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FEATURES
Low Cost 3.3V-CMOS MxFE for
MCNS-DOCSIS, DVB, DAVIC Compliant
Set-Top Box and Cable Modem Applications
232 MHz Quadrature Digital Upconverter
12-Bit Direct IF D/A Converter (TxDAC+®)
Up to 65 MHz Carrier Frequency DDS
Programmable Sampling Clock Rates
Selectable Interpolation Filter
Analog Tx Output Level Adjust
12-Bit, 33 MSPS Direct IF ADC
Dual 8-Bit, 16.5 MSPS Sampling IQ ADCs
Two 12-Bit ⌺-⌬ Auxiliary DACs
Direct Interface to AD8321/AD8323 or AD8322/AD8327
PGA Cable Driver
APPLICATIONS
Cable Modems
Set-Top Boxes
GENERAL DESCRIPTION
The AD9877 is a single-supply Cable Modem/Set-Top Box
Mixed-Signal Front End. The device contains a transmit path
interpolation filter, a complete quadrature digital upconverter
and transmit DAC. The receive path contains a 12-bit ADC and
Dual 8-bit ADCs. All internally required clocks and an output
system clock are generated by the PLL from a single crystal or
clock input.
The transmit path interpolation filter provides upsampling factors
of 12ϫ or 16ϫ with an output signal bandwidth as high as 5.8 MHz.
Carrier frequencies up to 65 MHz with 26 bits of frequency tuning
resolution can be generated by the direct digital synthesizer (DDS).
The transmit DAC resolution is 12 bits and can run at sampling
rates as high as 232 MSPS. Analog output scaling from 0 dB to
7.5 dB in 0.5 dB steps is available to preserve SNR when reduced
output levels are required.
Mixed-Signal Front End
Set-Top Box, Cable Modem
AD9877
FUNCTIONAL BLOCK DIAGRAM
COS
Tx
Tx DATA
PLL
SPORT
PROFILE
12
INTERPOLATOR
FILTER
DDS
3
SIN
12
4
CONTROL FUNCTIONS
12
2
8
RxIQ DATA
Tx
DAC
CA
⌺-⌬
SDELTA0
⌺-⌬
SDELTA1
OSCOUT
ADC
I IN
ADC
Q IN
ADC
IF IN
Rx
8
12
RxIF DATA
AD9877
The 12-bit ADC has excellent undersampling performance allowing
it to deliver better than 10 ENOBs with IF inputs up to 70 MHz.
The 12-bit IF ADC can sample at a rate up to 33 MHz, allowing it
to process wideband signal inputs.
Two programmable sigma-delta DACs are available which can be
used to control external components such as variable gain amplifiers
(VGAs) or voltage controlled tuners.
The AD9877 integrates a CA port which enables a host processor
to control the AD8321/AD8323 or AD8322/AD8327 programmable gain amplifier (PGA) cable drivers via the MxFE SPORT.
The AD9877 is available in a 100-lead MQFP package. It
offers enhanced receive path undersampling performance and
lower cost, compared with the pin-compatible AD9873. The
AD9877 is specified over the extended industrial (–40oC to +85oC)
temperature range.
MxFE is a trademark of Analog Devices, Inc.
TxDAC+ 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, nor for any infringements of patents or other rights of third parties that
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
www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2001
