Broadband Modem
Mixed-Signal Front End
a
AD9875
FUNCTIO NAL BLO CK D IAGRAM
FEATURES
Low Cost 3.3 V-CMOS Mixed-Signal Front End (MxFE™
Converter for Broadband Modems
10-/12-Bit D/A Converter (TxDAC+®)
64/32 MSPS Input Word Rate
2ꢀ/4ꢀ Interpolating LPF or BPF Transmit Filter
128 MSPS DAC Output Update Rate
Wide (26 MHz) Transmit Bandwidth
Power-Down Mode
10-/12-Bit, 50 MSPS A/D Converter
Fourth Order Low-Pass Filter 12 MHz or 26 MHz
with Bypass
–6 dB to +36 dB Programmable Gain Amplifier
Internal Clock Multiplier (PLL)
Clock Outputs
)
PWR DN
AD9875
Tx QUIET
10
10
GAIN
Tx [5:0]
Tx SYNC
Tx+
Tx–
Tx
MUX
Kx INTERPOLATION
LPF/BPF
TxDAC+
PLL-A
ꢀ L
V
REF
GATE
FB
CLK-A
CLK-B
CLOCK GEN
VRC
OSCIN
PLL-B
ꢀ M/N
XTAL
Rx SYNC
Voltage Regulator Controller
48-Lead LQFP Package
Rx+
Rx–
Rx
MUX
PGA
PGA
Rx [5:0]
SPORT
LPF
ADC
10
APPLICATIONS
Powerline Networking
Home Phone Networking
xDSL
3
REGISTER
CONTROL
Broadband Wireless
Home RF
P RO D UCT D ESCRIP TIO N
The receive path LPF cutoff frequency can be programmed to either
12 MHz or 26 MHz. 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.
T he AD9875 is a single supply Broadband modem mixed-
signal front end (MxFE) IC. T he devices contain a transmit
path Interpolation Filter and DAC, and a receive path PGA,
LPF and ADC supporting 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.
T he AD9875 provides 10-bit converter performance on both
the T x and Rx paths.
T he AD9875 provides a voltage regulator controller (VRC) that
can be used with an external power MOSFET transistor to form
a cost-effective 1.3 V linear regulator.
T he digital transmit and receive ports are each multiplexed to a
bus width of 5/6 bits and are clocked at a frequency of twice the
10-bit word rate.
T he T xDAC+ uses a selectable digital 2× or 4× interpolation
low-pass or band-pass filter to further oversample transmit
data and reduce the complexity of analog reconstruction filtering.
T he transmit path signal bandwidth can be as high as 26 M H z
at an input data rate of 64 M SPS. T he 10-bit D AC provides
differential current outputs for optimum noise and distortion
performance. T he D AC full-scale current can be adjusted
from 2 mA to 20 mA by a single resistor, providing 20 dB of
additional gain range.
T he AD9875 ADC and/or DAC can also be used at higher
sampling rates as high as 64 MSPS in a 5-bit resolution non-
multiplexed mode.
The AD9875 is pin-compatible with the 12-bit AD9876. Both are
available in a space-saving 48-lead LQFP package. They are speci-
fied over the industrial (–40°C to +85°C) temperature range.
The receive path consists of a PGA, LPF, and ADC. The two-stage
PGA has a gain range of –6 dB to +36 dB, and is programmable
in 2 dB steps, adding 42 dB of dynamic range to the receive path.
MxFE is a trademark of Analog Devices, Inc.
T xDAC+ is a registered 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.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
Fax: 781/326-8703
www.analog.com
© Analog Devices, Inc., 2001
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