DP83847 datasheet(18/60 Pages) NSC

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NRZ data from the code-group encoder. The result is a

scrambled data stream with sufficient randomization to

decrease radiated emissions at certain frequencies by as

much as 20 dB. The DP83847 uses the PHY_ID (pins

PHYAD [4:0]) to set a unique seed value.

3.2.3 NRZ to NRZI Encoder

After the transmit data stream has been serialized and

scrambled, the data must be NRZI encoded in order to

comply with the TP-PMD standard for 100BASE-TX trans-

mission over Category-5 Unsheilded twisted pair cable.

3.2.4 Binary to MLT-3 Convertor / Common Driver

The Binary to MLT-3 conversion is accomplished by con-

verting the serial binary data stream output from the NRZI

encoder into two binary data streams with alternately

phased logic one events. These two binary streams are

then fed to the twisted pair output driver which converts the

voltage to current and alternately drives either side of the

transmit transformer primary winding, resulting in a minimal

current (20 mA max) MLT-3 signal. Refer to Figure 5 .

Figure 5. Binary to MLT-3 conversion

binary_in

binary_plus

binary_minus

binary_in

binary_plus

binary_minus

COMMON

DRIVER

MLT-3

differential MLT-3

DP83847 Datasheet(PDF) 18 Page - National Semiconductor (TI)