CRO Time Base Signal Shape

The time base signal in a Cathode Ray Oscilloscope (CRO) is crucial for generating the horizontal sweep across the screen. This signal dictates how the electron beam moves from left to right over time.

Why Sawtooth Wave is Ideal

A sawtooth wave is the standard choice for the CRO's time base signal due to its specific characteristics:

• Linear Sweep: The gradually increasing voltage portion of the sawtooth wave causes the electron beam to move horizontally across the screen at a constant, uniform speed. This creates a linear time axis, essential for accurately measuring time intervals and observing signal shapes.
• Fast Retrace: The sharp, rapid drop in voltage at the end of the sawtooth cycle quickly resets the electron beam to the starting point on the left side of the screen. This minimizes the "flyback" or retrace time, allowing for continuous observation.

Other Waveforms Considered

While other waveforms can be generated, they are less suitable for the CRO's time base function:

• Sine Wave: The sweep speed varies non-linearly throughout the cycle, making time measurements difficult and distorting the display.
• Square Wave: It causes an instantaneous jump, not a continuous sweep, and is unsuitable for displaying waveforms over time.
• Triangle Wave: Although it has linear portions, the combination of increasing and decreasing linear ramps makes it less ideal than a pure sawtooth for a consistent sweep.

Conclusion on CRO Time Base

The unique ramp-up and sharp drop characteristics of the sawtooth wave make it the most effective signal for achieving a predictable and linear horizontal sweep required for oscilloscope operation.

Correct Answer: Option D (sawtooth wave)