XR-T5793 Datasheet, PDF (11/16 Pages) Exar Corporation – Quad E1 Line Interface Unit

XR-T5793
SYSTEM DESCRIPTION
This device is a quad E1 transceiver which provides
electrical interface for 2.048Mbps applications. Its unique
architecture includes four receiver circuits that convert
CCITT G.703 compliant bipolar signals to TTL compatible
logic levels. Likewise, in the other direction, four
transmitters translate TTL compatible logic levels to
G.703 compatible bipolar signals.
This device supports two different types of loopback
functions. Each of four channels can be independently
looped either in local or remote sides digitally. The
remote loopback is performed between the receiver input
and transmitter output. To activate the remote loopback
on channel n, LOOPENn and LPMODn inputs are driven
high. Local loopback on channel n, can be established
similarly by driving LOOPENn high and clearing LPMODn
inputs. More than one channel can be tested
simultaneously.
driver. External resistors are used to maintain an
accurate source impedance that has a high return loss to
the transformer or the capacitor. Each of the drivers can
be individually disabled, this is required in fault tolerant
applications where redundancy is a requirement. During
power-down mode of operation the bipolar outputs can be
disabled.
To protect the data integrity during a brownout, the output
pulse amplitudes are reduced by a factor of 25% if the
supply drops below an internally set limit.
Transmission is possible either with or without a clock. If a
clock is used, the transmit input data must consist of
full-width NRZ pulses, and the transmitter output pulse
width is determined by the duty cycle of the clock. If the
transmit clock is tied high, the transmitter output pulses
are determined by the input data pulse width. In this
mode, RZ data must be supplied to the device.
RECEIVERS
Each of the four identical E1 line receivers will accept
bipolar signals meeting the CCITT G.703 pulse mask
requirements. Each input stage consists of a slicing
circuitry which samples the incoming pulses at a fixed
percentage of the signals maximum amplitude. The
slicing voltage level is generated using a precision peak
detector. The receiver section can tolerate up to 12dB of
line loss (measured at 1.024MHz).
A loss of signal (LOS) is detected on any inputs by input
fail circuitry. There is an independent LOS pin dedicated
for each of the receivers. The LOS detection is based on
signal energy instead of number of zeros.
A balanced signal (100Ω or 120Ω) must be coupled by a
transformer. An unbalanced signal (75Ω) may be coupled
via capacitor or a transformer.
TRANSMITTERS
This device contains four identical CCITT G.703
compliant transmitters which meet the return loss
requirements. Each transmitter is a single-ended voltage
TXP TXN
RXIN _RX
TX ^TXOUT
RXP RXN
LPMOD=0
LPEN=1
Remote Loopback
TXP TXN
RXIN _RX
TX ^TXOUT
RXP RXN
LPMOD=0
LPEN=1
Local Loopback
Figure 4. Loopback Configurations
Rev. 2.00
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