Philips Semiconductors
Product specification
RDS/RBDS demodulator
FEATURES
•
Integrated switched capacitor filter
•
Demodulates European Radio Data System (RDS) or
the USA Radio Broadcast Data System (RBDS) signals
•
Oscillator frequencies: 4.332 or 8.664 MHz
•
Integrated ARI clamping
•
CMOS device
•
Single supply voltage: 5 V
•
Extended temperature range:
−40
to +85
°C
•
Low number of external components.
GENERAL DESCRIPTION
The RDS/RBDS demodulator is a CMOS device with
integrated filtering and demodulating of RDS/RBDS
signals coming from a multiplexed input data stream. Data
signal RDDA and clock signal RDCL are provided as
outputs for further processing by a suitable
microcomputer, for example CCR921 and CCR922.
The SAA6581T replaces SAA6579 in function and
pin-compatibility.
QUICK REFERENCE DATA
SYMBOL
V
DDA
V
DDD
I
DD(tot)
V
i(MPX)
f
i(xtal)
PARAMETER
analog supply voltage
digital supply voltage
total supply current
RDS input sensitivity at pin MPX
crystal input frequency
4.0
4.0
−
1
−
−
ORDERING INFORMATION
TYPE
NUMBER
SAA6581T
SAA6581HN
PACKAGE
NAME
SO16
HVQFN32
DESCRIPTION
plastic small outline package; 16 leads; body width 7.5 mm
plastic thermal enhanced very thin quad flat package; no leads;
32 terminals; body 5
×
5
×
0.85 mm
MIN.
5.0
5.0
6.0
−
4.332
8.664
TYP.
5.5
5.5
−
−
−
−
MAX.
APPLICATIONS
SAA6581
The RDS/RBDS system offers a large range of
applications from the many functions that can be
implemented. For car radios the most important are:
•
Program Service (PS) name
•
Traffic Program (TP) identification
•
Traffic Announcement (TA) signal
•
Alternative Frequency (AF) list
•
Program Identification (PI)
•
Enhanced Other Networks (EON) information.
UNIT
V
V
mA
mV
MHz
MHz
VERSION
SOT162-1
SOT617-1
2003 Oct 10
2
Philips Semiconductors
Product specification
RDS/RBDS demodulator
FUNCTIONAL DESCRIPTION
RDS/RBDS signal demodulation
B
ANDPASS FILTER
The bandpass 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
bandpass filter and a reconstruction filter at the output.
C
LOCKED COMPARATOR
The comparator digitizes the output signal from the 57 kHz
bandpass filter for further processing by the digital
RDS/RBDS demodulator. To attain high sensitivity and to
avoid phase distortion, the comparator input stage has
automatic offset compensation.
D
EMODULATOR
The demodulator provides all functions of the SAA6579
and improves performance under weak signal conditions.
Demodulator functions include:
•
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.
The RDS/RBDS demodulator recovers and regenerates
the continuously transmitted RDS/RBDS data stream in
the MPX signal and provides clock RDCL for the output
signals and data output RDDA for further processing by an
RDS/RBDS decoder, for example CCR921 or CCR922.
ARI
CLAMP
The demodulator checks the input signal for presence of
RDS only, or RDS plus ARI transmissions. After a fixed
test period, if the SYNC input is set HIGH the demodulator
locks in the ‘verified’ condition (see Table 1). If SYNC is set
LOW, the ARI clamping is reset (disabled). After SYNC
returns to HIGH, the demodulator resumes checking the
input signal.
Power supply and internal reset
Table 1
SYNC
LOW
HIGH
Control pin SYNC
SAA6581
ARI CLAMPING
internal ARI clamping disabled
ARI clamping allowed to be logged
S
IGNAL QUALITY DETECTION
Output QUAL indicates the safety of the regenerated RDS
data (HIGH = ‘good’ data; LOW = ‘unsafe’ data).
Oscillator and system clock generator
For good performance of the bandpass and demodulator
stages, the demodulator requires a crystal oscillator with a
frequency of 4.332 or 8.664 MHz. The demodulator can
operate with either frequency (see Table 2), so that a radio
set with a microcontroller can run, in this case, with one
crystal only. The demodulator oscillator can drive the
microcontroller, or vice versa.
Table 2
TCON
HIGH
HIGH
Control pins TCON and MODE
MODE
LOW
HIGH
OSCILLATOR FREQUENCY
4.332 MHz
8.664 MHz
The clock generator generates the internal 4.332 MHz
system clock and timing signal derivatives.
The demodulator has separate power supply inputs for the
digital and analog parts of the device. For the analog
functions an additional reference voltage (
1
⁄
2
V
DDA
) is
internally generated and available via the output pin V
ref
.
The demodulator requires a defined reset condition. The
demodulator generates automatically a reset signal after
the power supply V
DDA
is switched on, or at a voltage-drop.
2003 Oct 10
5
嵌入式系统
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