Calculator Inputs
Use nanoseconds for every timing field.
Plotly Graph
The graph compares minimum data arrival, required hold boundary, and hold slack.
Example Data Table
| Launch Clock | Capture Clock | Min Clock-to-Q | Min Logic Delay | Hold Time | Uncertainty | Extra Margin | Arrival | Required | Slack | Buffers |
|---|---|---|---|---|---|---|---|---|---|---|
| 0.05 ns | 0.12 ns | 0.08 ns | 0.16 ns | 0.06 ns | 0.02 ns | 0.01 ns | 0.30 ns | 0.20 ns | 0.10 ns | 0 |
Formula Used
Minimum Data Arrival = Launch Clock Arrival + Minimum Clock-to-Q + Minimum Combinational Delay + Extra Data Margin
Required Hold Boundary = Capture Clock Arrival + Capture Hold Time + Hold Uncertainty
Hold Slack = Minimum Data Arrival - Required Hold Boundary
Minimum Added Delay Needed = max(0, -Hold Slack)
Estimated Buffer Count = ceil(Minimum Added Delay Needed / Delay Per Buffer Cell)
A positive slack means the path passes the hold check. A negative slack means the data path is too fast and needs extra delay.
How to Use This Calculator
- Enter the launch and capture clock arrival times in nanoseconds.
- Provide the minimum clock-to-Q and minimum combinational delay.
- Enter the capture register hold time and hold uncertainty.
- Add any extra data margin you want included in the check.
- Enter an estimated delay for one fixing buffer cell.
- Click Check Hold Time to view slack, status, and fix guidance.
- Use the CSV or PDF buttons to export the computed summary.
Frequently Asked Questions
1. What does this hold check calculator measure?
It measures whether minimum data arrival stays later than the required hold boundary at the capture register. The result helps identify risky fast paths in synchronous digital timing analysis.
2. What does negative hold slack mean?
Negative hold slack means the launched data reaches the capture side too early. The path fails hold timing and usually needs added delay, clock adjustment, or routing changes.
3. Why is hold uncertainty included?
Hold uncertainty models timing variation such as jitter, extraction spread, and analysis guardband. Adding it makes the required boundary stricter and gives a more conservative engineering check.
4. What is extra data margin used for?
Extra data margin lets you include internal guardband for implementation risk, modeling simplification, or future optimization changes. It is useful when you want more than bare minimum timing closure.
5. How is the suggested buffer count estimated?
The calculator divides the missing delay by the average delay added by one buffer cell. It is an estimate only, because physical placement and library selection change real results.
6. Can this replace full static timing analysis?
No. It is a quick engineering calculator for scoping and checking ideas. Full timing closure still requires detailed path extraction, constraints review, corner analysis, and library-aware signoff tools.
7. Which unit should I use?
Use nanoseconds consistently for every input. The formulas assume all timing values share the same unit. Mixed units create wrong slack and misleading design decisions.
8. What are common hold-fix methods?
Common methods include adding delay buffers, detouring routing, resizing cells, adjusting clock skew deliberately, or changing path structure. The safest fix depends on layout, power, area, and setup impact.