TDA7580 datasheet(32/39 Pages) STMICROELECTRONICS

32 / 39 page

Functional description

TDA7580

32/39

8.12

Digital down converter (DDC)

The DDC module allows to evaluate the in-phase and quadrature components of the

incoming digital IF signal.

The I and Q computation is performed by the DDC block, which at the same time shifts down

to 0-IF frequency the incoming digital signal.

After the down conversion the rate is still very high (at the 37.05MHz rate); a SincK filter

samples data down by a factor of 32, decreasing it to 1.1578MHz. An additional decimation

is performed by the subsequent FIR filters, thus lowering the data rate at the final

289.45kHz, being the MPX data rate.

8.13

RDS

The RDS block is an hardware cell able to process RDS/RBDS signal, intended for

recovering the inaudible RDS/RBDS information which are transmitted by most of FM radio

broadcasting stations.

It comprises of the following:

●

Demodulation of the european radio data system (RDS)

●

Demodulation of the US radio broadcast data system (RDBS)

●

Automatic group and block synchronisation with flywheel mechanism

●

Error detection and correction

●

RAM buffer with a storage capacity of 24 RDS blocks and related status information

●

I2C and SPI interface, with pins shared with the DSP I2C/SPI

After filtering the oversampled MPX signal, the RDS/RDBS demodulator extracts the RDS

data clock, RDS data signal and the quality information.

The following RDS/RBDS decoder synchronizes the bitwise RDS stream to a group and

block wise information. This processing also includes error detection and error correction

algorithms.

In addition, an automatic flywheel control avoids exhausting the data exchange between

RDS/RDBS processor and the host.

8.14

AM/FM Detector (CORDIC)

The AM/FM detector is a fully programmable peripheral used to detect the phase, amplitude

and frequency information of an input complex signal (in-phase and quadrature signals). It

can be used to demodulate PM, AM and FM modulated signals. The detection is performed

using a high accuracy CORDIC algorithm, working essentially as a cartesian to polar

transformer.

Four CORDICs are available to allow concurrent software calls.

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