TDA3867T Philips Semiconductors, TDA3867T Datasheet - Page 5

• Manufacturer Part Number: TDA3867T
• Description: Quasi-split sound processor with two FM demodulators
• Manufacturer: Philips Semiconductors

Philips Semiconductors
FUNCTIONAL DESCRIPTION
The quasi-split sound processor is
suitable for all FM standards
(e. g. B/G).
The AGC detector uses peak sync
level. Sound carrier SC1 (5.5 MHz)
provides AF1, sound carrier SC2
(5.74 MHz) provides AF2. With no
sound carrier SC2 on pin 22, AF2
output is muted. The mute circuit
prevents false signal recognition in
the stereo decoder at high IF signal
levels when no second sound carrier
exists (mono) and an AF signal is
present in the identification signal
frequency range.
With 1 mV on pin 22, under
measurement conditions, AF2 is
switched on (see limiting amplifier).
Weak input signals at pins 27 and 28
generate noise on pin 22, which is
present in the intercarrier signal and
passes through the 5.74 MHz filter.
Noise on pin 22 inhibits muting. No
misinterpretation due to white noise
occurs in the stereo decoder; when
non-correlated noise masks the
identification signal frequencies,
which may be present in sustained
tone signals. The stereo decoder
remains switched to mono.
January 1992
Quasi-split sound processor with two FM demodulators
The series capacitor C
38.9 MHz resonant circuit provides a
notch at the sound carrier frequency
in order to provide more attenuation
for the sound carrier in the vision
carrier reference channel. The ratio of
parallel/series capacitor depends on
the ratio of VC/SC frequency and has
to be adapted to other TV
transmission standards if necessary,
according to
The result is an improved “intercarrier
buzz” (up to 10 dB improvement in
sound channel 2 with 250 kHz video
modulation for B/G stereo) or
suppression of 350 kHz video
modulated beat frequency in the
digitally-modulated NICAM
subcarrier. The picture carrier for
quadrature demodulation in the
intercarrier mixer is not exactly
90 degrees due to the shift variation
in the integrated phase shift network.
The tuning of the LC reference circuit
to provide optimal video suppression
at the intercarrier output is not the
same as that to provide optimal
intercarrier buzz suppression. In
order to optimize the AF signal
performance, a fine tuning for the
optimal S/N at the sound channel 2
(from 5.74 MHz) may be performed
with a 250 kHz square wave video
modulation.
C
S
=
C
P
f
VC
f
SC
5
2
- C
s
in the
P
.
Measurements at the demodulators:
For all signal-to-noise measurements
the generator must meet the following
specifications;
phase modulation errors 0.5 degree
for B/W-jumps intercarrier
signal-to-noise ratio as measured
with “TV demodulator AMF2”
(weighted S/N)
must be
modulation of the B/W-signal.
Signal-to-noise ratios are measured
with f =
f
by 5.3 dB.
m
27 kHz the S/N ratio is deteriorated
= 1 kHz; with a deviation of
60 dB at 6 kHz sine wave
50 kHz deviation and
Preliminary specification
TDA3867T