Question 1

Why propagation delay matters in digital logic: Propagation delay (input-to-output delay) directly impacts performance metrics. Which statement best captures its practical importance in timing design?

Accepted Answer

Introduction / Context: Propagation delay is the time required for a change at a logic input to produce a corresponding change at the output. It appears in virtually every datasheet and determines the performance ceiling of combinational paths and clocked systems. Given Data / Assumptions: Propagation delay is typically measured from the 50% voltage point at the input to the 50% point at the output. Maximum clock frequency depends on cumulative delays along the critical path plus setup/hold requirements of sequential elements. Not all gates in a system have identical delays; designers budget margins accordingly. Concept / Approach: The shorter the propagation delay, the faster a logic family can toggle reliably. In synchronous systems, the clock period must exceed the sum of path delays and register timing margins. Therefore, propagation delay places a hard upper bound on feasible clock frequency. Step-by-Step Solution: Identify definition: t_pd is input-to-output delay.Connect to system timing: clock period ≥ logic path delay + setup + clock skew + margins.Infer design impact: higher t_pd forces lower maximum operating frequency.Choose the statement that matches: it limits the maximum operating frequency. Verification / Alternative check: Timing analysis tools and STA reports compute maximum frequency from worst-case path delays, confirming the centrality of propagation delay. Why Other Options Are Wrong: “short break to prevent overheating”: Not related to thermal duty cycling.“how long the clock must be applied”: Misstates the meaning; clocks are periodic, not “applied until decision.”“all gates must have same delay”: Systems tolerate variation; designers use margins. Common Pitfalls: Confusing propagation delay with rise/fall time; ignoring clock uncertainty and setup/hold when determining the clock period. Final Answer: it limits the maximum operating frequency of a gate

Question 2

Pulse-injection troubleshooting tool: Identify the instrument used in digital troubleshooting that generates a short-duration logic pulse when manually triggered (often by a pushbutton).

Accepted Answer

Introduction / Context: When chasing faults in digital circuits, technicians often need to inject known, controlled pulses into a node to observe downstream behavior. This helps isolate a failing gate, trace signal flow, and verify that subsequent stages respond correctly. Given Data / Assumptions: The tool should deliver clean, short-duration logic-level pulses. It must be manually triggered for step-by-step testing. It interfaces safely with standard logic voltage levels (for example, 5 V TTL/CMOS, or 3.3 V devices as appropriate). Concept / Approach: A logic pulser is designed specifically for this role. It injects a brief HIGH or LOW pulse at the probe tip, allowing the user to see the effect on LEDs, logic probes, or oscilloscope traces. Other named items in the options are either jokes or unrelated components, not suitable for logic testing. Step-by-Step Solution: Determine required function: generate a short logic pulse.Match to instrument type: logic pulser provides pressed-button, debounced pulses.Eliminate distractors: terms like “cattle prod” and “jimmy rod” are not electronics tools; “bilateral switch” is a component, not a test instrument.Select “logic pulser.” Verification / Alternative check: Common toolkits for digital troubleshooting include a logic probe, logic pulser, and often a pulse generator or pattern generator for more advanced testing. Why Other Options Are Wrong: cattle prod / jimmy rod: Not electronics tools; included as humorous distractors.bilateral switch: An analog switch component (e.g., CD4066), not a handheld tester. Common Pitfalls: Confusing a bench pulse generator (more complex instrument) with a handheld logic pulser; applying pulses at unsafe voltage levels without checking the circuit family. Final Answer: logic pulser

Integrated-Circuit Logic Families Questions