SI2107-X-FM SILABS [Silicon Laboratories], SI2107-X-FM Datasheet - Page 20

• Manufacturer Part Number: SI2107-X-FM
• Description: SATELLITE RECEIVER FOR DVB-S/DSS WITH QUICKLOCK AND QUICKSCAN
• Manufacturer: SILABS [Silicon Laboratories]

5. Functional Description
The Si2107/08/09/10 is a family of highly-integrated
CMOS RF satellite receivers for DVB-S and DSS
applications. The device is an ideal solution for satellite
set-top boxes, digital video recorders, digital televisions,
and satellite PC-TV. The IC incorporates a tuner,
demodulator, and LNB controller into a single device
resulting in a significant reduction in board space and
external component count. The device supports symbol
rates of 1 to 45 Mbaud over a 950 to 2150 MHz range.
A full suite of features including automatic acquisition,
fade recovery, blind scanning, performance monitoring,
and DiSEqC™ Level 2.2 compliant signaling are
supported. The Si2110 and Si2108 further add short-
circuit protection, overcurrent protection, and a step-up
dc-dc controller to implement a low-cost LNB supply.
Furthermore, the Si2109 and Si2110 have an on-chip
blindscan accelerator. An I
configure and monitor all internal parameters.
5.1. Tuner
The tuner is designed to accept RF signals within a 950
to 2150 MHz frequency range. The inputs are matched
to a 75 Ω coaxial cable in a single-ended configuration.
The tuner block consists of a low-noise amplifier (LNA),
variable gain attenuators, a local oscillator, quadrature
downconverters, and anti-aliasing filters. The LNA and
variable gain stages provide balance between the noise
figure and linearity characteristics of the system. When
all gain stages are combined, the device provides more
than 80 dB of gain range. The desired tuning frequency
can be adjusted in intervals of 12.2 kHz, without the aid
of external varactors, using a unique two-stage tuning
algorithm that is supplied with the software driver. The
rapid settling time of the local oscillator improves
channel acquisition and switching performance. The
PLL loop filter has been completely integrated into the
device resulting in low tuner phase noise, improved
spurious response, and reduced BOM cost. An external
20 MHz crystal unit generates the reference frequency
for the system.
5.2. Demodulator
The
demodulation of channels between 1 to 45 Mbaud. It
incorporates the following functional blocks: analog-to-
digital converters (ADCs), dc notch filters, I/Q imbalance
corrector, decimation filters, matched filters, equalizer,
digital automatic gain controls, and a soft-decision
decoder. The demodulator supports rapid channel
acquisition using an advanced carrier offset estimation
algorithm. When combined with the Si2109/10’s blind
scanning capabilities, the device becomes an ideal
demodulator
supports
2
C bus interface is used to
QPSK
and
Preliminary Rev. 0.81
BPSK
solution for the free-to-air (FTA) and common interface
(CI) market. Automatic acquisition and fade recovery
sequencers are also included to reduce the required
amount of software interaction and to simplify the
overall design. The output of the demodulator is
quantized into a 4-bit number by the soft-decision
decoder. The use of soft-decision decoding improves
the error correction capabilities of the channel decoder.
5.3. DVB-S/DSS Channel Decoder
The Si2107/08/09/10 integrates a full-channel decoder,
which can be configured in either DSS or DVB-S mode
and consists of a soft-decision Viterbi decoder, de-
interleaver,
dispersal descrambler.
5.3.1. Viterbi decoder
The Viterbi decoder performs maximum likelihood
estimation of convolutional codes in compliance with
DVB-S and DSS standards. The decoder is capable of
detecting code rate, puncturing pattern phase, 90°
phase rotation, and I/Q interchange. Supported code
rates are listed in Table 14
The device allows monitoring of the Viterbi bit-error rate
(BER) over a finite or infinite measurement window.
5.3.2. Convolutional De-Interleaver
The deinterleaver disassembles the Reed-Solomon
(RS) code words, which were interleaved by the
modulator, to provide better resilience against burst
errors. The Si2107/08/09/10 performs deinterleaving
according to DVB-S and DSS standards.
5.3.3. Reed-Solomon Decoder
The Si2107/08/09/10 supports RS codes in compliance
with DVB-S and DSS specifications. Both standards use
a shortened Reed-Solomon code, which can correct up
to eight byte errors per information packet. DVB-S
utilizes 204 byte codes. DSS utilizes 146 byte codes.
Table 14. Viterbi Code Rates
Reed-Solomon
DVB-S
1/2
2/3
3/4
5/6
7/8
—
Si2107/08/09/10
decoder,
DSS
1/2
2/3
6/7
—
—
—
and
energy-
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