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AD724 Scheda tecnica(PDF) 10 Page - Analog Devices |
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AD724 Scheda tecnica(HTML) 10 Page - Analog Devices |
10 / 15 page REV. B –10– AD724 220 F 75 75 75 –5V FIN OSC 0.1 F +5V ** CRYSTAL 0.1 F +5V (VAA) * AGND DGND AD724 ENCD RIN GIN BIN HSYNC VSYNC SELECT STND CRMA LUMA CMPS APOS DPOS 10–30pF 0.1 F 10 F 0.1 F 10 F 75 75 JMP * PARALLEL–RESONANT CRYSTAL; 3.579545MHz (NTSC) OR 4.433620MHz (PAL) CAPACITOR VALUE DEPENDS ON CRYSTAL CHOSEN 75 COMPOSITE VIDEO 75 220 F 75 220 F Y C S-VIDEO (Y/C VIDEO) 75 75 75 B G R RGB MONITOR VSYNC HSYNC FROM VGA PORT +5V +5V 10k +5V 10k SELECT 75 JMP +5V VGA OUTPUT CONNECTOR *** *** 0.1 F CAPACITORS RECOMMENDED 649 649 649 649 649 649 **FSC OR 4FSC CLOCK; 3.579545MHz, 14.31818MHz (NTSC) OR 4.433620MHz, 17.734480MHz(PAL) 1/3 AD8013 1/3 AD8013 1/3 AD8013 0.1 F 0.1 F 0.1 F Figure 15. Interfacing the AD724 to the (Interlaced) VGA Port of a PC transmitted. Each output requires a 220 µF series capacitor to work with the 75 Ω resistance to pass these low frequencies. The CRMA signal has information mostly up at the chroma fre- quency and can use a smaller capacitor if desired, but 220 µF can be used to minimize the number of different components used in the design. Displaying VGA Output on a TV The AD724 can be used to convert the analog RGB output from a personal computer’s VGA card to the NTSC or PAL television standards. To accomplish this it is important to understand that the AD724 requires interlaced RGB video and clock rates that are consistent with those required by the television standards. In most computers the default output is a noninterlaced RGB signal at a frame rate higher than used by either NTSC or PAL. Most VGA controllers support a wide variety of output modes that are controlled by altering the contents of internal registers. It is best to consult with the VGA controller manufacturer to determine the exact configuration required to provide an inter- laced output at 60 Hz (50 Hz for PAL). Both the analog and digital ground pins should be tied to the ground plane by a short, low inductance path. Each power supply pin should be bypassed to ground by a low inductance 0.1 µF capacitor and a larger tantalum capacitor of about 10 µF. The three analog inputs (RIN, GIN, BIN) should be terminated with 75 Ω to ground close to the respective pins. However, as these are high impedance inputs, they can be in a loop-through configuration. This technique is used to drive two or more devices with high frequency signals that are separated by some distance. A connection is made to the AD724 with no local termination, and the signals are run to another distant device where the termination for these signals is provided. The output amplitudes of the AD724 are double that required by the devices that it drives. This compensates for the halving of the signal levels by the required terminations. A 75 Ω series resistor is required close to each AD724 output, while 75 Ω to ground should terminate the far end of each line. The outputs have a dc bias and must be ac coupled for proper operation. The COMP and LUMA outputs have information down to 30 Hz for NTSC (25 MHz for PAL) that must be |
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