Digital Pulse Generator Research Articles

고해상도 레이더용 광대역 디지털 첩 펄스 발생기 실험모델 개발

항공기나 위성에 탑재되어 지표면의 영상을 획득하기 위한 합성 개구 레이더의 영상 분해능은 거리 방향 분해능(Range Resolution)과 이에 수직한 방향의 분해능(Azimuth Resolution)으로 구분할 수 있다. 레이더 센서를 이용한 영상의 해상도를 향상시키기 위해서는 신호처리를 위한 첩 펄스를 광대역화 할 필요가 있으며, 본 논문에서는 고해상도의 영상을 획득 할 수 있는 디지털 첩 펄스 발생기를 설계하였다. 디지털 첩 펄스 발생기는 크게 AWG방식과 DDS방식으로 구분할 수 있으며 본 연구에서는 DDS방식의 첩 펄스 발생기로 선형 주파수 변조(LFM) 파를 발생시키는 300MHz 대역의 광대역 디지털 첩 펄스 발생기를 개발하였다. 개발된 첩 펄스 발생기는 거리 방향 분해능이 50cm 이상 되는 고해상도 영상 레이더 시스템을 구현할 수 있는 성능을 가진다. There are range and azimuth direction resolution of synthetic aperture radar on the aircraft or satellite. Wide bandwidth chirp pulse generation technology is prerequisite for SAR image with fine resolution. There are two kinds of digital chirp pulse generation technology as arbitrary waveform generator(AWG) and direct digital synthesizer(DDS). In this paper, we design and implement a digital chirp pulse generator to generate 300MHz wide bandwidth linear FM chirp pulse for the fine resolution image with direct digital synthesizer. Implemented chirp pulse generator can be useful for the SAR sensors to make 50cm range resolution image.

A swept frequency pulsed magnetic resonance spectrometer with particular application to NMR of ferromagnetic materials

We describe the design, construction and use of a new swept frequency pulsed magnetic resonance spectrometer that is particularly suitable for measurements of NMR in magnetically ordered materials but has also been used for ESR, NQR and conventional NMR. It includes computer control, digital pulse generation, measurements over the range 10-1000 MHz in one sweep, and calibration of signal and pulse power. The spectrometer can also be used to track the change of the NMR frequency of a sample, e.g., as a function of temperature.

Influence of Pulse Signal Spike and Liquid Characteristics on Performance of Uniform-Droplet Generator

The performance of a pulsed-chamber, uniform-droplet generator was enhanced through the development of a digital pulse generator system. A trapezoidal pulse signal, variable in terms of peak voltage, rise time, dwell time, and fall time, actuated a piezoelectric disk to force droplets through a precision orifice. Variable pulse control enabled precise delivery of either paraffinic oil or water droplets. The effects of each pulse variable on droplet size and velocity were examined using a phase-Doppler particle analyzer and a photographic technique. Droplet size increased with increased voltage, rise time, dwell time, fall time, and integrated area under the pulse curve. Air bubbles in the chamber did not prevent droplet delivery, except for certain combinations of bubble size and location. Dwell time was statistically the most important variable affecting oil droplet size and delivery. Liquid reservoir height was most important for water. Increased pulse voltage tended to increase droplet size and velocity because of increased impulse and momentum.

SYNCHRONIZATION FO A Q-SWITCHED Nd-YAG PUMPED DYE LASER AND AN EXCIMER LASER FOR TIME-RESOLVED RAMAN EXPERIMENTS

A time resolved resonance Raman experimental set-up is described. It is based on the use of two independent lasers : a Q-switched Nd-YAG pumped dye laser and an excimer laser. A synchronization electronic device has been made to fire the two lasers with variable delays in the range .0 ns -+ 10 ms with a 10 ns step variation. A drift control unit is used to prevent any slow drifts of the excimer laser. The overall jitter between the two laser pulses is 4.5 ns. INTRODUCTION Time resolved resonance Raman spectroscopy is becoming a very powerful technique for the caracterisation of reactive excited states and transient intermediates in fast photochemical reactions (1,2). It provides the means of identifying the transient species, analysing their structures and bonding, and also of monitoring their kinetics of formation and decay. The two-color pump probe method is generally applied. The pump beam is used to start the photochemical reaction by providing energy to the system and promoting the molecules to high excited states. The probe, which is delayed with respect to the pump, is used to excite resonance Rarnan spectra of the transient species. Both have to be tuned to an electric transition : pump to the absorption wavelength of the molecules in the ground state and probe to the transient absorption of the species being analysed. In recent experiments, we have recorded the resonance Raman spectra of excited states and radicals of various molecules using a Q-switched Nd-YAG pumped dye laser (3,4,5). In these cases, the third or the fourth harmonic of the YAG laser was used as the pump beam and the resonance Raman spectra were excited by the dye laser pumped by either the second or the third harmonic of the YAG. The probe beam was delayed by an optical delay line (3 ns/m). Unfortunately, the low quality of the laser beams makes it impossible to use large delays and most experiments were performed in the range 20-50 ns. These experimental conditions did not allow kinetic measurements to be made. In order to overcome this problem, one has to use two independent lasers and synchronize their firing to increase the delays time between the probe and pump beams. TIME-RESOLVED EXPERIMENTS WITH TWO LASERS We have developed a new time-resolved Rarnan experimental set-up using the same Q-switched Nd-YAG pumped dye laser for the probe beam. An excimer laser was preferred for the pump beam because it is less expensive than a second Nd-YAG pumped dye laser and it emits many wavelengths in the UV region (193, 222, 248, Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:19917123 C 7 4 6 4 JOURNAL DE PHYSIQUE IV 308, 351 nm) that are generally suitable to fit the absorption spectra of most organic compounds. We have used an YG 581 C QUANTEL YAG laser pumping a TDL 50 QUANTEL dye laser. The output of the dye laser can be continuously tuned from 220 nm to 750 nm by direct pumping of red dyes or coumarin using the second and the third harmonics of the YAG respectively, or by frequency-doubling and/or frequency mixing. The Excimer laser is a QUESTEK model 2420. The problem was to synchronize the two lasers with as low a jitter as possible. In all cases, the jitter time must be lower than the duration of the laser pulses, i.e. 7-9 ns for the dye and 20-30 ns for the Excimer. The repetition rate was fixed at 10 Hz because of the YAG laser. The YAG laser needs three trigger orders to be fired ; one to command the charge of the capacitors, the second to fire the flashlamps and the third to trig the pockels cell. The capacitors require about 80 ms to be charged. The excimer laser needs two trigger orders. One to command the charging of the capacitors and the second to fire the thyratron. For this laser, about 30 ms are needed to charge the capacitors. A digital pulse and delay generator has been designed to generate all the trigger orders, all the delays, and also to synchronize a gated multichannel detector with the YAG laser. The schematic diagram and the chronogram of this system are given in figures 1 and 2.

Synchronous pulse generator encompassing a wide range of time scales

A digital pulse generator has been developed that produces outputs synchronous with a 400-MHz master clock. Fifteen independent outputs may assume an arbitrary sequence of up to 2048 successive output states. The duration of each output state may be varied from 330 ns to several hours, with uniform 10-ns resolution. The generator has a new, simplified architecture that is easily programmed and requires a minimal amount of high-speed logic. The circuit was constructed in a commercially available CAMAC prototyping module.

State-machine digital pulse generator

An architecturally simple yet versatile memory-state-based digital pulse generator (or state machine) has been developed for control of instrumentation with PC-compatible microcomputers. The pulse-programming device uses parallel memory allocation to allow simultaneous output-state and address change capabilities. The pulse sequence is loaded into parallel sections of resident memory as a program consisting of output states, state durations, and partial pointers to succeeding states. The complete pointers are generated by concatenation of these address bits with the outputs of duration and loop counters, making complex jumps and loops possible. Minimum event duration and timing resolution is limited only by memory access time; fast or slow memory can be selected based on individual needs. The memory used in the device described has access times of 120 ns, allowing clock rates as high as 8 MHz. The cost of this device is under $200.

Fortschritte in der 2D‐NMR‐Spektroskopie mit Rauschanregung

AbstractStochastic excitation of nuclear spin systems and subsequent nonlinear analysis of acquired excitation/response (e/r) data pairs (multidimensional stochastic method, MUDISM) yields 2D NMR spectra which provide information similar to the conventional E‐COSY and NOESY pulse schemes. For the study of complex molecules such as peptides and proteins, hardware and software has been developped which allows the continuous recording of 106 e/r data pairs where one pair occupies one 16 bit word. Many such sets are commonly measured and stored on a large‐volume hard disk, the total number of pairs being 107–108 depending on the size of the spin system. The r.f. carrier is modulated with suitable pseudo random sequences which are generated in a home‐made computer‐controlled digital pulse generator. The design and properties of these sequences are described and quaternary noise is shown to provide an excellent compromise between ease of generation and similarity to Gaussian white noise. The spin response to this noise has been simulated for coherent and incoherent interactions in order to examine the overall procedure, most notably the dependence of the residual systematic noise upon the number of measured data for given resolution. Experimental results are reported for phenylacetylene (strong coupling case), glucose in water (strong solvent line), and the cyclic decapeptide cyclosporin (complex molecule). For the latter, 80 Megapairs raw data have been acquired for a total spectral range of 3246 Hz (7.5 h magnet time) from which 2D subspectra with 512·512 points at 0.4 Hz step size are calculated. They provide evidence that the structure of complex molecule may indeed be determinded with stochastic NMR.

Method and apparatus for a repetitively producing a noise‐like audible signal

A digital pulse generator and shift register repetitively produce bursts of digital pulses at a first adjustable repetition frequency. The repetition frequency of the pulses in each burst is also adjustable. A pink noise filter accentuates the lower burst frequency components near 7 hz and substantially attenuates all frequency components of the bursts above a first cut-off point near 10 Khz. A tunable band pass amplifier having a center frequency adjustable over a preselected range of frequencies optimally detectable by the average human ear accentuates the pink noise filter output near 2.6 Khz. The tunable amplifier drives an audible signal source with noise-like pulses of varying amplitudes and frequency components. A low pass amplifier may be connected to the pink noise filter to generate a train of pulses having a repetition frequency near 7 hz which pulses a light source in synchronism with the audible noise-like signal.

Fast digital two-channel pulse generator for controlling time-resolved experiments

A fast digital two-channel pulse generator for controlling initiation and investigation of time-dependent processes is described. A gating pulse is periodically swept through the period of the excitation pulses, thereby chopping the initiated process into measurable quantities. The same quartz-controlled time base, used throughout the whole generator, provides exact repetition times and high-quality long-term stability. Minimum pulse widths are 20 ns.