Setup Time Margin
Tmargin = Tclk − Tpd − Tsetup
Quick answer
This calculator solves Tmargin = Tclk − Tpd − Tsetup for Timing Margin. With Clock Period 47 ns, Propagation Delay 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
Setup time margin determines whether a synchronous digital circuit will operate reliably at a given clock frequency. Data must arrive and stabilize at the receiving flip-flop input at least Tsetup before the clock edge. The margin is the remaining time after accounting for propagation delay through combinational logic and the setup time requirement. A positive margin means the circuit meets timing; a negative margin indicates a timing violation that causes metastability or incorrect data capture.
Variables
- Tmargin — Available timing slack (s)
- Tclk — Clock period (s)
- Tpd — Total propagation delay through logic and routing (s)
- Tsetup — Flip-flop setup time requirement (s)
Practical Notes
Always analyze timing at worst-case conditions: maximum propagation delay (slow process, high temperature, low voltage) and maximum setup time. Hold time violations must also be checked separately. FPGA tools perform static timing analysis automatically, but board-level timing between chips must be verified manually.
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 |
| Tpd | Propagation Delay | 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, Propagation Delay 22 ns, Setup Time 10 ns
- 2. The relation: Tmargin = Tclk − Tpd − Tsetup
- 3. Substitute: Tclk = 47 ns, Tpd = 22 ns, Tsetup = 10 ns
- 4. Result: Timing Margin = 15 ns
Worked examples
Minimum range
Given: Clock Period 0.47 ns, Propagation Delay 0.22 ns, Setup Time 100 ps
Result: Timing Margin = 150 ps
Low range
Given: Clock Period 4.7 ns, Propagation Delay 2.2 ns, Setup Time 1 ns
Result: Timing Margin = 1.5 ns
Typical
Given: Clock Period 47 ns, Propagation Delay 22 ns, Setup Time 10 ns
Result: Timing Margin = 15 ns
High range
Given: Clock Period 0.47 µs, Propagation Delay 0.22 µs, Setup Time 100 ns
Result: Timing Margin = 150 ns
Maximum range
Given: Clock Period 4.7 µs, Propagation Delay 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, Propagation Delay 0.22 ns, Setup Time 100 ps → 150 ps
Solve for Clock Period
Timing Margin 100 ps, Propagation Delay 0.47 ns, Setup Time 47 ps → 0.617 ns
Solve for Propagation Delay
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, Propagation Delay 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 |
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<p><a href="https://vbatpower.com/formulas/digital-setup-margin/">Setup Time Margin</a> Calculator by vbatpower.com</p>Frequently asked questions
How do you calculate Setup Time Margin?
Use Tmargin = Tclk − Tpd − Tsetup. With Clock Period 47 ns, Propagation Delay 22 ns, Setup Time 10 ns, Timing Margin works out to 15 ns.
What is the formula for Setup Time Margin?
The formula is Tmargin = Tclk − Tpd − Tsetup. Setup time margin determines whether a synchronous digital circuit will operate reliably at a given clock frequency.
How do you find Clock Period when you know the other values?
Rearrange for Clock Period: with Timing Margin 100 ps, Propagation Delay 0.47 ns, Setup Time 47 ps, Clock Period is 0.617 ns.
How do you find Propagation Delay when you know the other values?
Rearrange for Propagation Delay: with Timing Margin 100 ps, Clock Period 0.22 ns, Setup Time 47 ps, Propagation Delay is 73 ps.
What units does Setup Time 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
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