213ConceptsTime Gating ConceptsUsing the Edge Mode or Level Mode for triggeringDepending on the trigger signal that you are working with, you can trigger the gate inone of two separate modes: edge or level. This gate-trigger function is separate fromthe normal external trigger capability of the signal analyzer, which initiates a sweepof a measurement trace based on an external signal.Edge ModeEdge mode lets you position the gate relative to either the rising or falling edge of atrigger signal. The left diagram of Figure 15-22 shows triggering on the positiveedge of the trigger signal while the right diagram shows negative edge triggering.Example of key presses to initiate positive edge triggering:Press Sweep, Gate, More, Polarity (Pos).Figure 15-22 Using Positive or Negative Edge TriggeringLevel ModeIn level gate-control mode, an external trigger signal opens and closes the gate.Either the TTL high level or TTL low level opens the gate, depending on the settingof Trig Slope. Gate delay affects the start of the gate but not the end. Gate length isapplicable when using level mode triggering. Level mode is useful when your triggersignal occurs at exactly the same time as does the portion of the signal you want tomeasure.
