TDA9881TS/V2-T NXP Semiconductors, TDA9881TS/V2-T Datasheet - Page 10

• Manufacturer Part Number: TDA9881TS/V2-T
• Description: Modulator / Demodulator IF DEMODULATOR
• Manufacturer: NXP Semiconductors

Specifications of TDA9881TS/V2-T

• Package / Case: SSOP-24
• Maximum Operating Temperature: + 70 C
• Maximum Power Dissipation: 385 mW
• Minimum Operating Temperature: - 20 C
• Modulation Type: Quadrature
• Mounting Style: SMD/SMT
• Operating Supply Voltage: 5 V
• Supply Current: 63 mA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: TDA9881TS/V2,518

Philips Semiconductors
9397 750 13417
Product data sheet
8.11 Single reference QSS mixer
8.12 FM demodulator and acquisition help circuit
With the present system high performance Hi-Fi stereo sound processing can be
achieved. For a simplified application without an SIF SAW filter, the single reference QSS
mixer can be switched to the intercarrier mode via pins SIF1 and SIF2; see
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. In this way the QSS mixer
operates as a quadrature mixer in the intercarrier mode and provides suppression of the
low frequency video signals.
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 narrow-band FM PLL detector consists of:
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
•
•
Gain controlled FM amplifier and AGC detector
Narrow-band PLL.
8.6.
Rev. 01 — 16 November 2004
Alignment-free vision and FM sound IF PLL demodulator
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
TDA9881
Table
7.
10 of 42