TDA9882TS/V1,118 NXP Semiconductors, TDA9882TS/V1,118 Datasheet - Page 11

• Manufacturer Part Number: TDA9882TS/V1,118
• Description: IC IF-PLL DEMOD 24-SSOP
• Manufacturer: NXP Semiconductors
• Type: Demodulatorr

Specifications of TDA9882TS/V1,118

• Package / Case: *
• Applications: Set-Top Boxes
• Mounting Type: Surface Mount
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 935273911118; TDA9882TS/V1-T; TDA9882TS/V1-T

Philips Semiconductors
9397 750 13507
Product data sheet
8.14 Audio amplifier and mute time constant
The intercarrier signal from the single reference QSS mixer is fed to the input of an
AC-coupled gain controlled amplifier with two stages. The gain controlled output signal is
fed to the phase detector of the narrow-band FM PLL (FM demodulator). For good
selectivity and robustness against disturbance caused by the video signal, a high linearity
of the gain controlled FM amplifier and of the phase detector as well as a constant signal
level are required. The gain control is done by means of an ‘in phase’ demodulator for the
FM carrier (from the output of the FM amplifier). The demodulation output is fed into a
comparator for charging or discharging the integrated AGC capacitor. This leads to a
mean value AGC loop to control the gain of the FM amplifier.
The FM demodulator is realized as a narrow-band PLL with an external loop filter, which
provides the necessary selectivity (bandwidth approximately 100 kHz). To achieve good
selectivity, a linear phase detector and a constant input level are required. The gain
controlled intercarrier signal from the FM amplifier is fed to the phase detector. The phase
detector controls, via the loop filter, the integrated low radiation relaxation oscillator. The
designed frequency range is from 4 MHz to 7 MHz.
The VCO within the FM PLL is phase-locked to the incoming 2nd SIF signal which is
frequency modulated. The VCO control voltage is superimposed by the AF voltage.
Therefore, the VCO tracks with the FM of the 2nd SIF signal. Thus, the AF voltage is
present at the loop filter and is typically 5 mV (RMS) for 27 kHz FM deviation. This
AF signal is fed via a buffer to the audio amplifier.
The correct locking of the PLL is supported by the digital acquisition help circuit; see
Section
The audio amplifier consists of two parts:
The AF preamplifier used for FM sound is an operational amplifier with internal feedback,
high gain and high common mode rejection. The AF voltage from the PLL demodulator is
5 mV (RMS) for a frequency deviation of 27 kHz and is amplified by 30 dB. By using a
DC operating point control circuit (with external capacitor C
decoupled from the PLL DC voltage. The low-pass characteristic of the amplifier reduces
the harmonics of the sound intercarrier signal at the AF output terminal.
For FM sound a switchable de-emphasis network (with external capacitor) is implemented
between the preamplifier and the output amplifier. The de-emphasis time constant with
50 s or 75 s depends on the FM carrier selection via pins FM0 and FM1; see
The AF output amplifier provides the required AF output level by a rail-to-rail output stage.
A preceding stage makes use of an input selector for switching between the FM sound,
AM sound and mute state.
Switching to the mute state is controlled automatically, depending on the digital acquisition
help circuit should the VCO of the FM PLL not be in the required frequency window. This
is done by a time constant: fast for switching to the mute state and slow (typically 40 ms)
for switching to the non-mute state.
Auto mute can be disabled via pins SIF1 and SIF2 with resistor; see
•
•
AF preamplifier
AF output amplifier.
8.6.
Rev. 01 — 16 November 2004
Multistandard vision and QSS FM sound IF PLL demodulator
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
AF
), the AF preamplifier is
Table
TDA9882
6.
Table
11 of 45
5.