Why these four numbers get confused
A datasheet line that reads "250 ps" can mean three different things depending on the column it sits in. Resolution, jitter, and accuracy are separate properties of a timing instrument, and drift is a fourth that lives off the spec sheet until your lab warms up. Choosing a delay generator on the wrong one of these is the most common way to buy more instrument than you need, or less.
Delay resolution: the smallest step you can ask for
Resolution is the granularity of the delay setting. A 250 ps resolution means you can place an edge at 100.00 ns or 100.25 ns, but nothing between. It is a quantization limit, not an error. The Model 577 and Model 575 resolve to 250 ps. The Model 765 family steps in 10 ps. The Model 745T reaches 1 ps on its precision channels, and 250 fs in channel-grouped mode. Resolution sets the floor on how finely you can dial timing; it says nothing about how repeatable that timing is.
RMS jitter: shot-to-shot wobble
Jitter is the statistical spread of the actual edge around its commanded position, quoted as an RMS value. It is the number that limits how cleanly you can overlap two events or gate a fast detector. Low jitter is what lets a pulse generator define a coincidence window or a pump-probe interval.
Jitter scales with where you measure it. Channel-to-channel jitter, the spread between two outputs of the same unit, is usually the tightest figure. Trigger-to-output jitter, measured from an external trigger, is larger because it includes the input comparator. The Model 588B specifies under 5 ps RMS, the lowest in the line. The Model 745T reaches roughly 5 ps at short delays in grouped mode. The Model 765 holds 4 ps period jitter, and the Model 577 stays under 50 ps channel to channel. By contrast a trigger input on the 575 or 577 carries around 800 ps RMS, a reminder that the slowest path sets your real budget.
Timing accuracy: how close to the truth
Accuracy is how far the mean edge position sits from the value you commanded. It is almost always written as a fixed term plus a fraction of the setpoint, for example 1 ns + 0.0001 times the delay. The fixed part dominates short delays; the proportional part, tied to the timebase, dominates long ones. The 577 and 588B quote 1 ns + 0.0001 times setpoint. The 745T specifies under 250 ps plus delay times ten to the minus eight, an exceptionally tight figure anchored to a 0.05 ppm timebase. Accuracy and jitter together describe a distribution: accuracy is where the center sits, jitter is how wide it spreads.
Drift: the slow one
Drift is the change in timing over minutes to hours, driven mostly by temperature and crystal aging. It does not appear as a single spec line; it hides inside the oscillator rating. A 25 ppm crystal, as in the Model 588, will wander more across a 20 degree swing than a 0.05 ppm timebase like the 745T. For short experiments drift is irrelevant. For a synchronization system that runs all day, it can swamp jitter entirely, which is why locking to an external 10 MHz reference matters. Most of the line accepts a 10 to 100 MHz external clock for exactly this reason.
How the models compare
| Model | Delay resolution | RMS jitter | Accuracy | Timebase |
|---|---|---|---|---|
| 525 | 4 ns | <50 ps (rate); <250 ps ch-to-ch | 10 ns + 0.0001 × setting | 50 MHz, 50 ppm |
| 575 | 250 ps | ~120–200 ps (50 ps in some configs) | 1 ns + 0.0001 × setpoint | (verify) |
| 577 | 250 ps | <50 ps ch-to-ch | 1 ns + 0.0001 × setpoint | 200 MHz PLL, 50 ppm |
| 588 | 250 ps | <50 ps | 1 ns + 0.0001 × period | 100 MHz PLL, 25 ppm |
| 588B | 250 ps | <5 ps | 1 ns + 0.0001 × delay | (verify) |
| 725 | 10 ns | 50 ps typ / 200 ps max (internal) | <0.0001% typ, 0.01% max | internal logic clock |
| 745T | 1 ps (250 fs grouped) | ~5 ps short delay; 25 ps ext trig | <250 ps + delay × 10⁻⁸ | 0.05 ppm |
| 765 | 10 ps | 4 ps period; <10 ps ch-to-ch | ±2 ppm | ±2 ppm |
| 765-HV | 10 ps | <15 ps | ±2 ppm | ±2 ppm |
Figures are taken from current Berkeley Nucleonics dossiers and should be verified against the latest released datasheet before use in a specification. Some 575 and 588B timebase details are not stated on the source page and are flagged as verify.
Reading the budget in practice
Add the relevant terms for your case, do not take the smallest number on the page. A pump-probe setup triggered externally inherits the trigger jitter, not the channel-to-channel figure. A long delay inherits the timebase term, not just the fixed accuracy. And a system that runs for hours inherits drift unless it is locked to a reference. The honest budget is the sum of the worst path you actually use.
Get help sizing the budget
Tell us the trigger source, the delays involved, and the runtime, and we will work the real jitter and accuracy budget with you, flagging anything that needs verification. Reach Berkeley Nucleonics at info@berkeleynucleonics.com or 800-234-7858, or browse the full Pulse & Delay Generators documentation.