Connect-Tek USB-2 Manuel d'utilisateur télécharger pdf (Page 5)

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Understanding and Performing USB 2.0 Physical Layer Testing and Debugging

Test Equipment

Drop tests require a multi-meter. The option USB compliance

test package aids in reporting the test results. The multi-meter

output for a drop test can be entered into the test package,

thus providing a consolidated report for the user.

Droop Test

Vdroop equals the difference in V

BUS

voltage when a no-load

condition is applied and when a 100 mA load is applied to the

port-under-test (PUT) (all other ports are fully loaded). The USB

2.0 speciﬁcation allows a maximum droop of 330 mV. The

droop test evaluates worst-case droop by alternately applying

a 100 mA load and no-load condition to the port under test

while all other ports are supplying the maximum load possible.

All V

BUS

measurements are relative to local ground.

Test Equipment

Droop tests require a real-time oscilloscope, such as a

DPO7254, and single-ended probes, like the TAP1500,

P6243

or P6245

. In addition, this testing requires

test software and a test ﬁxture, such as the option USB

compliance test package.

The test package automatically sets up the oscilloscope

for the desired test conﬁguration. Running the application

acquires the signal, provides the V

droop

measurement, and

subsequently provides a pass or fail indication and detailed

measurement results of the test.

USB 2.0 High-speed Tests

Fundamentally, USB 2.0 device compliance tests closely follow

the compliance test protocol for USB 1.1 devices. Primary

additions concern USB 2.0 high-speed mode. High-speed

mode adds a new level of complexity to USB device design.

USB 2.0 high-speed tests include receiver sensitivity, CHIRP,

monotonocity and impedance measurement tests.

Receiver Sensitivity Test

To increase robust operation in a noisy environment, a USB

2.0 high-speed device must respond to IN

*2b

tokens with

NAKs

*2b

when the signal level that equals or exceeds the

speciﬁed level. The test requires placement of the DUT in Test_

SE0_NAK mode. The host is then replaced by the signal from

a signal generator to continue to transmit IN tokens. The signal

amplitude is presented to the DUT at a level at or above

150 mV. At these levels, the DUT must be in the unsquelched

mode, responding to IN packets with NAKs. The amplitude is

then reduced to <100 mV and at this level, the DUT must be

squelched and does not respond to IN tokens with NAKs.

Requires a TPA-BNC adapter when used on an MSO/DPO5000 or DPO7000 Series model.

*2b

Please refer to the USB 2.0 speciﬁcations for more information about IN tokens and NAKs.

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Connect-Tek USB-2 Manuel d'utilisateur Page 5

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