Specifications

74 Chapter 4: Matrox Solios hardware reference
Adjusting the reference levels
For each acquisition path, you can adjust the signal’s black and white reference
levels so that the full dynamic range of each 10-bit A/D is used. Matrox Solios
eA/XA uses the offset-gain topology to adjust the black and white reference levels
of the signal. The topology uses a variable offset controller followed by a variable
gain controller; the signal can be routed through a 2:1 attenuator before being
restored and offset.
The variable offset controller vertically shifts the entire signal so that you can set
the lowest part of the video signal to 0 V, which is at the bottom of the A/D
conversion range. The offset adjustment range is -1 V to +1 V, in 4096 steps
(12-bit resolution).
The variable gain controller can then amplify the signal so that you can set the
highest part of the video signal to 1 V, which is at the top of the A/D conversion
range. The gain adjustment range is between 0 and 4, in 4096 step increment
(12-bit resolution).
Before passing to the DC restore and offset blocks, the signal can be routed through
an attenuator. The attenuator is a 2:1 voltage divider. The attenuator is present
because the variable gain controller cannot accept a positive or negative signal with
an amplitude above 1.2 V without distortion. The attenuator allows you to pass
a signal up to 2.4 V in amplitude (active video) without distortion. If the active
input video (excluding the sync pulse) is greater than 1.2 V in amplitude, the
attenuator should be enabled.
The maximum gain factors and the recommended video signal amplitude are as
follows:
2:1 attenuator Maximum gain Max recommended video signal
amplitude (terminated)
Min recommended video
signal amplitude
Off (bypassed) 4 1.2 V 0.25 V
On (active) 2 2.4 V 0.5 V
Filtered/
clamped
video signal
2:1 attenuator
Offset
control
Gain
control
Video signal
to A/D converter
DC
Restore