L64704 LSI Logic Corporation, L64704 Datasheet - Page 112

• Manufacturer Part Number: L64704
• Description: Satellite Decoder Technical Manual 5/97
• Manufacturer: LSI Logic Corporation

Table 5.2
Natural Frequency
as a Function of M
5.5.3
Output Symbol
Clock
5.5.4
Constraints on
Data Rates
Equation 5.5
5-8
Choose the natural frequency
operation, set the damping factor
Samples per
Symbol, M
2
3
4
8
For variable rate operation, set
decreases for higher oversampling, which corresponds to lower symbol
rates.
The AFC generates an internal symbol clock SCLK, that is used to clock
the demodulated symbols DEMI and DEMQ (see
Figure
an external PLL to generate a clock for the decoding pipeline.
The I and Q input samples may be 2x, 3x, or 4x oversampled, with a
maximum sampling rate of 62.5 Msamples/second.
For a given IF SAW filter characteristic and a given oversampling factor
N, the range of achievable data rates is limited by two constraints. These
constraints are described below and illustrated in
1. The signal spectrum must not be distorted by the IF filtering
Demodulator Module Functional Description
function—that is, the maximum signal frequency must lie within the -
1 dB bandwidth (2b
equation:
where b is the matched filter roll-off and T is the QPSK (or BPSK)
symbol duration.
-----------------
1 +
2 T
4.2). This clock can also be brought out on the PCLK pin to clock
b
Frequency,
3900
3178
2752
1950
1
n
(rad/s)
1
) of the IF SAW filter, as shown in the following
n
to one for the highest oversampling.
according to
to one.
Table
Figure
Figure 4.1
5.2. For fixed rate
5.4.
and
n