CX28331/CX28332/CX28333
2.0 Functional Description
Single/Dual/Triple E3/DS3/STS-1 Line Interface Unit
2.2 Transmitter
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
E3
Mode
+ Pulse
– Pulse
LBO
LBO = 0
Pulse
Shaper
Line Driver
LBO = 1
100604_008
100985A
Conexant
2-3
CONEXANT [ CONEXANT SYSTEMS, INC ]
