tda9808t NXP Semiconductors, tda9808t Datasheet - Page 7

• Manufacturer Part Number: tda9808t
• Description: Single Standard Vif-pll With Qss-if And Fm-pll Demodulator
• Manufacturer: NXP Semiconductors

Philips Semiconductors
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.
1999 Jun 04
Single standard VIF-PLL with QSS-IF and
FM-PLL demodulator
7
AF signal processing
The AF amplifier consists of two parts:
1. The AF pre-amplifier for FM sound is an operational
2. The AF output amplifier (10 dB) provides the required
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.
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.
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.
Product specification
TDA9808