TDA8961 Philips Semiconductors, TDA8961 Datasheet - Page 12

• Manufacturer Part Number: TDA8961
• Description: ATSC/NTSC digital TV front-end chipset
• Manufacturer: Philips Semiconductors

Philips Semiconductors
Carrier recovery
The carrier recovery circuit recovers the frequency and
phase of the pilot carrier signal. If, as in some cases, the
pilot signal is present at the higher edge of the VSB
spectrum, the I
that when the frequency is shifted, the pilot signal is DC.
Half Nyquist filtering
The half Nyquist filtering section is a square-root
raised-cosine filter with 11.5% roll-off.
Sync recovery
The sync recovery section performs several functions
including the recovery of segment sync and field sync.
When this section detects the data segment sync signal,
pin LOCKINDIC goes HIGH. The status of
pin LOCKINDIC can also be read via the I
bit LOCK_INDICATOR (see Table 16).
Timing recovery
The timing recovery section takes signals from the half
Nyquist filter and forms part of a closed loop in order to
acquire and maintain a constant sampling rate and clock
frequency for the complete system.
Adaptive equalizer
The adaptive equalizer comprises a forward filter and a
feedback filter section. At every symbol period, it receives
demodulated symbols from the sync recovery section.
The equalizer filters these symbols in an attempt to
eliminate the effects of multipath conditions on the symbol
stream during transmission. The coefficients of the filters
are updated every symbol period using the training
sequence and/or using blind equalization if required.
The equalizer is designed to correct a maximum pre-echo
of 2.32 s and a maximum post-echo of 22.5 s.
The equalizer has an optimized typical acquisition time of
12 training sequences, which corresponds to about
290 ms. It is defined that acquisition occurs when the
output signal-to-noise ratio reaches the Threshold Of
Visibility (TOV). For 8-VSB, the ATSC defines a TOV of
14.9 dB.
A Mean Square Error (MSE) signal is generated based on
the training signal and on the output of the equalizer.
The error signal represents a 16-bit value which is read via
the I
the channel adaptation process.
It is possible to use software control to extend the range of
the feedback filter to a maximum of 80 s.
2000 May 19
ATSC Digital Terrestrial TV
demodulator/decoder
2
C-bus bit MSE (see Table 18) and used to monitor
2
C-bus bit CR_INV can be set to ensure
2
C-bus
12
C
An integrated sophisticated finite state machine controls
the sequence of operations that must be performed to
correctly decode a valid VSB data signal into an MPEG-2
packetized transport stream.
After a reset has been applied, the finite state machine is
in state 0. When a valid VSB data signal is detected, the
finite state machine ensures that the following three states
occur.
State 1: channel acquisition
In this state there is either no channel signal present or a
channel signal is in the process of being acquired. Before
the channel signal can be acquired, the AGC, timing
recovery and carrier recovery loops must first lock onto it.
If segment sync lock is lost, either pin LOCKINDIC goes
LOW, or a hardware reset is applied to the TDA8961 and
the finite state machine returns to state 0.
State 2: equalizer training
The finite state machine remains in state 1 until the MSE
of the equalized training sequence falls between two
specific threshold values. It should be noted that in state 1,
the back-end section of the TDA8961 is continuously reset
to make sure that after its demodulator has locked onto a
signal, the trellis decoder and the following sections begin
processing at the start of the next complete data field.
The value of I
such as antenna pointing.
State 3: normal operation
Normally the finite state machine remains in state 2 unless
a synchronization error occurs. If the MSE of the equalized
training sequence exceeds 100 ms, the equalizer is reset
for one symbol period and the adaptation process restarts.
If the demodulator synchronization and equalization are
both locked, pin EQLOCKINDIC goes HIGH and I
bit LOCK_INDICATOR is set to 11 (see Table 16).
The filtered output signal is then routed to the NTSC
co-channel interference filter.
NTSC co-channel interference filter
The NTSC co-channel interference filter uses patented
Philips’ technology making its performance considerably
better than the ATSC specified comb filter. The filter can
be bypassed by setting I
Table 13).
ONTROL
2
C-bus bit MSE can be used for applications
2
C-bus bit FLT_BYPASS (see
Objective specification
TDA8961
2
C-bus