Digital delay elements – definition of a multitap delay line What best describes a multitap digital delay line implemented with basic logic and passive components?
-
Aa series of inverter gates with RC circuits between each one
-
Ba series of inverter gates with RL circuits between each one
-
Ca series of NAND gates with RC circuits between each one
-
Da series of NAND gates with RL circuits between each one
Answer
Correct Answer: a series of inverter gates with RC circuits between each one
Explanation
Introduction / Context:Multitap delay lines are used to create multiple well-defined timing references in digital systems (edge shaping, pulse stretching, time-stamping). Knowing their structure helps when analyzing propagation delay and jitter.
Given Data / Assumptions:
- The delay line is “digital” and “multitap.”
- We consider simple gate-level realizations using passives for timing.
- Taps provide intermediate delayed versions of the same signal.
Concept / Approach:A common discrete implementation chains inverters, each separated by an RC network to create incremental delays. Each node (tap) outputs a progressively delayed replica. Inverters are preferred because they provide restoration, squaring, and predictable propagation; RC networks introduce the controlled time constant. RL versions are uncommon in basic CMOS/TTL design, and using NANDs is unnecessary unless adding gating logic.
Step-by-Step Solution:
Identify the simplest delay element: inverter + RC forms a gate-level delay.Replicate stages and expose intermediate nodes as “taps.”Therefore, the best description is inverters with RC between each.Verification / Alternative check:Timing chains in many app notes show cascaded inverters with RC shaping or controlled delay cells; ECL/CMOS ICs also implement internal variants of this concept.
Why Other Options Are Wrong:
- Inverters with RL: RL is not typical for logic-level delay; inductors are bulky and less predictable on PCBs.
- NAND + RC / NAND + RL: A NAND is not required for pure delay; it adds logic functionality rather than simple timing.
Common Pitfalls:
- Thinking any multi-gate chain is a “multitap” even without RC timing control.
- Assuming inductive elements are common in digital delay blocks; they are not.
Final Answer:a series of inverter gates with RC circuits between each one