DS3150

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1.2 Transmitter

Transmit Clock. The clock applied at the TCLK input is used to clock in data on the TPOS/TNRZ and

TNEG pins. If the jitter attenuator is not enabled in the transmit path, the signal on TCLK is the transmit

line clock and must be transmission quality (i.e.,

±20ppm frequency accuracy and low jitter). If the jitter

attenuator is enabled in the transmit path, the signal on TCLK can be jittery and/or periodically gapped

(not exceeding 8 UI) but must still have an average frequency within

±20ppm of the nominal line rate.

When enabled in the transmit path, the jitter attenuator generates the transmit line clock from the signal

applied on the MCLK pin. The signal on MCLK must, therefore, be a transmission-quality clock

(

±20ppm frequency accuracy and low jitter). The duty cycle of TCLK is not restricted as long as the high

and low times listed in Section 3 are met.

To support a glueless interface to a variety of neighboring components, the polarity of TCLK can be

inverted using the ICE input pin. See the ICE pin description in Table 2-A for details.

Framer Interface Format and the B3ZS/HDB3 Encoder. Data to be transmitted can be input in

either NRZ or bipolar format. To select the bipolar format, wire the

ZCSE input pin high. In this format,

the B3ZS/HDB3 encoder is disabled, and the data to be transmitted is sampled on the TPOS and TNEG

input pins. Positive-polarity pulses are indicated by TPOS = 1 while negative-polarity pulses are indicated

by TNEG = 1. TPOS and TNEG should not be active at the same time.

To select the NRZ format, wire

ZCSE low. In this format, the B3ZS/HDB3 encoder is enabled, and the

data to be transmitted is sampled on the TNRZ pin. The TNEG pin is ignored in NRZ mode and should

be tied low.

Pattern Generation. The transmitter can generate a number of different patterns internally, including

unframed all ones (E3 AIS), 1010…, and DS3 AIS. See Figure 1-5 for the structure of the DS3 AIS

signal. The TDS0 and TDS1 inputs are used to select these on-board patterns. Table 2-B indicates the

possible selections.

Waveshaping, Line Build-Out, Line Driver. The waveshaping block converts the transmit clock,

positive data, and negative data signals into a single AMI signal that meets applicable

telecommunications standards when transmitted on 75

W coaxial cable. Table 1-C through Table 1-G and

Figure 1-4 show the waveform template specifications and test parameters from ANSI T1.102, Telcordia

GR-253-CORE and GR-499-CORE, and ITU-T G.703.

Because DS3 and STS-1 signals must meet the waveform templates at the cross-connect through any

cable length from 0 to 450 feet, the waveshaping circuitry includes a selectable LBO feature. For cable

lengths of 225 feet or greater, the LBO pin should be low. When LBO is low, output pulses are driven

onto the coaxial cable without any preattenuation. For cable lengths less than 225 feet, LBO should be

high. When LBO is high, pulses are preattenuated before being driven onto the coaxial cable. The LBO

circuitry provides attenuation that mimics the attenuation of 225 feet of coaxial cable.

To power down the transmitter and tri-state the TX+ and TX- output pins, pull the

TTS input pin low.

Interfacing to the Line. The transmitter interfaces to the outgoing DS3/E3/STS-1 coaxial cable (75

W)

through a 2:1 step-down transformer connected to the TX+ and TX- output pins. Figure 1-2 shows the

arrangement of the transformer and other recommended interface components.