?

The time delay between SOC signal and EOC signal is referred as conversion delay or conversion time.

7. What is the use of sample and hold circuit in analog to digital conversion?

In analog to digital conversion sampling circuit is used to convert the analog signal in to discrete signal and hold circuit is used to hold the analog input stable during the conversion process.

8. How many clock pulses are required in Successive approximation ADC?

In an n-bit Successive approximation ADC it requires n clock cycles for conversion.

9. What is the disadvantage with servo/tracking ADC?

    Servo/tracking ADC will not convert the voltages that changes instantaneously with time, tracking error is the drawback of servo/tracking ADC.

10. Why counter type ADC slow?

The conversion time of Counter type ADC too high so, it takes more amount of time to conversion.

11. What is quantization error?

         Error resulting from trying to represent a continuous analog signal with discrete, stepped digital data. The problem arises when the analog value being sampled falls between two digital “steps.” When this happens, the analog value must be represented by the nearest digital value, resulting in a very slight error. In other words, the difference between the continuous analog waveform and the stair-stepped digital representation is quantization error. 

12. State sampling theorem?

       The given analog signal is sampled at a rate of twice the maximum frequency of the given input signal

13. What are the control signals used in ADCs?

SOC (start of conversion) is used to start the conversion.

EOC (End of Conversion) is used to indicate that the conversion process has been completed.

14. List the drawbacks of binary weighted resistor technique of D/A conversion.

 a) Wide range of resistor values needed

 b) Difficulty in achieving and maintaining accurate ratios over a wide range of variations

15. What are the advantages and disadvantages of R-2R ladder DAC.  

Advantages:

b) Number of bits can be expanded by adding more sections of same R/2R values.

Disadvantage: a) In this type of DAC, when there is a change in the input, changes the current flow in the resistor which causes more power dissipation which creates non-linearity in DAC.

16. What is the difference between direct ADC and integrating type ADC.

a) The integrating type of ADC’s do not need a sample/Hold circuit at the input.

 b) It is possible to transmit frequency even in noisy environment or in an isolated form

17. Define monotonocity?

  A monotonic DAC is one whose analog output increases for an increase in digital input.

18. Define Linearity?

Output has to increase linearly with input signal.

19. Define Accuracy?

It is the maximum deviation between the actual converter output & the ideal converter output. It is the maximum deviation after gain & offset errors have been removed. The accuracy of a converter is also specified in form of LSB increments or % of full scale voltage

20. State the advantages and applications of sample and hold circuits.

A sample and hold circuit is one which samples an input signal and holds on to its last sampled value until the input is sampled again. This circuit is mainly used in digital interfacing, analog to digital systems, and pulse code modulation systems.

21. What is integrated type ADC?

It integrates the given input signal and performs the conversion process

22. What is the advantage of Inverted R-2R ladder DAC?

Current variations through the resistors are eliminated so that linearity in the output has improved.

23. List out applications of ADCs and DACs?

These are used in microprocessor based systems and communication, medical applications, image processing.

24. What is the indication of resolution?

Resolution indicates how fast the output is changing with respect to input voltage.