TDA9820 datasheet(5/20 Pages) PHILIPS

5 / 20 page

1996 Nov 20

Philips Semiconductors

Product speciﬁcation

Multistandard/dual channel TV FM

intercarrier sound demodulator

TDA9820

FUNCTIONAL DESCRIPTION

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.

Source selector

The intercarrier signal is fed through external ceramic

band-pass filters which are tuned to the sound carrier

frequencies.

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 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

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.

Stereo channel separation adjustment (optional)

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

2. VAF2 by a variable resistor in series with the

DC decoupling capacitor on pin 10 to the same

voltage as VAF1.

Second sound carrier mute

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.

Control unit

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

Note

1. In columns S1 and S2: 0 = LOW and 1 = HIGH.

STANDARD

(PIN 5)

(PIN 6)

FREQUENCY VCO1

(MHz)

FREQUENCY VCO2

(MHz)

SOURCE SELECTOR

CONNECTION

B/G

5.5

5.74

pin 1

4.5

4.72

pin 3

6.0

off

pin 16

D/K

6.5

6.74

pin 2

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