Clock Skew Timing Margin
Tmargin = Tclk − Tskew − Tsetup
Quick answer
This calculator solves Tmargin = Tclk − Tskew − Tsetup for Timing Margin. With Clock Period 47 ns, Clock Skew 22 ns, Setup Time 10 ns, the result is 15 ns. It solves in 4 directions, so you can enter the values you have and get the one you need.
Calculator
Formula
Description
Clock skew is the difference in clock arrival times at two different flip-flops due to different clock distribution path lengths. When data must travel from one flip-flop to another, the clock skew effectively reduces the available time for data propagation. Positive skew (clock arrives later at the destination) steals from the setup time budget, while negative skew adds to it. In board-level design with multiple ICs sharing a clock, trace length differences create skew that must be accounted for in the timing budget.
Variables
- Tmargin — Available timing slack (s)
- Tclk — Clock period (s)
- Tskew — Clock skew between source and destination (s)
- Tsetup — Setup time requirement of the destination flip-flop (s)
Practical Notes
Clock distribution techniques to minimize skew: clock trees (H-tree), clock buffers (zero-delay buffers like CY2305), and source-synchronous clocking (sending the clock alongside data). DDR memory uses source-synchronous DQS strobes to eliminate clock skew. For PCB-level clock distribution, match trace lengths to within 1-2mm for clock rates above 100 MHz.
Symbols and units
| Symbol | Meaning | Default unit | Accepted units |
|---|---|---|---|
| Tmargin | Timing Margin | ns | ps, ns, µs, ms, s, min, h |
| Tclk | Clock Period | ns | ps, ns, µs, ms, s, min, h |
| Tskew | Clock Skew | ns | ps, ns, µs, ms, s, min, h |
| Tsetup | Setup Time | ns | ps, ns, µs, ms, s, min, h |
Step by step
- 1. What you know: Clock Period 47 ns, Clock Skew 22 ns, Setup Time 10 ns
- 2. The relation: Tmargin = Tclk − Tskew − Tsetup
- 3. Substitute: Tclk = 47 ns, Tskew = 22 ns, Tsetup = 10 ns
- 4. Result: Timing Margin = 15 ns
Worked examples
Minimum range
Given: Clock Period 0.47 ns, Clock Skew 0.22 ns, Setup Time 100 ps
Result: Timing Margin = 150 ps
Low range
Given: Clock Period 4.7 ns, Clock Skew 2.2 ns, Setup Time 1 ns
Result: Timing Margin = 1.5 ns
Typical
Given: Clock Period 47 ns, Clock Skew 22 ns, Setup Time 10 ns
Result: Timing Margin = 15 ns
High range
Given: Clock Period 0.47 µs, Clock Skew 0.22 µs, Setup Time 100 ns
Result: Timing Margin = 150 ns
Maximum range
Given: Clock Period 4.7 µs, Clock Skew 2.2 µs, Setup Time 1 µs
Result: Timing Margin = 1.5 µs
Solving for each variable
Solve for Timing Margin
Clock Period 0.47 ns, Clock Skew 0.22 ns, Setup Time 100 ps → 150 ps
Solve for Clock Period
Timing Margin 100 ps, Clock Skew 0.47 ns, Setup Time 47 ps → 0.617 ns
Solve for Clock Skew
Timing Margin 100 ps, Clock Period 0.22 ns, Setup Time 47 ps → 73 ps
Solve for Setup Time
Timing Margin 100 ps, Clock Period 0.22 µs, Clock Skew 0.47 ns → 0.2194 µs
How Timing Margin changes with Clock Period
| Clock Period (input) | Timing Margin (result) |
|---|---|
| 35.25 ns | 3.25 ns |
| 47 ns | 15 ns |
| 70.5 ns | 38.5 ns |
| 94 ns | 62 ns |
| 0.188 µs | 156 ns |
| 0.329 µs | 0.297 µs |
| 0.47 µs | 0.438 µs |
The same result in other units
| Unit | Value |
|---|---|
| ps | 15000 |
| ns | 15 |
| µs | 0.015 |
Embed this calculator
Paste this into any page. It keeps working when this page updates, and credits the source.
<iframe src="https://vbatpower.com/embed/clock-skew-margin/" width="100%" height="460" style="border:1px solid #1f2a37;border-radius:12px" loading="lazy" title="Clock Skew Timing Margin"></iframe>
<p><a href="https://vbatpower.com/formulas/clock-skew-margin/">Clock Skew Timing Margin</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate Clock Skew Timing Margin?
Use Tmargin = Tclk − Tskew − Tsetup. With Clock Period 47 ns, Clock Skew 22 ns, Setup Time 10 ns, Timing Margin works out to 15 ns.
What is the formula for Clock Skew Timing Margin?
The formula is Tmargin = Tclk − Tskew − Tsetup. Clock skew is the difference in clock arrival times at two different flip-flops due to different clock distribution path lengths.
How do you find Clock Period when you know the other values?
Rearrange for Clock Period: with Timing Margin 100 ps, Clock Skew 0.47 ns, Setup Time 47 ps, Clock Period is 0.617 ns.
How do you find Clock Skew when you know the other values?
Rearrange for Clock Skew: with Timing Margin 100 ps, Clock Period 0.22 ns, Setup Time 47 ps, Clock Skew is 73 ps.
What units does Clock Skew Timing Margin use?
Timing Margin is shown in ps, ns, µs. Values are held in SI base units internally, so you can mix prefixes without converting by hand.
Related Concepts
All Digital Logic formulas →Need more features?
Save calculations, import telemetry data, simulate battery discharge, and collaborate with your team.
Try the App