Allied Guppy, Техническое руководство, Страница: 77 / 238

Description of the data path
GUPPY Technical Manual V4.0.1
77
Manual gain
As shown in Figure 32: Block diagram of AFE (Source: Analog Devices) on
page 71 and Figure 33: Signal path of MT9V022 (Guppy with CMOS sensor)
on page 72, all cameras are equipped with a gain setting, allowing the gain
to be
manually adjusted on the fly by means of a simple command register
write.
The following ranges can be used when manually setting the gain for the ana-
log video signal:
The increment length for CCD models is ~0.0354 dB/step.
The increment length for the CMOS model is:
0..15: ~0.2 dB/step (1 step = 1 LSB)
16..48: ~0.28 dB/step (1 step = 2 LSB)
Auto gain
In combination with auto white balance, all CCD and CMOS models are
equipped with auto gain feature.
When enabled auto gain adjusts the gain within the default gain limits or
within the limits set in advanced register F1000370h in order to reach the
brightness set in auto exposure register as reference.
Increasing the auto exposure value (aka target grey value) increases the aver-
age brightness in the image and vice versa.
The applied algorithm uses a proportional plus integral controller (PI control-
ler) to achieve minimum delay with zero overshot.
The following table shows both the gain and auto exposure CSR.
Type Range Range in dB
CCD cameras 0 ... 680 0 … 24 dB
CMOS camera 1 … 48 0 … 12 dB
Table 22: Manual gain range of the various GUPPY types
Note
L
• Setting the gain does not change the offset (black
value) for CCD models.
• A higher gain also produces greater image noise. This
reduces image quality. For this reason, try first to
increase the brightness, using the aperture of the cam-
era optics and/or longer shutter settings.