Digital-to-analog conversion (DAC) is the process of converting a digital signal into an analog signal. It is commonly used in various applications such as audio systems, communication systems, and control systems. There are different techniques used for digital-to-analog conversion, and among them, the following techniques are commonly employed:

Staircase Approximation:
- In the staircase approximation technique, the digital signal is approximated by a series of steps.
- The input digital signal is divided into several discrete levels, and each level is represented by a specific voltage.
- The analog output is generated by connecting a resistor ladder network to the digital input.
- The output voltage is determined by selecting the corresponding resistor in the ladder network based on the digital input level.

Linear Interpolation:
- Linear interpolation is another technique used for digital-to-analog conversion.
- In this technique, the digital input is approximated by a straight line between two adjacent reference points.
- The output voltage is determined by finding the intersection point of the straight line and the reference voltage levels.
- The analog output is obtained by connecting an operational amplifier to the reference voltage levels and the digital input.

Quadratic Interpolation:
- Quadratic interpolation is an advanced technique used for digital-to-analog conversion.
- In this technique, the digital input is approximated by a quadratic curve that passes through three adjacent reference points.
- The output voltage is determined by finding the intersection point of the quadratic curve and the reference voltage levels.
- The analog output is obtained by connecting an operational amplifier to the reference voltage levels and the digital input.

All of the Mentioned:
- The correct answer to the given question is "All of the mentioned" because all the mentioned techniques (staircase approximation, linear interpolation, and quadratic interpolation) are commonly used for digital-to-analog conversion.
- Each technique has its own advantages and disadvantages, and the choice of technique depends on the specific requirements of the application.

In conclusion, digital-to-analog conversion is an important process in various electrical engineering applications, and different techniques such as staircase approximation, linear interpolation, and quadratic interpolation are employed for this purpose. These techniques allow the conversion of digital signals into analog signals, enabling the transmission and processing of digital information in analog systems.