TDA9808 Просмотр технического описания (PDF) - Philips Electronics

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TDA9808

Single standard VIF-PLL with QSS-IF and FM-PLL demodulator

Philips Electronics 

Philips Semiconductors

Single standard VIF-PLL with QSS-IF and

FM-PLL demodulator

Product specification

TDA9808

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 filter for

attenuation of the video signal components to the output

pin 10. With this system a high performance hi-fi stereo

sound processing can be achieved.

FM-PLL demodulator

The FM-PLL demodulator consists of a limiter and an

FM-PLL. The limiter provides the amplification and

limitation of the FM sound intercarrier signal. 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.

Furthermore the AF output signal can be muted by

connecting a resistor between the limiter input pin 11 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.

AF signal processing

The AF amplifier consists of two parts:

1. The AF pre-amplifier 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

pin 10. 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

The bandgap 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.

1999 Jun 04

7

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