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pulses during the vertical interval. The COAST signal is generally not required for PC-generated signals. The logic sense of this pin is controlled by Coast Polarity (register 0FH, Bit 3). When not used, this pin may be grounded and Coast Polarity programmed to 1, or tied HIGH (to VD through a 10 k resistor) and Coast Polarity programmed to 0. Coast Polarity defaults to 1 at power-up. REF BYPASS Internal Reference BYPASS Bypass for the internal 1.25 V band gap reference. It should be connected to ground through a 0.1 µF capacitor. The absolute accuracy of this reference is ±4%, and the temperature coefficient is ±50 ppm, which is adequate for most AD9883A applications. If higher accuracy is required, an external reference may be employed instead. Midscale Voltage Reference BYPASS Bypass for the internal midscale voltage reference. It should be connected to ground through a 0.1 µF capacitor. The exact voltage varies with the gain setting of the BLUE channel. External Filter Connection For proper operation, the pixel clock generator PLL requires an external filter. Connect the filter shown in Figure 6 to this pin. For optimal performance, minimize noise and parasitics on this node.
MIDSCV
FILT
POWER SUPPLY VD
Main Power Supply These pins supply power to the main elements of the circuit. They should be as quiet and filtered as possible. Digital Output Power Supply A large number of output pins (up to 25) switching at high speed (up to 110 MHz) generate a lot of power supply transients (noise). These supply pins are identified separately from the VD pins so special care can be taken to minimize output noise transferred into the sensitive analog circuitry. If the AD9883A is interfacing with lower voltage logic, VDD may be connected to a lower supply voltage (as low as 2.5 V) for compatibility. Clock Generator Power Supply The most sensitive portion of the AD9883A is the clock generation circuitry. These pins provide power to the clock PLL and help the user design for optimal performance. The designer should provide �quiet,� noise-free power to these pins. Ground The ground return for all circuitry on chip. It is recommended that the AD9883A be assembled on a single solid ground plane, with careful attention to ground current paths.
VDD
VD
GND
21 20� TFT TV Service Manual 24/10/2003
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