Advance Data Sheet, Rev. 2
April 1999
TLIU04C1 Quad T1/E1 Line Interface
35
Lucent Technologies Inc.
Microprocessor Mode
(continued)
Jitter Attenuator
(continued)
Jitter Transfer Function
The jitter transfer function describes the amount of jitter that is transferred from the input to the output over a range
of frequencies. The jitter attenuator exhibits a single-pole roll-off (20 dB/decade) jitter transfer characteristic that
has no peaking and a nominal filter corner frequency (3 dB bandwidth) of less than 4 Hz for DS1 operation and
approximately 10 Hz for CEPT operation. Optionally, a lower bandwidth of approximately 1.25 Hz can be selected
in CEPT operation by setting JABW0 = 1 (register 12, bit 5) for systems desiring compliance with ETSI-TBR12/13
jitter attenuation requirements. When configured to meet ETSI-TBR12/13, the clock connected to the XCLK input
must be
±
20 ppm. For a given frequency, different jitter amplitudes will cause a slight variation in attenuation
because of finite quantization effects. Jitter amplitudes of less than approximately 0.2 UI will have greater attenua-
tion than the single-pole roll-off characteristic. The jitter transfer curve is independent of data patterns. Typical jitter
transfer curves of the jitter attenuator are given in Figure 11 and Figure 13.
Jitter Accommodation
The minimum jitter accommodation of the jitter attenuator occurs when the XCLK frequency and the input clock’s
long-term average frequency are at their extreme frequency tolerances. When the jitter attenuator is used in the
LIU transmit path, the minimum accommodation is 28 UIp-p at the highest jitter frequency of 15 kHz. Typical
receiver jitter accommodation curves including the jitter attenuator in the LIU receive path are given in Figure 10
and Figure 12.
When the jitter attenuator is placed in the data path, a difference between the XCLK/16 frequency and the incoming
line rate for receive applications, or the TCLK rate for transmit applications, will result in degraded low-
frequency jitter accommodation performance. The peak-to-peak jitter accommodation (JAp-p) for frequencies from
above the corner frequency of the jitter attenuator (fc) to approximately 100 Hz is given by the following equation:
where:
f
data
= 1.544 MHz for DS1 or 2.048 MHz for CEPT;
for JABW0 = 0, fc = 3.8 Hz for DS1 or 10 Hz for CEPT,
and for JABW0 = 1, fc = 1.25 Hz for CEPT;
f
xclk
= XCLK tolerance in ppm;
f
data
= data tolerance in ppm.
Note that for lower corner frequencies, the jitter accommodation is more sensitive to clock tolerance than for higher
corner frequencies. When JABW0 = 1 and the jitter attenuator is used in the receive data path, the tolerance on
XCLK should be tightened to ±20 ppm in order to meet the jitter accommodation requirements of TBR12/13 as
given in G.823 for line data rates of ±50 ppm.
JAp-p
64
2
-----------------------2
f
xclk
f
data
π
f
c
–
(
)
f
data
–
UI
=