Philips saa6579 DATASHEETS

INTEGRATED CIRCUITS

DATA SH EET

SAA6579

Radio Data System (RDS) demodulator

Product speciﬁcation Supersedes data of January 1994 File under Integrated Circuits, IC01

1997 Feb 24

Philips Semiconductors Product speciﬁcation

Radio Data System (RDS) demodulator SAA6579

FEATURES

• Anti-aliasing filter (2nd order)

• Integrated 57 kHz band-pass filter (8th order)

• Reconstruction filter (2nd order)

• Clocked comparator with automatic offset compensation

• 57 kHz carrier regeneration

• Synchronous demodulator for 57 kHz modulated RDS

signals

GENERAL DESCRIPTION

The integrated CMOS circuit SAA6579 is an RDS demodulator. It recovers the additional inaudible RDS information which is transmitted by FM radio broadcasting.

The data signal RDDA and the clock signal RDCL are provided as outputs for further processing by a suitable decoder (microcomputer).

The operational functions of the device are in accordance with the

“CENELEC EN 50067”

• Selectable 4.332/8.664 MHz crystal oscillator with variable dividers

• Clock regeneration with lock on biphase data rate

• Biphase symbol decoder with integrate and dump

functions

• Differential decoder

• Signal quality detector

• Subcarrier output.

QUICK REFERENCE DATA

SYMBOL PARAMETER MIN. TYP. MAX. UNIT

DDA

DDD

tot

i(rms)

amb

analog supply voltage (pin 5) 3.6 5.0 5.5 V digital supply voltage (pin 12) 3.6 5.0 5.5 V total supply current − 6 − mA RDS input amplitude (RMS value; pin 4) 1 −−mV HIGH level output voltage for signals RDDA, RDCL, QUAL and T57 4.4 −−V LOW level output voltage for signals RDDA, RDCL, QUAL and T57 −−0.4 V operating ambient temperature −40 − +85 °C

ORDERING INFORMATION

TYPE

NUMBER

NAME DESCRIPTION VERSION

PACKAGE

SAA6579 DIP16 plastic dual in-line package; 16 leads (300 mil); long body SOT38-1

SAA6579T SO16 plastic small outline package; 16 leads; body width 7.5 mm SOT162-1

1997 Feb 24 2

Philips Semiconductors Product speciﬁcation

Radio Data System (RDS) demodulator SAA6579

BLOCK DIAGRAM

handbook, full pagewidth

47 pF

4.332/8.664 MHz

82 pF

2.2 k

+5 V

Ω

0.1 µF

MPX

signal

+5 V

2.2 µF

330 pF

SCOUT

560 pF

0.1 µF

MUX



CIN

DDA

ref

ALIASING

FILTER

CLOCKED

COMPARATOR

REFERENCE

VOLTAGE

ANTI-

OSCOOSCI

57 kHz

BANDPASS

(8th ORDER)

COSTAS LOOP VARIABLE AND FIXED DIVIDER

RECONSTRUCTION

FILTER

OSCILLATOR

DIVIDER

BIPHASE SYMBOL

DECODER

AND

SAA6579

CLOCK

REGENERATION

AND SYNC

SSA

TEST LOGIC AND OUTPUT

SELECTOR SWITCH

9 MODE TEST

DDD

QUALITY BIT

GENERATOR

DIFFERENTIAL

DECODER

SSD

QUAL

RDDA

RDCL

T57

MEH162

Via pin MODE two different crystal frequencies can be used.

MODE CRYSTAL CLOCK

LOW 4.332 MHz HIGH 8.664 MHz

Fig.1 Block diagram and application circuit.

1997 Feb 24 3

Philips Semiconductors Product speciﬁcation

Radio Data System (RDS) demodulator SAA6579

PINNING

SYMBOL PIN DESCRIPTION

QUAL 1 quality indication output RDDA 2 RDS data output V

ref

3 reference voltage output (0.5V MUX 4 multiplex signal input V V

DDA SSA

5 +5 V supply voltage for analog part

6 ground for analog part (0 V) CIN 7 subcarrier input to comparator SCOUT 8 subcarrier output of reconstruction ﬁlter MODE 9 oscillator mode/test control input TEST 10 test enable input V V

SSD DDD

11 ground for digital part (0 V)

12 +5 V supply voltage for digital part OSCI 13 oscillator input OSCO 14 oscillator output T57 15 57 kHz clock signal output RDCL 16 RDS clock output

DDA

)

handbook, halfpage

QUAL

RDDA

ref

MUX

DDA

SSA

CIN

SCOUT

1 2 3 4 5 6 7 8

SAA6579

MGD684

16 15 14 13 12 11 10

RDCL T57 OSCO OSCI V

DDD

SSD

TEST MODE

Fig.2 Pin configuration. Fig.3 Pin configuration.

1997 Feb 24 4

handbook, halfpage

QUAL

RDDA

ref

MUX

DDA

SSA

CIN

SCOUT

1 2 3 4

SAA6579T

5 6 7 8

MGD685

16 15 14 13 12 11 10

RDCL T57 OSCO OSCI V

DDD

SSD

TEST MODE

Philips Semiconductors Product speciﬁcation

Radio Data System (RDS) demodulator SAA6579

LIMITING VALUES

In accordance with the Absolute Maximum Rating System (IEC 134); ground pins 6 and 11 connected together.

SYMBOL PARAMETER CONDITIONS MIN. MAX. UNIT

DDA

DDD

stg

amb

Notes

1. Equivalent to discharging a 200 pF capacitor via a 0 Ω series resistor.

2. Equivalent to discharging a 100 pF capacitor via a 1.5 kΩ series resistor.

analog supply voltage (pin 5) 0 6 V digital supply voltage (pin 12) 0 6 V voltage on all pins; grounds excluded −0.5 V

+ 0.5 V

DDX

storage temperature −40 +150 °C operating ambient temperature −40 +85 °C electrostatic handling for all pins except

pins 9 and 10

note 1 ±300 − V note 2 +1500 −3000 V

FUNCTIONAL DESCRIPTION

The SAA6579 is a demodulator circuit for RDS applications. It contains a 57 kHz bandpass filter and a digital demodulator to regenerate the RDS data stream out of the multiplex signal (MPX).

Filter part

The MUX signal is band-limited by a second-order anti-aliasing-filter and fed through a 57 kHz band-pass filter (8th order band-pass filter with 3 kHz bandwidth) to separate the RDS signals. This filter uses switched capacitor technique and is clocked by a clock frequency of

541.5 kHz derived from the 4.332/8.664 MHz crystal oscillator. Then the signal is fed to the reconstruction filter to smooth the sampled and filtered RDS signal before it is output on pin 8. The signal is AC-coupled to the comparator (pin 7). The comparator is clocked with a frequency of 228 kHz (synchronized by the 57 kHz of the demodulator).

Digital part

The synchronous demodulator (Costas loop circuit) with carrier regeneration demodulates the internal coupled, digitized signal. The suppressed carrier is recovered from the two sidebands (Costas loop). The demodulated signal is low-pass-filtered in such a way that the overall pulse shape (transmitter and receiver) approaches a cosinusoidal form in conjunction with the following Integrate and dump circuit.

The data-spectrum shaping is split into two equal parts and handled in the transmitter and in the receiver. Ideally, the data filtering should be equal in both of these parts.

The overall data-channel-spectrum shaping of the transmitter and the receiver is approximately 100% roll-off.

The Integrate and dump circuit performs an integration over a clock period. This results in a demodulated and valid RDS signal in form of biphase symbols being output from the integrate and dump circuit. The final stages of RDS data processing are the biphase symbol decoding and the differential decoding. After synchronization by data clock RDCL (pin 16) data appears on the RDDA output (pin 2). The output of the biphase symbol decoder is evaluated by a special circuit to provide an indication of good data (QUAL = HIGH) or corrupt data (QUAL = LOW).

Timing

Fixed and variable dividers are applied to the

4.332/8.664 MHz crystal oscillator to generate the

1.1875 kHz RDS clock RDCL, which is synchronized by the incoming data. Which ever clock edge is considered (positive or negative going edge) the data will remain valid for 399 µs after the clock transition. The timing of data change is 4 µs before a clock change. Which clock transition (positive or negative going clock) the data change occurs in, depends on the lock conditions and is arbitrary (bit slip).

During poor reception it is possible that faults in phase occur, then the clock signal stays uninterrupted, and data is constant for 1.5 clock periods. Normally, faults in phase do not occur on a cyclic basis. If however, faults in phase occur in this way, the minimum spacing between two possible faults in phase depends on the data being transmitted. The minimum spacing cannot be less than 16 clock periods. The quality bit changes only at the time of a data change.

1997 Feb 24 5

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