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TDA9811 Datenblatt(PDF) 7 Page - NXP Semiconductors |
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TDA9811 Datenblatt(HTML) 7 Page - NXP Semiconductors |
7 / 36 page 1998 Feb 09 7 Philips Semiconductors Product specification Multistandard VIF-PLL with QSS-IF and AM demodulator TDA9811 Video buffer For an easy adaption of the sound traps an operational amplifier with internal feedback is used in the event of B/G and L standard. This amplifier is featured with a high bandwidth and 7 dB gain. The input impedance is adapted for operating in combination with ceramic sound traps. The output stage delivers a nominal 2 V (p-p) positive video signal. Noise clipping is provided. 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. 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. Internal voltage stabilizer and 1 ⁄2VP-reference 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. For the audio output signal the constant reference voltage cannot be used because large output signals are required. Therefore this signal refers to half the supply voltage to achieve a symmetrical headroom. 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. |
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