HP 85108A, Системное руководство

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cycle is complete. This information is imp ortant for sync hronizing the pulse mo dulation to the
external trigger.
Shen a TTL pulse train is applied to the HP 8510 rear panel EXTERNAL TRIGGER INPUT
the trigger should stay low for at leas 100 nanoseconds. Excess triggers that o ccur while stop
sw eep is busy (low) are ignored. The next external trigger falling edge after stop sw eep is
ready will initiate the next measuremen t cycle and retrace is automatic.
Figure 3-21. External Trigger and Stop Sw eep Timing Diagram
When in ternal triggering is selected, the stop sw eep output do es not op erate (alw a ys in the
ready state). Timing diagrams for the pulse output signal and dev elopmen t of the in ternal
measuremen t trigger are sho wn in Figure 3-11 and Figure 3-12 .
When external triggering is selected, the falling edge of the external trigger input denes time
equals zero seconds for eac h measuremen t cycle. Stop sw eep falls immediately and stays low
un til the HP 8510 completes the measuremen t cycle and is ready to accept the next trigger.
The time p erio d that stop sw eep remains busy dep ends up on the next measuremen t function
to b e p erformed. Pulse output is turned O for external triggering. As for in ternal triggering,
the pulse prole measuremen t resolution p erio d is set b y the larger of pulse width and pulse
prole domain stop time.
Using External Triggering and Pulse Modulation
In applications where it is necessary to maintain close con trol o v er the PRP and dut y
cycle of the pulsed-RF stim ulus, y ou can use external equipmen t to pro vide the TTL pulse
mo dulation and external trigger signals. When using an external pulse mo dulation signal,
it is necessary to sync hronize the net w ork analyzer with the pulse mo dulation signal so
that the measuremen t is alw a ys made at the same time with resp ect to the stimulus. This
sync hronization is accomplished using the HP 8510 external trigger input.
Connect the Pulse Generator
A simple metho d to con trol the PRP and dut y cycle of the pulsed-RF stimulus is to use an
external pulse generator to pro vide the pulse mo dulation input to the RF source. Figure 3-22
sho ws a simple setup that pro vides the same pulsed-RF stimulus to the DUT regardless of the
3-26 Operation
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