XRT75L00D Datasheet, PDF (39/92 Pages) Exar Corporation – E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER

REV. 1.0.2
XRT75L00D
E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER
TABLE 11: JITTER AMPLITUDE VERSUS MODULATION FREQUENCY (JITTER TOLERANCE)
BIT RATE
(KB/S)
34368
44736
44736
51840
STANDARD
INPUT JITTER AMPLITUDE (UI _P-P)
A1
A2
A3
ITU-T G.823 1.5
0.15
-
GR-499
5
0.1
-
CORE Cat I
GR-499
10
0.3
-
CORE Cat II
GR-253
15
CORE Cat II
1.5
0.15
F1(HZ)
100
10
10
10
MODULATION FREQUENCY
F2(HZ) F3(KHZ) F4(KHZ) F5(KHZ)
1000
10
800
-
2.3k
60
300
-
669
22.3
300
-
30
300
2
20
6.2 JITTER TRANSFER - RECEIVER/TRANSMITTER:
Jitter Transfer function is defined as the ratio of jitter on the output relative to the jitter applied on the input
versus frequency.
There are two distinct characteristics in jitter transfer: jitter gain (jitter peaking) defined as the highest ratio
above 0 dB; and jitter transfer bandwidth.The overall jitter transfer bandwidth is controller by a low bandwidth
loop,which is part of the XRT75L00D.
The jitter transfer function is a ratio between the jitter output and jitter input for a component, or system often
expressed in dB. A negative dB jitter transfer indicates the element removed jitter. A positive dB jitter transfer
indicates the element added jitter.A zero dB jitter transfer indicates the element had no effect on jitter.
Table 12 shows the jitter transfer characteristics and/or jitter attenuation specifications for various data rates:
E3
ETSI TBR-24
TABLE 12: JITTER TRANSFER SPECIFICATIONS
DS3
STS-1
GR-499 CORE section 7.3.2
Category I and Category II
GR-253 CORE section 5.6.2.1
The XRT75L00D meets the above Jitter Specifications.
6.3 JITTER GENERATION:
Jitter Generation is defined as the process whereby jitter appears at the output port of the digital equipment in
the absence of applied input jitter. Jitter Generation is measured by sending jitter free data to the clock and
data recovery circuit and measuring the amount of jitter on the output clock or the re-timed data. Since this is
essentially a noise measurement, it requires a definition of bandwidth to be meaningful. The bandwidth is set
according to the data rate. In general, the jitter is measured over a band of frequencies.
6.4 Jitter Attenuator:
An advanced crystal-less jitter attenuator is included in the XRT75L00D. The jitter attenuator uses the internal
reference clock.
In Host mode, by clearing or setting the JATx/Rx bit in the control register selects the jitter attenuator either in
the Receive or Transmit path. In Hardware mode, JATx/Rx pin selects the jitter attenuator in Receive or
Transmit path.
The FIFO is either a 16-bit, 32-bit or 128-bit register. In Host mode, the bits JA0 and JA1can be set to
appropriate combination to select the different FIFO sizes or to disable the jitter attenuator. In Hardware mode,
appropriate setting of the pins JA0 and JA1 selects the different FIFO sizes or disable the jitter attenuator. Data
is clocked into the FIFO with the associated clock signal (TxClk or RxClk) and clocked out of the FIFO with the
dejittered clock. When the FIFO is within two bits of overflowing or underflowing, the FIFO limit status bit, FL is
set to “1” in the Alarm status register. Reading this bit clears the FIFO and resets the bit into default state.
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