- SS-HQ1 Application Notes -
Ver.1.0.0 January 7, 2005
84
Black level digital clamping
Fig 10.2-2 DRVOUT (AD input signal) and offset level
Under conditions where AGC is raised, such as when shooting a dark subject, the AD input signal (i.e.,
CXA2096N pin4 DRVOUT signal) contains a noise component. A DC offset (50 to 100[mV]) is added to the
DRVOUT signal in order to prevent the black level (OB area output of CCD) becoming under VRB level. (For
details, see the CXA2096N product specifications.) Therefore, the same DC offset is also added to the
effective video signal.
The processing of removing the DC offset equivalent to the black level from the AD-converted effective video
signal inside the DSP is called digital clamping.
Fig 10.2-3 Digital clamping process
AD Input
Level
PBLK
CLPOB
DRVOUT
AGCCONT =MAX
VRB = Blankng
PBLK
CLPOB
DRVOUT
VRB = Blankng
OFFSET
= Black Level
OFFSET with
AGC Noise
AGCCONT =MIN
Signal
Level
OB
Picture
Signals
with Offset
INTegral
OB_S1
INTegral
OB_S2
-
F/W
Filter
BLACKS2
OB_S1
CCD Picture
Signals
without
Offset
OB INT
CCD signals
(AD input)
-
BLACKS1
OB_S2
Picture_S1
Picture_S2