Introduction:
In electrical engineering, Pulse Width Modulation (PWM) is a technique used to encode information in the amplitude of a pulsating signal. It is widely used in various applications, such as motor control, power electronics, and communication systems. The output waveform of a single PWM is often characterized by its shape, which can be square, triangular, quasi-square, or sine wave.

The output voltage waveform:
The output voltage waveform in a single PWM is a quasi-square wave (option C). This means that the waveform resembles a square wave but has some variations or imperfections.

Explanation:
To understand why the output waveform in a single PWM is quasi-square, let's first understand the basic principle of PWM. In PWM, a fixed frequency signal (carrier signal) is modulated by varying the duty cycle (ratio of ON time to the total period) of the signal. The duty cycle determines the amplitude of the output waveform.

When the duty cycle is 0%, the output waveform is always 0V (OFF state). When the duty cycle is 100%, the output waveform is always the maximum voltage (ON state). In between these extremes, the output voltage varies proportionally with the duty cycle.

Now, let's consider a scenario where the duty cycle is varied continuously from 0% to 100% and then back to 0%. During this transition, the output waveform will exhibit some imperfections due to the finite switching time of the PWM signal.

Characteristics of the quasi-square wave:
The quasi-square wave in a single PWM has the following characteristics:

1. Finite rise and fall times: The rise and fall times of the waveform are not instantaneous, but they have a finite duration due to the switching time of the PWM signal. This results in sloped edges instead of abrupt transitions.

2. Non-zero voltage during transition: Unlike a perfect square wave, the quasi-square wave has non-zero voltage during the transition from the OFF state to the ON state and vice versa. This is because the duty cycle is continuously changing, and the output voltage is gradually increasing or decreasing.

3. Variable pulse width: The width of each pulse in the quasi-square wave is not constant but varies based on the duty cycle. As the duty cycle increases, the pulse width also increases, and vice versa.

4. Periodic repetition: The quasi-square wave repeats periodically with the same frequency as the carrier signal. This allows the encoded information to be recovered at the receiving end.

Conclusion:
In conclusion, the output voltage waveform in a single PWM is a quasi-square wave. This waveform exhibits characteristics such as finite rise and fall times, non-zero voltage during transition, variable pulse width, and periodic repetition. These imperfections are inherent to the switching nature of the PWM technique and have practical implications in various applications.