Matrox Solios eA, Установка и справочник по оборудованию, Страница: 75 / 196

Matrox Solios eA/XA acquisition section 75
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