BOARDCOM BCM3125

BCM312 5
PRODUCT
Brief
®
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
•
supports the ITU-T J.83 Annex A/B/C standards, as
well as OpenCable™, DOCSIS/EuroDOCSIS, and
DVB/DAVIC
• Connects directly to Broadcom digital TV ICs
supporting physical layer requirements including
out-of-band
• Integrated QPSK out-of-band receiver
• Baseband interface to dual 6-bit A/D converters or IF
• Represents a complete solution for dual
•
•
• Integrated analog front end for the dual downstream
•
•
downstream channels (in-band and out-of-band) and
the upstream channel
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
and upstream blocks reduces board complexity and
system costs
• Serial control interface results in reduced overall pin
count
• Integrated upstream transmitter
• Out-of-band QPSK receiver provides flexibility for
• Programmable Starvue
•
•
•
IF or baseband inputs
• Single, low-cost crystal solution eliminates costly
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
VCXOs
• Includes direct interface to the OpenCable point-ofdeployment (POD) module
• Single device supports both 6-MHz and 8-MHz
channels
• Control unit
• Allows direct connection to Broadcom ICs to support
• BSC/SPI compatible interface for configuration and
•
B E N E F I T S
• Universal set-top and cable modem front-end
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
®
•
•
•
O F
additional data and video channels for
DOCSIS/EuroDOCSIS/DAVIC systems and PVR settop boxes
device control
• RF tuner control
160-pin PQFP package
Set-Top Box Block Diagram
In-Band Channel
Tuner
Out-of-Band Channel
Upstream Channel
BCM3125
QAMLink®
Universal
Transmission
Solution
Audio
BCM7020/BCM7030
High Definition Video /
Graphics Subsystem
CPU
I/O
Memory
Video
B C M 3 1 2 5
O V E R V I E W
Variable
Interpolator
10-bit
D/A
0–65 MHz
10-bit
A/D
36/44 MHz
Pre-Equalizer
Variable
Interpolator
Nyquist
α = .25-.50
Variable
Interpolator
Nyquist
α = .12-.18
FEC
Phase
Recovery
and
Variable
Interpolator
Nyquist
α = .12-.18
32-tap
6-bit
A/D
IF/BB I Channel
Variable
Interpolator
Nyquist
α = .30-.50
IF/BB mode
6-bit
A/D
BB Q Channel
100-200 MHz LO
Agile PLL
Variable
Interpolator
DDS
ITU-T
J.83
Annex A/B/C
FEC
DFE
IB Acquisition and Tracking Loops
IB Tuner AGC
MCNS
DAVIC
DDS
Tuner Ctl.
Tuner Control
Starvue II
DDS
Amp Ctl.
Amp Control
Nyquist
α = .25-.50
JTAG Int.
OOB
4-tap
DCII
Equalizer
DAVIC
Nyquist
α = .30-.50
OB Acquisition and Tracking Loops
FEC
Micro Int.
US_CLK
US_DATA
US_ENAB
US_CLAV
US_SOC
IB_CLK
IB_DATA
IB_SYNC
IB_VALID
IB_ERR
JTAG Control
OB_CLK
OB_DATA
OB_SYNC
OB_VALID
OB_ERR
Micro Control
OOB AGC
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 inband 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, ITUT 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
The
BCM3125
provides
complete
Starvue
II,
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 squareroot 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