Modeling and Simulating SerDes Systems

Design, analyze, and deliver high-speed serial link models using SerDes Toolbox. From architecture exploration through IBIS-AMI model generation, covers the full workflow for NRZ and PAM-N links (PAM3 through PAM16).

When to Use

System design and architecture exploration

• Designing SerDes links for a target data rate, signaling scheme (NRZ, PAM4, PAM-N), and channel loss
• Evaluating equalization architectures (FFE, CTLE, DFE) and optimizing tap settings
• Sweeping design parameters to find optimal configurations
• Using industry reference designs (PCIe, USB4, DDR5, CEI, UCIe) as starting points
• Characterizing Tx/Rx analog effects (parasitic capacitance, rise time, termination impedance)
• Building custom datapath blocks for nonstandard equalization

Channel modeling and characterization

• Loading S-parameter Touchstone files into SerdesSystem
• Modeling channels with loss profiles, crosstalk (FEXT/NEXT), and aggressors
• Fitting CTLE transfer functions from measured data via ctlefit

IBIS-AMI model generation

• Building IBIS-AMI models for Tx, Rx, Redriver, or Retimer configurations
• Exporting to Simulink, configuring AMI parameters, and compiling .ami/.ibs/.dll/.so
• Scripting Simulink simulations and parameter sweeps with sim/parsim

Analysis and validation

• Running statistical and time-domain simulations
• Processing eye diagrams (eye height, eye width, COM, VEC, bathtub curves)
• Decomposing jitter (TJ, RJ, DJ, DDJ, DCD, ISI)
• Validating compiled AMI models against behavioral baselines
• Running compliance checks with eye masks and jitter budgets

When NOT to Use

• RF/microwave circuit design, antenna modeling, or baseband DSP filter design
• General Simulink model scripting unrelated to SerDes

Must-Follow Rules

System Setup

• SymbolTime / SampleInterval must yield an integer SamplesPerSymbol — fractional ratios cause silent errors
• `TxModel`/`RxModel` are `Transmitter`/`Receiver` objects — not cell arrays. Construct with Transmitter('Blocks', {block1, block2}). `Transmitter` requires single-quoted property names — Transmitter("Blocks", ...) throws an ismember error. Receiver and all other classes accept double quotes
• Signal conversion functions require column vectors — impulse2pulse, pulse2stateye, etc. error on row vectors
• Include `AnalogModel` and `JitterAndNoise` for realistic results — bare Transmitter/Receiver without analog models produce optimistic COM (1-2 dB higher). See reference/equalization-tuning.md for parameter guidance (rise time, parasitic C, termination R)

Equalization

• Set `WaveType` explicitly when using datapath blocks directly in MATLAB — Simulink sets this automatically, but MATLAB defaults to "Sample"
• Adapted DFE/CTLE parameters are in `results.outparams` — NOT on the block object. After analysis(), sys.RxModel.Blocks{k}.TapWeights still holds initial values. In system objects chains, adapted taps are the second output: [y, taps] = dfecdr(x)
• DFECDR Mode=0 is passthrough in Sample mode — DFE only applies with Mode≥1. Pre-load adapted taps from outparams with Mode=1 for instant convergence, or use Mode=2 with 10x EqualizationGain (9.6e-04) for self-converging chains
• Set `Modulation` on DFECDR for PAM-N in system objects chains — Simulink inherits it from the model workspace, but MATLAB defaults to 2 (NRZ). Without this, PAM4 DFE adaptation fails silently

Metrics and Waveforms

• `Metrics.summary.EW` is in picoseconds (already scaled) — do NOT multiply by 1e12. EH is in volts. PAM-N returns N-1 values per metric (e.g., PAM4 → 3 eyes, PAM8 → 7 eyes)
• Channel impulse from `analysis()` is in V/s — when using filter() for time-domain convolution, multiply by dt: filter(impulse * dt, 1, wave). Without scaling, amplitudes blow up by ~10^11
• `pulse2wave` operates on the stimulus provided — the output modulation depends on the input pattern (NRZ or PAM-N)

AMI and Simulink

• Init-Only models cannot adapt — if DFE taps or CDR converge at runtime, you need a Dual model (both Init and GetWave)
• AMI validation requires Signal Integrity Toolbox — serdes.AMI runner and the AMI Simulink block need both SerDes Toolbox and Signal Integrity Toolbox
• AMI GetWave: call in a chunked loop — serdes.AMI passes BlockSize (default 1024) to AMI_GetWave, so only BlockSize samples are processed per call. You must call the object in a for loop with BlockSize-length chunks. State is preserved between calls via the DLL memory handle
• AMI GetWave: set `SkipFirstBlock = false` when calling from MATLAB — the default (true) is for Simulink's internal signal buffering and causes the first block to pass through unprocessed
• AMI Init: `RowSize` must match impulse length — serdes.AMI crashes MATLAB (process termination, no error) if RowSize doesn't match numel(impulse)
• AMI generation requires Simulink model — use IbisAmiManager GUI or serdes.AMIExport with export() programmatically (see Programmatic AMI Generation)

Workflow

Design Exploration

Most projects start here. The goal is to find the right equalization architecture and settings for your channel.

1. Design — Create a SerdesSystem with Tx/Rx blocks and channel (loss model or S-parameters)
2. Analyze — Run analysis for statistical results, plotStatEye for eye diagrams, analysisReport for metrics
3. Sweep — Vary channel loss, FFE taps, CTLE gain, DFE taps, or jitter to map the design space
4. Compare — Evaluate architectures (FFE-only vs FFE+CTLE vs FFE+CTLE+DFE) using COM, eye height, eye width
5. Select — Choose the configuration that meets margin targets, then freeze equalization settings

Use SerdesSystem for programmatic exploration; serdesDesigner for interactive GUI work.

Waveform Processing

When you have a captured or imported waveform (e.g., from an oscilloscope or simulation) and want to equalize and analyze it directly:

1. Load — Import the waveform and define timing (SampleInterval, SymbolTime)
2. Equalize — Stream through datapath blocks (FFE, CTLE, DFECDR) with WaveType = "Sample"
3. Analyze — Build an eye diagram with eyeDiagramSI, extract metrics (eye height, COM, VEC)
4. Decompose jitter — Run jitter() on the equalized waveform for TJ, RJ, DJ, DDJ, ISI breakdown

DFECDR and DFE require a sample-by-sample for loop in Sample mode; FFE and CTLE accept full vectors. See reference/waveform-processing.md for the Direct Equalization pattern.

IBIS-AMI Model Delivery

When you need compiled models (.ami/.ibs/.dll/.so) for EDA tools or IP delivery:

1. Export — Call exportToSimulink(sys) to generate a Simulink model from the frozen design
2. Configure — Set AMI parameters, IBIS component/pin data, and model type via IbisAmiManager or serdes.AMIExport
3. Generate — Build .ami/.ibs and compile .dll/.so via serdes.AMIExport with export()
4. Validate — Load compiled DLL/SO with serdes.AMI, compare against behavioral reference (Init for impulse, GetWave for waveform)
5. Cross-check — The Simulink path (sim with Rx WaveOut) is the preferred time-domain reference. Compare against: statistical analysis(), system objects direct chain, and compiled AMI DLLs. See reference/simulink-serdes-simulation.md
6. Iterate — Fix discrepancies, re-export, re-validate until all paths agree

AMI Model Types

Choose the model type based on which equalization blocks need to adapt at runtime:

Every IBIS-AMI model implements AMI_Init (required), AMI_GetWave (optional), and AMI_Close (required) per the IBIS standard.

Key Classes

Datapath Blocks

Mode values: 0 = Fixed (not exported), 1 = Fixed (exported as AMI parameter), 2 = Adaptive (GetWave). Only CTLE, DFECDR, and DFE support Mode=2.

Set CTLE Specification before setting gain properties — using ACGain with the default spec triggers a warning. GPZ Matrix requires `Mode=1` for ConfigSelect to switch rows. See reference/equalization-tuning.md for the 4 specification options.

Patterns

Each reference file includes executable code patterns for its topic. Load the relevant reference before writing code — it contains correct calling conventions, constructor arguments, and property names. See the References table in Conventions below for the full routing map.

Common Mistakes

See reference/common-mistakes.md for 37 documented anti-patterns with wrong/correct code pairs covering API misuse, wrong property names, silent failures, and performance pitfalls.

Conventions

Design

• Use SerdesSystem for programmatic design; serdesDesigner for interactive exploration. Always run analysis/plotStatEye before exporting
• CRITICAL: ChannelLossFreq defaults to 5 GHz — always override to Nyquist (1/(2*SymbolTime)). Without this, 15 dB at 5 GHz becomes 40+ dB at Nyquist and the eye appears closed. Use SParameterChannel for real channels
• analysis() does not auto-optimize FFE taps — use canonical de-emphasis with sum(abs(taps)) ≈ 1.0
• DFE taps initialized to zero are optimized by the statistical solver automatically
• Industry reference designs: serdesDesigner or openExample('serdes/PCIe5TransmitterReceiverIBISAMIModelExample'). See reference/equalization-tuning.md for starting-point configurations

Visualization and Metrics

• All SerdesSystem plot methods (plotStatEye, plotImpulse, plotPulse, plotAlignedPulse, plotWavePattern) render into the current axes — use tiledlayout/nexttile or subplot for multi-panel layouts
• eyeDiagramSI (R2024a+) for waveform eye diagrams; jitter (R2024b+) for jitter decomposition
• DFECDR/DFE in "Sample" WaveType require scalar (sample-by-sample) input; FFE/CTLE accept full vectors
• When generating PRBS waveforms via pulse2wave, ask the user for PRBS order and symbol count — default PRBS-10 (1023 symbols) if unspecified
• Use serdes.utilities.SignalIntegrityColorMap (not hot/parula) for pulse2stateye plots. For compliance, use margin(eyeObj, eyeMask)
• See reference/visualization-and-metrics.md for all plot methods, metrics fields/units, eyeDiagramSI, and jitter

AMI Export and Validation

• Use serdes.AMIExport with export() for programmatic AMI generation — not slbuild (legacy, R2025b and earlier only)
• Validate compiled DLLs/SOs with serdes.AMI before sending to EDA tools — both Init (impulse correlation) and GetWave (waveform chain)
• Simulink is the preferred time-domain path — sim() with Rx WaveOut is the ground truth for adaptive systems. Compare against system objects chain and compiled AMI DLLs as cross-checks. Use the same PRBS stimulus across all time-domain paths
• AMI export parameters on Simulink blocks use *AMI suffix ('ModeAMI', 'TapWeightsAMI'); model-level settings go through IbisAmiManager or serdes.AMIExport
• No compiled DLLs/SOs ship with the toolbox. Cross-compile for Linux .so via serdes.utilities.createCrossCompiler

Script-First Workflow

For design, analysis, or sweep tasks — write code to .m files on disk, not inline MCP snippets. For quick one-off checks, inline evaluate_matlab_code is fine.

1. Create a .m file (e.g., serdes_pam4_design.m), run via run_matlab_file, iterate by editing and re-running
2. Deliver a polished script — %% Parameters block at top, %% Section headers, summary fprintf at end

References

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