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AD8122 датащи(PDF) 11 Page - Analog Devices |
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AD8122 датащи(HTML) 11 Page - Analog Devices |
11 / 13 page Preliminary Technical Data AD8122 Rev. PrC | Page 11 of 13 16 RED BLUE GREEN CMV RED CMV BLUE CMV AD8122 16 12 7 4 PEAK 25 26 27 28 V V FILTER V GAIN HSYNC OUT VSYNC OUT 32 31 GREEN 35 34 38 37 3 2 8 9 RECEIVED RED VIDEO RECEIVED GREEN VIDEO RECEIVED BLUE VIDEO RED VIDEO OUT GREEN VIDEO OUT BLUE VIDEO OUT ANALOG CONTROL INPUTS POWER DOWN CONTROL PD 1 2 1k Ω 1k Ω 49.9 Ω 49.9 Ω 49.9 Ω 475 Ω 49.9 Ω 49.9 Ω 49.9 Ω 47pF 47pF 19 RED GAIN 15 GREEN GAIN 11 BLUE GAIN 23 V OFFSET 30 CABLE SELECT CONTROL COAX/UTP Figure 8. Basic Application Circuit with Common-Mode Sync Extraction (supplies and input protection not shown) SYNC PULSE EXTRACTION USING COMPARATORS The AD8122 is useful in many systems that transport computer video signals, which are typically comprised of red, green, and blue video signals and separate horizontal and vertical sync signals (RGBHV). Because the sync signals are separate and not embedded in the color signals, it is advantageous to transmit them using a simple scheme that encodes them among the three common-mode voltages of the RGB signals. The AD8134, AD8142, AD8147, and AD8148 triple differential drivers are natural complements to the AD8122 because they perform the sync pulse encoding with the necessary circuitry on-chip. The sync encoding equations follow: [ ] H V K V Red CM − = 2 (1) [ ] V 2 2 − = K V Green CM (2) [ ] H V K V Blue CM + = 2 (3) where: Red VCM, Green VCM, and Blue VCM are the transmitted common- mode voltages of the respective color signals. K is an adjustable gain constant that is set by the driver. V and H are the vertical and horizontal sync pulses, defined with a weight of −1 when the pulses are in their low states, and a weight of +1 when they are in their high states. The AD8134, AD8142 and AD8146/AD8147/AD8148 data sheets contain further details regarding the encoding scheme. Figure 8 illustrates how the AD8122 comparators can be used to extract the horizontal and vertical sync pulses that are encoded on the RGB common-mode voltages by the aforementioned drivers. USING THE VPEAK, VGAIN, VFILTER, AND VOFFSET INPUTS The VPEAK input is the main peaking control and is used to compensate for the low-pass roll-off in the cable response. The VGAIN input controls the wideband flat gain and is used to compensate for the cable loss that is nominally flat. The output of each channel contains an on-chip adjustable lowpass filter to reduce high frequency noise. In most applications, the filter cutoff frequency control, VFILTER, is connected directly to the VPEAK voltage in order to provide maximum bandwidth and minimum noise for a given VPEAK setting. External lowpass filters are generally not required. The VOFFSET input is used to produce an offset at the AD8122 output. The output offset is equal to the voltage applied to the VOFFSET input, limited by the output swing limits. |
Аналогичный номер детали - AD8122 |
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Аналогичное описание - AD8122 |
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