48
Theory of Operation
X64-AN Quad User's Manual
DC Restoration
DC Restoration uses a programmable clamp pulse. The horizontal back porch is used to establish the
reference video black level.
Two parameters are required to locate the region used as the reference. The
clamp_start
and
clamp_end
parameters are referenced to the start of HS. The
clamp_width
is the time difference
between
clamp_start
and
clamp_end
. See below for diagram.
DC Restoration (Clamping)
Comp. Video
Clamp
start
HS
Clamp
end
Back
Porch
Front
Porch
Figure 27: DC restoration timing
Note:
With Internal Sync mode, the horizontal reference is the edge of HD. With this synchronization
scheme, clamp start and clamp end values refer to first edge of HD, not to HS coming from composite
video.
Sapera parameters for ADC Converter:
CORACQ_PRM_PIXEL_CLK_INT: Internal pixel clock frequency (in Hz)
CORACQ_PRM_PIXEL_DEPTH = 8
CORACQ_PRM_DC_REST_MODE =
{CORACQ_VAL_DC_REST_MODE_AUTO,
CORACQ_VAL_DC_REST_MODE_ON,
CORACQ_VAL_DC_REST_MODE_OFF}
CORACQ_PRM_DC_REST_START: Start of clamp pulse relative to HS or HD
CORACQ_PRM_DC_REST_WIDTH: Clamp pulse duration
