Connect-Tek USB-2 Bedienungsanleitung PDF herunterladen (Seite 2)

Application Note

www.tektronix.com/usb2

USB 2.0 Compliance Testing Basics

USB 2.0 is a serial bus that utilizes a 4-wire system — V

BUS

D-, D+ and Ground. D- and D+ are the prime carriers of the

information. V

BUS

supplies power to devices that derive their

primary power from the host or hub.

USB 2.0 describes the following speed selections and rise

times:

USB 2.0 devices can be either self-powered (having their own

power supply) or bus-powered (drawing power through the

host). It is imperative for the self-powered devices to draw

as little power as possible. Tests are outlined in the USB 2.0

speciﬁcations for this aspect.

USB 2.0 Electrical Tests

USB 2.0 electrical tests include signal quality, in-rush current

check, and drop and droop tests.

Signal Quality Test

Maintenance of signal quality is one of the keys to ensure that

a USB 2.0 device is compliant and will be awarded the USB

2.0 certiﬁed logo.

The signal quality test includes:

Eye Diagram testing

Signal rate

End of Packet (EOP) width

Cross-over voltage range

Paired JK Jitter

Paired KJ Jitter

Consecutive jitter

Rise time

Fall time

The eye diagram test is unique and the ﬁrst of its kind for serial

data applications.

The test set-ups for signal quality testing vary for upstream

and downstream testing. In the case of upstream testing,

signals transmitted from the device to the host are

captured, whereas in the case of downstream testing,

signals transmitted from the host are captured for testing.

Downstream testing is usually performed on ports of a hub.

Data Rates Rise Times

Low Speed (LS) 1.5 Mb/s 75 ns – 300 ns

Full Speed (FS) 12 Mb/s 4 ns – 20 ns

High-Speed (HS) 480 Mb/s 500 ps

1 2 3 4 5 6 7 ... 15 16

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