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TDA9882TS Datasheet(PDF) 10 Page - NXP Semiconductors |
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TDA9882TS Datasheet(HTML) 10 Page - NXP Semiconductors |
10 / 45 page 9397 750 13507 © Koninklijke Philips Electronics N.V. 2004. All rights reserved. Product data sheet Rev. 01 — 16 November 2004 10 of 45 Philips Semiconductors TDA9882 Multistandard vision and QSS FM sound IF PLL demodulator 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 Ω in parallel with 3 pF. 8.10 SIF AGC detector 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 (fc < 20 Hz for the closed AGC loop). For reducing this AM sound time constant in the 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. 8.11 Single reference QSS mixer 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. 8.12 AM demodulator 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. 8.13 FM demodulator and acquisition help circuit The narrow-band FM PLL detector consists of: • Gain controlled FM amplifier and AGC detector • Narrow-band PLL. |
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