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PDF TDA4657 Data sheet ( Hoja de datos )
| Número de pieza | TDA4657 | |
| Descripción | Generic multi-standard decoder | |
| Fabricantes | NXP Semiconductors | |
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INTEGRATED CIRCUITS
DATA SHEET
TDA4657
Generic multi-standard decoder
Preliminary specification
File under Integrated Circuits, IC02
June 1993
1 page  
Philips Semiconductors
Generic multi-standard decoder
Preliminary specification
TDA4657
FUNCTIONAL DESCRIPTION
The IC contains all functions required for the identification
and demodulation of signals with the standards PAL,
SECAM 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 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.
ACC stage
The chrominance signal is fed into the asymmetrical input
(pin 9) 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 20. The generated error current is fed into
an external storage capacitor at pin 10. 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 11. The hue control circuit
is switched off during scanning.
The reference frequency (2 × fsc) is available at pin 16 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 8.
The oscillator requires an external resistor at pin 6. 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
occurring every second line, (R−Y) in the (B−Y) Channel
and (B−Y) 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 demodulated signal. The result is an
identification signal (PIDT, pin 13) that is positive for a PAL
signal in PAL mode, for a SECAM signal in SECAM mode
June 1993
5
5 Page 
Philips Semiconductors
Generic multi-standard decoder
Preliminary specification
TDA4657
Table 1 Specification of quartz crystals in HC-49/U13 holder; standard application.
SYMBOL
PARAMETER
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
VALUE
9922 520 00385
8.867570
series resonance
±20
≤ 60
tbn
UNIT
MHz
ppm
Ω
Ω
2Rr (+25 °C)
14.0
3.6
−10 to +60
±20
Ω
fF
pF
°C
ppm
June 1993
11
11 Page | ||
| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet TDA4657.PDF ] | |
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