TAN-042
Designing the XRT71D00 and the XRT73L00 Devices to
operate in the Host Mode, and to be accessed via a single Chip
Select pin.
Preliminary
July 19, 2001
Revision 1.03
21
5.0 POWER CONDITION CONSIDERATIONS FOR THE
XRT73L00 AND THE XRT71D00 DEVICES
The XRT73L00 is a 1-Channel DS3/E3/STS-1 Transceiver (Line Interface Unit) IC that
is designed for use in multi-standard Networking and Transmission Systems. Likewise,
the XRT71D00 is a 1-Channel DS3/E3/STS-1 Jitter Attenuator IC that is also designed
for use in these same multi-standard Networking and Transmission Systems.
The XRT73L00 device is a mixed signal device that supports the transmission and
reception of data at the DS3, E3 and STS-1 rates. Hence, this chip handles both digital
inputs and output signals (which switch at very fast rates and generate a lot electrical and
radio frequency noise). Additionally, this chip also consists of an independent sensitive
analog receiver. As a consequence, the user must be careful in how to handle the VDD
and GND pins, in order to ensure high-quality performance of the XRT73L00 device.
The XRT71D00 device is also a mixed signal device. This particular device consists of
an Analog and Digital PLL. Each of these PLLs is used to generate high-speed signals
that support loop filtering within the Jitter Attenuator IC. This loop filtering essentially
defines the Jitter Transfer Characteristics of the XRT71D00 device. As a consequence,
the user must also be careful in how to handle the VDD and GND pins, in order to ensure
high-quality performance of the XRT71D00 device.
In particular, the user’s PCB layout and handling of the VDD and GND signals must
accomplish the following:
1. It must provide good isolation between the Transmit and Receive signals.
2. It must provide good isolation between the Analog and Digital signals.
3. It must provide good isolation between signals from other components on the
board.
In many networking or transmission systems, the source of power is a DC-to-DC
converter, which uses a switching converter to transform a –48VDC input to a +3.3VDC
output. The switching converter typically uses a switching frequency from 20kHz to
1MHz and the 3.3VDC power normally carries a significant amount of “ripple” noise at
this switching frequency. This ripple noise can adversely affect performance of analog
circuits in the mixed signals devices (e.g., XRT73L00 and XRT71D00).
