TDA3853T Datasheet, PDF (4/18 Pages) NXP Semiconductors – TV IF amplifier and demodulator with TV-identification

Philips Semiconductors
TV IF amplifier and demodulator with
TV-identification
Preliminary specification
TDA3853T
PINNING
SYMBOL PIN
DESCRIPTION
V_{i a}
TOP
1 balanced vision IF input a
2 tuner AGC take over adjustment point (TOP)
C_BL
3 capacitor for black level
n.c.
4 not connected
VIDOFF 5 video off input, identification capacitor
IDENT 6 TV identification output
TRSW 7 set input for tracking switch, tracking hold capacitor
AFT
8 automatic frequency tracking output
n.c.
9 not connected
RES1
10 resonance reference circuit for vision carrier
RES2
11 resonance reference circuit for vision carrier
CVBS 12 CVBS output (positive)
TRAP
13 video buffer amplifier input from sound trap
VIDEO 14 video and sound intercarrier output
V_P
C_stab
GND
15 +5 V supply voltage
16 decoupling capacitor for voltage stabilizer
17 ground (0 V)
C_AGC
AGC
18 capacitor for AGC
19 AGC output to tuner
V_{i b}
20 balanced vision IF input b
Fig.2 Pin configuration.
FUNCTIONAL DESCRIPTION
The TDA3853T is a TV IF
amplifier/demodulator for negative
modulation.
The IF input signal is amplified,
gain-controlled and demodulated
(Fig.1).
Vision IF amplifier and
demodulator
The vision IF amplifier consists of
three AC-coupled differential
amplifiers. Gain control is achieved by
current divider stages. Emitter
feedback resistors in the differential
amplifiers are optimized with respect
to noise and signal capability.
Synchronous demodulator
The demodulator has a reference
amplifier consisting of a differential
amplifier with resistive load to provide
passive vision carrier regeneration.
This allows capacitive coupling of the
resonance circuit to obtain a notch
filter characteristic and tracking of the
resonance circuit.
A cascaded limiter amplifier follows
the reference amplifier to eliminate
amplitude modulation. The limited IF
reference signal is fed to the
demodulator. The unlimited IF signal
is fed via a phase correction network
to the demodulator. The video
amplifier is an operational amplifier
with a wide bandwidth and internal
feedback. The video and sound
intercarrier signal is output on pin 14.
Video buffer amplifier
This operational amplifier has a wide
bandwidth with internal feedback and
frequency compensation. Gain and
input impedance are adapted to
operate with a ceramic sound trap.
The switching functions are described
in Table 1.
AGC detector and IF gain control
The video signal is fed through
low-pass filters to attenuate the sound
carriers and then is fed to the AGC
detector.
Peak-sync AGC detection.
A special network provides current
pulses to fast charge the AGC
capacitor on pin 18 (gain reduction).
This achieves a minimum of video
distortion.
The AGC control converts the AGC
capacitor voltage to three separate
voltages to control the IF stages.
January 1992
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