VP310

PRELIMINARY DATA

13

1.5.2 Symbol Rate and Code Rate Search mode

Where the Symbol rate and/or the Viterbi code rate are unknown, the VP310 can be programmed

to search for QPSK/BPSK signals. The user should define the range(s) over which the search is

required. The VP310 will then locate and track any signal detected. Failure to find a QPSK signal

specified frequency and specified symbol rate ranges will be indicated by interrupts. VP310 will

carry on searching these ranges after issuing these interrupts. When the VP310 has locked onto

a signal, the Symbol rate in MBaud may be read from the MONITOR registers. The Viterbi code

rate may be read from the FEC_STATUS register. This search facility is primarily for the initial

installation of a set top box.

1.6 Applications Information

1.6.1 IF conversion

The VP310 has been designed for maximum flexibility in the satellite application and many

options are available. The diagram shown below employs a single conversion system with an IF

of 480MHz. The SAW filter is selected for the maximum data rate expected and a SAW resonator

is used with the I/Q down converter to mix the input down to baseband I and Q channels for the

VP310 to digitise. The fixed sampling frequency of the VP310 is selected to be either 90MHz or

60 MHz depending on the maximum Symbol rate the application must work with. The sample

rate must be greater than or equal to twice the Symbol rate. For a table showing SAW bandwidth

versus Symbol rate.

Tuner

SL2017

I/Q Down-

converter

SL1720

Channel

Decoder

VP310

Synthesiser

SP5769

SAW

Resonator

SAW

filter

I²C bus control

AGC control

Transport

stream O/P

I²C control

I I/P

Q I/P

RF I/P

AGC control

Tank

AGC

AMP

I/P

filter

Figure 11. Single Conversion System Diagram.