ST7285C datasheet(68/117 Pages) STMICROELECTRONICS

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ST7285C

4.8 RDS DEMODULATOR

The RDS demodulator is a fully digital Radio Data

System demodulator. The module includes 57KHz

carrier recovery, RDS clock (1187.5Hz) recovery,

bi-phase decoder, fast ARI indicator and signal

quality indicator. the module is controlled through

ST7 registers. The RDS signal is fed in through the

pin RDSCOMP. The reference frequency is de-

rived from the ST7 quartz oscillator. Therefore, the

quartz frequency must be 8.664MHz.

4.8.1 Features

– Pure digital RDS demodulator without external

components.

– Phase polarity data extractor.

– Phase integral data extractor.

– Data extractor selectable:

a) automatically via quality detector;

b) via software.

– Selectable quality indicator:

a) RDS signal quality;

b) polarity difference and integral data.

– Selectable time constant for 57KHz PLL.

– Selectable inhibit of PLL regulation to be used for

AF tests and temporary field strength weakness

(i.e. tunnels or other obstacles to radio recep-

tion).

– Fast ARI indicator, controlled by software.

Figure 33. RDS Demodulator Block Diagram

RDSCOMP

arp aren

lock upr

qen

lck1 lck0

57KHz PLL

Fast ARI Indicator

“Polarity” Bi-phase

Decoder

“Integral” Bi-phase

Decoder

Differential

Decoder 1

dat1

Differential

Decoder 2

dat2

sdat

RDS Dat

qual2

Quality

Detector

qual1

lck3 lck2 squal

RDS Clock

QUALITY

1187.5Hz Bit PLL

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