Digital delay generator

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A digital delay generator is a piece of electronic test equipment that provides precise delays for triggering, syncing, delaying and gating events. The digital delay generator is similar to a pulse generator in function but with a digital delay generator the timing resolution is much finer and the delay and width jitter much less.

Some manufacturers, calling their units digital delay and pulse generators, have added independent amplitude polarity and level control to each of their outputs in addition to both delay and width control. Now each channel provides its own delay, width and amplitude control, with the triggering synchronized to an external source or internal rep rate generator - like a general-purpose pulse generator.

Some delay generators provide precise delays (edges) to trigger devices. Others provides precise delays and widths to also allow a gating function. Some delay generators provide a single channel of timing; others provide multiple channels of timing.

Digital delay generator outputs are typically logic level, but some offer higher voltages to cope with electromagnetic interference (EMI) environments. For very harsh environments, optical outputs and/or inputs, with fiber optic connectors, are also offered as options by some manufacturers. In general, a delay generator operates in a 50 ohm transmission line environment with the line terminated in its characteristic impedance to minimize reflections and timing ambiguities.

Historically, digital delay generators were single channel devices with delay-only (see DOT reference below). Now, multi-channel units with delay and gate from each channel are the norm. Some allow referencing to other channels and combining the timing of several channels onto one for more complex, multi-triggering applications. Multiple-lasers and detectors can be triggered and gated. (see second reference on "Experimental study of laser ignition of a methane/air mixture by planar laser-induced fluorescence of OH." Another example has a channel pumping a laser with a user-selected number of flash lamp pulses. Another channel may be used in Q-switching that laser. A third channel can then be used to trigger and gate a data acquisition or imaging system a distinct time after the laser fires. (see sensorsportal.com reference below) A delay generator can also be used to delay and gate high speed photodetectors in high speed imaging applications. (see reference on high speed photography below)

Digital delay generators are usually the heart of the timing for larger systems and experiments. Users generally create a GUI, graphical user interface to provide a single control to the entire system or experiment. Digital delay generator manufacturers have added remote programming schemes that facilitate the creation of such GUI's. Industry standards such as GPIB, RS232, USB and ethernet are available from a variety of manufacturers.

Experimental fluid dynamics uses digital delay generators in its investigations of fluid flow. The field of PIV, particle image velocimetry, encompasses several subsets which would use digital delay generators as the main component of its timing where multiple lasers may be triggered. Multiple channels may trigger multiple lasers. One is also able to multiplex the timing of several channels onto one channel in order to trigger or even gate the same device multiple times. A single channel may trigger a laser or gate a camera with its multiple, multiplexed pulses.

A new development are Digital delay generators that have gating and external triggering capabilites. The gate allows the user to enable outputs and/or triggers with an electronic signal.

LIDAR applications use digital delay generators. A channel is used to trigger a laser. A second channel is used to provide a delayed gate for the data acquisition system. Gating allows regions of interest to be processed and stored while ignoring the bulk of unwanted data.

[edit] References

Target Speed Simulator Based on Digital Delay Generator - US Dept of Transportation DOT HS 809 811 Section 4.10.

http://psfvip4.univ-fcomte.fr/Fpsfvip4/sources/F4022.pdf "Experimental study of laser ignition of a methane/air mixture by planar laser-induced fluorescence of OH"

http://flow.kaist.ac.kr/upload/paper/2003/2003____EIF_34_06_0697-707.pdf "Measurement of local forcing on a turbulent boundary layer using PIV"

http://www.sensorsportal.com/HTML/DIGEST/february_06/Pulse_Generator.htm

http://psicorp.com/publications/PDF/sr-0922.pdf "Repetitively pulsed ruby lasers as light sources for high speed photography applications"

http://www.idquantique.com/products/files/id200-appnote.pdf "Single photon detector module"

http://www.engineering.sdstate.edu/~tans/lidarremotesensing.htm "Lidar remote sensing"