Broadband Modem
a
Mixed-Signal Front End
AD9975
FEATURES
FUNCTIONAL BLOCK DIAGRAM
Low Cost, 3.3 V-CMOS, Mixed Signal, Front End
Converter for Broadband Modems
10-Bit D/A Converter (TxDAC+®)
50 MSPS Input Word Rate
2؋
Interpolating Low-Pass Transmit Filter
100 MSPS DAC Output Update Rate
Wide (21 MHz) Transmit Bandwidth
Power-Down Modes
10-Bit, 50 MSPS A/D Converter
Fourth Order LPF with Selectable Cutoff Frequency
Dual Mode Programmable Gain Amplifier
Internal Clock Multiplier (PLL)
Two Auxiliary Clock Outputs
AD9975
TXEN
RXEN
TX+
10
10
K
TxDAC+
TX–
TXCLK
RXCLK
CLK1
CLK2
ADIO[9:0]
CLK-GEN
OSCIN
XTAL
48-Lead LQFP Package
RX+
RX–
10
ADC
LPF
PGA
PGA
APPLICATIONS
Powerline Networking
Home Phone Networking
3
3
AGC[2:0]
SPORT
REGISTER
CONTROL
GENERAL DESCRIPTION
The filter cutoff frequency can also be tuned or bypassed where
filter requirements differ. The 10-bit ADC uses a multistage
differential pipeline architecture to achieve excellent dynamic
performance with low power consumption.
The AD9975 is a single-supply, broadband modem, mixed
signal, front end (MxFE™) IC. The device contains a transmit
path interpolation filter and DAC and a receive path PGA,
LPF, and ADC required for a variety of broadband modem
applications. Also on-chip is a PLL clock multiplier that pro-
vides all required clocks from a single crystal or clock input.
The digital transmit and receive ports are multiplexed onto a
10-bit databus and have individual TX/RX clocks and TX/RX
enable lines. This interface connects directly to Homelug 1.0
PHY/MAC chips from Intellon and Conexant.
The TxDAC+ uses a digital 2× interpolation low-pass filter to
oversample the transmit data and ease the complexity of analog
reconstruction filtering. The transmit path bandwidth is 21 MHz
when sampled at 100 MSPS. The 10-bit DAC provides differen-
tial current outputs. The DAC full-scale current can be adjusted
from 2 to 20 mA by a single resistor, providing 20 dB of additional
gain range.
The AD9975 is available in a space-saving 48-lead LQFP pack-
age. The device is specified over the commercial (–40°C to
+85°C) temperature range.
The receive path consists of a PGA, LPF, and ADC. The program-
mable gain amplifier (PGA) has two modes of operation. One
mode allows programming through the serial port and provides a
gain range from –6 dB to +36 dB in 2 dB steps. The other mode
allows the gain to be controlled through an asynchronous 3-pin
port and offers a gain range from 0 dB to 48 dB in 8 dB steps
with the use of an external gain stage. The receive path LPF
cutoff frequency can be selected to either 12 MHz or 26 MHz.
TxDAC+ is a registered trademark and MxFE is a trademark of Analog Devices, Inc.
REV. 0
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, norforanyinfringementsofpatentsorotherrightsofthirdpartiesthat
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices.
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Tel: 781/329-4700
Fax: 781/326-8703
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© Analog Devices, Inc., 2002