DS2188
T1/CEPT Jitter Attenuator
www.dalsemi.com
FEATURES
PIN ASSIGNMENT
Attenuates clock and data jitter present in T1
or CEPT lines
Meets the jitter attenuation templates
outlined in TR62411, TR-TSY-000170,
G.735, and G.742
Only one external component required; either
a 6.176 MHz (T1) or 8.192 MHz (CEPT)
crystal
Selectable buffer size of 128 or 32 bits
Jitter attenuation is easily disabled
Single +5V supply; low-power CMOS
technology
Available in 16-pin DIP and 16-pin SOIC
(DS2188S)
Companion to the DS2186 Transmit Line
and DS2187 Receive Line Interface
DJA
1
16
VDD
RPOS
2
15
RRPOS
RNEG
3
14
RRNEG
RCLK
4
13
RRCLK
BDS
5
12
RST
TEST
6
11
BL
XTAL OUT
7
10
XTAL2
VSS
8
9
XTAL1
ORDERING INFORMATION
DS2188
DS2188S
DS2188N
DS2188SN
16 Pin dip
16 Pin SOIC
16 Pin dip
16 Pin SOIC
(0ºC-F70ºC)
(0º-+70ºC)
(-40ºC-+85ºC)
(-40ºC-+85-ºC)
DESCRIPTION
The DS2188 T1/CEPT Jitter Attenuator Chip contains a 128 X 2-bit buffer which, in conjunction with an
external 4X crystal, is used to attenuate the incoming jitter present in clock and data. The device meets all
of the latest applicable specifications including those outlined in TR 62411 (Accunet* T1.5 Service
Description and Interface Specifications, December 1990), TR-TSY-000170 (Digital Cross-Connect
System Requirements and Objectives, November 1985), and the CCITT Recommendations G.735 and
G.742. The DS2188 is compatible with the DS2180A T1/ISDN Primary Rate Transceiver and DS2181A
CEPT Transceiver and is the companion to the DS2187 T1/CEPT Receive Line Interface and DS2186
T1/CEPT Transmit Line Interface. It can also be used in conjunction with the DS2190 T1 Network
Interface Unit.
OVERVIEW
The RCLK input is fed to a 128 x 2-bit FIFO where it drives the write pointer for the positive (RPOS) and
negative (RNEG) data. The read pointer of the FIFO and RRCLK is generated by dividing the frequency
of the crystal connected to XTAL1 and XTAL2 by four. The frequency of the crystal is adjusted by a
DPLL to the long-term average frequency of RCLK. As long as the jitter present at RCLK is less than
120 unit intervals peak-to-peak (UIpp), then the FIFO buffer will be able to absorb the incoming jitter and
it will be attenuated in accordance with TR 62411 (December 1990). In this situation, the BL (Buffer
Limit) pin will remain low. Figures 1 and 2 illustrate the DS2188 Jitter Attenuator performance.
If the incoming jitter has excursions greater than 120 UIpp, then the crystal is adjusted to track the shortterm frequency variations of the incoming signal so that there is no loss of data. This adjustment is
accomplished by dividing the 4X crystal by either 3 ½ or 4 ½ instead of 4. When the incoming jitter is
1 of 10
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