Rainbow Electronics DS2154 - Manual (Page 47)

DS2154
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nal is present at RTIP and RRING, a Receive Carrier
Loss (RCL) condition will occur and the RCLKO will be
sourced from the clock applied at the MCLK pin. If the
jitter attenuator is either placed in the transmit path or is
disabled, the RCLKO output can exhibit slightly shorter
high cycles of the clock. This is due to the highly over-
sampled digital clock recovery circuitry. If the jitter
attenuator is placed in the receive path (as is the case in
most applications), the jitter attenuator restores the
RCLK to being close to 50% duty cycle. Please see the
Receive AC Timing Characteristics in Section 14 for
more details. 12.2 TRANSMIT WAVESHAPING AND LINE
DRIVING
The DS2154 uses a set of laser–trimmed delay lines
along with a precision Digital–to–Analog Converter
(DAC) to create the waveforms that are transmitted onto
the E1 line. The waveforms created by the DS2154
meet the ITU G.703 specifications. See Figure 12–3.
The user will select which waveform is to be generated
by properly programming the L2/L1/L0 bits in the Line
Interface Control Register (LICR). The DS2154 can set
set up in a number of various configurations depending
on the application. See Table 12–2 and Figure 12–1.
LINE BUILD OUT SELECT IN LICR Table 12–2
LLL
210 APPLICATION TRANSFORMER
RETURN
LOSS
RT (SEE
FIGURE 12–1)
000 75 ohm normal (See Note 1) 1:1.15 step–up NM 0 ohms
001 120 ohm normal 1:1.15 step–up NM 0 ohms
010 75 ohm w/ protection resistors 1:1.15 step–up NM 8.2 ohms
011 120 ohm w/ protection resistors 1:1.15 step–up NM 8.2 ohms
100 75 ohm w/ high return loss 1:1.15 step–up 21dB 27 ohms
110 75 ohm w/ high return loss 1:1.36 step–up 21dB 18 ohms
100 120 ohm w/ high return loss 1:1.36 step–up 21dB 27 ohms
NOTE:
1. This LBO is not recommended for use in the A2 revision of the DS2154.
Due to the nature of the design of the transmitter in the
DS2154, very little jitter (less then 0.005 UIpp broad-
band from 10 Hz to 100 KHz) is added to the jitter pres-
ent on TCLK. Also, the waveforms that they create are
independent of the duty cycle of TCLK. The transmitter
in the DS2154 couples to the E1 transmit shielded
twisted pair or COAX via a 1:1.15 or 1:1.36 step up transformer as shown in Figure 12–1. In order for the
devices to create the proper waveforms, this trans-
former used must meet the specifications listed in
Table 12–3 The line driver in the DS2154 contains a cur-
rent limiter that will prevent more than 50 mA (rms) from
being sourced in a 1 ohm load.
TRANSFORMER SPECIFICATIONS Table 12–3
SPECIFICATION RECOMMENDED VALUE
Turns Ratio 1:1 (receive) and 1:1.15 or 1:1.36 (transmit)
±
5%
Primary Inductance 600 uH minimum
Leakage Inductance 1.0 uH maximum
Intertwining Capacitance 40 pF maximum
DC Resistance 1.2 ohms maximum