HP 54750A, User Manual, Page: 443 / 478

How the Instrument W orks
Standard and Enhanced T rigger Modes
2-12 GHz mode (Option 100 only)
The 2-12 GHz enhanced bandwidth mode allows direct triggering on signals
with wider bandwidth. This mode is useful with HP 83480A plug-in modules
that display signals with up to 50 GHz bandwidth. The 2-12 GHz mode
increases the bandwidth capabilities but may , in some instances , reduce the
signicance of the displayed data.
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. The input
threshold of the IC is set for maximum sensitivity and bandwidth, and it will
operate correctly on a sine wave input from 2 GHz to 12 GHz . Typically , the
upper frequency limit is 15 GHz for 200 mV p-p sine wave inputs . Square
wave triggers , or other sharp-edged transitions will function down to DC, but
this is not specied because it depends on the characteristics of the signal
edges .
If no trigger signal is applied, the divider self-oscillates , providing a freerun
trigger for the oscilloscope . When a trigger signal is applied, the divider will
recognize it and provide a stable reference . No adjustments to sensitivity are
provided, because the circuit will operate correctly for any signal between the
200 mV minimum and the 2 V maximum. Under these conditions , the trigger
timing jitter is specied to be less than 2 ps rms for small time delays . The
divider provides an output transition to the trigger circuit every 16
th
input
cycle . However , since the analyzer samples at a maximum rate of 40 kHz , not
every output of the divider is recognized as a valid trigger event.
One typical application of the 2-12 GHz trigger mode would be viewing a
10 Gb/s eye diagram with a recovered 10 GHz clock as shown in Figure 13-12.
13-23