TDA9550 PHILIPS [NXP Semiconductors], TDA9550 Datasheet - Page 63

• Manufacturer Part Number: TDA9550
• Description: TV signal processor-Teletext decoder with embedded m-Controller
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
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 -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
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 (AUDOUT/AMOUT) via the volume control.
Switching between the QSS output and AM output is made
by means of the AM bit in subaddress 29H (see also
Table 1).
FM demodulator
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. To improve the selectivity an internal bandpass
filter is connected in front of the PLL circuit. This bandpass
filter can be switched off by means of the BPB bit in
subaddress 2CH.
2000 Jun 22
TV signal processor-Teletext decoder with
embedded -Controller
63
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
possible to frequencies of 4.74 and 5.74 MHz so that a
second sound channel can be demodulated. In the latter
application an external bandpass filter has to be applied to
obtain sufficient selectivity (the sound input can be
activated by the SIF bit in subaddress 28H). The setting to
the wanted frequency is realised by means of the control
bits FMA, FMB and FMC in the control bit 29H.
From the output status bytes it can be read whether the
PLL frequency is inside or outside the window and whether
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 signal amplitude is independent 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.
In versions with QSS amplifier and mono intercarrier
sound circuit the FM radio mode is available. This mode is
activated by means of the FMR-bit (subaddress 2CH). The
selectivity must be made by means of a SAW filter at the
sound input with a centre frequency of 33.4 MHz for
Europe and 41.25 MHz for the USA. For this application
the IF demodulator must be set to a fixed frequency (42
MHz for Europe and 48 MHz for the USA). The resulting
input frequency for the FM demodulator is then 8.6 MHz for
Europe and 6.75 MHz for the USA. This frequency must be
selected by means of the bits FMA, FMB and FMC (see
table 108).
Audio circuit and input signal selection
The audio control circuit contains an audio switch with 1
external input and a volume control circuit. The selection
of the various inputs is made by means of the ADX bit. In
various 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. 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
CBM0/1 bits (in subaddress 22H). When the AVL is active
it automatically stabilises the audio output signal to a
certain level.
-Controller/Teletext decoder as a reference. It is also
TDA955X/6X/8X PS/N1 series
Tentative Device Specification