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TDA8722M 数据表(PDF) 6 Page - NXP Semiconductors |
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TDA8722M 数据表(HTML) 6 Page - NXP Semiconductors |
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6 / 28 page  1998 Jun 23 6 Philips Semiconductors Product specification I2C-bus programmable modulator for negative video modulation and FM sound TDA8722 To bias the audio input it is necessary to put a resistor in the application between pin 1 and ground. The resistor has a typical value of 12 k Ω. The RF part of the oscillator consists of: • An oscillator which operates at the required video carrier frequency. The range of the oscillator is determined in the application by C5, C6, L5 and D5. • An RF mixer. It first combines the video signal and the sound subcarrier to build a baseband TV channel. Then the baseband signal is mixed with the oscillator signal to get the RF TV channel. The mixer has two outputs which can be used as two independent asymmetrical outputs, or as one symmetrical output. In the event of asymmetrical use, the unused output must be loaded with a 75 Ω resistor (see Fig.7). The oscillator frequency is set by a programmable PLL frequency synthesizer in accordance with equation: fosc =8 × N × fref Where: fosc is the local oscillator frequency. N is a 12-bit dividing number (10 bits are programmable by the I2C-bus). fref is the crystal frequency (4 MHz) divided by 128 (31.25 kHz). The circuit allows a step of 250 kHz but because only 10 bits are programmable, the programming steps are 1 MHz. When the PLL loop is locked, both inputs of the phase comparator are equal, which gives equation: During the test mode operation, fDIV and fref can be monitored on the output Port pin (pin 14). Software information The synthesizer is controlled via a two-wire I2C-bus receiver. For programming, the address byte (C8 HEX) has to be sent first. Then one or two data bytes are used to set the 10 programmable bits of the dividing number N, the test bits (see Table 1) and the output Port state. Note that after power-up of the IC, the two data bytes must be sent. f DIV f osc 8N × ------------- f xtal 128 ---------- f ref == = Fig.3 Test pattern signal. handbook, full pagewidth 010 20 30 40 50 60 64 70 MBE395 t ( µs) |
类似零件编号 - TDA8722M |
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类似说明 - TDA8722M |
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