SI2107 SILABS [Silicon Laboratories], SI2107 Datasheet - Page 23

• Manufacturer Part Number: SI2107
• Description: SATELLITE RECEIVER FOR DVB-S/DSS
• Manufacturer: SILABS [Silicon Laboratories]

sequencer.
After the completion of a search, the estimated carrier
offset is stored in the carrier frequency error register,
CFER. If no signal is found, the CEF bit is asserted. The
value contained in CFER may be optionally transferred
to the CFO register to adjust the search center
frequency and permit the utilization of a smaller search
range for subsequent acquisitions. This relationship can
be expressed by the following equation:
6.4.3. Symbol Rate Estimation (Si2109/10 Only)
The Si2109/10 supports the ability to automatically
detect the symbol rate of a channel when it is unknown.
This feature is ideal for FTA/CI applications where it is
often desirable to rapidly scan (blind scan) and detect
the available channels of a given satellite. If symbol rate
estimation is not required, the user should program the
symbol rate explicitly into the SR register. This is the
only mode of operation for Si2107/08.
On Si2109/10, the symbol rate unknown bit, SRUK, can
be changed from its default value to activate symbol
rate estimation. The search range must then be
bounded by programming the symbol rate maximum
and minimum registers, SRMX and SRMN. If the
symbol rate search is successful, the estimated symbol
rate is automatically written to the SR register. Smaller
search ranges result in faster search times. Note that
the values stored in the symbol rate, symbol rate
maximum, and symbol rate minimum registers are
sample rate-dependent. This relationship is described
by the following equation:
When symbol rate estimation is complete, the SRL bit is
asserted. If an error is detected during symbol rate
estimation, the SRF bit is also set. The symbol rate
estimator commences under the control of the
acquisition sequencer.
6.4.4. Carrier Recovery Loop
The carrier recovery loop is responsible for acquiring
frequency and phase lock to the incoming signal. When
lock is achieved, the carrier recovery lock indicator,
CRL, is asserted. If carrier recovery lock is not achieved
within a predefined timeout period, the device declares
carrier recovery failure by asserting the CRF bit. The
carrier recovery loop commences under the control of
the acquisition sequencer.
6.4.5. Symbol Timing Loop
Search center frequency
Actual Symbol Rate
=
Symbol Rate
=
f
desired
+
CFO
×
------- -
2
f
24
s
×
MHz
------- -
2
f
15
s
Preliminary Rev. 0.7
Hz
The symbol timing recovery loop is responsible for
acquiring and tracking the symbol timing of the
incoming data signal. When lock is achieved, the
symbol timing loop lock indicator, STL, is asserted. If
symbol timing lock is not achieved within a predefined
timeout period, the device declares symbol timing loop
failure by asserting the STF bit. The symbol timing
recovery loop commences under the control of the
acquisition sequencer.
6.4.6. Automatic Fade Recovery
The device is designed to automatically recover lock in
the event of a fade condition. Fade recovery is
performed when any stage loses synchronization after
receiver lock has been achieved. It is assumed that
symbol rate, code rate, and puncturing pattern have not
changed; so, these parameters remain fixed during the
attempted reacquisition. The fade recovery sequence is
shown in Figure 10.
The fade recovery sequence continues until either
receiver lock is achieved or a new acquisition is
initiated.
Unlock
Unlock
Unlock
Unlock
Unlock
Figure 10. Fade Recovery Sequence
Fail
Si2107/08/09/10
Carrier Frequency Loop
Symbol Rate Estimation
Symbol Timing Loop
Analog AGC Search
CFO Estimation
Receiver locked
Viterbi Search
Frame Search
Calibration
LO Tuning
(Limited)
lock
lock
lock
lock
Done
Done
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