Analog & Time to Digital Converter Glossary



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amplitude converter, data analyzer, digitizer, transient recorder, analog-to-digital converter, Msps, Gsps, GByte/s

Analog-to-digital Converters are integrated circuits that quantize a voltage or current into a stream of digital data. Board level products that make ADCs with sample rates of hundreds of Mega samples per Seconds (Msps) or several Giga samples per seconds (Gsps) accessible to the software are often called "digitizers" or "transient recorders". Unlike other ADC boards, our digitizers are optimized to detect pulses on the fly and stream the extracted sample data directly to the main memory, minimizing latency and CPU load. This is enabled by our custom 6GByte/s PCIe DMA controller that manages the buffer data structures directly without software intervention.

You also might like to have a look at the cronologic ADCs Ndigo5G-10 and Ndigo6G-12.


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An averager is an ADC digitizer that does not present single acquired waveforms to the user but does calculate the average of multiple waveforms before readout. This greatly reduces the amount of data that needs to be read out. It also takes away flexibility and makes it impossible to do processing on the individual pulses to improve the measurement results. Our Ndigo6G implements zero suppression together with very high readout bandwidth to enable software-based averaging without losing the ability to operate on individual pulses. Contact us to talk about the option of performing hardware averaging in the Ndigo6G.

Avalanche photodiodes

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Avalanche photodiodes are highly sensitive, fast photodiodes and count among the avalanche diodes, i.e. they are optical sensors based on a silicon substrate. They form the basis for modern silicon photomultipliers (SiPM) and use the internal photoelectric effect to generate charge carriers and the avalanche effect for internal amplification. Similar to conventional photomultiplier tubes (PMT), they use the effects of impact ionization to generate secondary charge carriers. However, they get by with a significantly lower supply voltage and reach limit frequencies of up to the Gigahertz range. Their extremely high sensitivity enables the detection of weak light right down to individual photons. They are therefore also used for the detection of individual particles in high-energy physics. With regard to TCSPC, modern analog SiPM offer the possibility of inferring the photon rate directly from the voltage output. Read also: SPADs and HPDs.


bin size

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bin size jitter, FWHM, RMS, quantization error

In time-to-digital converters, the bin size is the unit of quantization for time measurements. In our TDCs other jitter sources are smaller than the quantization error. Therefore the measurement error for short intervals is dominated by the bin size in our devices. Under these circumstances, the maximum measurement error is close to half a bin. The rooted mean square (RMS) error is about 0.8 bins and the full width half maximum error is about 2 bins.



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cold target recoil-ion momentum spectroscopy, corresponding experimental setups are often called reaction microscopes, as well

Cold target recoil-ion momentum spectroscopy is a momentum imaging technique used to measure the complete fragmentation of an atomic or molecular few-body system. All charged fragments from an atomic, molecular, or surface reaction are projected onto large area position- and time-sensitive detectors. By measuring the individual particles’ times-of-flight and positions of impact on the detector, their 3D- momentum vectors are deduced. COLTRIMS measurements are coincidence measurements as many final-state fragments of single molecules or atoms are detected. Typical setups include a supersonic gas jet (i.e. molecular beam) as a target for the investigations and multi-hit capable MCP detectors with delay line position-readout for single particle detection.


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triggered measurements, common-stop

In a common-start setup, time intervals are measured relative to a trigger signal on the "start"-input that is arriving before the pulses shall be measured. In such a scenario, the gate signal specifies the start time of the time measurement while the individual channel inputs end the time period.


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triggered measurements, common-start

In a common-stop setup, time intervals are measured relative to a trigger signal that is arriving after the pulses that shall be measured. In such a configuration, the individual channel inputs deliver the start signal and the gate signal stops the measurement.

constant fraction discriminator

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When measuring the arrival time of pulses with a fixed threshold the time measured exhibits a measurement error that is a function of the pulse amplitude. For setups where pulses have varying amplitudes but a constant rise time, a constant fraction discriminator (CFD) can reduce this error. Measuring a signal at two or three fixed thresholds with a high-resolution TDC can achieve the same quality of time walk correction as a CFD.

cycle to cycle jitter

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short-term jitter, C2C jitter

Cycle-to-cycle jitter is a measure for the uncertainty in the interval between any two adjacent clock periods. In many TDC products, this is a major source of measurement error. For cronologic products, the cycle-to-cycle jitter is much less than the bin size. Care must be taken when comparing jitter specifications as various characteristics of the clock cycle distribution can be specified. Common specifications are the one sigma interval or the 95% interval of the distribution.



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Discriminators are circuits that are used to create a digital signal for time measurement from an analog input waveform. The simplest form is a threshold discriminator that compares the input with a fixed voltage. Commonly used are constant fraction discriminators that compare against a voltage proportional to the pulse height. 


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data acquisition

DAQ is the abbreviation for data acquisition. This is the process of sampling signals that measure real-world (analog) physical conditions and making them available to application software. In personal computers, this is accomplished by data acquisition cards such as cronologic ADCs and TDCs.

dead time

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Dead time describes a time interval during which a measurement device is not capable to acquire new measurements because it is still busy processing the previous one. Our products are optimized to minimize dead time. Read out always happens in parallel to measurement without disturbing it.


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Digitizer is a common name for board-level analog-to-digital converter products with high sample rates such as our Ndigo series of products, such as Ndigo5G-10 and Ndigo6G-12.

delay-line detector

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A delay-line position readout is used to measure the position of impact of a particle on a (typically larger area) microchannel plate detector with a resolution of approx. 100µm. The electron cloud, which is emitted at the location of the particle impact on the detector on the back of an MCP-stack induces a signal in a wire. The signal travels along the wire towards the wire’s two ends. By measuring the arrival time difference of the induced signal at each end of the wire, the position of impact on the wire can be deduced. In order to cover a larger area, the detection wire (i.e. the delay-line) is wound around a detector body. 2D-position of impact information can be obtained by employing a set of two orthogonal windings.

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fluorescence lifetime imaging microscopy, photoluminescence decay measurements

Fluorescence Lifetime Imaging Microscopy (FLIM) is a microscopy imaging technique where time-correlated single-photon counting (TCSPC) is performed on each pixel of the image. The sample is scanned by a high-frequency pulsed laser beam, single photons of the emitted fluorescence light are detected, and the arrival time of each photon in the laser pulse period is determined by the TCSPC system and recorded in a histogram.


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Functional Near-Infrared Spectroscopy

Functional Near-Infrared Spectroscopy (fNIRS) is a non-invasive method for brain imaging. In time-domain (TD) fNIRS the time-of-flight distribution (DTOF) of scattered photons is detected by multichannel time-to-digital converters

frequency counting

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frequency acquisition

In measuring the frequency of a periodic electronic signal, the number of cycles of oscillation, or pulses per second are counted. When it comes to recovering the frequency of the data pattern in a very short time or only in a few cycles, fast TDCs can improve the traditional method.


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FCS, fluorescence lifetime correlation spectroscopy (FLCS)

Fluorescence-correlation-spectroscopy is a highly sensitive, time-resolved optical measurement method that can be used to study the mobility of fluorescent particles and molecular interactions. The widely used measurement method is based on a confocal microscope and reveals interesting biochemical parameters. During measurement fluctuations in the fluorescence emission intensity over time are recorded, which are caused by individual fluorophores that pass through the detection volume. With FCS, the size or shape of particles, diffusion constants, concentrations, and bonds between different diffusing species can be determined. 

A combination of the time-correlated single photon counting (TCSPC) with the above-mentioned classic fluorescence correlation spectroscopy is called fluorescence lifetime correlation spectroscopy (FLCS). With this method, the time-resolved detection of fluorescence is used to separate the contribution of different processes to the measurement signal. The time resolution is in the picosecond range, which means that high-performance TDCs or ADCs are the best choices for data acquisition for such applications.


gate inputs

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In order to decrease the amount of data transmitted to the PC, some of our products include independent gating units that allow suppressing measurements during a time interval relative to the main trigger or a separate input signal.


hybrid photodetector

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hybrid detector, hybrid PMT, HPD, hybrid photomultiplier tube

A hybrid photo detector is a device for detecting very small amounts of light. Due to the low fluctuation, hybrid photodetectors are able to precisely determine the number of photoelectrons initially generated, as long as the maximum recording capacity is not exceeded. These detectors combine the properties of photomultipliers and avalanche photodiodes. Incoming photons are detected by an HPD using a photocathode (e.g. made of gallium arsenide phosphide), which emits a photoelectron with the highest possible quantum yield. This is strongly accelerated within a photomultiplier tube by means of high voltage in a vacuum, so that it finally hits an avalanche diode (electron bombardment). As a result, numerous electrons are released in the APD, so that the original photoelectron is duplicated more than a thousand times. In this way, measurable signals are generated that can be used for data acquisition.

The extremely light-sensitive detectors are used in fluorescence microscopy, fluorescence lifetime microscopy and fluorescence correlation spectroscopy.


impulse response function

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IRF, delta-distribution, Dirac delta function, unit impulse function

Impulse response analysis is an important aspect of digital signal processing with regard to the characterization of dynamic systems, such as measurement setups. The impulse response function (IRF) describes the reaction of the dynamic system to an external change. In digital measurement technology, this characterizes the deviation of the output signal for the case that an extremely short impulse is given to the input, whereby the impulse response describes the reaction of the system as a function of time. The so-called „unit impulse function“ has zero width, infinite height and an integral (area) of one. Since it is impossible in practice to generate such a perfect impulse as input for measuring the impulse response, the shortest possible impulse is used to approximate the ideal impulse to determine the impulse response. It is important that the impulse is short enough compared to the measured impulse response so that the result is close to the true impulse response and thus still provides a usable result for assessing a measurement setup.


jitter counter

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A jitter counter is an instrument to measure timing jitter in clocks generators or communication systems. All cronologic TDC products can be used as jitter counters.

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LiDAR, and LADAR, "light detection and ranging", "laser imaging, detection, and ranging", "3-D laser scanning, Lidar mapping"

Light Detection And Ranging is a method where the round-trip time of a laser reflection is measured using a time-to-digital converter (TDC). It is used 3-D laser scanning both airborne and stationary, for computer vision especially in autonomous vehicles and meteorological measurements. 

low count rate detection

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particle detection, radiation detection, neutron detection, Geiger–Müller counter, scintillation counter, scintillation tracker, scintillation detector

Using single ion counting, low levels of radiation can be detected and characterized. In the area of radiation safety and non-proliferation small amounts of unknown nuclear material can be detected and identified using its spectra signature. Examples are special nuclear material (SNM) and shielded highly enriched uranium (HEU). 



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Matrix-assisted laser desorption/ionization

Matrix-Assisted Laser Desorption and Ionization is an ionization technique that can be used on large molecules with minimal fragmentation. This technology allows building time-of-flight (TOF) mass spectrometers for these molecules.

MCP detector

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MCP microchannel plate detection, microchannel plate imaging, mcp imaging

Microchannel plate detectors (MCP) detect electrons, ions, or high-energy photons. They can be viewed as a further development of simple channeltrons (CEMs) and consist of a plate-shaped array of glass capillaries (between 10μm and 100μm inside diameter), which are provided with a semiconductor material on the inside. This layer on the capillary walls has electron-emitting properties, whereby the lead glass ensures a high electrical resistance between the capillaries. Each of the capillaries acts as an electron multiplier during detection: an accelerating voltage is applied between the two metalized plate sides and the capillary is arranged slightly tilted relative to the plate axis, so that incident electrons are certain to hit the wall of the respective capillary several times and generate secondary electrons again and again. These can then be recorded as measurable pulses with the help of fast TDCs or ADCs. Microchannel plates work with particularly low noise and, thanks to the matrix arrangement, also provide spatial information if required. MCP configurations with double or Z-stack MCP detectors are available for better resolution.

multi-channel scaler

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multi-channel detector scaler, MCS, multi-hit TDC, multi-hit converter

A multi-channel scaler (MCS) is a pulse counting instrument that records the number of events that occur during a specified time interval and provides a time-histogram of counts versus time. MCS are commonly used in single-photon counting applications. All cronologic time measurement products can be used as multi-channel scalers.



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Nuclear Instrumentation Module standard

The NIM standard, originally an acronym for Nuclear Instrumentation Module, was developed in nuclear and high-energy physics in 1964. The included standards define mechanical and electrical specifications for modular systems with bus connections.


Optical Coherence Tomography

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Optical coherence tomography is a high-resolution imaging system. It obtains 2- and 3-dimensional images from scattering materials (e.g. biological tissue). As a non-invasive diagnostic instrument, it is mostly used for ophthalmological examination of the retina. In this application, analog signals are sampled with ADCs so that the resulting digital pattern represents the analog signal as a function of the change in wavelength of the light source.


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optical time-domain reflectometry

In optical fiber communications, the losses in optical fibers can be measured with optical time domain reflectometers. The measuring method works similar to radar but works with very low light levels and helps to localize poor fiber splices or faulty optical components. For measurement, a fast rise time pulse is injected into the cable system at one end. If the traveling impulses arrive at a location where the impedance differs from the characteristic impedance of the cable (e.g. at a faulty link), some of these signals will be reflected back to the source and can be detected with photon-counting detectors, photomultipliers, or avalanche photodiodes. With help of a fast ADC, the time parameters of the reflection are measured in order to determine the location of the impedance discontinuity.


PALM microscopy

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photoactivated localization microscopy, PALM imaging, Single-molecule imaging, Single-molecule localization microscopy, SMLM, single-molecule microscopy

Photoactivated Localization Microscopy (PALM) is a super-resolution imaging technique that achieves nanometre-scale resolution by exploiting the properties of photoactivatable fluorophores to reveal spatial details of tightly packed molecules. This method enables the detection of individual molecules such as proteins in a cellular context. The method offers a high level of detail when depicting 3D structures in cell bodies and works like this: 

Exposing fluorophores to low-power activating lasers of a certain wavelength leads to a change in their emission spectra. This conversion is implemented stochastically so that only a few fluorophores will turn into their active state. The stochastic excitation of the fluorophore ensures that each fluorescence point comes from a single fluorophore. A high-power laser beam briefly exposes these activated molecules, after which they are immediately returned to their inactive state (e.g. by photobleaching). This process is then repeated over thousands of images and the frames are merged into a super-resolution image.

photon counting

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single-photon detectors, SPD, detection of individual photons, photosensors, multi-pixel photon counter

See also: TCSPC. In single-photon counting, a single-photon detector (SPD) emits an electric pulse every time a photon is detected so that individual photons can be counted. Photon counting is used in telecommunication, biophysics imaging (e.g. FLIM), quantum optics and high-resolution (single-pixel) LIDAROTDR (optical time-domain reflectometry) and Quantum Key Distribution (QKD).


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PCI eXtensions for Instrumentation

PCI eXtensions for Instrumentation is a bus system for measurement and automation technology. It is based on the older xPCI bus technology but uses the point-to-point PCI express standard for communication. Our standard PCIe products allow customers to build systems that deliver the same performance as a PXI setup at a fraction of the cost.

photomultiplier tubes

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Classic photomultiplier tubes (PMT) work in the ultraviolet, visible and near infrared range of the electromagnetic spectrum. These are electron tubes that pick up weak light signals (up to individual photons) and amplify them to such an extent that free electrons produce more free electrons of lower energy, whereby the weak input signals are converted into measurable currents. They typically consist of a photocathode and a downstream secondary electron multiplier (SEM) in an evacuated glass bulb. A further development of the PMT, the hybrid photodetector, combines this with avalanche photodiodes.


Quantum key distribution

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The quantum key distribution enables tap-proof encryption of data. For this purpose, the quantum properties of light are used to transmit encrypted data. Single-photon sources (SPS) are used for optimal performance. Our fast TDCs can be used in single-photon counting receiver modules that convert single-photon detection events into streams of timestamps.

quadrupol mass analyzers

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Quadrupole mass analyzers can be used as an upstream mass filter in TOF mass spectrometry (QTOF). With their help, all ions can be eliminated for the detection of certain substances that are not within the desired range from mass to charge. A quadrupole mass analyzer consists of the arrangement of two oppositely identical electrical or magnetic dipoles with a fixed distance over their entire length. In mass filter analysis with an electric quadrupole, the inertia of the introduced particles is used for selection: the light particles are destabilized in one of the levels and the heavy particles in the other level by means of an applied alternating voltage. Quadrupoles can also be used to focus the ion beam in a mass spectrometer, e.g. to align the ions with a collision cell and to record the fragments produced there by means of time-of-flight measurement.

Note: There are also mass spectrometers that use quadrupoles and similar arrangements to record an entire mass spectrum (QMS). In terms of their detection capabilities, these do not come close to the performance of the TOF-MS, because in these devices the stability range is scanned over the entire m / Q range and a new measurement is carried out at every step. As a result, such measurements require a significantly higher investment of time. Triple quadrupole mass spectrometers (TQMS) should also be mentioned at this point. These are tandem mass spectrometers, which consist of two quadrupole mass analyzers connected in series and are separated by a (non-mass-resolving) high-frequency quadrupole, which serves as a cell for the collision-induced dissociation. The aim is to increase the sensitivity of the measurement. However, this coupling does not achieve the performance of a TOF measurement either.


reciprocal counter

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A reciprocal counter measures a frequency by measuring the time between a certain number of edges of a clock signal. This is opposed to the approach of a simple counter that counts the number of signal edges in a certain time interval. All of our TDCs can be used as reciprocal counters with very high precision. To measure frequencies that are higher than the maximum count rate of a given TDC an external prescaler is required.


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mass reflectron

A reflectron is used to improve the mass resolution in a mass spectrometer. It is used to reverse the direction of the ions by creating an electric field with a gradient. The field decelerates the ions and then accelerates them again in the opposite direction. This reduces the influence of their kinetic energy distribution on the flight time, because the ions with higher kinetic energy penetrate deeper into the electrical field of the reflector and cover a correspondingly longer distance, which largely compensates for the flight time differences.

The background to this feature is, that it is technically not exactly easy to ensure in a mass spectrometer that all ions really absorb the same amount of energy. During the measurement, the sample is in a gaseous state, which means that the energy distribution of the gas particles within the ion source follows a Boltzmann distribution. During the acceleration phase, different parts of the sample are therefore exposed to the electric field to a greater or lesser extent than others. As a result, they do not consume the same amount of energy, which would, however, be a prerequisite for correct measurements. Therefore a deviation occurs and particles with the same mass-to-charge ratio are nevertheless accelerated to different speeds. These ions have different kinetic energies and this energy dispersion acts as a blurring in the mass spectrum. The energy dispersion can be minimized with the help of a reflector.

See graphic below: The single-stage reflector uses a homogeneous field and can compensate for small energy fluctuations in the ions leaving the ion source. In the reflection by means of such an ion mirror, the more energetic ion (red) travels a longer distance but arrives at the detector at the same time as the lower-energy ion (green) of the same mass.


single photon avalanche diodes

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Single photon avalanche diodes (SPAD) are solid-state photodetectors and belong to the same family as photodiodes and avalanche photodiodes (APDs). While APDs show their strengths in the undistorted amplification of low-intensity optical signals, the behavior of SPADs is more closely related to the basic diode behavior. SPADS enable the direct counting of pulses and thus provide an indication of the optical intensity of the input signal, while the pulses can simultaneously trigger timing circuits to enable precise measurements of the time of arrival. These sensors are used in particular in time-of-flight 3D imaging, LIDAR technology, PET scanning, TCSPC, fluorescence lifetime microscopy and optical communication, especially in quantum key distribution. You might also be interested in HPDs.

single molecule fluorescence spectroscopy

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SMD, single molecule detection, single-particle tracking, SPT, PALM microscopy, single-molecule imaging, single-molecule localization microscopy, SMLM

Single molecule fluorescence spectroscopy is a method of physical chemistry in which individual molecules can be made visible. Thus the dynamics and interactions in cellular systems can be examined. The technique has developed rapidly in recent years, especially in the area of high-throughput single molecule detection. In biomolecular analysis, the method enables the identification of subpopulations and the localization of molecules with sub-wavelength precision. The technology is used in biological, clinical and medical research to follow the movement of individual molecules in living cells, e.g. for ultra-sensitive and specific DNA sequencing or for the detection of diseases.

During the process, the sample is brought under a special light microscope, which is optimized for the extremely small detection volume, and then excited by means of a laser. The photons emitted during the resulting fluorescence triggered can be tracked over longer periods of times with the aid of a microscope (single-particle tracking, SPT) or may also be put underneath a time-correlating single photon measurement.



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Time Correlated Single Photon Counting, time domain FLIM, tdFLIM

In Time-correlated single-photon counting (TCSPC) fluorescence decays are measured over the time axis. The method is an essential part of fluorescence lifetime imaging microscopy (FLIM). Time-Correlated Single Photon Counting is considered a particularly gentle measurement technique because the light pulses required for sample excitation have low pulse energy. This is possible because only a single photon is processed at a time. TCSPC is based on the detection of these individual photons and the measurement of their arrival times in relation to a reference signal, which is usually the time of emission of the laser pulse that was used to excite the sample. This laser pulse occurs with a high repetition rate so that a sufficiently high number of individual photons can be determined for the resulting measurement of the fluorescence lifetime.


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Timing Generator

Most of our ADC and TDC products are equipped with this feature which is a great help to control your experimental setup. The TiGer can be used to output periodic Timing patterns, delayed copies of other signals, or random triggers among other use cases.

trigger matrix

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trigger blocks, mapping

In most cronologic products, any digital input can be used to trigger any triggerable circuit. The mapping is performed by the configurable trigger matrix. Inputs can be input connectors, TiGer pattern generators, software triggers, and others. Triggerable circuits can be input gates, TiGer pattern generators, auxiliary ADC measurements among others. 

transient recorder

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Transient recorders are oscilloscopes that are designed to measure waveforms with very high bandwidth. Unlike equivalent time sampling scopes a transient recorder acquires the measurement in a single shot. The signal does not need to be repetitive. For digital data acquisition products, the terms ADC, digitizer, and transient recorder are mostly used interchangeably. 


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TOF- & MASS- spectroscopy / spectrometry detectors, TOFMS, ion-counting, ionization spectroscopy

In time-of-flight mass spectrometers ions are accelerated in an electric field. The time it takes for the ion to reach a detector is used to determine the mass-to-charge ratio of the ion. With a constant-fraction-discriminator (CFD) and time-to-digital converters, the flight time of the ion can be easily be measured with high precision. In setups where a high number of ions of the same mass is created, an ADC digitizer can be used instead to also obtain information on the pulse height and thus on the number of ions in each measured pulse.

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zero suppression

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All of our ADCs feature onboard zero suppression. The idea of this feature is, that only data that meet specifications predefined by the user are transmitted. This reduces PCIe busload in order to make maximum use of the available readout bandwidth. When set up correctly, only relevant pulses (above a certain threshold level) are detected, so that the amount of data that needs to be copied and analyzed is reduced drastically.