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参数资料
| 型号： | TDA3853T-T |
| 厂商： | NXP SEMICONDUCTORS |
| 元件分类： | 接收器 |
| 英文描述： | AM, VIDEO DISCRIMINATOR, PDSO20 |
| 文件页数： | 13/18页 |
| 文件大小： | 152K |
| 代理商： | TDA3853T-T |
January 1992
4
Philips Semiconductors
Preliminary specication
TV IF amplier and demodulator with
TV-identication
TDA3853T
PINNING
SYMBOL
PIN
DESCRIPTION
Vi a
1
balanced vision IF input a
TOP
2
tuner AGC take over adjustment point (TOP)
CBL
3
capacitor for black level
n.c.
4
not connected
VIDOFF
5
video off input, identication capacitor
IDENT
6
TV identication 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 amplier input from sound trap
VIDEO
14
video and sound intercarrier output
VP
15
+5 V supply voltage
Cstab
16
decoupling capacitor for voltage stabilizer
GND
17
ground (0 V)
CAGC
18
capacitor for AGC
AGC
19
AGC output to tuner
Vi 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 amplier 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 amplier
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.
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