TDA9882 Philips Semiconductors, TDA9882 Datasheet - Page 8

• 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
8.4 FPLL detector
8.5 VCO and divider
8.6 AFC and digital acquisition help circuit
For positive modulation, the white peak level voltage is compared with a reference voltage
(nominal white level) by a comparator which charges (fast) or discharges (slow) the
external AGC capacitor directly for the generation of the required VIF gain. The need of a
very large time constant for VIF gain increase is caused by the fact that the peak white
level may appear only once in a field. In order to reduce this time constant, an additional
level detector increases the discharging current of the AGC capacitor (fast mode) in the
event of a decreasing VIF amplitude step controlled by the detected actual black level
voltage. The threshold level for fast mode AGC is typical 6 dB video amplitude. The fast
mode state is also transferred to the SIF AGC detector for speed-up. In case of missing
peak white pulses, the VIF gain increase is limited to typical 3 dB by comparing the
detected actual black level voltage with a corresponding reference voltage.
The VIF amplifier output signal is fed to a frequency detector and a phase detector via a
limiting amplifier to remove the video AM.
During acquisition the frequency detector produces a current that is proportional to the
frequency difference between the VIF and the VCO signal. After frequency lock-in the
phase detector produces a current that is proportional to the phase difference between
the VIF and the VCO signal. The currents from the frequency and phase detector are
charged into the loop filter which controls the VIF VCO and locks it to the frequency and
phase of the VIF carrier.
For a positive modulated VIF signal, the charging currents are gated by the composite
sync in order to avoid signal distortion in case of overmodulation. The gating depth is set
to 0 %.
The VCO of the VIF FPLL operates as an integrated low radiation relaxation oscillator at
twice the picture carrier frequency. The control voltage, required to tune the VCO to
actually double the picture carrier frequency, is generated at the loop filter by the
frequency phase detector. The possible frequency range is 50 MHz to 140 MHz (typical
value).
The oscillator frequency is divided-by-two to provide two differential square wave signals
with exactly 90 degrees phase difference, independent of the frequency, for use in the
FPLL detectors, the video demodulator and the single reference QSS mixer.
Each relaxation oscillator of the VIF PLL and FM PLL demodulator has a wide frequency
range. To prevent false locking of the PLLs, with respect to the catching range, the digital
acquisition help circuit provides an individual control until the frequency of the VCO is
within the preselected standard dependent lock-in window of the PLL.
The VIF carrier frequencies 38.9 MHz (M/N, B/G, I, D/K and L standard), 45.75 MHz
(NTSC standard) and 33.9 MHz (L-accent standard) can be selected via pin VIF0 and
pin QSSO with resistor; see
The FM carrier frequencies can be selected via pin FM0 and pin FM1; see
Rev. 01 — 16 November 2004
Multistandard vision and QSS FM sound IF PLL demodulator
Table
4.
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
TDA9882
www.DataSheet4U.com
Table
5.
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