BCM3125 Datasheet, PDF (2/2 Pages) Broadcom Corporation. – UNIVERSAL TRANSMISSION SOLUTION

BCM3125 OVERVIEW
0–65 MHz
Amp Control
36/44 MHz
Tuner Control
IB Tuner AGC
IF/BB I Channel
BB Q Channel
100-200 MHz LO
OOB AGC
10-bit
D/A
Amp Ctl.
DDS
10-bit
A/D
DDS
Tuner Ctl.
6-bit
A/D
IF/BB mode
6-bit
A/D
Agile PLL
DDS
Variable
Interpolator
Nyquist
α = .25-.50
Pre-Equalizer
Variable
Interpolator
Nyquist
α = .25-.50
Variable
Interpolator
Nyquist
α = .12-.18
Variable
Interpolator
Nyquist
α = .12-.18
Phase
Recovery
and
32-tap
DFE
IB Acquisition and Tracking Loops
Variable
Interpolator
Nyquist
α = .30-.50
Variable
Interpolator
Nyquist
α = .30-.50
4-tap
Equalizer
OB Acquisition and Tracking Loops
Starvue II
MCNS
DAVIC
FEC
ITU-T
J.83
Annex A/B/C
FEC
JTAG Int.
OOB
DCII
DAVIC
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
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
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 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: [phone]
FAX: [phone]
Email: [e-mail]
Web: www.broadcom.com