XRT75VL00D datasheet(30/92 Pages) EXAR

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XRT75VL00D

E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER

REV. 1.0.3

An example of B3ZS encoding is shown in Figure 14. If the encoder detects an occurrence of three

consecutive zeros in the data stream, it is replaced with either B0V or 00V, where ‘B’ refers to Bipolar pulse

that is compliant with the Alternating polarity requirement of the AMI (Alternate Mark Inversion) line code and

‘V’ refers to a Bipolar Violation (e.g., a bipolar pulse that violates the AMI line code). The substitution of B0V or

00V is made so that an odd number of bipolar pulses exist between any two consecutive violation (V) pulses.

This avoids the introduction of DC component into the line signal.

4.2.2

HDB3 Encoding:

An example of the HDB3 encoding is shown in Figure 15.If the HDB3 encoder detects an occurrence of four

consecutive zeros in the data stream, then the four zeros are substituted with either 000V or B00V pattern. The

substitution code is made in such a way that an odd number of bipolar (B) pulses exist between any

consecutive V pulses. This avoids the introduction of DC component into the analog signal.

NOTES:

When Dual-Rail data format is selected, the B3ZS/HDB3 Encoder is automatically disabled.

In Dual-Rail format, the Bipolar Violations in the incoming data stream is converted to valid data pulses.

Encoder and Decoder is enabled only in Single-Rail mode.

4.3

TRANSMIT PULSE SHAPER:

The Transmit Pulse Shaper converts the B3ZS encoded digital pulses into a single analog Alternate Mark

Inversion (AMI) pulse that meet the industry standard mask template requirements for STS-1 and DS3. See

Figure 8 and Figure 9.

FIGURE 14. B3ZS ENCODING FORMAT

FIGURE 15. HDB3 ENCODING FORMAT

TClk

Line

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TClk

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