TTI TG501, Руководство по обслуживанию

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Waveform Generation - Trigger Circuit
In the Trig or Gate modes the waveform is clamped at the Start/Stop Phase point under control of
IC14b (described earlier).
Q19 and IC15b form a Schmitt trigger which ensures correct operation from DC to 5MHz. R71 and
R72 with C27 fix the input threshold at <1.5V over the whole frequency range.
In the trigger mode the output of IC15b is routed through IC15c and IC16a to the monostable
formed by IC16b and c. For every high going transition at the trigger input or depression of the
manual button a 50 nanosecond pulse at IC16c output is generated. This pulse goes from high to
low, and back to high after 50ns and is used to set the flip flop IC14b which releases the waveform
clamp. The flip flop now waits for a rising edge on its clock input; this occurs when the triangle wave
changes from a negative slope to a positive slope. This edge resets the flip flop and enables the
waveform clamp circuit which stops the waveform at a point determined by the Start/Stop Phase
control.
In the gate mode the monostable around IC16b and c is disabled and the signal bypasses IC16b.
When a high level signal is applied to Trig in, the output of IC16c goes low and releases the
waveform clamp. The generator now free runs until the Trig in signal goes low and IC16c output
goes high. IC14b flip flop now waits for a rising edge on its clock input as in trigger mode and stops.
In the run mode IC14b flip flop is permanently set by SW9b, disabling the waveform clamp so that
the generator free runs.
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