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AD9849 数据表(PDF) 29 Page - Analog Devices |
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AD9849 数据表(HTML) 29 Page - Analog Devices |
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29 / 36 page  REV. 0 AD9848/AD9849 –29– COLOR STEERING CONTROL 4:1 MUX 3 GAIN0 GAIN1 GAIN2 GAIN3 PxGA PxGA STEERING MODE SELECTION 2 6 VD HD PxGA GAIN REGISTERS CONTROL REGISTER BITS D0–D2 SHP/SHD VGA CDS Figure 17. PxGA Block Diagram RGr R Gr Gb B Gb B RGr R Gr Gb B Gb B GAIN0, GAIN1, GAIN0, GAIN1... LINE0 GAIN2, GAIN3, GAIN2, GAIN3... LINE1 GAIN0, GAIN1, GAIN0, GAIN1... LINE2 CCD: PROGRESSIVE BAYER MOSAIC SEPARATE COLOR STEERING MODE Figure 18a. CCD Color Filter Example: Progressive Scan RGr R Gr RGr R Gr RGr R Gr RGr R Gr GAIN0, GAIN1, GAIN0, GAIN1... LINE0 GAIN0, GAIN1, GAIN0, GAIN1... LINE1 GAIN0, GAIN1, GAIN0, GAIN1... LINE2 CCD: INTERLACED BAYER EVEN FIELD VD SELECTED COLOR STEERING MODE Gb B Gb B Gb B Gb B Gb B Gb B Gb B Gb B GAIN2, GAIN3, GAIN2, GAIN3... LINE0 GAIN2, GAIN3, GAIN2, GAIN3... LINE1 GAIN2, GAIN3, GAIN2, GAIN3... LINE2 ODD FIELD Figure 18b. CCD Color Filter Example: Interlaced The same Bayer pattern can also be interlaced, and the VD selected mode should be used with this type of CCD (see Figure 18b). The Color Steering performs the proper multi- plexing of the R, G, and B gain values (loaded into the PxGA gain registers), and is synchronized by the user with vertical (VD) and horizontal (HD) sync pulses. For more detailed information, see the PxGA Timing section. The PxGA gain for each of the four channels is variable from –2 dB to +10 dB, controlled in 64 steps through the serial interface. The PxGA gain curve is shown in Figure 19. PxGA GAIN REGISTER CODE 10 32 40 48 58 0 8 16 24 31 8 6 4 2 0 –2 (011111) (100000) Figure 19. PxGA Gain Curve Variable Gain Amplifier The VGA stage provides a gain range of 2 dB to 36 dB, pro- grammable with 10-bit resolution through the serial digital interface. Combined with 4 dB from the PxGA stage, the total gain range for the AD9848/AD9849 is 6 dB to 40 dB. The minimum gain of 6 dB is needed to match a 1 V input signal with the ADC full-scale range of 2 V. When compared to 1 V full-scale systems (such as ADI’s AD9803), the equivalent gain range is 0 dB to 34 dB. The VGA gain curve is divided into two separate regions. When the VGA Gain Register code is between 0 and 511, the curve follows a (1 + x)/(1 – x) shape, which is similar to a “linear-in-dB” characteristic. From code 512 to code 1023, the curve follows a “linear-in-dB” shape. The exact VGA gain can be calculated for any Gain Register value by using the following two equations: Code Range Gain Equation (dB) 0 – 511 Gain = 20 log10 ([658 + code]/[658 – code]) – 0.4 512 – 1023 Gain = (0.0354)(code) – 0.04 VGA GAIN REGISTER CODE 36 0 127 255 383 511 639 767 895 1023 30 24 18 12 6 0 Figure 20. VGA Gain Curve (Gain from PxGA Not Included) |
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