Rainbow Electronics DS2151Q - Manual (Page 29)

DS2151Q
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clock is applied to the ACLKI pin, then it should be tied to
RVSS to prevent the device from falsely sensing a
clock. See Table 12–1. If the jitter attenuator is either
placed in the transmit path or is disabled, the RCLK out-
put can exhibit short high cycles of the clock. This is due
to the highly oversampled digital clock recovery cir- cuitry. 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.
SOURCE OF RCLK UPON RCL Table 12–1
ACLKI PRESENT? RECEIVE SIDE JITTER
ATTENUATOR
TRANSMIT SIDE JITTER
ATTENUATOR
Yes ACLKI via the jitter attenuator ACLKI
No centered crystal TCLK via the jitter attenuator
12.2 Transmit Waveshaping and Line Driving
The DS2151Q 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 T1 line. The waveforms created by the DS2151Q
meet the latest ANSI, AT&T, and CCITT specifications.
See Figure 12–3. The user will select which waveform
is to be generated by properly programming the L0 to L2
bits in the Line Interface Control Register (LICR).
LBO SELECT IN LICR Table 12–2
L2 L1 L0 LINE BUILD OUT APPLICATION
0 0 0 0 to 133 feet/0 dB DSX–1/CSU
0 0 1 133 to 266 feet DSX–1
0 1 0 266 to 399 feet DSX–1
0 1 1 399 to 533 feet DSX–1
1 0 0 533 to 655 feet DSX–1
1 0 1 –7.5 dB CSU
1 1 0 –15 dB CSU
1 1 1 –22.5 dB CSU
Due to the nature of the design of the transmitter in the
DS2151Q, very little jitter (less then 0.005 UIpp broad-
Band from 10Hz 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 DS2151Q couples to the T1 transmit twisted pair
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 wavefroms, the transformer used must meet the
specifications listed in Table 12–3.