TDA9321 데이터 시트보기 (PDF) - Philips Electronics
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TDA9321 Datasheet PDF : 44 Pages
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Philips Semiconductors
I2C-bus controlled TV input processor
Preliminary specification
TDA9321H
FUNCTIONAL DESCRIPTION
Vision IF amplifier
The VIF amplifier contains 3 AC-coupled control stages
with a total gain control range which is higher than 66 dB.
The sensitivity of the circuit is comparable with that of
modern IF-ICs.
The video signal is demodulated by a PLL carrier
regenerator. This circuit contains a frequency detector and
a phase detector. During acquisition the frequency
detector will tune the VCO to the correct frequency.
The initial adjustment of the oscillator is realized via the
I2C-bus. The switching between SECAM L and L’ can also
be realized via the I2C-bus. After lock-in the phase
detector controls the VCO so that a stable phase
relationship between the VCO and the input signal is
achieved. The VCO operates at twice the IF frequency.
The reference signal for the demodulator is obtained by
means of a frequency divider circuit. To get a good
performance for phase modulated carrier signals the
control speed of the PLL can be increased by bit FFI.
The AFC output is obtained by using the VCO control
voltage of the PLL and can be read via the I2C-bus.
For fast search tuning systems the window of the AFC can
be increased with a factor 3. The setting is realized with
bit AFW.
The AGC detector operates on top-sync and
top-white-level. The demodulation polarity is switched via
the I2C-bus. The AGC detector time constant capacitor is
connected externally; this is mainly because of the
flexibility of the application. The time constant of the AGC
system during positive modulation is rather long, this is to
avoid visible variations of the signal amplitude. To improve
the speed of the AGC system a circuit has been included
which detects whether the AGC detector is activated every
frame period. When, during 3 field periods, no action is
detected the speed of the system is increased. For signals
without peak white information the system switches
automatically to a gated black level AGC. Because a black
level clamp pulse is required for this mode of operation the
circuit will only switch to black level AGC in the internal
mode.
The circuits contain a video identification (ident) circuit
which is independent of the synchronization circuit.
Therefore search tuning is possible when the display
section of the receiver is used as a monitor. However, this
ident circuit cannot be made as sensitive as the slower
sync ident circuit (bit SL). It is recommended to use both
ident outputs to obtain a reliable search system. The ident
output is supplied to the tuning system via the I2C-bus.
The input of the ident circuit is connected to pin 14
(see Fig.3). This has the advantage that the ident circuit
can also be made operative when a scrambled signal is
received (descrambler connected between pins 10
and 14). A second advantage is that the ident circuit can
be used when the VIF amplifier is not used (e.g. with
built-in satellite tuners). The video ident circuit can also be
used to identify the selected CBVS or Y/C signal.
The switching between the 2 modes can be realized with
bit VIM.
The TDA9321H contains a group delay correction circuit
which can be switched between the BG and a flat group
delay response characteristic. This has the advantage that
in multistandard receivers no compromise has to be made
for the choice of the SAW filter. Both the input and output
of the group delay correction circuit are externally
available so that the sound trap can be connected
between the VIF output and the group delay correction
input. The output signal of the correction circuit can be
supplied to the internal video processing circuit and to the
external SCART plug.
The IC has several (I2C-bus controlled) output ports which
can be used to switch sound traps or other external
components.
When the VIF amplifier is not used the complete VIF
amplifier can be switched off with bit IFO.
Sound circuit
The SIF amplifier is similar to the VIF amplifier and has a
gain control range of approximately 66 dB. The AGC
circuit is related to the SIF carrier levels (average level of
AM or FM carriers) and ensures a constant signal
amplitude to the AM demodulator and the QSS mixer.
The single reference QSS mixer is realized by a multiplier.
In this multiplier the SIF signal is converted to the
intercarrier frequency by mixing it with the regenerated
picture carrier from the VCO. The mixer output signal is
supplied to the output via a high-pass filter for attenuation
of the residual video signals. With this system a high
performance hi-fi stereo sound processing can be
achieved.
The AM sound demodulator is realized by a multiplier.
The modulated SIF signal is multiplied in phase with the
limited SIF signal. The demodulator output signal is
supplied to the output via a low-pass filter for attenuation
of the carrier harmonics.
1998 Dec 16
7
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