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AD9883ABST-110 Arkusz danych(PDF) 9 Page - Analog Devices |
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AD9883ABST-110 Arkusz danych(HTML) 9 Page - Analog Devices |
9 / 28 page REV. B AD9883A –9– DESIGN GUIDE General Description The AD9883A is a fully integrated solution for capturing analog RGB signals and digitizing them for display on flat panel monitors or projectors. The circuit is ideal for providing a computer interface for HDTV monitors or as the front end to high performance video scan converters. Implemented in a high performance CMOS process, the interface can capture signals with pixel rates up to 110 MHz. The AD9883A includes all necessary input buffering, signal dc restoration (clamping), offset and gain (brightness and contrast) adjustment, pixel clock generation, sampling phase control, and output data formatting. All controls are programmable via a 2-wire serial interface. Full integration of these sensitive analog functions makes system design straightforward and less sensitive to the physical and electrical environment. With a typical power dissipation of only 500 mW and an operating temperature range of 0 °C to 70°C, the device requires no special environmental considerations. Digital Inputs All digital inputs on the AD9883A operate to 3.3 V CMOS levels. However, all digital inputs are 5 V tolerant. Applying 5 V to them will not cause any damage. Input Signal Handling The AD9883A has three high impedance analog input pins for the Red, Green, and Blue channels. They will accommodate signals ranging from 0.5 V to 1.0 V p-p. Signals are typically brought onto the interface board via a DVI-I connector, a 15-pin D connector, or via BNC connectors. The AD9883A should be located as close as practical to the input connector. Signals should be routed via matched-impedance traces (normally 75 Ω) to the IC input pins. PIN FUNCTION DESCRIPTIONS (continued) Pin Name Function CLAMP External Clamp Input This logic input may be used to define the time during which the input signal is clamped to ground. It should be exer- cised when the reference dc level is known to be present on the analog input channels, typically during the back porch of the graphics signal. The CLAMP pin is enabled by setting control bit Clamp Function to 1, (register 0FH, Bit 7, default is 0). When disabled, this pin is ignored and the clamp timing is determined internally by counting a delay and duration from the trailing edge of the Hsync input. The logic sense of this pin is controlled by Clamp Polarity register 0FH, Bit 6. When not used, this pin must be grounded and Clamp Function programmed to 0. COAST Clock Generator Coast Input (Optional) This input may be used to cause the pixel clock generator to stop synchronizing with Hsync and continue producing a clock at its current frequency and phase. This is useful when processing signals from sources that fail to produce horizontal sync 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 Ω 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. MIDSCV 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. FILT 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. POWER SUPPLY VD Main Power Supply These pins supply power to the main elements of the circuit. They should be filtered and as quiet as possible. VDD Digital Output Power Supply A large number of output pins (up to 25) switching at high speed (up to 110 MHz) generates 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, V DD may be connected to a lower supply voltage (as low as 2.5 V) for compatibility. PVD 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. GND 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 given to ground current paths. |
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