HP 54750A, User Manual, Page: 445 / 478

How the Instrument W orks
Standard and Enhanced T rigger Modes
12 GHz/Gate mode (Option 100 only)
The 2-12 GHz Gate mode will trigger selectively on distinct groups of high
speed signals . It is the most complex trigger mode of the analyzer and is
primarily intended for experienced users .
As in the 2-12 GHz mode , a high-speed IC is used to divide the incoming
signal frequency by a factor of 16. This divided signal is applied to the
existing trigger circuitry . The trigger input is A C-coupled to the divider IC.
A low speed (<1 MHz maximum frequency) TTL level gating signal is applied
to a BNC connector on the rear panel of the analyzer . Only when that
signal is at a logical high will the trigger divider recognize input transitions .
Because the speed of the gating function is much less than that of the trigger
input, there must be some signicant separation of the desired and excluded
trigger signals . This mode , if used to separate out individual segments of a
continous trigger , will result in trigger artifacts . Refer to the Trigger Artifacts
section later in this chapter for additional information. The gate mode allows
measurements of signals that previously were dicult, or even impossible ,
to view . However , there are signicant tradeos . The rest of this section
discusses the tradeos and oers suggestions on how to minimize their
impact,
T rigger sensitivity In the gate mode , the analyzer should only trigger when both the gate enable
signal is present and a trigger transition occurs . Therefore , the free running
eect of the divided trigger is suppressed by biasing the divider IC to prevent
self-oscillation. This reduces the sensitivity of the trigger . In the standard
divided mode , the jitter is specied as 2 ps rms from 2 GHz to 12 GHz with a
200 mV p-p sine wave input. See Figure 13-13.
13-25