CMOS Inverter Delay Calculator

Frank Wanlass invented the CMOS inverter at Fairchild Semiconductor in 1963, pairing an N-channel and P-channel MOSFET in a complementary configuration. His key insight: only one transistor conducts at a time in steady state, so the static current is essentially zero — just leakage. Dynamic power (charging and discharging capacitance) dominates instead, which is why CMOS became the foundation of every low-power digital IC from the 1970s onward.

The classic delay formula tp = 0.69·R_on·CL comes from first-order RC analysis: the inverter's pull-up or pull-down transistor acts as a resistor driving the load capacitance, and 0.69 = ln(2) is the time to reach the 50% crossing point. In practice, R_on varies with gate-source voltage (hence saturation and triode regions), and more accurate α-power-law models (Sakurai 1990) are used in modern EDA tools.

Dennard scaling (1974) predicted that as MOSFETs shrink, gate capacitance shrinks proportionally while speed increases — enabling Moore's Law's doubling cadence through the 1990s. Dennard scaling broke down around 2005 when leakage currents (sub-threshold, gate-oxide tunneling) stopped shrinking, forcing the industry to multi-core architectures and FinFET transistors. But the fundamental tp = 0.69·Ron·CL relationship still governs every internal logic cell in a modern SoC.

Enter supply voltage Vdd, load capacitance CL, transistor on-resistance R_on, and switching frequency. The tool returns propagation delay tp = 0.69·R_on·CL (50% to 50%), 10-90% rise/fall time 2.2·R_on·CL, dynamic power P = CL·Vdd²·f (the classic CMOS dynamic-power formula), and a rough maximum frequency estimate.

Note: this is an idealized single-stage analysis. Real chip power includes short-circuit current (during transitions when both transistors conduct briefly), leakage current (which dominates at > 45 nm process nodes), and clock-tree distribution power. For full SoC power analysis, use EDA tools like Synopsys PrimePower or Cadence Voltus. Everything runs client-side; no values leave your browser.