XRT6164_07 Datasheet, PDF (6/10 Pages) Exar Corporation – Digital Line Interface Transceiver

XRT6164
SYSTEM DESCRIPTION
The XRT6164 is a general purpose line interface chip
that contains the receive and transmit circuitry neces-
sary to convert TTL logic levels to a bipolar signal both
to and from a twisted pair cable.
Receiver
The XRT6164 receiver section converts a balanced
bipolar signal that has been attenuated and distorted
by up to 10dB of twisted pair cable to active-low TTL
compatible logic levels.
The cable is transformer coupled to the receiver differ-
ential inputs (RX+IP, RX-IP) which are biased through
the input transformer secondary winding by a voltage
generated on-chip (I/P BIAS). The bipolar receive
signal is applied to a peak detector, and to a pair of data
comparators. The peak detector output voltage
charges an external capacitor connected to PEAK
CAP. This voltage generates a data comparator bias
level that is approximately 50% of the peak input pulse
amplitude. Thus, data slicing is automatically accom-
plished at the optimum level over the full cable loss
range. TTL compatible output stages buffer the re-
ceiver digital outputs (S+R, S-R) and provide active
low signals corresponding to received positive and
negative input pulses.
Loss of input signal is detected by a comparator that
monitors input signal level. An active-low TTL compat-
ible logic level (RX ALARM) indicates signal loss.
Comparator hysteresis prevents chatter on this output.
Ping-pong operation is made possible by the time
compression multiplex control input (TCM CON). A
logic 0 applied to this pin during transmission stores the
peak detector output voltage by disconnecting the
peak detector storage capacitor charge and discharge
paths. Since the receive data comparator bias voltage
is stored during transmit mode, it is immediately
available when receive mode resumes.
Transmitter
The XRT6164 transmitter section contains two
matched open collector output drivers that are capable
of driving the line transformer directly with a current up
to 40mA. The transmitter output drivers include diode
clamps to ensure non-saturating operation. Transmit-
ter digital inputs, which are active-high, are TTL com-
patible. External resistors are used between the trans-
mitter outputs and the output transformer primary to set
the output pulse amplitude.
APPLICATION INFORMATION
Figure 2 shows a general line driver application circuit
using the XRT6164. This device converts bipolar
transmit and receive signals in the 64Kbps to
1.544Mbps range to active-low TTL compatible logic
levels.
Bipolar signals that have been attenuated and dis-
torted by twisted pair cable are transformer-coupled to
the line side of the XRT6164 as shown on the left side
of Figure 2. Suggested transformers for both the input
and output applications are the Pulse types PE-65535
or TTI–7147 for 64Kbps use and the PE-65835 for
1.544Mbps applications.
The right side of Figure 2 shows the TTL compatible
digital inputs and outputs. Please refer to the pin
description section of this data sheet for detailed
information about each signal.
Rev. 4.0.0
6