Tektronix 2212 Service Manual page 95

Block Diagram
From Composite Video to
TfL
Composite
Sync
(Diagram 26)
2212 Service Manual
Video Option
(Option05)
This subsection describes the optional TV. sync.separator analog part
(Section 9: Diagram 26) and the digital part (Section 9: Diagram 27).
For an overview of the complete sync. separator, see the block diagram in Figure
9-9 in Section 9:
Diagrams.
In the center of the block diagram is the video control register located. This
register receives control data from the 2212 main processor and passes it on to
the various functional blocks on the video board (A25).
The input signal from the 2212 trigger circuit is called TRIG_SIG.
The input stage (U2601, Q2601, Q2602, Q2603, Q2604) is an amplifier with
controlled gain. The gain control signal is generated by the SYNC TIP CLAMP
(Q2610, U2609).
The input stage also has a polarity switch function. The polarity of the output
signal of this stage is controlled by the setting in the MENU.
It
must be a nega-
tive sync at this point. This feature adapts the circuitry for positive- or negative-
sync TV. systems.
The second stage is a fixed gain amplifier (U2608).
The gain is very high (almost a comparator) that outputs the horizontal sync
pulses of the input video signal, together with some rudimentary video signal.
The offset control signal is generated by the TRIGGER BACKPORCH CLAMP
(Q2611, U2610).
From the fixed gain amplifier the signal runs to the sync pickoff comparator
(Q2612, Q2613). The output signal of the sync pickoff comparator is a clean,
TTL compatible composite sync signal with positive going sync pulses
(COMPSYNC_0). These pulses are used in the digital part of the video option.
Revised 3/93
3- 37