The -BR Burst Mode Option

The -BR option adds a burst function to Avtech pulse generators. Most GPIB-equipped Avtech pulse generators can be triggered by four different sources:

Normally, a single output pulse is generated in response to a trigger event (regardless of the source). However, when the -BR option is added, the instrument can generate 1-500 pulses for each individual trigger event. The number of output pulses in each burst can be adjusted from 1 to 500 using the front-panel controls, or by a computer command. The time between pulses (i.e., from the falling edge of one pulse to the rising edge of the next pulse) can also varied from the front panel, or by computer command.

The figure below shows burst mode operation used with internal triggering:

Burst mode waveforms, for internal triggering

The figure below shows burst mode operation used with external triggering:

Burst mode waveforms, for external triggering

The pulse spacing is constrained by several factors:

  1. The maximum PRF limitation of the instrument applies within the burst. That is, timing between two consecutive leading edges must lie between a minimum of 1/PRFMAX and a maximum of 1.0 seconds, where PRFMAX is the maximum pulse repetition frequency specification for the instrument. (For instance, if the maximum PRF for the instrument is 1 MHz, the time between two leading edges within the burst may not be smaller than 1.0 microseconds). The total number of pulses per second (i.e., Trigger Frequency x Burst Count) must also be less than PRFMAX.
  2. The maximum duty cycle limitation of the instrument can not be exceeded inside the burst. Within the burst, the duty cycle may be calculated using DCBURST = 100% x Pulse Width / (Pulse Width + Pulse Separation). The total average duty cycle is equal to DCAVG = 100% x Pulse Width x Burst Count x Trigger Frequency. Both DCBURST and DCAVG must be less than the rated maximum duty cycle of the instrument, and DCBURST can not exceed 50%.
  3. The burst pulse separation can not be smaller than 50 ns.

Some instruments can be modified to allow the duty cycle within a burst to exceed the average duty cycle limit, or to allow closer pulse spacings within the burst. Contact the factory with your special requirement.

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