TDA7580_07 Datasheet, PDF (32/39 Pages) STMicroelectronics – FM/AM digital IF sampling processor

Functional description
TDA7580
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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