TDA9882 Philips Semiconductors, TDA9882 Datasheet - Page 10

• Manufacturer Part Number: TDA9882
• Description: Alignment-free multistandard vision and QSS FM sound IF PLL demodulator
• Manufacturer: Philips Semiconductors

Philips Semiconductors
9397 750 13507
Product data sheet
8.10 SIF AGC detector
8.11 Single reference QSS mixer
8.12 AM demodulator
8.13 FM demodulator and acquisition help circuit
8.9 SIF amplifier
The SIF amplifier consists of three AC-coupled differential stages. Gain control is
performed by emitter degeneration. The total gain control range is typical 66 dB. The
differential input impedance is typical 2 k in parallel with 3 pF.
SIF gain control is performed by the detection of the DC component of the
AM demodulator output signal. This DC signal is directly corresponding to the SIF voltage
at the output of the SIF amplifier so that a constant SIF signal is supplied to the
AM demodulator and to the single reference QSS mixer.
By switching the gain of the input amplifier of the SIF AGC detector dependent on
modulation select, the internal SIF level for FM sound is 5.5 dB lower than for AM sound.
This is done to adapt the SIF AGC characteristic to the VIF AGC characteristic. The
adaption is ideal for a picture-to-sound FM carrier ratio of 13 dB.
Via a comparator the integrated AGC capacitor is charged or discharged for the
generation of the required SIF gain. Due to AM sound, the AGC reaction time is slow
(f
event of a decreasing IF amplitude step, the load current of the AGC capacitor is
increased (fast mode) when the VIF AGC detector (at positive modulation mode) operates
in the fast mode too. An additional circuit (threshold approximately 7 dB) ensures a very
fast gain reduction for a large increasing IF amplitude step.
With the present system high performance Hi-Fi stereo sound processing can be
achieved.
The single reference QSS mixer generates the 2nd FM TV sound intercarrier signal. It is
realized by a linear multiplier which multiplies the SIF amplifier output signal and the
VIF PLL VCO signal which is locked to the picture carrier.
The QSS mixer output signal is fed internally via a high-pass and low-pass combination to
the FM demodulator as well as via an operational amplifier to the QSS output pin QSSO.
The amplitude modulated SIF amplifier output signal is fed both to a two-stage limiting
amplifier for removing the AM and to a linear multiplier. The result of the multiplication of
the SIF signal with the limiter output signal is AM demodulation (passive synchronous
demodulator). The demodulator output signal is fed via a low-pass filter for the attenuation
of carrier harmonics and via the input amplifier of the SIF AGC detector to the audio
amplifier.
The narrow-band FM PLL detector consists of:
c
•
•
< 20 Hz for the closed AGC loop). For reducing this AM sound time constant in the
Gain controlled FM amplifier and AGC detector
Narrow-band PLL.
Rev. 01 — 16 November 2004
Multistandard vision and QSS FM sound IF PLL demodulator
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
TDA9882
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