Agilent Technologies E1439 manual Trigger and phase in multi-module systems

Using the Agilent E1439

Managing multiple modules

Trigger and phase in multi-module systems

When you use triggering in multiple modules, you do not need to measure phase differences between two or more channels if the channels are set up identically in terms of digital filtering and LO frequency, and the digital filters and LOs are correctly synchronized. Since the filters and LOs are synced together, their actual trigger delays and LO phases are identical and will cancel out of relative phase measurements. Any remaining delay should be less than 10ns between two modules in the same mainframe.

Only the module that generates the trigger has knowledge of the delay between the trigger event and the start of data collection. Therefore, if you need the actual delay from the trigger, you should use the trigger delay correction from the module that generated the trigger. Likewise, you should obtain the LO phase at the time of the trigger from the module that generated the trigger. See “Delay and phase in triggered measurements” on page 25.

	External sample synchronization in multi-module systems
	There are two general instances where you might want to use an external sample clock in a system
	with multiple E1439s:
	• You wish to have the ADC's sample at a rate other than the 95 MHz clock supplied with the
	E1439.
	• You wish more precise simultaneous sampling than can be provided by the normal scheme
	that uses the internal VCXOs within the modules locked together by a 2.5 MHz reference that
	is distributed from module to module. By exercising care in matching the skew of the sample
	clocks fed into each module, channel-to-channel group delays at low frequencies can be well
	below a nanosecond.
Note	External sample is specified only for use with baseband path.
	To use external sample clocks with multiple modules and still perform synced measurements, you
	need to use either the AGE1439_FRNT_SYNC_EXT_SAMP or AGE1439_REAR_SYNC_
	EXT_SAMP clock setups (see “age1439_clock_setup” on page 78). These setups use the signal
	that you feed into the Ext Clock/Ref BNC input of the E1439 as a sample clock for the ADC. A
	counter within the E1439 generates two lower frequency clocks, one for the DSP circuitry and
	one to clock the measurement SYNC signal between multiple modules. Since these clocks are
	generated independently within each module, the counters in each module must be synced
	together with a common externally generated signal in order to make properly synced and
	triggered measurements involving multiple channels. You feed this "external sample sync" signal
	into the External Trigger BNC and the module uses the signal to reset the counters to a known
	phase.
	The external sample sync signal should be generated on the falling edge of the external sample
	clock, and fed into each module in the system by an identical length coax cable. Likewise, the
	sample clock should be fed into each Ext Clock/Ref BNC by an identical length coax cable from a
	common driver.

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