STANDARD PRODUCT
PM4351 COMET
DATA SHEET
PMC-1970624
ISSUE 10
COMBINED E1/T1 TRANSCEIVER
Jitter Generation
In the absence of input jitter, the output jitter shall be less than 0.025 UIpp. This
complies with the AT&T TR 62411 requirement of less than 0.025 UIpp of jitter
generation.
9.27 Timing Options (TOPS)
The Timing Options block provides a means of selecting the source of the
reference signal for the transmit digital PLL and the clock source used to derive
the output TCLKO signal.
9.28 Line Transmitter
The line transmitter generates Alternate Mark Inversion (AMI) transmit pulses
suitable for use in the DSX-1 (short haul T1), short haul E1, long haul T1 and
long haul E1 environments. The voltage pulses are produced by applying a
current to a known termination (termination resistor plus line impedance). The
use of current (instead of a voltage driver) simplifies transmit Input Return Loss
(IRL), transmit short circuit protection (none needed) and transmit tri-stating.
The output pulse shape is synthesized digitally with current digital-to-analog
(DAC) converters which produce 24 samples per symbol. The current DAC’s
produce differential bipolar outputs that directly drive the TXTIP[1:0] and
TXRING[1:0] pins. The current output is applied to a terminating resistor
(optional) and line-coupling transformer in a differential manner, which when
viewed from the line side of the transformer produce the output pulses at the
required levels and insures a small positive to negative pulse imbalance.
The pulse shape is user programmable. For T1 short haul, the cable length
between the TLONG and the cross-connect (where the pulse template
specifications are given) greatly affects the resulting pulse shapes. Hence, the
data applied to the converter must account for different cable lengths. For CEPT
E1 applications the pulse template is specified at the transmitter, thus only one
setting is required. For T1 long haul with a LBO of 7.5 dB the previous bits effect
what the transmitter must drive to compensate for inter-symbol interference; for
LBO’s of 15 dB or 22.5 dB the previous 3 or 4 bits effect what the transmitter
must send out.
Refer to the Operation section for details on creating the synthesized pulse
shape.
PROPRIETARY AND CONFIDENTIAL
62
PMC [ PMC-SIERRA, INC ]
