Philips Semiconductors
Product specification
Multistandard/dual channel TV FM
intercarrier sound demodulator
TDA9820
FUNCTIONAL DESCRIPTION
Stereo channel separation adjustment (optional)
The complete circuit consists of two separate channels,
each consisting of a limiter-amplifier, FM demodulator and
AF amplifier. Circuit operation is also described in Fig.1.
Optimal stereo channel separation is achieved by
adjusting VAF1 (pin 8) and VAF2 (pin 7) as follows:
1. VAF1 by a resistor in series with the DC decoupling
capacitor at pin 9
Source selector
2. VAF2 by a variable resistor in series with the
DC decoupling capacitor on pin 10 to the same
The intercarrier signal is fed through external ceramic
band-pass filters which are tuned to the sound carrier
frequencies.
voltage as VAF1
.
Second sound carrier mute
One of the four filtered sound carriers from
pins 1, 2, 3 or 16 is fed to limiter-amplifier 1 via the
appropriate electronic switch in the source selector.
The electronic switch of the sound carrier is selected by
the control unit (see Table 1).
The output of the second FM demodulator is muted when
the signal level (signal and/or noise) at pin 15 is less than
typically 0.5 mV (RMS value). This avoids an incorrect
stereo or dual sound identification when a mono signal is
transmitted. Therefore, with a mono transmission, there is
no audio output at pin 7. When the signal level at pin 15 is
greater than typically 1.0 mV (RMS value) mute is
switched off.
The second sound carrier of the intercarrier signal is
directly fed from pin 15 to limiter-amplifier 2.
FM demodulators
Each limiter-amplifier is AC-coupled into a
Control unit
FM demodulator. The integrated FM demodulator PLLs
are alignment-free. The FM demodulator outputs are
amplified to 500 mV (RMS value). High amplification and
DC error signals of the PLLs, which are superimposed on
the FM demodulator outputs, require DC decoupling at
pins 9 and 10 of the AF amplifier inputs.
The control unit selects the required sound standard
according to the voltages on pin 5 and pin 6. The control
unit performs the following:
1. selects the free-running frequencies of VCO1 and
VCO2
2. switches the source selector (the four possible
combinations are shown in Table 1).
Table 1 Logic table; note 1
S1
S2
FREQUENCY VCO1
(MHz)
FREQUENCY VCO2
(MHz)
SOURCE SELECTOR
CONNECTION
STANDARD
B/G
(PIN 5) (PIN 6)
1
1
0
0
1
0
1
0
5.5
4.5
6.0
6.5
5.74
4.72
off
pin 1
pin 3
pin 16
pin 2
M
I
D/K
6.74
Note
1. In columns S1 and S2: 0 = LOW and 1 = HIGH.
1996 Nov 20
5
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