LYNX Manual RA02
2.7
GAIN and OFFSET
The camera has dual analog signal processors (or Analog Front End – AFE), one
per channel. It features two independent 12 bit 40 MHz processors, each
containing a differential input sample-and-hold amplifier (SHA), digitally
controlled variable gain amplifier (VGA), black level clamp and a 12-bit ADC.
The programmable internal AFE registers include independent gain and black
level adjustment. There are 1024 possible gain levels (
gcode
0 to 1023) and 256
offset (clamp) levels (
ocode
0 to 255). Figure 2.44 shows the relationship between
the video signal output level and gain/offset. Theoretically, the black level should
reside at 0 volts and the gain changes should only lead to increasing the amplitude
of the video signal. Since the camera has two separate video outputs coming out
of the CCD, there is always some offset misbalance between the video outputs.
Thus, changing the AFE gain leads to a change in the offset level and to a further
misbalance between the two video signals. To correct the balance between two
signals for a particular gain, the user should always adjust the offset for each
output – refer to the Camera Configuration section. The overall camera gain can
be calculated using formula 7.1
VGA Gain [dB] = FG [dB] + 0.0351 x
gcode
(7.1)
CAUTION NOTE
1.
Increasing the gain simultaneously increases the camera noise.
2.
Fixed gain (FG) = 0 dB for IPX-1M48-L, FG = 6dB for the rest of
the cameras.
light intensity
video output
black level
pixel output
0 V
AFE gain
AFE output
~ 20 mV offset
Figure 2.44 - AFE Gain and Offset
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