ADF7020 datasheet(20/40 Pages) AD

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ADF7020

Preliminary Technical Data

Rev. PrH | Page 20 of 40

Maximum AFC Range

The maximum AFC frequency range is ±100 kHz. This is set by

the maximum IF filter bandwidth of 200 kHz. Using the

minimum IF filter bandwidth of 100 kHz, the AFC range is

±50 kHz.

When AFC errors have been removed using either the internal

or external AFC, further improvement in the receiver’s sensi-

tivity can be obtained by reducing the IF filter bandwidth using

Bits R1_DB(22:23).

AUTOMATIC SYNC WORD RECOGNITION

The ADF7020 also supports automatic detection of the sync or

ID fields. To activate this mode, the sync (or ID) word must be

preprogrammed into the ADF7020. In receive mode, this

preprogrammed word is compared to the received bit stream

and, when a valid match is identified, the external pin

INT/LOCK is asserted by the ADF7020.

This feature can be used to alert the microprocessor that a valid

channel has been detected. It relaxes the computational

requirements of the microprocessor and reduces the overall

power consumption. The INT/LOCK is automatically de-

asserted again after nine data clock cycles.

The automatic sync/ID word detection feature is enabled by

selecting demod mode 2 or 3 in the demodulator setup register.

Do this by setting R4_DB(25:23) = [010] or [011]. Bits

R5_DB(4:5) are used to set the length of the sync/ID word,

which can be either 12, 16, 20, or 24 bits long. The transmitter

must transmit the MSB of the sync byte first and the LSB last to

ensure proper alignment in the receiver sync byte detection

hardware.

For systems using FEC, an error tolerance parameter can also be

programmed that accepts a valid match when up to three bits of

the word are incorrect. The error tolerance value is assigned in

R5_DB(6:7).

ADF7020 Datasheet(PDF) 20 Page - Analog Devices