Question 8-26C4

A comparator, like the one implied in Fig. 8C11, converts an analog input into a digital output by comparing it to a reference voltage. When the input is a sinusoid and the comparator functions as an inverting zero-crossing detector (meaning the sinusoidal input is applied to the inverting input and the non-inverting input is at 0V), the output transitions high when the input falls below the reference. For an inverting zero-crossing detector: * When the input sine wave is positive, the output is low. * When the input sine wave crosses zero and becomes negative, the output goes high. A positive zero crossing of a sine wave typically occurs at 0 degrees. The input then becomes positive. The negative zero crossing (where the input goes from negative to positive, or, in this case, where it crosses zero to become negative) occurs 180 degrees after the positive zero crossing. Therefore, the "leading edge" (or rising edge) of the output waveform, which occurs when the input goes negative, happens 180 degrees after the positive zero crossing of the input. Options B, C, and D describe scenarios where the output transition occurs at 45 or 135 degrees relative to specific input points, which would typically only happen with a non-zero reference voltage or hysteresis, not a simple zero-crossing detection as implied by the most straightforward interpretation of the question.