TDA8980 データシートの表示（PDF） - Philips Electronics
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TDA8980 Datasheet PDF : 36 Pages
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Philips Semiconductors
ATSC Digital Terrestrial TV
demodulator/decoder
Objective specification
TDA8961
The incoming data has a sample rate of 36 MHz. This is
internally converted to a sample rate of 21.52 MHz which
is twice the 8-VSB symbol rate. This patented Philips
Semiconductors’ technology eliminates the need for
external symbol timing recovery loop components. When
the TDA8980 is decoding analog NTSC, the TDA8961 can
be set to a ITU656 bypass mode which allows the 8-bit
ITU656 data output from the TDA8980 to appear at the
TDA8961 Moving Pictures Expert Group (MPEG-2)
transport stream output, from where it can be fed to the
main graphics display device in the system.
The recovery of the carrier is performed entirely within the
TDA8961. This function consists of a digital frequency and
Frequency Phase-Locked Loop (FPLL).
Data shaping is performed by a square-root raised-cosine
(half Nyquist) filter having a roll-off factor of 11.5%.
After the TDA8961 has performed carrier recovery,
Nyquist filtering and symbol timing recovery, it then
performs adaptive equalization. The adaptive equalizer
uses a DFE structure with equalization based on the ATSC
field sync (trained equalization) and/or the 8-VSB data
itself (blind equalization).
The equalizer is followed by a patented NTSC co-channel
interference filter which removes any unwanted NTSC
signal interference from the 8-VSB terrestrial DTV signal.
After trellis decoding, the stream is de-interleaved to a
depth of 52 by a convolutional de-interleaver whose
memory is provided on-chip. The Reed Solomon decoder
is ATSC-compliant, with a length of 207, and able to
correct up to 10 bytes. The decoded stream is then
de-randomized using a pseudo-random binary sequence
(PRBS) and the data passed to a FIFO which prevents the
appearance of irregular gaps in the output data.
The output of the TDA8961 is a clock signal and an
ATSC-compliant MPEG-2 packetized data stream. Signal
flag outputs are provided to indicate the occurrence of
sync bytes, valid data bytes and uncorrected Reed
Solomon blocks. The packetized data stream is available
in either an 8-bit parallel, or a 1-bit serial format for
connection to an MPEG-2 transport stream demultiplexer.
An application using the TDA8961 and a stand-alone
TDA9829 Downconverter for DVB (Digital Video
Broadcast) with an A/D converter is shown in Fig.2. A tuner
converts the incoming RF signal to a fixed IF centered at
44 MHz. The output signal from the tuner is filtered using
two Surface Acoustical Wave (SAW) filters and then down
converted to an IF of 4 MHz by the TDA9829. The signal
is then digitized by an A/D converter at a sample rate of
36 MHz using the clock signal output from the TDA8961.
The full input range of the A/D converter is utilized by
placing it within what is effectively a fine-AGC loop
integrator circuit which has a variable gain stage at the
output of the IF downmixer section. However, it is also
possible to apply the AGC control output of the TDA8961
to the tuner via the integrator. The peak level of the input
signals to the TDA8961 is determined by the AGC output
detector which is located just after the A/D.
handbook, full pagewidth
RF
SAW
FILTER
TUNER RF
integrator
Vref
AGC
44 MHz
SAW
FILTER
VAGC
ViIF
VoDVB
TDA9829
IF DOWNMIXER
VCO
96 MHz
OSCILLATOR
AGCOUT
A
ADIN9 to PDO7 to
D
ADIN0
PDO0
TDA8961
ADCLK
CLK36 XTALI
12 MHz
÷8
MPEG-2
transport
stream
MGU086
Fig.2 Front-end design for the TDA8961 using a stand-alone IF down converter (TDA9829) and A/D converter.
2000 May 19
4
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