CX28331 datasheet(35/68 Pages) CONEXANT

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CX28331/CX28332/CX28333

2.0 Functional Description

Single/Dual/Triple E3/DS3/STS-1 Line Interface Unit

2.2 Transmitter

100985A

Conexant

2-3

2.2 Transmitter

This section describes the detailed operation of the various blocks in the CX2833i

transmitter.

2.2.1 AMI B3ZS/HDB3 Encoder

ENDECDIS and the E3MODE pins configure the encoder mode.

When ENDECDIS = 0, the encoder is receiving non-encoded Nonreturn to

Zero (NRZ) data on the TNRZ (TPOS) pin alone, and the NC (no connect)

(TNEG) pin is ignored.

Data is encoded into a representation of a three-level B3ZS (E3MODE = 0) or

HDB3 (E3MODE = 1) signal (conforming to the coding rules as specified in

Appendix A) before going on to the pulse shaper in the form of two binary signals

representing the positive and negative three-level pulses.

When ENDECDIS = 1, the encoder is disabled. The encoder passes

already-encoded data over TPOS (TNRZ) and TNEG (NC) to the pulse shaper.

The transmit digital data is clocked into the chip via a rising TCLK edge,

which must be equal to the symbol rate (line rate). A small delay added to the data

provides a certain amount of negative data hold time.

2.2.2 Pulse Shaper

The pulse shaper converts the two digital (clocked) positive and negative pulses

into a single analog three-level Alternate Mark Inversion (AMI) pulse. The pulses

are in Return to Zero (RZ) format, meaning that all positive and negative pulses

have a duration of the first half of the symbol period.

For the E3 rate (E3MODE = 1), the AMI pulse is a full-amplitude,

square-shaped pulse with very little slope.

Figure 2-2. Pulse Shaper

100604_008

Pulse

Shaper

LBO

Mode

LBO = 0

LBO = 1

+ Pulse

– Pulse

Line Driver

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