TDA9814 Ver la hoja de datos (PDF) - Philips Electronics
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TDA9814 Datasheet PDF : 36 Pages
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Philips Semiconductors
Multistandard VIF-PLL with QSS-IF
and dual FM-PLL/AM demodulator
Product specification
TDA9814T
Video demodulator and amplifier
The video demodulator is realized by a multiplier which is
designed for low distortion and large bandwidth. The vision
IF input signal is multiplied with the ‘in phase’ signal of the
travelling wave divider output. In the demodulator stage
the video signal polarity can be switched in accordance
with the TV standard.
The demodulator output signal is fed via an integrated
low-pass filter for attenuation of the carrier harmonics to
the video amplifier. The video amplifier is realized by an
operational amplifier with internal feedback and high
bandwidth. A low-pass filter is integrated to achieve an
attenuation of the carrier harmonics for B/G and
L standard. The standard dependent level shift in this
stage delivers the same sync level for positive and
negative modulation. The video output signal is 1 V (p-p)
for nominal vision IF modulation.
Single reference QSS mixer
The single reference QSS mixer is realized by a multiplier.
The SIF amplifier output signal is fed to the single
reference QSS mixer and converted to intercarrier
frequency by the regenerated picture carrier (VCO). The
mixer output signal is fed via a high-pass for attenuation of
the video signal components to the output pin 17. With this
system a high performance hi-fi stereo sound processing
can be achieved.
AM demodulator
The AM demodulator is realized by a multiplier. The
modulated SIF amplifier output signal is multiplied in
phase with the limited (AM is removed) SIF amplifier
output signal. The demodulator output signal is fed via an
integrated low-pass filter for attenuation of the carrier
harmonics to the AF amplifier.
Video buffer
For an easy adaption of the sound traps an operational
amplifier with internal feedback is used in the event of B/G
and L standard. This amplifier is featured with a high
bandwidth and 7 dB gain. The input impedance is adapted
for operating in combination with ceramic sound traps. The
output stage delivers a nominal 2 V (p-p) positive video
signal. Noise clipping is provided.
SIF amplifier and AGC
The sound IF amplifier consists of two AC-coupled
differential amplifier stages. Each differential stage
comprises a controlled feedback network provided by
emitter degeneration.
The SIF AGC detector is related to the SIF input signals
(average level of AM or FM carriers) and controls the SIF
amplifier to provide a constant SIF signal to the AM
demodulator and single reference QSS mixer. The SIF
AGC reaction time is set to ‘slow’ for nominal video
conditions. But with a decreasing VIF amplitude step the
SIF AGC is set to ‘fast’ mode controlled by the VIF-AGC
detector. In FM mode this reaction time is also set to ‘fast’
controlled by the standard switch.
FM-PLL demodulator
Each FM-PLL demodulator consists of a limiter, an
FM-PLL and an AF amplifier. The limiter provides the
amplification and limitation of the FM sound intercarrier
signal before demodulation. The result is high sensitivity
and AM suppression. The amplifier consists of 7 stages
which are internally AC-coupled in order to minimize the
DC offset and to save pins for DC decoupling.
The second limiter is extended with an additional level
detector consisting of a rectifier and a comparator. By
means of this the AF2 signal is set to mute and the
PLL VCO is switched off, if the intercarrier signal at pin 14
is below 1 mV (RMS) in order to avoid false identification
of a stereo decoder. Note that noise at pin 14 disables the
mute state (at low SIF input signal), but this will not lead to
false identification. This ‘auto-mute’ function can be
disabled by connecting a 5.6 kΩ resistor from pin 14 to VP
(see Fig.13).
Furthermore the AF output signals can be muted by
connecting a resistor between the limiter inputs pin 14 or
pin 15 and ground.
1998 Feb 09
7
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