Jitter Budget Calculator

Input Parameters

Responsive form grid: 3 columns large, 2 columns medium, 1 column mobile.

Engineering

Data Rate (Gbps)

Used to compute UI in picoseconds.

Target BER

Example: 1e-12, 1e-9, 1e-15

Setup + Hold Reserve (ps)

Receiver timing requirement.

Extra Eye Reserve (ps)

Design guard band.

TX Deterministic Jitter (ps)

Channel Deterministic Jitter (ps)

RX Deterministic Jitter (ps)

Duty Cycle Distortion (ps)

ISI Jitter (ps)

Crosstalk Jitter (ps)

TX Random Jitter RMS (ps)

Channel Random Jitter RMS (ps)

RX Random Jitter RMS (ps)

Reference Clock RJ RMS (ps)

CDR / PLL RJ RMS (ps)

Example Data Table

Parameter	Example Value	Unit	Purpose
Data Rate	10	Gbps	Converts timing to one UI.
Target BER	1e-12	ratio	Sets statistical jitter multiplier.
Total DJ Inputs	68	ps	Combined deterministic timing spread.
RJ RMS Inputs (RSS)	≈2.82	ps	Combined random RMS jitter.
Setup + Hold	35	ps	Receiver timing window reserve.
Extra Reserve	40	ps	Additional design margin.

Formula Used

All timing inputs are in picoseconds (ps). Data rate is in Gbps.

UI (ps) = 1000 ÷ Data Rate (Gbps)
Total DJ(pp) = TX DJ + Channel DJ + RX DJ + DCD + ISI + Crosstalk
Total RJ(rms) = √(TX RJ² + Channel RJ² + RX RJ² + RefClk RJ² + CDR RJ²)
Q-Factor = |N^-1(BER ÷ 2)|
RJ Contribution @ BER = 2 × Q × Total RJ(rms)
Total Jitter TJ(pp) = Total DJ(pp) + RJ Contribution @ BER
Allowed Budget = UI − (Setup/Hold Reserve + Extra Eye Reserve)
Margin = Allowed Budget − Total Jitter TJ(pp)

How to Use This Calculator

Enter your serial link data rate and target BER.
Fill deterministic jitter contributions from transmitter, channel, receiver, and pattern-related effects.
Enter random jitter RMS values for each independent source.
Add setup/hold reserve and any extra guard band you want to preserve.
Click Calculate Jitter Budget to see the summary above the form.
Use Download CSV for spreadsheets and Download PDF for review reports.

Why Jitter Budgeting Matters

Jitter budgeting converts timing uncertainty into a design control metric for serial links. In fast interfaces, each source adds picoseconds that reduce eye opening and raise error probability. A disciplined budget separates bounded deterministic effects from statistical random effects, then compares the combined total against the available unit interval after timing reserves. This method supports repeatable reviews, earlier risk detection, and clearer communication across signal integrity, hardware, and validation teams.

How the Calculator Builds Total Jitter

The calculator begins by converting data rate to unit interval using UI equal to 1000 divided by Gbps, which yields picoseconds per bit. Deterministic components are summed directly because bounded shifts accumulate linearly. Random components are combined with root sum square because they are treated as independent RMS processes. The selected BER target is converted to a Q factor, and that factor scales random jitter into a peak to peak contribution for budgeting analysis.

Source Allocation Strategy

Practical budgets improve when the path is partitioned into transmitter, channel, and receiver groups. Transmitter terms often include duty cycle distortion and output timing asymmetry. Channel terms usually capture intersymbol interference and crosstalk caused by loss, impedance discontinuities, and aggressor coupling. Receiver terms can include reference clock noise, CDR behavior, and sampling uncertainty. This separation highlights the highest leverage mitigation, such as equalization tuning, routing cleanup, or clock source improvement actions.

Margin and Compliance Interpretation

Margin interpretation matters as much as total jitter. Positive margin means the link still meets timing after setup and hold reserve plus extra guard band are removed from the unit interval. Negative margin indicates likely compliance risk, especially across voltage, temperature, and process corners. Teams should track margin in both picoseconds and UI, because absolute time drives implementation details while normalized UI values enable direct comparison across data rates and protocol families.

Validation and Lifecycle Use

During validation, engineers can use the output table to document assumptions and compare predicted jitter with oscilloscope or BERT measurements. If measured total jitter is higher than expected, revise source allocations instead of only increasing reserve. If margin is healthy, teams can test cost reductions, simpler routing, or higher throughput targets with evidence. Consistent budgeting also improves manufacturing daily handoffs, where pass fail criteria and debug thresholds must stay aligned with design intent.

FAQs

1. Which units should I enter?

Use picoseconds for all jitter values and reserves, and Gbps for data rate. The calculator converts data rate into unit interval automatically, then reports margin in both picoseconds and UI.

2. Why does BER change the final total jitter?

Lower BER targets require a larger Q factor, which increases the random jitter peak to peak contribution. That raises total jitter and usually reduces available margin.

3. Can I combine all random sources by simple addition?

If sources are independent, combine random jitter using root sum square. If two sources are correlated, estimate correlation separately and avoid blindly adding them as independent RMS terms.

4. Why are deterministic and random jitter treated differently?

Deterministic jitter is bounded and typically summed linearly. Random jitter is statistical, so the calculator converts RMS random jitter to a BER based peak to peak value using the Q factor.

5. What should I do if the margin is negative?

Negative margin means estimated total jitter exceeds the allowed budget after timing reserves. Reduce major jitter contributors, improve equalization, relax reserves where valid, or lower data rate for more UI.

6. How often should I update the budget during development?

Start with measured transmitter, channel, and receiver allocations, then compare calculator output with lab results. Update source values when new data arrives so reviews, compliance checks, and production limits remain consistent.