## 25/03/2020

### Analog To Digital & Digital To Analog Interview Question - 2

What is resolution of the 4 – bit DAC?

% Resolution = 1 / ( 2N – 1)

Where N = Number of bit

Therefore, resolution of the 4 – bit DAC is

% Resolution = 1 / ( 24 – 1)

= 1 / 15

=  6.67%

A 4 – bit DAC has a step size of 10mV. What is output voltage and percentage resolution?

A 4 – bit DAC has 15 ( 24 – 1 ) steps of 10 mV. Therefore the full scale output is equal to 0.15 V ( 15 × 10 mV ). The percentage resolution is ( 10 mV / 0.15 ) × 100 = 6.67%

A 4 – bit DAC has output voltage of 0.10 V for digital input of 0101. What is full scale output?

The full-scale output of the DAC is equal to product of step size and number of steps.

Full scale output = 0.10 V ( 24 – 1)  = 1.5V

Explain the term : Unipolar DAC and Bi – polar DAC

Unipolar DAC

It is a DAC in which the binary input is an unsigned number and the output is a positive voltage or current.

Bi- polar DAC

It is a DAC in which the binary input is a signed number and the output is a either positive or negative value.

What is reason behind the name ‘R – 2R ladder type DAC’?

The R – 2R ladder type DAC consists of series parallel combination of two resistors R and 2R therefore it is known as the R – 2R ladder type DAC.

Why high impedance circuit is used at the output of the R – 2R ladder type DAC?

Write only the name of different types of DAC.

Different types of DAC

R – 2R Ladder type DAC

Weighted resistor type DAC

Switched current source type DAC

Switched capacitor type DAC

Which is the most popular DAC?

The R – 2R type DAC

Which is the simplest type ADC?

Counter

Which is the fastest type ADC?

Flash or parallel or simultaneous

Which is the slowest type ADC?

Dual slope

By which factor the input of the weighted resistor DAC is amplify?

The input of the Weighted resistor DAC is amplified by the ratio of the feedback resistor to the input resistor.

Describe the disadvantage of the weighted resistor type DAC

There must be each bit position of the digital input for different value of precision resistor.

What are the different types of the switched type voltage source DACs? Why it is called as switched type voltage source DACs?

The R – 2R type DAC and weighted resistor type DAC are the examples of the voltage source DACs. When an input position goes high, the output high voltage switched in the circuit which is summed to other input voltages, therefore it is called as switched type voltage source DAC.

What is advantage of the current source type DACs over the voltage source type DACs?

The switching in and out of the current type DACs is faster than the voltage source type DACs.

Give reason ‘ The switched current type DAC is sometime called as multiplying DAC’

When the output of the switched current type DAC is product of digital input and analog reference voltage, it is called as multiplying DAC.

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