In signal systems, which statement about D/A (digital-to-analog) conversion is correct if the goal is to reproduce the original band-limited signal accurately from discrete samples?

Introduction / Context:Digital-to-analog conversion transforms discrete-time, quantized samples back into a continuous-time waveform. The output of a basic zero-order hold (ZOH) DAC is a staircase signal that contains the desired baseband along with spectral images centered at multiples of the sampling frequency. Recovering a high-fidelity analog signal requires proper filtering at the output.

Given Data / Assumptions:

• The input is band-limited and adequately sampled before conversion.
• The DAC output without filtering includes images and high-frequency components.
• We seek the statement that is generally true for accurate reconstruction.

Concept / Approach:The correct practice is to employ a reconstruction (anti-imaging) low-pass filter after the DAC to remove images while preserving the baseband. Statement (b) confuses A/D sampling criteria (Nyquist) with D/A itself; Nyquist pertains to how fast one must sample to avoid aliasing at acquisition. Statement (a) is false because a DAC produces an analog voltage/current, not a binary code. Therefore, the accurate choice is the requirement for post-DAC filtering.

Step-by-Step Solution:

Verification / Alternative check:Textbook DAC block diagrams always show a reconstruction filter following the hold stage to attenuate images at fs, 2fs, and so on.

Why Other Options Are Wrong:

Common Pitfalls:Assuming the DAC alone yields a smooth waveform; ignoring reconstruction filtering and proper anti-imaging design.

Final Answer:It must be passed through a reconstruction (low-pass) filter to recover the original signal accurately