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PDF TDA4655T Data sheet ( Hoja de datos )
| Número de pieza | TDA4655T | |
| Descripción | Generic multi-standard decoder | |
| Fabricantes | NXP Semiconductors | |
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INTEGRATED CIRCUITS
DATA SHEET
TDA4655
Generic multi-standard decoder
Preliminary specification
File under Integrated Circuits, IC02
June 1993
1 page  
Philips Semiconductors
Generic multi-standard decoder
Preliminary specification
TDA4655
FUNCTIONAL DESCRIPTION
The IC contains all functions required
for the identification and
demodulation of signals with the
standards PAL, SECAM, NTSC 3.5
with 3.58 MHz colour-carrier
frequency and NTSC 4.3 with
4.43 MHz colour-carrier frequency.
When an unknown signal is fed into
the input, the circuit has to detect the
standard of the signal, and has to
switch on successively the
appropriate input filter, crystal (8.8 or
7.2 MHz) and demodulator and
finally, after having identified the
signal, it has to switch on the colour
and, in event of NTSC reception, the
hue control. At the outputs the two
colour difference signals −(R−Y)* and
-(B−Y)* are available. The
identification circuit is able to
discriminate between NTSC signals
with colour-carrier frequencies of
3.58 MHz or 4.43 MHz.
ACC-stage
The chrominance signal is fed into the
asymmetrical input (pin 11) of the
ACC-stage (Automatic Colour
Control). The input has to be AC
coupled and has an input impedance
of 20 kΩ in parallel with 10 pF.
To control the chrominance amplitude
the modulation independent burst
amplitude is measured during the
burstkey pulse which is derived from
the sandcastle pulse present at pin
24. The generated error current is fed
into an external storage capacitor at
pin 12. The integrated error voltage
controls the gain of the ACC stage so
that its output is independent of input
signal variations.
The measurement is disabled during
the vertical blanking to avoid failures
because of missing burst signals.
Reference signal generation
The reference signal generation is
achieved by a PLL system. The
reference oscillator operates at twice
the colour-carrier frequency and is
locked on the burst of the
chrominance signal (chr). A divider
provides reference signals (fSC) with
the correct phase relationship for the
PAL/NTSC demodulator and the
identification part. In the SECAM
mode the two f0 frequencies are
derived from the PAL crystal
frequency by special dividers. In this
mode the oscillator is not locked to
the input signal. In the NTSC mode
the hue control circuit is switched
between ACC stage and PLL. The
phase shift of the signal can be
controlled by a DC voltage at pin 13.
The hue control circuit is switched off
during scanning. The reference
frequency (2 × fSC) is available at pin
19 to drive a PAL comb filter for
example.
Demodulation
The demodulation of the colour signal
requires two demodulators. One is
common for PAL and NTSC signals,
the other is for SECAM signals.
The PAL/NTSC demodulator consists
of two synchronized demodulators,
one for the (B−Y) Channel and the
other for the (R−Y) Channel. The
required reference signals (fSC) are
input from the reference oscillator. In
NTSC mode the PAL switch is
disabled.
The SECAM demodulator consists of
a PLL system. During vertical
blanking the PLL oscillator is tuned to
the f0 frequencies to provide a fixed
black level at the demodulator output.
During demodulation the control
voltages are stored in the external
capacitors at pins 4 and 10.
The oscillator requires an external
resistor at pin 7. Behind the PLL
demodulator the signal is fed into the
de-emphasis network which consists
of two internal resistors (2.8 kΩ and
5.6 kΩ) and an external capacitor
connected at pin 2 (220 pF).
After demodulation the signal is
filtered and then fed into the next
stage.
Blanking, colour-killer, buffers
As a result of using only one
demodulator in SECAM mode the
demodulated signal has to be split up
in the (B−Y) Channel and the (R−Y)
Channel. The unwanted signals
occuring every second line, (R−Y) in
the (B−Y) Channel and (B−Y) and in
the (R−Y) Channel, have to be
blanked. This happens in the blanking
stage by an artificial black level being
inserted alternately every second
line.
To avoid disturbances during line and
field flyback these parts of the colour
differential signals are blanked in all
modes.
When no signal has been identified,
the colour is switched off (signals are
blanked) by the colour killer. At the
end of the colour channels are
low-ohmic buffers (emitter followers).
The CD output signals −(B−Y)* and
−(R−Y)* are available at pins 1 and 3.
Identification and system control
The identification part contains three
identification demodulators.
The first demodulates in PAL mode. It
is only active during the burstkey
pulse. The reference signal (fSC) has
the (R−Y) phase.
The second demodulator (PLL
system) operates in SECAM mode
and is active also during the burstkey
pulse, but delayed by 2 µs.
The PLL demodulator discriminates
the frequency difference between the
unmodulated f0 frequencies of the
incoming signal (chr) and the
reference frequency input from the
crystal oscillator.
These two demodulators are followed
by an H/2 switch ‘rectifying’ the
June 1993
5
5 Page 
Philips Semiconductors
Generic multi-standard decoder
Preliminary specification
TDA4655
Table 1 Specification of quartz crystals in HC-49/U13 holder; standard application.
SYMBOL
PARAMETER
VALUE
UNIT
9922 520 00385 9922 520 00387
fn
CL
∆fn
Rr
Rdld max
Rn
C1
C0
Tamb
∆fn
nominal frequency
load capacitance
adjustment tolerance of fn at +25 °C
resonance resistance over temperature range
in the drive level range between 10−12 W and 1.0 × 10−3 W,
the resonance resistance may not exceed (at +25 °C) the
value of Rdld max
resonance resistance of unwanted response
motional capacitance (±20%)
parallel capacitance (±20%)
operating ambient temperature
frequency tolerance over temperature
8.867570
7.159090
series resonance
±20
≤ 60
tbn tbn
14.0
3.6
2Rr (+25°C)
19.5
4.4
−10 to +60
±20
MHz
ppm
Ω
Ω
Ω
fF
pF
°C
ppm
June 1993
11
11 Page | ||
| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet TDA4655T.PDF ] | |
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