USB3.2 Transmitter specification Rev1.0 (section 6.7.2) defines a Low Power Transmitter operation.
In addition to the full swing transmitter specification, an optional low power swing
transmitter is also specified for SuperSpeed applications. A low power swing transmitter is
typically used in systems that are sensitive to power and noise interference, and have a
relatively short channel. The requirement as to whether a transmitter needs to support full
swing, low power swing, or both swings, is dependent on its usage model. All SuperSpeed
transmitters must support full swing, while support for low power swing is optional. The
method by which the output swing is selected is not defined in the specification, and is
implementation specific.

LFPS Tx test procedures specific for Captive Cable devices are included in the below document.

More details may be found in the document located here.

Receiver Sensitivity (EL_17) and Squelch (EL_16) Histogram measurement areas defined

The histogram measurements for EL_16 and EL_17 are to be taken in the multi-bit areas at the end of the data packet as these areas are the least likely to be affected by reflections.

The waiver is derived like this:

Receiver Sensitivity and Squelch measurements are supposed to be made at the upstream port pins as defined in Table 7-3 and Figure 7-12 of the USB 2.0 Specification. However, the test fixture used at USB-IF workshops and test facilities does not permit measurement at the upstream port pins. Because the voltage at the measurement point is higher than at the upstream port, the USB-IF provides a 50mV allowance for the voltage drop between the two points. Again, the voltage at the measurement point is higher than at the upstream port pins, so the 50mV allowance has to be added to the spec requirement -- not subtracted.

Voltage is differential, so there is a positive and negative voltage level. The text of the waiver was meant to add 50 to the positive voltage and add -50 to the negative voltage.

EL_16

The USB 2.0 specification in Section 7.1.7.2 requiressquelch (EL_16) to occur below 100mV magnitude. So no packets must be acknowledged between -100mV and +100mV. This has always been the requirement. Full squelch may occur at higher voltages, but it is mandatory between -100mV and +100mV.

The USB-IF applies the specification requirement (100mV) to measurements made at the test fixture instead of the upstream port. So the voltage drop acts like a built-in waiver for test procedure EL_16. Thus, THERE IS NO 50mV WAIVER FOR EL_16. The HS Test Procedure is incorrect for stating a waiver for EL_16.

EL_17

Receiver sensitivity requires all packets to be reliably received down to 150mV magnitude. Packets may be received at lower voltages, but it is mandatory at levels above 150mV magnitude. Again, this measurement is to be made at the upstream pins but the test fixture does not allow this. So the USB-IF grants a generous 50mV waiver to compensate for the voltage drop away from the upstream pins. Thus, the USB-IF requires packets to be reliably received at levels above 200mV for EL_17. Packets can, but do not need to be, received between -200mV and +200mV.

So looking at EL_16 and EL_17 together with the waiver, the graph looks like this:

Please note that it is the combination of EL_16 and EL_17 that validates the 'transmission detection envelope' defined in section 7.1.4.2 of the USB 2.0 Specification.

Examples

Example 1:
A device exhibits full squelch below 300mV magnitude.

• EL_16 is a pass because full squelch occurs below 100mV magnitude.
• EL_17 fails because packets are not reliably received above 200mV with the waiver

• EL_16 is a pass because squelch occurs below 100mV magnitude
• EL_17 is a pass because packets are reliably received above 150mV magnitude

• EL_16 is a fail because packets are received below 100mV magnitude
• EL_17 is a pass because packets are reliably received above 150mV magnitude

• EL_16 is a pass because squelch occurs below 100mV magnitude
• EL_17 is a waiver because packets are reliably received within 50mV of 150mV magnitude

• EL_16 is a pass because squelch occurs below 100mV magnitude
• EL_17 is a fail because packets are not reliably received within 50mV of 150mV magnitude

An Engineering Change Notice to the USB 2.0 Specification named 'Suspend Current Limit Changes' has been issued in April 2008. This ECN changes the maximum ICCSL value to 2.5mA.

The purpose of this ECN is to allow any USB peripheral to consume up to 2.5mA during suspend. It does not matter whether the peripheral is low-power or high-power, and it does not matter whether remote wakeup is enabled.

Please note, however, that the InterChip suspend current requirements does not change and remains at 150uA.

The 'Suspend Current Limit Changes' ECN is included with the download of the USB 2.0 Specification.

The USB Electrical Analysis Tool, USBET, has a major update and is available for download. With a new name and version, USBET20, version 1.20, is the only official electrical analysis tool of the USB-IF. There are no changes in measurements or pass/fail criteria, however. Please see the USB Tools webpage for download information.

Once installed, documentation can be found at: Start->All Programs->USB-IF Test Suite->USBET20->Documentation

For best results, please use the new Hi-Speed Signal Quality Test Fixture.

EL_22 - Interpacket Delay for Hosts with Embedded Hubs

Hosts are permitted to embed a high-speed hub and expose the hub's downstream ports. Because the embedded hub must relay the data of the host, the interpacket gap timing is affected when transmitting after receiving a packet.

Section 7.1.19.2 of the USB 2.0 Specification identifies high-speed delay times for cables and hubs. With a max propagation of 26ns for a cable and a max hub repeater delay of 36 bits +4ns (Test Spec EL_48), there is sufficient information for determining what the maximum response time to a device packet behind one tier of hubs should be.

Max delay from downstream port of hub to the downstream port of the host is:

Multiplied by two since it is a 'round trip' yields:

Add in the max turnaround time for the host, 192bits

So the maximum interpacket delay of a host's response to a device is <= 264 bit times + 60ns, which equates to 610ns or 292 bit times.

Measurement Method

A region starts when the current rises above 100 mA and ends when the current is below 100 mA for at least 100 µs. There may be multiple regions during the 100mS period. The analysis tool calculates the charge above 100 mA in each region. The charge of each region is listed in the report. Pass or fail is based on the region with the largest charge. The regions are shown on the plot by vertical yellow lines marking the start and end of each region.

Effective January 2019, the following requirement is deprecated.

Revision 2.0 of the USB On-The-Go Supplement defines an Attach Detection Protocol (ADP) for hosts and peripherals. This protocol enables peripherals and hosts to detect when a device attach occurs when VBus is turned off. In order for ADP to work from a host's perspective, peripherals are required to have a minimum of 1uF (C_RPB) capacitance on their VBus pin.

This ECN is part of the download of the USB 2.0 Specification and should be reviewed for specific details.

The USB-IF no longer requires EL_8: Test_J and Test_K to be performed as a condition for USB Certification. USB certification of high-speed USB devices (hosts, hubs and peripherals) no longer requires execution or passing of EL_8: Test_J and Test_K tests. EL_8 is defined in the USB 2.0 Electrical Test Specification and measures the data line voltage when driven high. The nature of this test measures the DC voltage level of the data line when driven, which is not a real-world representation of the functionality of the

There has always been a problem accurately measuring rise and fall times, especially on high speed devices. The measurement of interest is the edge rate, or slew rate, during the state change time. To help improve accuracy of the measurement, the USB-IF is standardizing on one test fixture for high-speed signal quality.

Aside from the fixturing and probes used to take the measurements, major contributors to the inaccuracies in these measurements are the shape of the edge, noise on the signal and the method of calculating the 10% and 90% points as defined in Sections 7.1.2.1 and 7.1.2.2 of the USB 2.0 Specification.

A waveform with slow corners (see sample eye diagram below) will result in a measured rise time that is slower than the actual edge rate would indicate. Also a small change in the position of the 10% and 90% points due to noise on the signal, etc., can cause a relatively large change in the measured rise time.

In order to optimize the repeatability of this measurement a slew rate, or edge rate, will be used. The results are expressed in terms of volts per micro-second ( V/us ). The conversion from rise time to slew rate uses the specified rise time over 80% of the nominal peak to peak signal amplitudes for each of the signaling rates.

High Speed:
Edge Rate(max-nominal) = (0.8V * 0.8)/300e-12 = 2133V/us (Volts per nano-second)
Edge Rate(max-warning) = (0.8V * 0.8)/100e-12 = 6400V/us (Volts per nano-second)

Full Speed:
Edge Rate(min) = (3.3V * 0.8)/20e-9 = 130V/us
Edge Rate(max) = (3.3V * 0.8)/4e-9 = 660V/us

Low Speed:
Edge Rate(min) = (3.3V * 0.8)/300e-9 = 8.8V/us
Edge Rate(max) = (3.3V * 0.8)/75e-9 = 35.2V/us

The actual slew rates are measured within the limits of the inner vertical eye of the far-end template for each test type. This method eliminates the subjective location of the vertical measurement points of the 10/90 method since a fixed voltage range is used.

Note that the calculations use the relaxed edge rate values of 300ps and 100ps for high-speed signaling. Calculating slew rates in USBET20 provides a common measurement method and should result in more consistent results between test equipment manufacturers, test facilities and USB-IF compliance workshops.

This measurement continues to be informational for FS and LS. However, this measurement is required for HS.

The current version of the USBET20 tool converts the slew rate into an equivalent rise and fall time.

In the 32-bit HSET utility, the EHCI driver is automatically swapped out with a proprietary EHCI test driver. This feature is not available in the 64-bit version (at this time). So you will need to manually replace the Windows EHCI driver with the test EHCI driver.

1. Within Device Manager, locate the Enhanced Host Controller located under the Universal Serial Bus controllers
2. Right click and Update the Driver Software
3. Select 'Browse the Computer for Driver Software'
4. Select 'Pick from a List of Device Drivers'
5. Make sure the 'Show compatible hardware' is checked
6. Select the 'Intel® USB 2.0 Enhanced Host Controller' then choose 'Have Disk'
7. Browse to C:Program FilesUSB-IF Test SuiteEHCI HS ELectrical Test ToolkitEHCIDrivers (or something similar) and locate the hcdriver.sys file. At this point, the 'Intel EHCI Compliance Test Tool' should be displayed in the hardware model window. Select it and choose 'Next.'
8. Windows Security will issue a warning. Install the driver anyway.
9. The Windows EHCI stack should now be replaced by the 'Intel EHCI Compliance Test Tool' driver the next time the PC is booted.
10. Reboot the system. The 'Intel EHCI Compliance Test Tool' driver is not signed and Windows will not automatically load an unsigned driver. Prior to Windows loading, press F8 and disable driver signature enforcement in order to load the unsigned driver.

To restore the original Windows EHCI driver, uninstall the Intel Test Stack driver and rescan for hardware changes.

The USB 2.0 Specification, which was written in the late 1990's, limits the transition time of hi-speed signals to 500ps, minimum. At that time, 500ps edge rates were considered very fast. However, process improvements and shrinkage in silicon design can easily cause hi-speed signals to transition significantly faster than the specification limit. Consequently, the USB-IF has relaxed the rise and fall time requirements for certification, but measuring these fast transitions are proving very problematic. Fast transitions act like a TDR pulse and signal quality test fixtures available today are not designed for these fast transitions. Also, the various differential probe designs of the scope manufactures react very differently to fast edges giving very different test results.

In order to obtain more consistent test measurements, the USB-IF is standardizing on a single test fixture for measuring hi-speed signal quality. This test fixture uses SMA connectors that eliminate the need to use probes. Studies have shown that eliminating the use of probes and using one test fixture design significantly improves the consistency and accuracy of hi-speed USB signal quality analysis.

The 'USB 2.0 Hi-Speed Signal Quality Test Fixtures' are available from the USB-IF eStore. USB cables are provided with the fixture but the SMA cables are not. The USB-IF does not sell or provide SMA cables and it is the vendor's responsibility to obtain them. One recommendation for SMA cables includes the following: Agilent 15443A Matched Cable Pair (or equivalent).

By August 2013, this test fixture will be used for all certification tests of hi-speed capable devices at all compliance workshops and by all authorized test laboratories. Device vendors may continue to use any test solution available that meets their needs, but USB-IF certification tests will be conducted using the new test fixture.