Calculator Inputs
Formula Used
This calculator combines a logical effort estimate with an RC-based delay estimate, then applies process, voltage, temperature, and design margin adjustments.
1) Wire capacitance: Cwire = Wire Length × Wire Capacitance per µm
2) Effective load: Ceff = External Load + Cwire + (Fanout × Cin)
3) Stage effort: f = (Ceff / Cin)^(1 / N)
4) Logical effort estimate: Dlogic = N × τ × (g × f + p)
5) RC estimate: Drc = N × (Tintrinsic + 0.69 × Rdriver × (Ceff / N))
6) Slew penalty: based on input slew, fanout, and wire length
7) Total estimate: Dtotal = (0.60 × Dlogic + 0.40 × Drc + Slew Penalty) × P × V × T × Margin
This is a planning estimator for engineering work. Use signoff timing or SPICE for final verification.
How to Use This Calculator
- Select the gate type and enter the number of stages in the timing path.
- Choose the process node, supply voltage, temperature, and process corner.
- Enter transition, fanout, wire, and load information from your design estimate.
- Add a design margin if you want a conservative early-stage result.
- Use custom intrinsic delay or resistance only when measured library data is available.
- Press Calculate Delay to see the result above the form.
- Review the summary table, stage breakdown, and graph for bottlenecks.
- Download CSV or PDF for design notes, reviews, or comparison studies.
Example Data Table
| Case | Gate | Stages | Node | Voltage | Corner | Input Slew | Load | Fanout | Wire | Approx. Delay |
|---|---|---|---|---|---|---|---|---|---|---|
| Example A | 2-Input NAND | 4 | 45 nm | 1.0 V | TT | 30 ps | 18 fF | 2 | 250 µm | ~120 ps |
| Example B | Inverter | 3 | 28 nm | 0.9 V | FF | 18 ps | 10 fF | 1.5 | 120 µm | ~55 ps |
| Example C | 2-Input XOR | 5 | 65 nm | 1.1 V | SS | 45 ps | 30 fF | 3 | 400 µm | ~240 ps |
Example results are illustrative. Actual numbers depend on the entered assumptions and library behavior.
Frequently Asked Questions
1) What does this calculator estimate?
It estimates average propagation delay, rise delay, fall delay, contamination delay, effective load, and a rough maximum toggle frequency for a logic path.
2) Is this suitable for signoff timing?
No. It is best for early planning, architecture comparisons, and quick sensitivity studies. Final signoff should use static timing analysis and transistor-level verification.
3) Why do voltage and temperature matter?
Lower voltage reduces drive current, and higher temperature usually increases resistance and slows switching. Both effects typically raise gate delay.
4) What is fanout in this model?
Fanout represents how many gate inputs the driving stage must charge. Larger fanout increases effective capacitance and pushes delay upward.
5) Why is wire length included?
Interconnect adds capacitance and can dominate delay in modern paths. Longer routes usually increase both stage loading and transition time.
6) When should I use custom intrinsic delay?
Use it when you already have measured library data, SPICE characterization, or vendor timing information that better matches your target gate.
7) What does the graph show?
The graph compares estimated delay per stage against cumulative path delay. It helps reveal whether delay grows evenly or shifts toward later stages.
8) Can I export the results?
Yes. After calculation, use the CSV button for spreadsheet work and the PDF button for reports, reviews, or archived engineering notes.