T0 is the heartbeat

Every delay on a Berkeley Nucleonics generator is measured from a single reference moment called T0. Each channel then places its edge at a programmed delay after that instant. Understand where T0 comes from and you understand the whole timing system, because everything else is referenced to it. The question that defines your setup is simply: what creates T0?

Internal triggering

In internal mode the instrument's own rate generator produces T0 at a programmed repetition rate. This is the default for free-running experiments where the generator sets the pace. The Model 577 runs its internal rate from 0.001 Hz to 20 MHz; the Model 575 and Model 588 to 10 MHz; the compact Model 525 to 20 MHz. The rate generator is locked to a low-jitter PLL, so the internal trigger is usually the cleanest source you have. If nothing external needs to drive the timing, internal mode gives the lowest jitter path to T0.

External triggering

In external mode an outside event creates T0. A photodiode watching a laser, a TTL pulse from another instrument, the sync from a power supply. The input comparator decides when the incoming edge crosses threshold, and that decision adds jitter. On the 575 and 577 the trigger input accepts thresholds from roughly 0.2 to 15 V, slope-selectable, with an insertion delay around 110 to 180 ns and trigger jitter near 800 ps RMS. The 765 family clocks external triggers up to 40 MHz with under 30 ps added jitter below 15 MHz. The practical lesson: external triggering ties your timing precision to the input stage, so a clean, fast-edged trigger matters.

Gated operation

A gate does not create T0; it permits or blocks output while the generator runs. Raise the gate and pulses pass, lower it and they stop. Berkeley Nucleonics units distinguish pulse inhibit, which suppresses the pulse, from output inhibit, which holds the output line, with different insertion delays for each. Gating is how you window a continuous train to a region of interest, for example admitting laser pulses only while a sample is in position. The 575, 577, and 588 all expose a global gate with per-channel enables, so you can gate the whole instrument or selected channels.

Burst mode

Burst mode emits a fixed, counted number of pulses from a single trigger, then waits for the next. It bridges single-shot and continuous operation. Need exactly 50 pulses per trigger for a pump sequence? Burst delivers them and stops. The 577 counts bursts from 1 to 10,000,000 pulses, the 575 the same, and the 525 from 1 to 1,000,000. Duty-cycle mode is the sibling: a programmed count on, a programmed count off, repeated, useful for thermal management of a driven load.

Synchronizing multiple units

When one chassis runs out of channels, you tie several together. The standard method shares a common reference clock so every unit's timebase agrees, then distributes a common trigger so every unit's T0 fires together. Most of the line accepts a 10 to 100 MHz external clock in and can pass a clock out, which lets you daisy-chain timebases. The 588 and 588B add Ethernet and SCPI control for coordinating instruments across a rack or a room. For the tightest skew, lock every unit to the same physical 10 MHz source rather than trusting independent crystals.

The Model 725 and programmable trigger logic

The Model 725 takes a different approach to synchronization. Instead of one T0 fanning out to delayed channels, it provides eight inputs, eight outputs, and eight independent timers, with programmable boolean logic between them. Inputs can be combined with AND, OR, XOR, and negation before they start a timer, so an output can fire only when several conditions coincide. Throughput delay is about 11 ns with roughly 1 ns spread, and delay resolution is 10 ns. This is the tool for multi-trigger experiments: ballistics, explosive and airbag-squib testing, shock tubes, and two-pulse laser work where the trigger is a logical condition, not a single edge. Up to 64 complete settings can be stored for standalone operation.

Trigger I/O at a glance

Model	Trigger modes	Max trigger rate	Trigger threshold	Trigger jitter
525	Internal, external, gate, burst, duty cycle	20 MHz (rate)	up to 30 V peak, edge-selectable	(verify)
575	Internal, external, gate, burst, duty cycle	5 MHz ext trig	0.2–15 VDC	~800 ps RMS
577	Internal, external, gate, burst, duty cycle	5 MHz ext trig	0.2–15 VDC	<800 ps RMS
588	Internal, external, gate, burst, duty cycle	10 MHz ext trig	0.2–15 VDC	<800 ps RMS
588B	Normal, single shot, burst; gate/dual trigger	(verify)	(verify)	<5 ps RMS ch-to-ch
725	8 inputs, programmable AND/OR/XOR/negate logic	100 MHz ext clock	5 mV hysteresis	50 ps typ (internal)
745T	External (pos/neg), internal, burst, prescaler, gate	(per config)	0.1–5.0 V	25 ps ext trig
765	Single, continuous, burst, gated	40 MHz ext trig	±8 V threshold, 50 Ω/1 kΩ	<30 ps (≤15 MHz)
765-HV	Single, continuous, burst, gated	40 MHz ext trig	±8 V threshold, 50 Ω/1 kΩ	<30 ps (≤15 MHz)

Specifications come from current Berkeley Nucleonics dossiers and should be confirmed against the latest released datasheet. Several 525 and 588B trigger figures are not stated on the source pages and are flagged as verify.

Choosing your trigger source

If the generator should set the pace, use internal triggering for the cleanest T0. If an external event owns the timing, accept the input-stage jitter and feed it the fastest edge you can. Use a gate to window a running train, burst to emit a counted set, and the 725 when your start condition is a logical combination of several signals. For more channels than one chassis holds, share a clock and a trigger across units.

Plan a synchronization scheme with us

Describe your triggers, the number of timed events, and how many channels you need, and we will lay out a single-unit or multi-unit scheme and flag anything to verify against the datasheet. Reach Berkeley Nucleonics at info@berkeleynucleonics.com or 800-234-7858, or browse the full Pulse & Delay Generators documentation.