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AD8180 Datasheet(PDF) 8 Page - Analog Devices |
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AD8180 Datasheet(HTML) 8 Page - Analog Devices |
8 / 12 page AD8180/AD8182 –8– REV. B APPLICATIONS Multiplexing two RGB Video Sources A common video application requires two RGB sources to be multiplexed together before the selected signal is applied to a monitor. Typically one source would be the PC’s normal output, the second source might be a specialized source such as MPEG video. Figure 23 shows how such a circuit could be realized using the AD8180 and AD8182 and three current feedback op amps. The video inputs to the multiplexers are terminated with 75 Ω resistors. This has the effect of halving the signal amplitude of the applied signals. Because all three multiplexers are permanently active, the ENABLE pins are tied permanently low. The three SELECT pins are tied together and this signal is used to select the source. In order to drive a 75 Ω back terminated load (R L = 150 Ω), the multiplexer outputs are buffered using the AD8001 current feed- back op amp. A gain of two compensates for the signal halving by the AD8001 output back termination resistor so that the system has an overall gain of unity. If lower speed and crosstalk can be tolerated, either of the triple op amps, AD8013 or AD8073, can replace the three AD8001 op amps in the above circuit. Because both devices have bandwidths in the 100 MHz to 140 MHz range at a gain of +2, these ampli- fiers will dominate the frequency response of the circuit. With no signal present, the total quiescent current of the cir- cuit in Figure 23 is 25.6 mA (3.8 mA + 6.8 mA + 3 × 5 mA), or about 8.5 mA per channel. If either the AD8013 or AD8073 are used, the quiescent current will decrease to about 6.5 mA per channel. To reduce power consumption further, three AD8011 single op amps can be used. With a quiescent current of 1 mA, this will reduce the per channel quiescent current to about 4.5 mA. Table II. Amplifier Options for RGB Multiplexer Op Amp Comments AD8001 Highest Bandwidth, 440 MHz (G = +2), ISY = 5 mA AD8011 Lower Power Consumption, Bandwidth (G = +2) = 210 MHz, ISY = 1 mA AD8013 Triple Op Amp, Bandwidth (G = +2) = 140 MHz, ISY = 3.4 mA AD8073 Lower Power Triple Op Amp, Bandwidth (G = +2) = 100 MHz, ISY = 3.5 mA 8 7 6 5 ENABLE ENABLE A –VS ENABLE B –VS +VS 0.1 F 10 F 0.1 F 10 F 0.1 F +VS + 75 75 75 75 75 75 RG B COMPUTER GRAPHICS RG B +VS 0.1 F 10 F 75 681 –VS 10 F 0.1 F +VS 0.1 F 10 F 75 681 681 –VS 10 F 0.1 F +VS 0.1 F 10 F 75 681 –VS 10 F 0.1 F SELECT MONITOR 1 2 3 4 AD8180 +1 +1 1 2 3 4 14 13 12 11 AD8182 5 6 7 10 9 8 DECODER +1 +1 DECODER +1 +1 + + MPEG RTERM AD8001 681 AD8001 681 AD8001 R G B 0.1 F 10 F + 10 F DECODER Figure 23. Multiplexing Two Component Video Sources |
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