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TDA9813T

VIF-PLL with QSS-IF and dual FM-PLL demodulator

Philips Electronics 

Philips Semiconductors

VIF-PLL with QSS-IF and

dual FM-PLL demodulator

Product specification

TDA9813T

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.

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. It should be noted 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.11).

Furthermore the AF output signals can be muted by

connecting a resistor between the limiter inputs pin 14 or

pin 15 and ground.

The FM-PLL consists of an integrated relaxation oscillator,

an integrated loop filter and a phase detector.

The oscillator is locked to the FM intercarrier signal, output

from the limiter. As a result of locking, the oscillator

frequency tracks with the modulation of the input signal

and the oscillator control voltage is superimposed by the

AF voltage. The FM-PLL operates as an FM demodulator.

The AF amplifier consists of two parts:

1. The AF preamplifier for FM sound is an operational

amplifier with internal feedback, high gain and high

common mode rejection. The AF voltage from the PLL

demodulator, by principle a small output signal, is

amplified by approximately 33 dB. The low-pass

characteristic of the amplifier reduces the harmonics of

the intercarrier signal at the sound output terminal.

An additional DC control circuit is implemented to keep

the DC level constant, independent of process spread.

2. The AF output amplifier (10 dB) provides the required

output level by a rail-to-rail output stage. This amplifier

makes use of an input selector for switching to FM or

mute state, controlled by the mute switching voltage.

Internal voltage stabilizer and 1⁄2VP reference

The band gap circuit internally generates a voltage of

approximately 1.25 V, independent of supply voltage and

temperature. A voltage regulator circuit, connected to this

voltage, produces a constant voltage of 3.6 V which is

used as an internal reference voltage.

For all audio output signals the constant reference voltage

cannot be used because large output signals are required.

Therefore these signals refer to half the supply voltage to

achieve a symmetrical headroom, especially for the

rail-to-rail output stage. For ripple and noise attenuation

the 1⁄2VP voltage has to be filtered via a low-pass filter by

using an external capacitor together with an integrated

resistor (fg = 5 Hz). For a fast setting to 1⁄2VP an internal

start-up circuit is added.

1999 Sep 16

7

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