BCM312 5
PRODUCT
®
Brief
O F
B E N E F I T S
BCM312 5
QAMLink
®
UNIVERSAL TRANSMISSION SOLUTION
B C M 3 1 2 5
F E AT U R E S
S U M M A R Y
•
Integrated QAMLink
•
•
•
•
in-band receiver
10-bit A/D converter with input AGC amplifier
Variable symbol rate 256-QAM receiver
Digital demodulator, Nyquist filters, tracking loops,
and 32-tap adaptive decision feedback equalizer
ITU-T J.83 Annex A/B/C compatible FEC decoder
®
•
Universal set-top and cable modem front-end
supports the ITU-T J.83 Annex A/B/C standards, as
well as OpenCable™, DOCSIS/EuroDOCSIS, and
DVB/DAVIC
supporting physical layer requirements including
out-of-band
downstream channels (in-band and out-of-band) and
the upstream channel
and upstream blocks reduces board complexity and
system costs
count
•
Connects directly to Broadcom digital TV ICs
•
Represents a complete solution for dual
•
Integrated QPSK out-of-band receiver
•
•
•
•
•
Baseband interface to dual 6-bit A/D converters or IF
interface to signal A/D converter
Variable symbol rate QPSK receiver
Digital demodulator, Nyquist filters, tracking loops,
and 4-tap adaptive decision feedback equalizer
DigiCipher
®
II/DVB/DAVIC FEC decoder
MPEG transport output interface/DAVIC MAC
output interface
•
Integrated analog front end for the dual downstream
•
Serial control interface results in reduced overall pin
•
Out-of-band QPSK receiver provides flexibility for
IF or baseband inputs
VCXOs
•
Integrated upstream transmitter
•
Programmable Starvue
II/DOCSIS™/EuroDOCSIS™/DVB/ DAVIC FEC
encoder
•
Pre-equalization filter
•
Up to 6 MBaud variable rate QPSK/16-QAM modulator
•
10-bit D/A converter with output power control
interfaces
•
Single, low-cost crystal solution eliminates costly
•
Includes direct interface to the OpenCable point-of-
deployment (POD) module
channels
•
Control unit
•
•
Single device supports both 6-MHz and 8-MHz
•
Allows direct connection to Broadcom ICs to support
additional data and video channels for
DOCSIS/EuroDOCSIS/DAVIC systems and PVR set-
top boxes
•
BSC/SPI compatible interface for configuration and
device control
•
RF tuner control
160-pin PQFP package
Set-Top Box Block Diagram
In-Band Channel
BCM3125
QAMLink
®
Universal
Transmission
Solution
Audio
BCM7020/BCM7030
High Definition Video /
Graphics Subsystem
Video
Tuner
Out-of-Band Channel
Upstream Channel
CPU
I/O
Memory
B C M 3 1 2 5
O V E R V I E W
Variable
Interpolator
0–65 MHz
10-bit
D/A
Nyquist
α
= .25-.50
Pre-Equalizer
Starvue II
MCNS
DAVIC
US_CLK
US_DATA
US_ENAB
US_CLAV
US_SOC
DDS
Variable
Interpolator
Variable
Interpolator
Nyquist
α
= .25-.50
Nyquist
α
= .12-.18
Phase
Recovery
and
Variable
Interpolator
Nyquist
α
= .12-.18
32-tap
DFE
FEC
Amp Control
Amp Ctl.
ITU-T
J.83
Annex A/B/C
FEC
IB_CLK
IB_DATA
IB_SYNC
IB_VALID
IB_ERR
36/44 MHz
10-bit
A/D
DDS
Tuner Control
IB Tuner AGC
IF/BB I Channel
Tuner Ctl.
IB Acquisition and Tracking Loops
6-bit
A/D
IF/BB mode
Variable
Interpolator
Nyquist
α
= .30-.50
4-tap
Equalizer
Variable
Interpolator
Nyquist
α
= .30-.50
6-bit
A/D
JTAG Int.
JTAG Control
OOB
DCII
DAVIC
FEC
OB_CLK
OB_DATA
OB_SYNC
OB_VALID
OB_ERR
BB Q Channel
100-200 MHz LO
OOB AGC
Agile PLL
DDS
OB Acquisition and Tracking Loops
Micro Int.
Micro Control
The Broadcom
BCM3125
combines an in-band 256-QAM
receiver, an out-of-band QPSK receiver and a 4/16-QAM
transmitter, providing an integrated set-top box or cable modem
front-end solution.
The in-band receiver in the
BCM3125
directly samples a
36–44 MHz carrier frequency with a l0-bit A/D converter, which
is preceded by a programmable gain amplifier (PGA). The in-
band demodulator consists of a quadrature mixer and multirate
filters that convert the oversampled IF data stream to a baseband
complex data stream. The I and Q baseband signals are then
filtered by dual square-root Nyquist filters that can accommodate
rolloff factors of 12–18% for various ITU-T J.83 Annex A/B/C
applications. A 32-tap decision feedback equalizer (DFE) with 8
feed-forward taps and 24 feedback taps is implemented to
remove the ISI generated by worst-case coaxial cable and
wireless cable channels. The equalizer coefficients are updated
every baud cycle for fast convergence. Two distinct forward error
correction (FEC) methods are supported. The first standard, ITU-
T J.83 Annex A/C, is also referred to as the DVB, DVB
interactive or DAVIC standard. The second, ITU-T J.83 Annex
B, is variously known as DigiCipher
®
II, DOCSIS/EuroDOCSIS
and SCTE DVS-031.
Broadcom
®
, the pulse logo,
QAMLink
®
, and
Connecting everything
®
are trademarks of
Broadcom Corporation and/or its subsidiaries in the United States and certain other countries.
All other trademarks are the property of their respective owners.
The out-of-band receiver in the
BCM3125
contains a frequency
agile oscillator that can downconvert any channel in the
70–130 MHz frequency range to a SAW centered IF. The desired
channel is then subsampled by a 6-bit A/D converter at a rate that
is more than 4 times the symbol rate. An additional 6-bit A/D is
provided to allow for direct input of baseband signals
BCM3125
provides
complete
Starvue
II,
The
DOCSIS/EuroDOCSIS
and
DVB/DAVIC
compatible
4/16-QAM upstream burst FEC encoder and modulator
functionality. A 1-KB burst FIFO buffer provides input data rate
decoupling. The FEC encoder consists of a programmable
randomizer and Reed-Solomon encoder. There is also a
programmable preamble prepend, symbol mapper, and
transmitter pre-equalizer. The modulator consists of dual square-
root raised cosine filters with programmable excess bandwidth,
α=0.25
or
α=0.50,
interpolation filters, and a digital upconverter
which translates the shaped pulse to a digitally tunable RF center
frequency from 0–65 MHz. A 10-bit D/A then converts this
signal to an analog waveform with programmable output power
levels.
The
BCM3125
includes an BSC/SPI interface for setup and
control by the host processor. In addition, an RF tuner controller
is also provided.
®
BROADCOM CORPORATION
16215 Alton Parkway, P.O. Box 57013
Irvine, California 92619-7013
© 2002 by BROADCOM CORPORATION. All rights reserved.
3125-PB08-R 11.20.02
Phone: 949-450-8700
FAX: 949-450-8710
Email: info@broadcom.com
Web: www.broadcom.com
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