參數(shù)資料
型號： TDA935X
廠商： NXP Semiconductors N.V.
英文描述： TV signal processor-Teletext decoder with embedded m-Controller
中文描述： 電視信號處理器與嵌入式米圖文電視解碼器控制器
文件頁數(shù)： 87/140頁
文件大?。?/td> 570K
代理商： TDA935X
1999 Sep 28
87
Philips Semiconductors
Preliminary Device Specification
TV signal processor-Teletext decoder with
embedded
μ
-Controller
TDA935X/6X/8X series
FUNCTIONAL DESCRIPTION OF VIDEO PROCESSOR
Vision IF amplifier
The vision IF amplifier can demodulate signals with
positive and negative modulation. The PLL demodulator is
completely alignment-free.
The VCO of the PLL circuit is internal and the frequency is
fixed to the required value by using the clock frequency of
the
μ
-Controller/Teletext decoder as a reference. The
setting of the various frequencies (38, 38.9, 45.75 and
58.75 MHz) can be made via the control bits IFA-IFC in
subaddress 27H. Because of the internal VCO the IF
circuit has a high immunity to EMC interferences.
QSS Sound circuit (QSS versions)
The sound IF amplifier is similar to the vision IF amplifier
and has an external AGC decoupling capacitor.
The single reference QSS mixer is realised 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 realised by a multiplier. The
modulated sound IF 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. The AM signal is supplied to the
output (pin 44) via the volume control.
It is possible to get the AM output signal (not controlled on
amplitude) on the QSS intercarrier output. The selection is
made by means of the AM bit in subaddress 29H.
Another possibility is that pin 35 is transferred to external
audio input pin and pin 32 to (non-controlled) AM output
pin. This can be realised by means of the setting the
control bits CMB0 and CMB1 in subaddress 22H.
FM demodulator and audio amplifier (mono versions)
The FM demodulator is realised as narrow-band PLL with
external loop filter, which provides the necessary
selectivity without using an external band-pass filter. To
obtain a good selectivity a linear phase detector and a
constant input signal amplitude are required. For this
reason the intercarrier signal is internally supplied to the
demodulator via a gain controlled amplifier and AGC
circuit. The nominal frequency of the demodulator is tuned
to the required frequency (4.5/5.5/6.0/6.5 MHz) by means
of a calibration circuit which uses the clock frequency of
the
μ
-Controller/Teletext decoder as a reference. The
setting to the wanted frequency is realised by means of the
control bits FMA and FMB in control byte 29H.
When required an external sound band-pass filter can be
inserted in front of the narrow-band PLL. In that case pin
32 has to be switched to sound IF input by means of the
bits SIF (subaddress 21H) and CMB0/CMB1 (subaddress
22H). When the sound IF input is selected the subcarrier
output (90
°
versions) or AVL function (110
°
versions) are
not available.
From the output status bytes it can be read whether the
PLLfrequencyisinsideoroutsidethewindowandwhether
the PLL is in lock or not. With this information it is possible
to make an automatic search system for the incoming
sound frequency. This can be realised by means of a
software loop which switches the demodulator to the
various frequencies and then select the frequency on
which a lock condition has been found.
The deemphasis output signalamplitude isindependent of
the TV standard and has the same value for a frequency
deviation of
±
25 kHz at the 4.5 MHz standard and for a
deviation of
±
50 Khz for the other standards.
The audio control circuit contains an audio switch and
volume control. In the mono intercarrier sound versions
the Automatic Volume Levelling (AVL) function can be
activated. The pin to which the external capacitor has to be
connected depends on the IC version. For the 90
°
types
the capacitor is connected to the EW output pin (pin 20).
For the 110
°
types a choice must be made between the
AVL function and a sub-carrier output for comb filter
applications. This choice is made via the CBM0 and
CMB1bits (in subaddress 22H). When the AVL is active it
automatically stabilises the audio output signal to a certain
level.
The signal on the deemphasis pin (28) can be supplied to
the SCART connector via a buffer stage. It is also possible
to use this pin as additional audio input. In that case the
internal signal must, of course, be switched off. This can
be realised by means of the sound mute bit (SM in
subaddress 29H). When the IF circuit is switched to
positive modulation the internal signal on the deemphasis
pin is automatically muted.
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