Philips Semiconductors
Product specification
RDS/RBDS pre-processor
FUNCTIONAL DESCRIPTION
General
The following functions are performed by the SAA6588:
•
Selection of the RDS/RBDS signal from the MPX input
signal
•
57 kHz carrier regeneration
•
Demodulation of the RDS/RBDS signal
•
Symbol decoding
•
RDS/RBDS block detection
•
Error detection and correction of transmission errors
•
Fast block synchronization and synchronization control
•
Detection of multi-path distortion and audio signal
pauses
•
Determination of the signal quality
•
Mode control of processing and RDS/RBDS data output
via I
2
C-bus interface
•
Sensing of pause and multi-path, information via extra
output pins.
The block diagram of the RDS/RBDS pre-processor is
shown in Fig.1. For the application of the device only a few
external components are required. The pre-processors
functional blocks are described in the following sections.
RDS/RBDS signal demodulation
B
AND
-
PASS FILTER
The band-pass filter has a centre frequency of 57 kHz.
It selects the RDS/RBDS sub-band from the multiplex
signal MPX and suppresses the audio signal components.
The filter block contains an analog anti-aliasing filter at the
input followed by an 8th order switched capacitor
band-pass filter and a reconstruction filter at the output.
C
LOCKED COMPARATOR
The comparator digitizes the output signal from the 57 kHz
band-pass filter for further processing by the digital
RDS/RBDS demodulator. To attain high sensitivity and to
avoid phase distortion, the comparator input stage
contains an automatic offset compensation.
D
EMODULATION
SAA6588
The demodulator provides all functions of the SAA6579
but has improved performance under weak signal
conditions.
The demodulator includes:
•
57 kHz carrier regeneration from the two sidebands
(Costas loop)
•
Symbol integration over one RDS clock period
•
Bi-phase symbol decoding
•
Differential decoding
•
Synchronization of RDS/RBDS output data with clock.
The RDS/RBDS demodulator recovers and regenerates
the continuously transmitted RDS/RBDS data stream out
of the multiplex signal (MPX) and provides the internal
signals clock (RDCL) and data (RDDA) for further
processing by the RDS/RBDS decoder block.
RDS/RBDS data processing
The RDS/RBDS data processing of the pre-processor
handles the complete processing and decoding of the
continuous serial RDS/RBDS demodulator output data
stream.
Different data processing modes are software controllable
by the external main controller via I
2
C-bus.
Processed RDS/RBDS data blocks, decoder status
information and signal quality information are also
available via I
2
C-bus.
RDS/RBDS
DECODER
The RDS/RBDS decoder contains:
•
RDS/RBDS block detection
•
Error detection and correction
•
Synchronization
•
Flywheel for synchronization hold
•
Bit slip correction
•
Data processing control
•
RDS/RBDS data output.
1997 Sep 01
6
PHILIPS [ NXP SEMICONDUCTORS ]
