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TDA8722 Datasheet(PDF) 5 Page - NXP Semiconductors |
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TDA8722 Datasheet(HTML) 5 Page - NXP Semiconductors |
5 / 28 page 1998 Jun 23 5 Philips Semiconductors Product specification I2C-bus programmable modulator for negative video modulation and FM sound TDA8722 PINNING SYMBOL PIN DESCRIPTION AUDIO 1 audio input SOSCA 2 sound oscillator A SOSCB 3 sound oscillator B UOSCB 4 UHF oscillator B OGND 5 RF oscillator ground UOSCA 6 UHF oscillator A AMP 7 tuning amplifier output CP 8 charge pump output XTAL 9 crystal oscillator DGND 10 digital ground VDDD 11 digital supply voltage SCL 12 serial clock input (I2C-bus) SDA 13 serial data input (I2C-bus) P0 14 NPN open-collector output Port RFB 15 asymmetrical RF output B RFA 16 asymmetrical RF output A ADJUST 17 modulation depth and picture-to-sound distance adjustment pin AGND 18 analog ground VIDEO 19 video input VDDA 20 analog supply voltage Fig.2 Pin configuration. handbook, halfpage TDA8722 MBE394 1 2 3 4 5 6 7 8 9 10 20 19 18 17 16 15 14 13 12 11 CP DGND XTAL SCL SDA AMP P0 UOSCA RFB OGND RFA UOSCB ADJUST SOSCB AGND SOSCA VIDEO AUDIO VDDD VDDA FUNCTIONAL DESCRIPTION The TDA8722 is a programmable modulator which can be divided into two main blocks: • A modulator for negative video modulation and FM sound TV standards • A programmable PLL frequency synthesizer. The video part of the modulator consists of a clamping circuit which sets the internal reference voltage to the bottom of the synchronizing pulse, followed by a white clip which avoids over modulation in case the video signal is too strong. Typically, the IC starts to clip the video signal when the voltage at the video input (pin 19) is >560 mV (p-p) while the normal voltage at the video input is 500 mV (p-p). This clipping function ensures that the video modulation depth is not too high. The modulation depth is adjusted in the application between at least 65 and 90% by changing the resistor value between pin 17 and ground (R17). The value can change between 47 k Ω and infinite (R17 removed); see Fig.10. The video part also contains a test pattern signal generator to simplify the adjustment of the receiving channel of the TV set to the required channel of the modulator. The pattern consists of a synchronization pulse and two vertical white bars on screen (see Fig.3). The audio part of the modulator contains an FM sound modulator. The frequency of the sound subcarrier is set in the application by external components (C3, L3 and R3). The difference between the video carrier level and the sound subcarrier level is adjusted in the application by changing the value of the capacitor between pin 17 and ground (C17). The value can change between 0 and 47 pF. The distance between the video carrier and the sound subcarrier can be adjusted between at least −10 and −18 dB (see Fig.11). |
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