Datasheet

REV. A
AD9848/AD9849
–27–
PxGA
The PxGA provides separate gain adjustment for the individual
color pixels. A programmable gain amplifier with four separate
values, the PxGA has the capability to “multiplex” its gain value on
a pixel-to-pixel basis (see Figure 17). This allows lower output
color pixels to be gained up to match higher output color pixels.
Also, the PxGA may be used to adjust the colors for white balance,
reducing the amount of digital processing that is needed. The
four different gain values are switched according to the “Color
Steering” circuitry. Seven different color steering modes for
different types of CCD color filter arrays are programmed in the
AD9848/AD9849 AFE Register, ctlmode, at Address 0x06 (see
Figures 16a to 16g for timing examples). For example, Mosaic
Separate steering mode accommodates the popular “Bayer”
arrangement of Red, Green, and Blue filters (see Figures 18a
and 18b).
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
RGrRGr
Gb B Gb B
RGrRGr
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
RGrRGr
RGr R Gr
RGrRGr
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 multiplexing 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
PxGA GAIN – dB
40 48 58 0 8 16 24 31
8
6
4
2
0
–2
(011111)(100000)
Figure 19. PxGA Gain Curve