What is the key difference between an ideal DAC and a real DAC in terms of glitch impulse and settling time?

• A. Real DAC exhibits glitches and settling time; ideal DAC does not
• B. Ideal DAC switches instantly without glitches or settling delay; real DAC exhibits glitches and finite settling time
• C. Ideal DAC has infinite bandwidth; real DAC has zero bandwidth
• D. Ideal DAC uses binary weighted resistors; real DAC uses R-2R ladder

Answer: (B)

The key idea is that real DACs have non-ideal switching behavior that creates transient effects, while an ideal DAC is considered to switch perfectly instantly. When a digital input changes, a real DAC’s output is influenced by parasitics, output impedance, and the way bits flip, especially if several bits change at once. This causes a brief glitch impulse—a tiny, unwanted spike in the output—and it also takes a short amount of time for the output to settle to the new target value, because of RC charging/discharging and other dynamic responses. In contrast, an ideal DAC is imagined to switch instantly without any glitches and with zero settling time. So the best description is that an ideal DAC would switch instantly without glitches or settling delay, while a real DAC exhibits glitches and finite settling time. The other options describe aspects like bandwidth or architecture that aren’t the focal point of this distinction.