Character Generator Sync Separator And Keyer (5200-36) - evertz 5010 SIE Instruction Manual

Model 5010-SIE Source ID Encoder Manual
The starting position of the VITC on the line is fixed internally in the LCA
such that the first bit of code is 10.5 µsec (11.5 µsec for PAL) after the
leading edge of horizontal sync.
Once per field, the MCU loads the VITC bit pattern for a particular line into
static RAM U10. On lines where VITC is enabled, the LCA accesses the
static RAM and fetches the VITC data one byte (8 bits) at a time. The
VITC sync bits and cyclic redundancy check byte (CRC) are generated
internally in the LCA and inserted into the VITC bit stream in the
appropriate place. The VITC data is clocked out of the LCA on the
KEYFILL output ( U7 pin 7) and into buffer U8a. The VITC keyer is
controlled by the KEY signal generated in the LCA (U7 pin 6). The data is
clocked out of the LCA with the VITC clock so that the bit width is not
dependent on propagation delays in the LCA. VITC bits are shaped by
U6b and associated components and presented to the video keyer.
Composite video is AC coupled and buffered by Q1 before going into the
sync separator LM1881 U4. The sync separator provides H Sync, V Sync,
a Frame pulse (active low for field 1) and a back porch clamp pulse to drive
the DC restorer circuitry U1, Q2, and Q3 and associated components. The
back porch clamp pulse allows U1 to compare the actual DC level of the
video to ground potential. If they are not equal, U1 generates an error
signal which adjusts the bias point of Q2 thus ensuring proper operation of
the video keyer with varying video and sync levels.
The Video keyer U2 is controlled by the KEY signal generated in the LCA.
KEY switches U2 between the program video path and the KEYFILL data.
When the KEY signal is LOW the active video is passed through the keyer.
When the KEY signal is HIGH the KEYFILL data is added to the black level
of the video.
To calibrate the video keyer, connect colour bars from your sync generator
to the Video input loop of the 5010 and to channel A of your oscilloscope
and terminate it. Connect the video output to channel B of your scope and
terminate it. Adjust the GAIN trimpot (VR2) so that the output amplitude
matches the input. Adjust the LEVEL trimpot (VR1) so that the inserted
VITC/characters are approximately 550 millivolts above video black level.

4.3.4. Character Generator Sync Separator and Keyer (5200-36)

The Character inserter composite video is taken from the Reader Video
input loop and is buffered by Q2 and distributed to the character generator
sync separator and keyer/ amplifier. The sync separator U54 provides H
Sync, V Sync, a Frame pulse (active high for field 1) and a back porch
clamp pulse to drive the DC restorer circuitry U55 and associated
components.
The Video keyer U40 is controlled by the VCGKEY signal generated in the
LCA U36. VCGKEY switches U40 between the program video path and
the VCGWHITE data. When the VCGKEY signal is LOW the active video
is passed through the keyer. When the VCGKEY signal is HIGH the
VCGWHITE data is added to the black level of the video.
TECHNICAL DESCRIPTION Page 4-8