Interconnecting CMOS and TTL Evaluate the statement: “Because CMOS logic draws extremely low power, any number of CMOS and TTL gates can be interconnected without concern.”

Introduction / Context: While CMOS inputs draw negligible static current, practical digital design is still constrained by fan-out limits, input capacitance, rise/fall times, logic-level compatibility, and supply differences between families (TTL vs. CMOS). Therefore, “any number” is never a safe assumption.

Given Data / Assumptions:

• CMOS inputs have high impedance but non-zero capacitance that must be driven during transitions.
• TTL outputs have specified source/sink current limits and logic-level thresholds that may not align with CMOS without level translation (e.g., V_OH(min) vs. V_IH(min)).
• Interfacing sometimes requires pull-ups, level shifters, or the HCT family to ensure compatibility.

Concept / Approach: Fan-out is determined not just by static current but also by dynamic loading (C_load). As the number of driven inputs increases, edge rates slow and timing can fail. Furthermore, TTL HIGH output minimum (≈ 2.4 V) may not meet CMOS HIGH input minimum at 5 V for some families, necessitating HCT or buffers for safe interfacing.

Step-by-Step Solution:

Verification / Alternative check: Data sheets specify maximum fan-out and input capacitance; timing analysis demonstrates degraded rise/fall times as loads increase, confirming limits exist.

Why Other Options Are Wrong: “Correct” disregards practical constraints. Open-drain or higher supply voltages do not eliminate level and loading concerns by themselves.

Common Pitfalls: Assuming static input current is the only factor; in reality, capacitive loading and threshold compatibility often dominate.

Final Answer: Incorrect