The document outlines the USB 2.0 compliance testing process, focusing on electrical and physical layer tests to ensure reliable communication between USB entities. It details the necessary test points, compliance requirements, and the use of specific tools and fixtures for accurate signal quality measurements. Additionally, it emphasizes the importance of automation in simplifying the testing procedure and reporting results.

1. USB 2.0 Compliance Testing

2. Agenda
l Overview of USB 2.0 physical layer compliance
l Compliance test points
l Fixtures and probing
l Eye pattern measurement
l USB 2.0 electircal compliance tests
l Signal quality
l Packet parameters
l Chirp timing
l J/K SE0 NAK
l Receiver sensitivity
l Measurement example
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3. USB 2.0 Compliance Testing
Purpose
Ensure that USB entities (hub, host and device) reliably communicate
Originally performed during "plugfests"
Electrical measurements included in USB 1.0 and expanded in version
2.0 of the specification
Electrical tests measure the signal quality, speed negotiation and timing
of the interface signals
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4. Upstream and Downstream Tests
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5. USB 2.0 Electrical Compliance Tests
l Signal quality
l Signal amplitude and jitter
l Signaling rate
l Data packet content (sync field, etc.)
l Packet parameters
l Timing between transmit and response
l EOP width
l Chirp timing
l Timing and ability to shift from low speed to high speed when HS device
is connected
l J/K SE0 NAK
l Absolute voltage levels for J and K levels as well as single ended zero
(SE0) used for EOP
l Receiver sensitivty
l Minimum detectable signal at device receiver
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6. USB 2.0 Electrical Test Tool (USBHSET)
l Controls host computer placing DUT into test mode
l Designed to control Intel EHCI (Enhanced Host Control Interface)
l Available from USB-IF (www.USB.org)
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7. Test Points for Signal Quality Tests
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8. Optional and Mandatory Mask Templates
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9. Mask Template Region Definitions
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10. USB 2.0 Signal Quality Test Fixture
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11. Signal Quality Test Connections
Fixture using differential probe
Fixture using direct connecition
l Test fixture connects DUT to host running USBHSET
l Command DUT to transmit test packet
l Switch disconnects host and terminates transmit lines of DUT once packet transmission
begins
l DUT stops transmitting only when powered off
l Probe signal at termination using a differential probe ( minimum 2 GHz)
l Required for logo compliance: direct connection to 2 oscilloscope channels
(+ and -) using RF cables
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12. Considerations for fixture/probes
l Impedance matching is critical
l Must be 90Ω differential impedance over the operating frequency range
l Probe loading is also an important factor (loading increases with
frequency)
l Loading at 240 MHz is important for accurate amplitude measurement
l Frequency response of the measurement system
l Fixture + probe + oscilloscope
l High frequency loading and roll-off increases overshoot
l Low frequency flatness impacts signal amplitude
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13. Bandwidth – Requirements of the Test Signal
l Required scope bandwidth depends
on test signals frequency components
l e.g. digital “square” waveform is composed
of odd sine wave harmonics
Rule of thumb:
Amplitude
BWScope = 3 … 5x fmax of Test Signal
fFundamentalf3rd harm.f5th harm.
Frequency

14. Frequency Response and Measurement Accuracy
l Example of a well matched oscilloscope and probe
l Less than 0.25 dB loss at 240 MHz (11 mV or 3%)
l A system with 1 dB dip would result in a 49 mV error (10%)
l The compliance mask tolerance is 100 mV
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15. Probe Loading
R
Z 90Ω C R
2fRC  1
Probe loading
Impedance becomes small at high frequency due to
capacitance
For example, R = 1MΩ and C = 0.6 pf
Z = 1105Ω at 240 MHz resulting in an 8% amplitude error
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16. Fixture Loading
45Ω
45Ω
1
Vo  V   0.504 R 50
45( R  155.8) 0.509 for R=52Ω
1
(15.8  R ) *143 (4% termination error)
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17. USB 2.0 Test Packet
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18. Eye pattern of a data packet
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19. Eye Opening
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20. Signal Quality Test Results
l Signal waveform from test packet is acquired using a real
time oscilloscope
l Waveform processed to generate eye pattern and measure
key parameters
l Software supplied by instrument manufacturer or USB-IF
(USBETT)
l ESBETT required for logo certification
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21. High Speed Packet Parameters
l Downstream (from host) signal is slightly smaller than
upstream (from the DUT) signal
l Measure delay from host packet to DUT response
l Ensure that EOP has the proper length and sync field is the
correct number of bits
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22. Chirp Timing
Not allowed in a
HS device
l Device must switch to HS termination when connected to a
host
l Speed negotiation takes place using termination
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23. Chirp Timing
l Events occurring after HS device is connected to the host
l Switch from low speed to full speed termination
l Begin HS differential signaling
l Switch in HS termination
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24. Device J/K SE0 NAK
l J level ( 400 mV on + line 0 mV on – line)
l K level (400 mV on – line and 0 mV on + line)
l SE0 (single ended zero) both lines at 0 mV
l Used to acknowledge receipt of packet from host
l Measured using DMM or equivalent
l Cannot be accurately measured with a scope due to accuracy
requirement
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25. Suspend, Resume, Reset
suspend resume
l Suspend from high speed
mode
l Resume high speed mode
from full speed
l Reset from HS mode
l Pass/fail rather than
parametric reset
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26. Receiver Sensitivity
Cables to
AWG DUT
To DUT
fixture AWG
Switch out
To host Host during test
computer host
l Place DUT into SE0 NAK (loop back) mode
l Transmit IN packet to DUT from signal source (AWG) and
determine if ACK is sent from DUT
l Measure minimum level of IN packet where ACK occurs
l Measure maximum level of IN packet where ACK does not
occur
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27. Receiver Sensitivity
NAK
IN Packet
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28. Conclusion
l USB 2.0 requires both electrical and interoperability tests for
compliance
l Electrical testing requires signal integrity along with timing
measurements and is performed using a digital oscilloscope
l Specialized fixtures required to connect to and properly terminate the
signal
l Active differential probes can be used but direct connection is required
for full compliance
l USBHSET software is required to place the DUT into test modes
l Automation software is available to simplify the measurement
process, step through the test sequence and report test
results
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29. For more information
l Visit http://rohde-schwarz-scopes.com
l Call (888) 837-8772 to speak to a local Rohde & Schwarz
expert
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