Agilent Technologies E1439 manual Delay and phase in triggered measurements

(sigBw-1)

Using the Agilent E1439

Delay and phase in triggered measurements

Delay and phase in triggered measurements

It is important to note that the trigger delay is specified in terms of output samples. When using the digital filters within the E1439 to reduce the sample rate, there are multiple ADC samples corresponding to each output sample. In order to determine the relationship between the first output sample of a block and the actual ADC sample where the trigger occurred, you must read the actual delay from the module using age1439_trigger_delay_actual_get.

This relationship varies from block to block and is a function of the particular value of counters within the digital filters at the time the trigger occurs. Thus the actual delay from the trigger event is the delay from age1439_trigger_delay_get multiplied by 2sigBw (from age1439_filter_bw_get

if filter decimation is used, or 2 if filter decimation is off). From this value, subtract the value returned by age1439_trigger_delay_actual_get. The result is in periods of the ADC sample clock. Special considerations apply in multi-module systems. See “Trigger and phase in multi-module systems” on page 40.

When doing a zoomed measurement, it may also be helpful to know the phase of the digital LO at the time the trigger occurred, since the LO is also running continuously and it has an arbitrary phase relationship with the trigger event. age1439_trigger_phase_actual_get returns the phase of the LO at the trigger point. The LO phase could be used in time domain averaging of blocks, or other operations involving zoomed blocks of data, so that the varying phase of the LO can be removed from the calculation.

The trigger_delay value is the time, measured in output samples, from the desired trigger point to the start of the time record. The trigger_delay_actual value is the time, measured in input samples, from the desired trigger point to the actual trigger point.

Start of	Desired	Actual
time record	trigger point	trigger point

signal

trigger_delay trigger_delay_ actual

time

The following example illustrates how trigger_delay and trigger_delay_actual can be combined. In this example:

filter_bw=4 (2.4 MHz span) filter_decimate = 1 (on)

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