參數(shù)資料
型號(hào)： SAA3500H
廠商： NXP SEMICONDUCTORS
元件分類： 消費(fèi)家電
英文描述： Digital audio broadcast channel decoder
中文描述： SPECIALTY CONSUMER CIRCUIT, PQFP100
封裝： 14 X 20 MM, 2.70 MM HEIGHT, PLASTIC, MO-112, SOT-317-1, QFP-100
文件頁(yè)數(shù)： 8/32頁(yè)
文件大?。?/td> 156K
代理商： SAA3500H
2000 Jun 14
8
Philips Semiconductors
Preliminary specification
Digital audio broadcast channel decoder
SAA3500H
8
FUNCTIONAL DESCRIPTION
The 2.048 MHz IF signal is digitized by an 8-bit flash
Analog-to-Digital Converter (ADC), which samples at
8.192 MHz. The required input level is limited to a
peak-to-peak voltage of 2 V. Due to a fast
sample-and-hold circuit sub-sampling is possible, so that
all IF frequencies of N
×
8.192
±
2.048 MHz can be used.
If a higher resolution ADC is wanted, an external ADC can
be connected.
The digital mixer accepts a 2.048 MHz IF signal at its input
and converts it to baseband with In-phase (I) and
Quadrature-phase (Q) components. The mixer frequency
is adjusted on a DAB frame basis with 1 Hz resolution to
prevent performance degradation. The mixer output
signals are digitally filtered and subjected to internal
Automatic Gain Control (AGC) before entering the
subsequent Fast Fourier Transform (FFT) stage.
The output of the digital AGC detectors indicates for each
input sample whether the level is below or above the
reference input level. By means of external filtering and
gain control, the signal can be used to adjust the input
signal level of the analog-to-digital converter (external
AGC).
The on-chip null detector operates on the digital baseband
signal and indicates the coarse position of the DAB null
symbol (FSO = LOW), which is used for time base
initialization. The spacing of detected null symbols is used
to detect the DAB transmission mode.
The time base counts samples on a symbol and a frame
basis in order to generate the internal control windows for
the FFT and to generate a frame sync signal (FSO) during
thenullsymbol.Initializationofthetimebaseisdetermined
by the null detector signal (FSI) and the selected DAB
mode. After time base initialization the SAA3500H will be
in symbol processing mode and the null detector will be
deactivated.
The OFDM symbol demodulator applies a real-time FFT
and differential demodulation to the baseband signal. The
output is quantized to 4-bit metrics for the Viterbi decoder.
The position of the FFT window is adjusted on a DAB
frame basis in order to avoid Inter-Symbol Interference
(ISI).
TheFFTresultofthereferencesymbolisprocessedbythe
synchronization core, which performs two functions:
estimation of the frequency error of the baseband signal,
which is needed to adjust the digital mixer (AFC), and
calculation of the Channel Impulse Response (CIR) to be
used for positioning of the FFT window and the system
clock.Alltimingand frequencycontrolloopsare realizedin
the synchronization core and can be influenced from the
control interface.
The Viterbi decoder is preceded by frequency and time
de-interleaving of the incoming metrics in external RAM, to
distribute burst errors caused by channel fading. Variable
rate decoding is done with 3.072 Mb/s decision speed.
Output bits are re-encoded and compared to
corresponding input bits in order to generate an error flag
signal.
Sub-channel selection is done on a Capacity Unit (CU)
basis. All standardized Unequal Error Protection (UEP)
puncturing schemes for audio and Equal Error Protection
(EEP) schemes for data are provided. Up to
64 sub-channelscanbeselectedseparately,whichmeans
virtually unlimited DAB decoding capabilities.
The output interface provides a full-speed standardized
Receiver Data Interface (RDI) for all sub-channel data.
This allows to extend every DAB receiver with external
decoders for all kind of services. A dedicated interface is
provided for the Philips SAA2502H audio source decoder,
which completes the DAB receiver.
The system clock of 24.576 MHz, can be generated by an
integrated DCXO, which is internally locked to the DAB
signal. The clock is available on the MCLK pin to provide a
synchronous clock to the MPEG decoder and
microcontroller.
The I
2
C-bus or L3-bus configurable control interface
provides access to Automatic Frequency Control (AFC),
Channel Impulse Response (CIR), Fast Information
Channel (FIC) and sub-channel selection controls.
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