AD9822 Analog Devices, AD9822 Datasheet - Page 13

• Manufacturer Part Number: AD9822
• Description: Complete 14-Bit CCD/CIS Signal Processor
• Manufacturer: Analog Devices

Figure 12 shows how the OFFSET pin may be used in a CIS
application for coarse offset adjustment. Many CIS signals have
dc offsets ranging from several hundred millivolts to more than
1 V. By connecting the appropriate dc voltage to the OFFSET
pin, the CIS signal will be restored to “zero.” After the large dc
offset is removed, the signal can be scaled using the PGA to
maximize the ADC’s dynamic range.
Programmable Gain Amplifiers
The AD9822 uses one Programmable Gain Amplifier (PGA) for
each channel. Each PGA has a gain range from 1x (0 dB) to
5.8x (15.5 dB), adjustable in 64 steps. Figure 6 shows the PGA
gain as a function of the PGA register code. Although the gain
curve is approximately “linear in dB”, the gain in V/V varies
nonlinearly with register code, following the equation:
where G is the decimal value of the gain register contents, and
varies from 0 to 63.
REV. A
CIS MODULE
VREF FROM
DC OFFSET
Figure 12. SHA-Mode Used with External DC Offset
R1
R2
AVDD
GREEN
BLUE
Gain
RED
0.1 F
OFFSET
VING
VINB
VINR
1
4 7
AD9822
.
5 7
.
63
63
SHA
SHA
SHA
G
RED-OFFSET
GREEN-OFFSET
BLUE-OFFSET
–13–
15
12
9
6
3
0
0
Figure 13. PGA Gain Transfer Function
4
8 12 16 20 24 28 32 36 40 44 48 52 56 60 63
PGA REGISTER VALUE – Decimal
AD9822
5.7
5.0
4.0
3.0
2.0
1.0