14. Logic families and gates
Logic voltage levels
Formula
Tags
Detail
Levels VOH VOL VIH VIL bound valid high and low on the VTC.
Explore the idea
Variables
- V
- s
- Ω
- fan-out and fan-indimensionless.
Conditions
- Logic family on a fixed supply; static levels.
Intuitive explanation
For “Logic voltage levels”: VOH, VOL, VIH and VIL set noise margins and the CMOS VTC inverts between rails.
Worked example
If , , and , the required order is preserved.
Common mistakes
- confusing VIH with VOH
- forgetting noise margin
- computing fan-out without input current
Frequently asked questions
- What must be checked before using the Logic voltage levels relation?
- Use the family levels and measure margins in DC.
Also known as
- VOH VOL, noise margin, CMOS VTC, fan-out, propagation delay
Conventions
- V, s or dimensionless
Last reviewed: 2026-09-19