XRD98L61_01 Datasheet, PDF (21/38 Pages) Exar Corporation – CCD Image Digitizers with CDS, PGA and 12-Bit A/D

XRD98L61
BLACK LEVEL OFFSET CALIBRATION
To get the maximum color resolution and dynamic
range, the XRD9861 uses a digitally controlled cali-
bration circuit to correct for offset in the CCD signal as
well as offset in the CDS, PGA & ADC signal path. This
calibration is done while the CCD outputs Optical Black
(OB) pixels. In the “Line” timing mode, the OB pixels at
the start or end of each scan line are used for calibra-
tion.
CCD
signal
CDS
+
PGA
+
12-bit ADC
Reg
DB[11:0]
ManCAL
CDAC, FDAC
Coarse
Accumulator
Fine
Accumulator
Black Level
Offset Calibration
Loop
12
Hot Pixel
Clipper
From Serial
Interface
Registers
Wait[11:0]
OB Lines[7:0]
Offset Calibration Logic
DNS
Filter
+
+
Pixel
Averager
-
Hold, FastCal
DNS[1:0]
PGA[9:0]
OB[7:0]
Avg[2:0]
Figure 9. Black Level Offset Calibration Block Diagram
Offset Register
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
X
X
0
0
0
0
0
0
0
0
X
X
0
0
0
0
0
0
0
1
X
X
0
0
0
0
0
0
1
0
.
.
.
X
X
1
1
1
1
1
1
1
0
X
X
1
1
1
1
1
1
1
1
Table 3. Black Level Output Control
ADC Output
Black Level (LSB)
Do Not Use
Do Not Use
2 (Minimum offset code)
.
.
.
254
255
Rev. 2.00
21