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TDA9819T 数据表(PDF) 7 Page - NXP Semiconductors |
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TDA9819T 数据表(HTML) 7 Page - NXP Semiconductors |
7 / 40 page 1998 Jul 14 7 Philips Semiconductors Product specification Multistandard vision and sound-IF PLL with DVB-IF processing TDA9819 SIF amplifier and 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 signals (average level of AM or FM carriers) and controls the SIF amplifier to provide a constant SIF signal to the AM demodulator and single reference QSS mixer. 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 also set to ‘fast’ controlled by the standard switch. 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 20. 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 pins 31 and 32 to ground (see note 18 of Chapter “Characteristics”). In this mode the sound-IF passes the VIF SAW filter and the composite IF signal is fed to the single reference QSS mixer. This IF signal is multiplied by the 90 ° TWD output signal for converting the sound-IF to intercarrier frequency. By using this quadrature detection, the low frequency video signals are removed. Due to the sound-IF attenuation in the VIF filter (sound shelf), the audio signal-to-noise (S/N) figure decreases. AM demodulator The AM demodulator (French L standard) 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 detector The FM detector consists of a limiter, an FM-PLL and an AF amplifier. The limiter provides the amplification and limitation of the FM sound intercarrier signal before demodulation. 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 and to save pins for DC decoupling. 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. The AF amplifier consists of two parts: 1. The AF preamplifier 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 30 dB. The low-pass characteristic of the amplifier reduces the harmonics of the intercarrier signal at the sound output terminal. 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 or mute state, controlled by the standard switching voltage and the mute switching voltage. Internal voltage stabilizer and 1 ⁄ 2VP reference The band gap 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. For all audio output signals the constant reference voltage cannot be used because large output signals are required. Therefore these signals refer to half the supply voltage to achieve a symmetrical headroom, especially for the rail-to-rail output stage. For ripple and noise attenuation the 1 ⁄2VP voltage has to be filtered via a low-pass filter by using an external capacitor together with an integrated resistor (fg = 5 Hz). For a fast setting to 1⁄2VP an internal start-up circuit is added. |
类似零件编号 - TDA9819T |
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类似说明 - TDA9819T |
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