Tektronix 070-8462-03, Инструкция по эксплуатации

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Theory of Operation
4–16
1735 HD High Definition Waveform Monitor
Comparator U7C determines the leading edge of horizontal blanking by clocking
U9B. C13, R26, and CR3 form a differentiator that detects the trailing edge of
horizontal sync. U5 (pin 19) ends horizontal blanking by clearing U9B. The
slave processor can inhibit horizontal blanking by setting /HBLANK EN high at
U5, pin 9.
U10D provides a means for the slave processor to choose whether horizontal
blanking will be generated on the next sync. U9B Preset lets the slave micropro-
cessor blank the sweep directly when necessary.
1-Field Sync Generator.
The 1FLDSYNC negative edge identifies the first line of
field 1 for the slave microprocessor. U7B outputs a positive edge at one quarter
line, and U7A outputs a positive edge at three quarters line. U6 is an asynchro-
nous state machine that looks at where broad pulses occur to recognize fields.
Clamp Pulse Generator.
The clamp pulse occurs during back porch. Its position
and width are independently programmable by the slave microprocessor. The
clamp ramp generator is comprised of a current source controlled by DAC U19,
timing capacitor C53, and reset switch Q13. The clamp ramp starts and resets at
the same time as horizontal blanking ramp. A voltage divider catches the clamp
ramp at about 6 V.
Comparator U16A provides the clock to start the clamp pulse and U16B clears.
The comparator thresholds are controlled by dual DAC U28. Back porch clamps
are inhibited during broad pulses. They can also be inhibited directly by the slave
processor to turn off the clamp pulses.