AD9849 Analog Devices, AD9849 Datasheet - Page 29

• Manufacturer Part Number: AD9849
• Description: CCD Signal Processors with Integrated Timing Driver
• Manufacturer: Analog Devices

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.
CDS
CCD: PROGRESSIVE BAYER
Gb
Gb
Gb
Gb
Gb
Gb
R
R
R
R
R
R
SHP/SHD
CCD: INTERLACED BAYER
EVEN FIELD
VD
HD
Gr
Gr
ODD FIELD
Gr
Gr
Gr
Gr
B
B
B
B
B
B
PxGA
6
Gb
Gb
Gb
Gb
Gb
Gb
R
R
R
R
R
R
STEERING
CONTROL
COLOR
2
MUX
Gr
Gr
Gr
Gr
Gr
Gr
4:1
B
B
B
B
B
B
VGA
LINE0
LINE1
LINE2
LINE0
LINE1
LINE2
LINE0
LINE1
LINE2
MOSAIC SEPARATE COLOR
STEERING MODE
VD SELECTED COLOR
STEERING MODE
3
GAIN0
GAIN1
GAIN2
GAIN3
PxGA STEERING
GAIN0, GAIN1, GAIN0, GAIN1...
GAIN2, GAIN3, GAIN2, GAIN3...
GAIN0, GAIN1, GAIN0, GAIN1...
GAIN0, GAIN1, GAIN0, GAIN1...
GAIN0, GAIN1, GAIN0, GAIN1...
GAIN0, GAIN1, GAIN0, GAIN1...
GAIN2, GAIN3, GAIN2, GAIN3...
GAIN2, GAIN3, GAIN2, GAIN3...
GAIN2, GAIN3, GAIN2, GAIN3...
SELECTION
PxGA GAIN
REGISTERS
MODE
CONTROL
REGISTER
BITS D0–D2
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
512 – 1023
(100000)
10
–2
8
6
4
2
0
36
30
24
18
12
32
6
0
0
40
Gain = 20 log
Gain = (0.0354)(code) – 0.04
127
48
255
PxGA GAIN REGISTER CODE
VGA GAIN REGISTER CODE
58
383
10
([658 + code]/[658 – code]) – 0.4
0
511
AD9848/AD9849
8
639
16
767
24
895
(011111)
31
1023