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DS00001898A-page 15

USB3280

6.2

High-speed Signaling Eye Patterns

High-speed USB signals are characterized using eye patterns. For measuring the eye patterns 4 points have been

defined (see Figure 6-3). The Universal Serial Bus Specification Rev.2.0 defines the eye patterns in several ‘templates’.

The two templates that are relevant to the PHY are shown below.

The eye pattern in Figure 6-4 defines the transmit waveform requirements for a hub (measured at TP2 of Figure 6-3) or

a device without a captive cable (measured at TP3 of Figure 6-3). The corresponding signal levels and timings are given

in table below. Time is specified as a percentage of the unit interval (UI), which represents the nominal bit duration for

a 480 Mbit/s transmission rate.

FIGURE 6-3:

EYE PATTERN MEASUREMENT PLANES

FIGURE 6-4:

EYE PATTERN FOR TRANSMIT WAVEFORM AND EYE PATTERN DEFINITION

USB Cable

Transceiver

Device Circuit Board

Transceiver

Hub Circuit Board

Connector

Traces

Traces

A

Connector

B

TP1

TP2

TP3

TP4

Differential

-400mV

Differential

400mV

Unit Interval

100%

Level 2

Level 1

Point 1

Point 2

Point 4

Point 3

Point 6

Point 5

0%

0 Volts

Differential