TDA8349 View Datasheet(PDF) - Philips Electronics
Part Name
Description
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TDA8349 Datasheet PDF : 17 Pages
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Philips Semiconductors
Multistandard IF amplifier and demodulator
PINNING
PIN
1,2
3
4
5
6
7
8
9
10
11
12
13
14
15,16
17
18
19
20
DESCRIPTION
balanced IF inputs
tuner AGC starting point adjustment
tuner AGC output
AGC time constant
AFC on/off switch and sample-and-hold capacitor
video switch
AFC output Q1
AFC output Q2
video switch external input
video output
video switch internal input
video switch output
positive supply voltage
reference tuned circuit for demodulator
ground
mute output
coincidence filter
system switch
Product specification
TDA8349A
FUNCTIONAL DESCRIPTION
General
The IC consists of the following parts as illustrated in Fig.1:
• Gain controlled video IF amplifier
• Quasi-synchronous demodulator
• Video amplifier/buffer with white spot clamp/inverter and
noise clamp
• AGC circuit which operates either on top sync level
(negative modulation) or on white level (positive
modulation) or on top level (MAC)
• AFC circuit with sample-and-hold circuit for negatively
modulated signals, on/off switch and a digital or analog
output (switchable)
• Circuit for switching between positive and negative
modulation
• Video recognition circuit for sound muting and tuning
indication
• Video switch which facilitates selection between two
different video signals, with different gain settings
IF amplifier
The IF amplifier consists of three AC coupled differential
gain stages with adjustable feedback in the emitter. The
AC coupling allows simple biasing, cascades can be used
and no DC feedback is required. This provides a control
range above 70 dB with good linearity. The minimum input
signal to obtain the nominal output amplitude is
50 µV RMS.
Demodulator
The demodulator is a quasi-synchronous circuit that
employs passive carrier regeneration and a tuned circuit
for selectivity. The regenerated carrier signal is limited by
a clamping circuit before it is fed to the demodulator.
Switching between positive and negative modulation is
achieved by the system switch which provides currents to
the demodulator in a positive or negative direction.
Video amplifier
The video amplifier based on the feedback principle
improves the linearity of the video output buffer. It has an
internal bandgap reference to ensure a stable video output
at different supply voltages and temperatures. This
February 1991
4
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