78P2344JAT
4-port E3/DS3/STS-1 LIU
with Jitter Attenuator
FEBRUARY 2004
DESCRIPTION
The 78P2344JAT is a low-power, 4-port
DS3/E3/STS1 Line Interface Unit (LIU) with
integrated Jitter Attenuator (JAT). It includes all the
required clock recovery and transmitter pulse
shaping functions for applications using 75-ohm
coaxial cable at distances up to 1350 feet. These
applications include DSLAMs, T1,3/E1,3 digital
multiplexers, SONET Add/Drop multiplexers, PDH
equipment, DS3 to Fiber optic and microwave
modems and ATM WAN access for routers and
switches.
The receiver recovers clock and data from a B3ZS
or HDB3 coded AMI signal. It can compensate for
over 12dB of cable and 6dB of flat loss. The
transmitter generates a signal that meets the
standard pulse shape requirements.
The
78P2344JAT includes optional B3ZS/HDB3 ENDEC
with a receive line code violation detector, loop-back
modes, Loss of Signal detector, clock polarity
selection, and the ability to receive a DSX3 monitor
signal.
FEATURES
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Transmit and receive interfaces for E3, DS3 and
STS-1 applications
Designed for use with 75 ohm coaxial cable
lengths up to 1350 ft
Receives DS3-high and DSX3 monitor signals
Local and Remote loopbacks
Selectable B3ZS/HDB3 ENDEC with line code
violation detector
Standards-based LOS detector
Optional serial-port based mode selection and
channel status monitoring
Adaptive digital clock recovery (uses line-rate
reference clock input)
Receive output clock maintains nominal line-rate
frequency at all times
Fully integrated Jitter Attenuation function
provided for all line rates (no external VCXO
required)
Jitter Attenuator configurable for transmit or
receive path
Transmit line fault monitor
Requires no external current-setting resistor or
loop filter components
Single 3.3V supply operation
Available in 100-pin Exposed Pad JEDEC LQFP
STANDARDS
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Telcordia GR-499-CORE and GR-253-CORE
ITU-T G.823, G.824, G.775, and G.703
ETSI TBR-24, ETS 300 686, ETS 300 687, and
ETS EN 300 689
ANSI T1.102-1993, T1.231-1997, T1.404-1994,
and T1.105.03b
BLOCK DIAGRAM
Controls
Flags
RLBK
LBO E3 DS3
TXEN
TPOS
TNEG
TCLK
Jitter
Attenuator
RPOS
RNEG
RCLK
B3ZS /
HDB3
Decoder
B3ZS /
HDB3
Encoder
Transmit
Monitor
TXNW
Pulse
Shaper
LOUTP
LOUTN
Attenuator
ENDEC
Data
Detector
Adaptive
Equalizer
AGC
LINP
LINN
MON
TCLKP
RCLKP
Power
Distribution
Clock
Recovery
Signal
Detector
LLBKA
LLBKB
Signals from
Adjacent Port
CS
SCK
SDI
SDO
Control
Registers
LOS
PDTX PDRX
CKREF
Each Channel
Master
Bias
Generator
CKREF
-1-
78P2344JAT
4-port E3/DS3/STS-1 LIU
with Jitter Attenuator
FUNCTIONAL DESCRIPTION
The 78P2344JAT contains all the necessary
transmit and receive circuitry for connection
between E3, DS3, or STS-1 line interfaces and
digital Framer/Mapper ICs.
OPERATING RATE
The Master Control Register (MSCR) determines
which mode the device operates in according to the
table below. The MSL0 pin is also provided for
mode selection in applications without a serial
control interface. Upon power-up or reset, the state
of the MSL0 pin is sensed and mapped into the DS3
and E3 register bits representing the appropriate
mode of operation. After power-up/reset, the state of
the MSL0 pin is ignored.
Standard
E3
DS3
STS-1
STS-1
MSL0 pin
L
H
Z
Z
DS3 bit
0
1
0
1
E3 bit
1
0
0
1
The jitter tolerance of 78P2344JAT meets the
requirements of ITU-T G.823 for E3 rates; the
requirements of ITU-T G.824 and Telcordia GR-499
(Cat I and II) for DS3 rates; and the requirements of
Telcordia GR-253 for STS1 rates.
With the Jitter Attenuator disabled, the jitter transfer
function meets the requirements of GR-499 for
Category II DS3 interfaces.
When the Jitter Attenuator is enabled, the
78P2344JAT meets the requirements of GR-499
and GR-253 for all categories of DS3/STS1
equipment and the ETSI TBR-24 requirements for
E3 rates.
To check conformance with other
standards,
please
refer
to
the
JITTER
ATTENUATOR TRANSFER FUNCTION section for
more detailed info.
RECEIVER MONITOR MODE
When in monitor mode, 20dB of flat gain is applied
to the incoming signal before it is fed to the receive
equalizer. This mode is controlled by the MON bit in
the Mode Control Register.
SIGNAL DETECT
When the received signal is below a minimum
threshold, the corresponding LOS signal (bit) is
asserted. A time delay is provided before this output
is active so that transient interruptions do not cause
false indications. The LOS signal can also be used
to trigger an interrupt on the INTRx pin when serial
interface control is not available. This is controlled
by setting the RXER bit in the Interrupt Control
Register (INTC).
Note: In DS3 or STS-1 mode, when LBO is not
enabled, the transmitters have to be properly
terminated to ensure reliable LOS detection. If a
transmitter is not terminated, the resultant 2x signal
is large enough to couple to the neighboring
receivers through the ESD diodes, causing false
Signal Detect indication.
RECEIVER OPERATION
The receiver input is either transformer-coupled or
capacitor-coupled to the line signal. In applications
where the highest performance and isolation are
required, a 1:1 transformer is used in the receive
path. In applications where isolation is provided
elsewhere in the circuit, capacitor coupling can be
used. The receiver input should be line terminated
externally with a termination resistor.
The AMI signal first enters an AGC, which has a
selectable gain range setting. In normal operation,
the AGC can compensate for signals with up to 6dB
of flat loss. When Receiver Monitor Mode is
enabled, the AGC can compensate for a DSX3
monitor signal with 16 to 20 dB of flat loss. The
signal then enters a high performance adaptive
equalizer. The equalizer is designed to overcome
inter-symbol interference caused by long cable
lengths. Because the equalizer is adaptive, the
circuit will work with all square-shaped signals such
as DS3-high or 34.368 Mbit/s E3. The variable gain
differential amplifier automatically controls the gain
to maintain a constant voltage level output
regardless of the input voltage level.
-2-
78P2344JAT
4-port E3/DS3/STS-1 LIU
with Jitter Attenuator
LOCAL LOOPBACK AND REDUNDANCY MUX
Each receiver has a 4-input MUX as shown in the
adjacent figure. In multiport applications where
redundant channels are required, the receiver MUX
can be configured to provide the necessary
multiplexing functions. This allows the user to use
one port as a redundant monitor for the other port.
The tables below show the register settings for
selecting the desired receiver input source.
LLBKA
(Port 1)
0
0
1
1
LLBKA
(Port 2)
0
0
1
1
LLBKA
(Port 3)
0
0
1
1
LLBKA
(Port 4)
0
0
1
1
LLBKB
(Port 1)
0
1
0
1
LLBKB
(Port 2)
0
1
0
1
LLBKB
(Port 3)
0
1
0
1
LLBKB
(Port 4)
0
1
0
1
Receiver #1 Input
Source
LINP1/LINN1
LOUTP1/LOUTN1
LINP2/LINN2
LOUTP2/LOUTN2
LOUTP3, LOUTN3
LOUTP1, LOUTN1
Transmitter
#1
00
01
10
11
LINP1, LINN1
Receiver
#1
LLBKA,B(1)
LOUTP2, LOUTN2
Transmitter
#2
00
01
10
11
LINP2, LINN2
Receiver
#2
LLBKA,B(2)
Receiver #2 Input
Source
LINP2/LINN2
LOUTP2/LOUTN2
LINP1/LINN1
LOUTP1/LOUTN1
Transmitter
#3
00
01
10
11
LINP3, LINN3
Receiver
#3
LLBKA,B(3)
LOUTP4, LOUTN4
Receiver #3 Input
Source
LINP3/LINN3
LOUTP3/LOUTN3
LINP4/LINN4
LOUTP4/LOUTN4
Receiver #4 Input
Source
LINP4/LINN4
LOUTP4/LOUTN4
LINP3/LINN3
LOUTP3/LOUTN3
Transmitter
#4
00
01
10
11
LINP4, LINN4
Receiver
#4
LLBKA,B(4)
When serial interface control is not available, the
respective LPBKx pin for each of the channels can
also be used to activate local loopback mode as
shown below. Note that redundant channel modes
can only be activated using the serial interface.
LPBKx
pin
L
Z
H
Loopback Mode
Normal Operation
Same as LLBKA,B = ‘00’
Remote (Digital) Loopback
Same as RLBK = ‘1’
Local (Analog) Loopback
Same as LLBKA,B = ‘01’
Note: The LLBKA and LLBKB bits are located in the
Mode Control Register (MDCR).
The Register
Control bit, REGEN, should be enabled when using
the register settings to avoid conflict with external
loopback setting pins.
-3-
78P2344JAT
4-port E3/DS3/STS-1 LIU
with Jitter Attenuator
B3ZS/HDB3 ENDEC WITH LINE CODE VIOLATION
DETECT
The 78P2344JAT includes a selectable B3ZS/HDB3
Encoder/Decoder (ENDEC). The ENDEC function
can be enabled or disabled through pin selection or
register setting as shown below.
ENDECB
bit/pin
0/L
1/H
RPOSx
NRZ data
Positive AMI
RNEGx
Receive Line Code
Violation Indicator
Negative AMI
On the transmit side, when the ENDEC is enabled,
NRZ input data is encoded to Positive and Negative
AMI logic data following the B3ZS (for DS3/STS-1)
or HDB3 (for E3) substitution codes. The NRZ data
is input to the TPOS pin as shown below:
ENDECB
bit/pin
0/L
1/H
TPOSx
NRZ data
Positive AMI
TNEGx
‘Don’t Care’
Negative AMI
TRANSMITTER OPERATION
Transmitters 1-4 are enabled by their corresponding
TXEN bit. When enabled, each transmitter accepts
logic level clock and data signals and generates
current pulses on the LOUTPx and LOUTNx pins.
When properly connected to a 1:2CT center-tapped
transformer, a standards compliant AMI pulse is
generated which can drive a 75
Ω
coaxial cable.
When the recommended transformer is used and
when DS3 mode is selected, the transmitted pulse
shape at the end of the 75
Ω
terminated cable of 0 to
450 feet will fit the DS3 template found in ANSI
T1.102-1993 and Telcordia GR-499-CORE. For
STS-1 applications, the transmitted pulse for a short
cable meets the requirements of Telcordia GR-253-
CORE. For E3 applications, the transmitted pulse
for a short cable meets the requirements of ITU-T
G.703.
In either DS3 and STS-1 modes, the LBOx pin or
LBO bit should be set high for short cable (< 225 ft),
and should be set low for long cable (> 225 ft). The
LBO settings are ignored in E3 mode.
RCLK/TCLK POLARITY REVERSAL
To simplify the interface with various framer circuitry,
TCLK polarity can be internally inverted by setting
the TCLKP bit, and RCLK polarity can be inverted
by setting the RCLKP bit. Both bits are located in
the Master Control Register (MSCR).
REMOTE (DIGITAL) LOOPBACK
When the Register Control bit, REGEN, is disabled
and the LPBKx pin is floating; or when the Register
Control bit, REGEN, is enabled and the RLBK bit is
set, RCLKx, RNEGx, and RPOSx outputs are
internally looped back to the TCLKx, TNEGx, and
TPOSx inputs respectively.
When the ENDEC is enabled, the decoder
generates a composite NRZ logic data stream
following the B3ZS (for DS3/STS-1) or HDB3 (for E3)
substitution codes via the RPOSx pins:
The decoder also detects Receive Line Code
Violations (RLCV) and outputs a pulse via the
RNEG pin. Three different classes of line code
violations are detected.
1) Too many zeros:
More than two (three)
consecutive zeros in B3ZS (HDB3) mode.
2) Not enough zeros between bipolar pulse (B)
and bipolar violation pulse (V): (B,V) for B3ZS.
(B,V) or (B,0,V) for HDB3.
3) Code violation: Even number of bipolar pulses
(B) detected between bipolar violation pulses
(V).
When the ENDEC is disabled, the 78P2344JAT
outputs a dual rail data stream via the RPOSx and
RNEGx pins. In this mode, the Framer/Mapper
providing the ENDEC function typically detects Line
Code Violations.
-4-
78P2344JAT
4-port E3/DS3/STS-1 LIU
with Jitter Attenuator
LINE BUILD-OUT
The Line Build-Out (LBO) function controls the
transmit amplitude and pulse shape in DS3 and
STS-1 modes. The selection of LBO depends on
the amount of cable the transmitter is connected to.
When less than 225 ft of cable is used, the
corresponding LBOx pin or LBO bit should be high.
When 225ft or more cable is used the corresponding
LBO setting (LBOx pin or LBO bit) should be low.
LBO can be controlled either from pins or from
register settings, depending on the status of the
Register Control bit, REGEN.
TRANSMIT ENABLE
The TXEN bit in the Mode Control Register controls
the transmitter output.
When logic zero, the
transmitter output is disabled. This feature is used to
disable ports as well as to multiplex two or more
transceivers to one port. The transmitter of any port
can also be disabled by floating the respective LBOx
pin, in which case it will also power-down the entire
transmitter.
See section on the Power-Down
Function for more info.
TRANSMIT MONITOR
The transmit monitor function detects activity on the
transmitter output at the LOUTPx and LOUTNx pins.
When there is a transmitter fault, in the case of an
open or short on the chip, the transformer, or the
circuit board, the transmit signal amplitude will be
altered. The transmit monitor detects the amplitude
of the driven signal. The TXNW signal (bit) goes
high when the amplitude of the transmit signal is
outside a valid amplitude range. When the signal
amplitude is either too high or too low for longer than
a specified duration, the TXNW bit goes high (See
Transmit Monitor Specifications, pg.28). The TXNW
signal can be also used to trigger an interrupt on the
INTRx pin when serial interface control is not
available.
JITTER ATTENUATOR
Jitter Attenuation function is provided on-chip. The
Jitter Attenuator can be configured to be in the
transmit or the receive path. When configured in the
transmit path, the input clock at TCLK pin is passed
through a very low bandwidth digital PLL. The
corresponding transmit data is buffered into a FIFO
and clocked out using the de-jittered output clock of
the PLL. When configured in the receive path, the
recovered clock is passed through the low
bandwidth digital PLL, and the corresponding
receive data is buffered into the FIFO and clocked
out using the de-jittered clock.
When serial interface control is not available, the
MSL1 pin is provided for global Jitter Attenuator
mode selection. Upon power-up or reset, the state
of the MSL1 pin is sensed and mapped into the
JAEN and JASL register bits for all channels,
representing the appropriate mode of operation.
After power-up or reset, the state of the MSL1 pin is
ignored. The state of the MSL1 pin, and the
corresponding Jitter Attenuator configuration is
shown below.
MSL1 pin
L
H
Z
PLL Bandwidth
A PLL response with effectively one pole below 27
Hz is adequate to meet the ETSI TBR24 E3
standards. A PLL response with one pole below 40
Hz is adequate to meet the GR-499 (Cat I) DS3
standards. One of two bandwidths can be selected
via register settings.
The PLL bandwidth is
proportional to the data rate as follows:
Line Rate
E3
DS3
STS1
JABW bit
0
1
0
1
0
1
PLL Bandwidth
(Hz)
*13
188
*17
245
20
*283
Jitter Attenuator Mode
Jitter Attenuator in receive path
Jitter Attenuator in transmit path
Jitter Attenuator disabled
The Jitter Attenuator can be configured
independently for each channel by writing to the
Jitter Attenuator Control Register (JACR) as follows:
JAEN
bit
0
1
1
JASL
bit
X
0
1
Jitter Attenuator Mode
Jitter Attenuator disabled
Jitter Attenuator configured
to be in the receive path
Jitter Attenuator configured
to be in the transmit path
* The default state of the JABW bit depends on
which line-rate is selected through the MSL0 pin. If
E3 or DS3 mode is selected, the default state is ‘0’.
If STS1 mode is selected, the default state is ‘1’.
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