L64724 LSI Logic Corporation, L64724 Datasheet - Page 149

• Manufacturer Part Number: L64724
• Description: Satellite Receiver
• Manufacturer: LSI Logic Corporation

5.7.2.2 Loop Characteristics
Figure 5.8
Carrier Loop Filter Parameters
The phase detector uses two gain values depending on the signal to
noise ratio. The SNR is internally estimated and compared to the
SNR_THS[7:0] 8-bit threshold (Group 4, APR 27). The plot in
shows the relationship between the SNR_THS[7:0] parameter and the
actual E
value of 100 is recommended for SNR_THS[7:0]. The value of 100
corresponds to an actual E
of the estimated SNR to the threshold is stored in the Demod_SNR bit
(Group 3, APR 6, bit 7). A 12-bit value for this SNR estimate is available
from SNR[11:0] in Group 3, APR 22 and 23.
Figure 5.7
To set the parameters of the carrier recovery loop (natural frequency and
damping factor), the user must select the values the microprocessor
writes into the CAR_MU_SEL and CAR_LAMBDA_SEL (Group 4,
APR 28) registers.
The values of CAR_MU_SEL and CAR_LAMBDA_SEL are computed
according to
Carrier Recovery Loop
s
/N
o
(symbol energy to noise power density) seen in-circuit. A
Equation
SNR Threshold vs. E
5.18,
s
/N
Equation
E
s
o
/N
of 11 dB. The result of the comparison
o
[dB]
s
/N
5.19, and
o
Equation
5.20.
Figure 5.7
5-17