Digital delay generator
Encyclopedia
A digital delay generator is a piece of electronic test equipment
that provides precise delays for triggering, syncing, delaying and gating events. These generators are used in many types of experiments, controls and processes where electronic timing of a single event or multiple events to a common timing reference is needed. The digital delay generator may initiate a sequence of events or be triggered by an event. What differentiates it from ordinary electronic timing is the synchronicity of its outputs to each other and to the initiating event.
in function but 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 while others provide multiple channels of timing.
Digital delay generator outputs are typically logic level, but some offer higher voltages to cope with electromagnetic interference
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)
Pulse selection or pulse picking of a single laser pulse from a stream of laser pulses generated via mode-locking is another useful feature of some delay generators. By using the mode-locked rate as an external clock to the digital delay generator one may adjust a delay and width to select a single pulse and synchronize other events to that single pulse.
s 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 GUIs. Industry standard
s 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. Another useful setup is to have one channel drive flash lamps a preset number of times, followed by a single Q-switch, followed by a delay and gate for the data acquisition or imaging system.
Negative delay is available with digital delay generators that can select some other channel as a reference . This would be useful for applications where an event must occur in advance of the reference. An example would be to allow for the opening of a shutter prior to the reference.
The multi-trigger versions have programmable logic controller type functionality for incorporating interlocks, latches, dynamic delay adjustment and trigger noise suppression. Triggers are formed by logically combining the various inputs and outputs in And, Or, Xor and Negated forms.
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.
Dual-trigger digital delay generators provide two independently triggered digital delay generators in one package. Since benchtop digital delay generators are now multi-channel, it is possible to have two or more input triggers and select the channels which respond to each of the triggers. A interesting concept to provide dual-trigger capability converts an instrument that has separate trigger and gate inputs to allow the gate to operate as a second trigger.
precision but that are not quantized to the edges of the reference oscillator. There are a number of techniques used in digital delay generation.
Electronic test equipment
Electronic test equipment is used to create signals and capture responses from electronic Devices Under Test . In this way, the proper operation of the DUT can be proven or faults in the device can be traced and repaired...
that provides precise delays for triggering, syncing, delaying and gating events. These generators are used in many types of experiments, controls and processes where electronic timing of a single event or multiple events to a common timing reference is needed. The digital delay generator may initiate a sequence of events or be triggered by an event. What differentiates it from ordinary electronic timing is the synchronicity of its outputs to each other and to the initiating event.
Equipment
The digital delay generator is similar to a pulse generatorPulse generator
A pulse generator is either an electronic circuit or a piece of electronic test equipment used to generate rectangular pulses. This article describes the test equipment.-Bench pulse generators:...
in function but the timing resolution is much finer and the delay and width jitter
Jitter
Jitter is the undesired deviation from true periodicity of an assumed periodic signal in electronics and telecommunications, often in relation to a reference clock source. Jitter may be observed in characteristics such as the frequency of successive pulses, the signal amplitude, or phase of...
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
Pulse generator
A pulse generator is either an electronic circuit or a piece of electronic test equipment used to generate rectangular pulses. This article describes the test equipment.-Bench pulse generators:...
.
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 while others provide multiple channels of timing.
Digital delay generator outputs are typically logic level, but some offer higher voltages to cope with electromagnetic interference
Electromagnetic interference
Electromagnetic interference is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit...
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
Channel (communications)
In telecommunications and computer networking, a communication channel, or channel, refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio 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
Q-switching
Q-switching, sometimes known as giant pulse formation, is a technique by which a laser can be made to produce a pulsed output beam. The technique allows the production of light pulses with extremely high peak power, much higher than would be produced by the same laser if it were operating in a...
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)
Pulse selection or pulse picking of a single laser pulse from a stream of laser pulses generated via mode-locking is another useful feature of some delay generators. By using the mode-locked rate as an external clock to the digital delay generator one may adjust a delay and width to select a single pulse and synchronize other events to that single pulse.
Uses
A delay generator can also be used to delay and gate high speed photodetectorPhotodetector
Photosensors or photodetectors are sensors of light or other electromagnetic energy. There are several varieties:*Active pixel sensors are image sensors consisting of an integrated circuit that contains an array of pixel sensors, each pixel containing a both a light sensor and an active amplifier...
s 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
Graphical user interface
In computing, a graphical user interface is a type of user interface that allows users to interact with electronic devices with images rather than text commands. GUIs can be used in computers, hand-held devices such as MP3 players, portable media players or gaming devices, household appliances and...
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 GUIs. Industry standard
Industry Standard
Industry Standard is a 1982 album by The Dregs. It is their only album featuring vocals and garnered the group their fourth Grammy nomination.-Track listing:All tracks are written by Steve Morse, except where noted.#"Assembly Line" – 4:25...
s such as GPIB, RS232, USB and ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
are available from a variety of manufacturers.
Experimental fluid dynamics
Fluid dynamics
In physics, fluid dynamics is a sub-discipline of fluid mechanics that deals with fluid flow—the natural science of fluids in motion. It has several subdisciplines itself, including aerodynamics and hydrodynamics...
uses digital delay generators in its investigations of fluid flow. The field of PIV, particle image velocimetry
Particle image velocimetry
Particle image velocimetry is an optical method of flow visualization used in education and research. It is used to obtain instantaneous velocity measurements and related properties in fluids...
, 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. Another useful setup is to have one channel drive flash lamps a preset number of times, followed by a single Q-switch, followed by a delay and gate for the data acquisition or imaging system.
Negative delay is available with digital delay generators that can select some other channel as a reference . This would be useful for applications where an event must occur in advance of the reference. An example would be to allow for the opening of a shutter prior to the reference.
Multi-trigger digital delay generators
A new development are digital delay generators that have gating and external triggering, dual or multi-trigger capabilities. The gate allows the user to enable outputs and/or triggers with an electronic signal. Some units have gate or trigger capabilities using a single or separate connectors. Dual or multi-trigger digital delay generators have several input triggers. These triggers can be selectively used to trigger any or all channels.The multi-trigger versions have programmable logic controller type functionality for incorporating interlocks, latches, dynamic delay adjustment and trigger noise suppression. Triggers are formed by logically combining the various inputs and outputs in And, Or, Xor and Negated forms.
LIDAR
LIDAR
LIDAR is an optical remote sensing technology that can measure the distance to, or other properties of a target by illuminating the target with light, often using pulses from a laser...
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
Data acquisition
Data acquisition is the process of sampling signals that measure real world physical conditions and converting the resulting samples into digital numeric values that can be manipulated by a computer. Data acquisition systems typically convert analog waveforms into digital values for processing...
system. Gating allows regions of interest to be processed and stored while ignoring the bulk of unwanted data.
Dual-trigger digital delay generators provide two independently triggered digital delay generators in one package. Since benchtop digital delay generators are now multi-channel, it is possible to have two or more input triggers and select the channels which respond to each of the triggers. A interesting concept to provide dual-trigger capability converts an instrument that has separate trigger and gate inputs to allow the gate to operate as a second trigger.
DDG Design
A key issue in the design of DDGs is to generate triggered delays having crystal-oscillatorCrystal oscillator
A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency...
precision but that are not quantized to the edges of the reference oscillator. There are a number of techniques used in digital delay generation.
- The simplest scheme simply uses a digital counter and a free-running crystal oscillator to time intervals with 1-clock ambiguity, resulting in output edge jitter of one clock period peak-to-peak relative to an asynchronous trigger. This technique is used in the Quantum Composers and Berkeley Nucleonics instruments.
- Triggered crystal, LC, or delay-line oscillators may be started at trigger time, and subsequently counted to make coarse delays, followed by an analog fine or "vernier" delay to interpolate between clock periods. An enhancement is to use a phase-locked loop to lock the startable oscillator to a more accurate continuous-running crystal oscillator using a technique that preserves the original trigger alignment. The classic Hewlett Packard 5359A Time Synthesizer used a triggered ECL delay-line oscillator which was synchronized to a crystal oscillator using a heterodyne phaselock technique; the technique was subsequently used in several Berkeley Nucleonics and LeCroy delay generators. Highland Technology uses a triggered LC oscillator and a DSP phaselock scheme. Jitter below 10 ps RMS relative to an external trigger can be achieved.
- It is possible to design an analog-ramp delay generator, using a current source to charge a capacitor, that spans some tens of nanoseconds of delay range. One can then suspend the ramp current for some integral number of clocks, as timed by a crystal oscillator. The freezing of the ramp extends the range of delays without the requirement to synchronize the oscillator to the trigger. This technique is described in US patent 4,968,907 and was used in the Signal Recovery instrument. Low delay jitter is possible, but leakage current becomes a serious error contributor for delays in the millisecond range.
- A flipflop-based dual-rank synchronizer can be used to synchronize an external trigger to a counter-based delay generator, as in case (1) above. It is then possible to measure the skew between the input trigger and the local clock and adjust the vernier delay, on a shot-by-shot basis, to compensate for most of the trigger. Jitter in the tens of picoseconds RMS can be achieved with careful calibration. This technique is used by Stanford Research Systems.
External links
- http://www.berkeleynucleonics.com/resources/575_Multiplexing(1).pdf "Sync'ing, delaying and gating with multiple pulse trains"
- http://www.home.agilent.com/agilent/product.jspx?nid=-536900193.536882162.00&cc=US&lc=eng
- http://www.quantumcomposers.com/
- http://www.greenfieldtechnology.com/
- http://www.signalrecovery.com/9650Apage.htm
- http://www.thinksrs.com/products/DG645.htm
- http://www.highlandtechnology.com/DSS/T560DS.html
- http://zone.ni.com/devzone/cda/epd/p/id/6131 FPGA-based