USB High-Speed Validation¶

This guide covers comprehensive high-speed validation techniques for USB implementations using oscilloscopes and BERTs, characterizing SuperSpeed, SuperSpeed+, and USB4 signals for compliance and design validation.

Equipment Requirements¶

Oscilloscope Requirements by USB Generation¶

USB Gen	Data Rate	Min Bandwidth	Recommended BW	Min Sample Rate
USB 3.2 Gen1	5 Gbps	8 GHz	12 GHz	25 GSa/s
USB 3.2 Gen2	10 Gbps	12 GHz	16 GHz	40 GSa/s
USB4 Gen2	10 Gbps	12 GHz	16 GHz	40 GSa/s
USB4 Gen3	20 Gbps	20 GHz	25 GHz	80 GSa/s
USB4 Gen4	40 Gbps	33 GHz	50 GHz	128 GSa/s

BERT Requirements by USB Generation¶

USB Gen	Data Rate	BERT Requirement	Pattern Support
USB 3.2 Gen1	5 Gbps	8+ Gbps	CP0-CP7
USB 3.2 Gen2	10 Gbps	15+ Gbps	CP0-CP8
USB4 Gen3	20 Gbps	25+ Gbps	Compliance patterns
USB4 Gen4	40 Gbps	50+ Gbps	Compliance patterns

Recommended Equipment¶

Real-Time Oscilloscopes:

Keysight Infiniium UXR (up to 110 GHz)
Keysight Infiniium MXR (up to 16 GHz)
Tektronix DPO70000SX (up to 70 GHz)
Teledyne LeCroy LabMaster (up to 100 GHz)

Sampling Oscilloscopes:

Keysight 86100D DCA-X
Tektronix DSA8300

BERTs:

Keysight M8040A/M8045A (64 Gbaud)
Anritsu MP1900A Signal Quality Analyzer

Oscilloscope Configuration¶

Vertical Settings¶

Parameter	USB 3.2	USB4 Gen3	USB4 Gen4
Scale	100-200 mV/div	100 mV/div	100 mV/div
Offset	Center	Center	Center
Coupling	DC	DC	DC
Impedance	50Ω	50Ω	50Ω
Bandwidth	Full	Full	Full

Horizontal Settings¶

Parameter	Recommendation
Time/Division	5-10 UI for waveform, 1-2 UI for eye
Sample Rate	Maximum available
Memory Depth	Sufficient for analysis type
Trigger Position	10% for packet capture

Trigger Configuration¶

Trigger Type	Application
Edge Trigger	Basic waveform capture
Pattern Trigger	Training sequence capture
Protocol Trigger	Link state capture
LFPS Trigger	Low-frequency signaling

Transmitter Testing with Oscilloscope¶

Output Amplitude Measurement¶

Test Point: At compliance point (typically after connector)

Tx Measurement Setup:

    DUT Tx ════ Test Fixture ════ Oscilloscope
                     │
              Compliance Point

Specifications:

Parameter	USB 3.2	USB4 Gen3
Vdiff (p-p)	800-1200 mV	800-1200 mV
Vcm	-150 to +150 mV	-200 to +200 mV

Rise/Fall Time Measurement¶

Parameter	USB 3.2 Gen1	USB 3.2 Gen2	USB4 Gen3
Rise Time (20-80%)	50-150 ps	30-100 ps	20-75 ps
Fall Time (80-20%)	50-150 ps	30-100 ps	20-75 ps

De-emphasis Measurement¶

USB uses de-emphasis (not pre-emphasis):

De-emphasis Measurement:

    First bit after    Subsequent bits
    transition         (de-emphasized)
         │                   │
         ▼                   ▼
    ────┬────┬────┬────┬────┬────
        │    │    │    │    │
      Full  De-emp De-emp

    De-emphasis ratio = 20 × log10(De-emp / Full) dB

Generation	De-emphasis
USB 3.2 Gen1	-3.5 dB
USB 3.2 Gen2	-3.5 dB or configurable
USB4 Gen3	Configurable presets

Transmitter Testing with BERT¶

BERT Tx Measurement Setup¶

    DUT Tx ════ Test Fixture ════ BERT Rx (Error Detector)
                     │
              Compliance Point

Pattern Selection for USB¶

Pattern	Application
CP0	Compliance pattern 0 (basic)
CP1-CP7	Additional compliance patterns
PRBS	Stress testing
Custom	Protocol-specific

Tx Measurements with BERT¶

Measurement	Method
Eye Height	BER contour scan
Eye Width	Timing bathtub
Jitter	TIE measurement
Amplitude	Statistical distribution

Receiver Testing with BERT¶

Stressed Eye Calibration¶

USB Stressed Eye Parameters (USB 3.2 Gen2 example):

Parameter	Value
Eye Height	50 mV minimum
Eye Width	0.3 UI minimum
SJ	Per specification
RJ	Per specification

Rx Sensitivity Testing¶

    BERT Tx (Stressed Eye) ════ Fixture ════ DUT Rx
            │                                   │
    Calibrated                           Loopback
    Impairments                          (internal)
                                              │
                                        BERT Rx

Procedure:

Calibrate BERT stressed eye output
Connect to DUT receiver
Configure DUT for loopback
Run BER measurement
Verify BER < 10^-12

Jitter Tolerance (JTOL) Testing¶

JTOL Test with BERT:

Inject sinusoidal jitter at specified frequency
Increase amplitude until BER exceeds threshold
Record maximum tolerated jitter
Repeat across frequency range
Compare to specification mask

Eye Diagram Analysis¶

Oscilloscope Eye Measurement¶

Configuration:

Enable eye diagram mode
Set clock recovery per USB specification
Accumulate 10,000+ waveforms
Enable mask testing

BERT Eye Measurement (BER Contour)¶

BER Contour Eye:

    Voltage
      ↑
      │  ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓
      │  ▓▓▓       ▓▓▓▓▓
      │  ▓   10^-12  ▓▓▓
      │  ▓    eye    ▓▓▓
      │  ▓▓▓       ▓▓▓▓▓
      │  ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓
      └─────────────────▶ Time

Eye Mask Testing¶

Parameter	USB 3.2 Gen1	USB 3.2 Gen2
Min Eye Height	150 mV	100 mV
Min Eye Width	0.4 UI	0.35 UI

LFPS Characterization¶

Low Frequency Periodic Signaling¶

LFPS is used for link initialization and power management:

LFPS Waveform:

    ─────┬─────┬─────┬─────┬─────┬─────┬─────
         │     │     │     │     │     │
    ─────┴─────┴─────┴─────┴─────┴─────┴─────
         │◀─────────────────────────────▶│
              LFPS Burst Duration

LFPS Measurements¶

Parameter	Specification
Frequency	20-50 MHz
Amplitude	200-1200 mV (diff)
Duty Cycle	40-60%
Burst Duration	Per LFPS type

Oscilloscope LFPS Measurement¶

Trigger on LFPS burst start
Measure frequency (cycle-to-cycle)
Measure amplitude (peak-to-peak)
Verify duty cycle
Measure burst timing

USB4 Specific Testing¶

Multi-Lane Capture¶

USB4 supports multiple lanes (×1, ×2):

Configuration	Description
Single Lane	1 Tx + 1 Rx
Dual Lane	2 Tx + 2 Rx (bonded)

Lane Bonding Verification¶

Measurement	Description
Lane-to-lane skew	Timing alignment
Lane amplitude matching	Signal uniformity
Lane training	Successful bonding

Tunneling Protocol Verification¶

USB4 tunnels multiple protocols:

Protocol	Verification
USB 3.2	Tunneled USB traffic
DisplayPort	Video tunneling
PCIe	PCIe tunneling

Protocol-Synchronized Capture¶

Training Sequence Capture¶

Sequence	Purpose	Trigger
TSEQ	Training sequence	Pattern trigger
TS1/TS2	Link training	Serial pattern
Compliance	Compliance mode	Mode entry

Link State Capture¶

State	Capture Method
Detect	LFPS trigger
Polling	Training pattern
U0	Normal data
U1/U2/U3	Power states

Jitter Analysis¶

Oscilloscope Jitter Measurement¶

Measurement	Method
TJ	Total jitter (TIE-based)
RJ	Random jitter extraction
DJ	Deterministic jitter
DDJ	Data-dependent jitter

BERT Bathtub Curve¶

Provides timing margin at target BER:

Bathtub Curve:

    BER
    │
10^-6┤▓▓                              ▓▓
     │  ▓▓                          ▓▓
10^-9┤    ▓▓                      ▓▓
     │      ▓▓                  ▓▓
10^-12┤       ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓
     └──┬───┬───┬───┬───┬───┬───┬──
        0   0.25  0.5  0.75  1.0
                   UI

Best Practices¶

Oscilloscope Best Practices¶

Practice	Rationale
Calibrate before test	Measurement accuracy
Use proper fixtures	Controlled impedance
De-embed cables/fixtures	Accurate DUT measurement
Sufficient accumulation	Statistical validity

BERT Best Practices¶

Practice	Rationale
Calibrate stressed eye	Specification compliance
Verify pattern lock	Valid measurement
Sufficient bit count	Statistical confidence
Document all settings	Reproducibility

Common Issues¶

Issue	Cause	Solution
Low eye height	Loss, noise	Check fixture, improve shielding
LFPS failures	Amplitude, timing	Verify LFPS generator
BER floor	Instrument noise	Improve isolation
Trigger instability	Signal quality	Adjust trigger settings

Test Configurations¶

Tx Compliance Test¶

    DUT Tx ════ Compliance Fixture ════ Oscilloscope/BERT
                       │
               Compliance Test Point

Rx Sensitivity Test¶

    BERT (Stressed Tx) ════ Fixture ════ DUT Rx
                                           │
                                     Loopback
                                           │
                                       BERT Rx

Eye Diagram Analysis - Eye measurement techniques
Jitter Measurement - Jitter analysis
S-Parameter Analysis - Channel characterization
Oscilloscope Fundamentals - Instrument basics
BERT Fundamentals - BER testing

References¶

USB-IF SuperSpeed Electrical Compliance Test Specification
USB4 Electrical Compliance Test Specification
USB-IF SigTest software documentation
Oscilloscope and BERT manufacturer application notes