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TDA9818 Folha de dados(PDF) 8 Page - NXP Semiconductors |
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TDA9818 Folha de dados(HTML) 8 Page - NXP Semiconductors |
8 / 41 page 2004 Jun 29 8 Philips Semiconductors Product specification Single/multistandard VIF/SIF-PLL and FM-PLL/AM demodulators TDA9817; TDA9818 Sound IF amplifier and SIF AGC The sound IF amplifier consists of two AC-coupled differential amplifier stages. Each differential stage comprises a controlled feedback network provided by emitter degeneration. The SIF AGC detector is related to the SIF input signal (average level of AM or FM carrier) and controls the SIF amplifier to provide a constant SIF signal to the AM demodulator and single reference QSS mixer. At L standard (AM sound) the SIF AGC reaction time is set to ‘slow’ for nominal video conditions. But with a decreasing VIF amplitude step the SIF AGC is set to ‘fast’ mode controlled by the VIF AGC detector. In FM mode this reaction time is always ‘fast’. Single reference QSS mixer The single reference QSS mixer is realized by a multiplier. The SIF amplifier output signal is fed to the single reference QSS mixer and converted to intercarrier frequency by the regenerated picture carrier (VCO). The mixer output signal is fed via a high-pass for attenuation of the video signal components to the output pin QSS. With this system a high performance hi-fi stereo sound processing can be achieved. For a simplified application without a sound IF SAW filter the single reference QSS mixer can be switched to the intercarrier mode by connecting pin SIF2 to ground. In this mode the sound IF passes the vision IF SAW filter and the composite IF signal is fed to the single reference QSS mixer. This IF signal is multiplied with the 90 degree TWD output signal for converting the sound IF to intercarrier frequency. This composite intercarrier signal is fed to the output pin QSS, too. By using this quadrature detection, the low frequency video signals are removed. AM demodulator The AM demodulator is realized by a multiplier. The modulated SIF amplifier output signal is multiplied in phase with the limited (AM is removed) SIF amplifier output signal. The demodulator output signal is fed via an integrated low-pass filter for attenuation of the carrier harmonics to the AF amplifier. FM-PLL demodulator The FM-PLL demodulator consists of a limiter and an FM-PLL. The limiter provides the amplification and limitation of the FM sound intercarrier signal. The result is high sensitivity and AM suppression. The amplifier consists of 7 stages which are internally AC-coupled in order to minimize the DC offset. Furthermore the AF output signal can be muted by connecting a resistor between the limiter input pin FMin and ground. The FM-PLL consists of an integrated relaxation oscillator, an integrated loop filter and a phase detector. The oscillator is locked to the FM intercarrier signal, output from the limiter. As a result of locking, the oscillator frequency tracks with the modulation of the input signal and the oscillator control voltage is superimposed by the AF voltage. The FM-PLL operates as an FM demodulator. Audio Frequency signal processing The AF amplifier consists of two parts: 1. The AF pre-amplifier for FM sound is an operational amplifier with internal feedback, high gain and high common mode rejection. The AF voltage from the PLL demodulator, by principle a small output signal, is amplified by approximately 33 dB. The low-pass characteristic of the amplifier reduces the harmonics of the intercarrier signal at the sound output terminal pin Vde-em at which the de-emphasis network for FM sound is applied. An additional DC control circuit is implemented to keep the DC level constant, independent of process spread. 2. The AF output amplifier (10 dB) provides the required output level by a rail-to-rail output stage. This amplifier makes use of an input selector for switching to AM, FM de-emphasis or mute state, controlled by the standard switching voltage and the mute switching voltage. Internal voltage stabilizer The bandgap circuit internally generates a voltage of approximately 1.25 V, independent of supply voltage and temperature. A voltage regulator circuit, connected to this voltage, produces a constant voltage of 3.6 V which is used as an internal reference voltage. |
Nº de peça semelhante - TDA9818 |
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Descrição semelhante - TDA9818 |
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