J. Basilio Simoes

Pulse processing architectures

Abstract This paper introduces and discusses the features of a new multiprocessor architecture that aims at performing digital pulse processing at high throughput rates. It is based on a master Digital Signal Processor (DSP), special purpose trigger pulse locator and data routing circuits and an expandable array of slave peripheral DSPs. An historical perspective about the evolution of pulse spectrometry systems over the last 40 years is given. It is recognized that, up to the very recent commercial outcome of digital pulse processing systems, a tremendous evolution of technology but little change in their basic architecture has occurred.

A mixed analog-digital pulse spectrometer

Abstract This paper presents and discusses some applications and advantages of a hybrid spectrometer system that contains a high performance Pulse-Height Analyzer (PHA) and a Digital Pulse Processor (DPP). This mixed analog-digital system, based on a TMS320C31 Digital Signal Processor (DSP), is implemented in a single board to be hosted in the Personal Computer’s ISA bus. Beyond the independent use of the PHA and the DPP units, their integration allow for additional features to be performed without the need of external equipment. Among those features are pileup rejection, pulse shape discrimination, ballistic deficit correction and the capability to measure the experimental noise in order to optimize the pulse shaping parameters or to correct the pulse heights given by the analog PHA.

Characterization of a double probe for local pulse wave velocity assessment.

Local pulse-wave velocity (PWV) is an accurate indicator of the degree of arteriosclerosis (stiffness) in an artery, providing a direct characterization of the properties of its wall. Devices currently available for local PWV measurement are mainly based on ultrasound systems and have not yet been generalized to clinical practice since they require high technical expertise and most of them are limited in precision, due to the lack of reliable signal processing methods. The present work describes a new type of probe, based on a double-headed piezoelectric (PZ) sensor. The principle of PWV measurement involves determination of the pulse transit time between the signals acquired simultaneously by both PZs, placed 23 mm apart. The double probe (DP) characterization is accomplished in three main studies, carried out in a dedicated test bench system, capable of reproducing a range of clinically relevant properties of the cardiovascular system. The first study refers to determination of the impulse response (IR) for each PZ sensor, whereas the second one explores the existence of crosstalk between both transducers. In the last one, DP time resolution is inferred from a set of three different algorithms based on (a) the maximum of cross-correlation function, (b) the maximum amplitude detection and (c) the zero-crossing point identification. These values were compared with those obtained by the reference method, which consists of the simultaneous acquisition of pressure waves by means of two pressure sensors. The new probe demonstrates good performance on the test bench system and results show that the signals do not exhibit crosstalk. A good agreement was also verified between the PWV obtained from the DP signals (19.55 ± 2.02  ms(-1)) and the PWV determined using the reference method (19.26 ± 0.04  ms(-1)). Although additional studies are still required, this probe seems to be a valid alternative to local PWV stand-alone devices.

A very low-cost portable multichannel analyzer

A very, low-cost portable Multichannel Analyzer (MCA) built with off-the-shelf commercial components is presented. Built around an universal microcontroller based platform for portable instruments, previously developed in our group, this intelligent portable MCA is operated by multicell Li-ion batteries and has power and memory autonomy for several hours of spectra collecting. The MCA integrates a basic front-end pulse shape amplifier, a base line restorer, a peak detector and logic control circuitry. The growing of the radiation spectrum can be easily observed on site through a dot-matrix graphic display. To save the acquired data and allow for the configuration of setup parameters, it connects to any host computer through standard USB, IrDA or RS-232 serial interfaces being also prepared to interface a GPS unit. Software application programs in both the portable MCA and the host PC are presented.

Testing high-resolution digitizers using conventional signal sources

This paper presents a method to evaluate the performance of high-resolution digitizers using signal sources that may be of lower specification than the device under test. The method is based on the best fitting of a straight line to a set of measures of the signal to noise ratio, excluding the harmonic distortion, obtained for several amplitudes of the test signal. Theoretical derivations and both computer simulated and experimental data are included. It is shown that the effective number of bits estimated using this method is not affected by the leakage effects that occur when other frequency domain tests are used and the input signal is sampled along a non-integer number of cycles.

A fully programmable VME based, arbitrary waveform generator, with 1 MSPS, 64 kWords memory, 8 independent channels

Abstract This paper describes a fully programmable, VME based, eight channel, arbitrary waveform generator, specially adequate for the control of operation of high temporal resolution diagnostics of nuclear physics experiments. Each channel is built around an 1 Mega-sample-per-second, 12 bit, digital-to-analog converter and it is provided with 8 kWords of FIFO memory allowing operation in a free running mode. The main operational features of this module are described. Methods for assessing its performance are discussed and the test results are presented. Application of this multiple waveform generator on the operation of two diagnostics of the tokamak ISTTOK is referred.

A Windows CE stand-alone digital spectrometer

A stand-alone digital spectrometer based on a multiprocessor DSP system that runs the Windows CE real time operating system is presented. The system is built around the PC104 industrial PC bus and contains 3 stackable modules: CPU, ethernet controller, and a dedicated multi-DSP pulse processing board. The CPU module can be any commercially available one provided it is able to run the user friendly Windows CE operating system. The ethernet module allows for an easy remote configuration and data exchanging over the TCP/IP network protocol. The multi-DSP pulse processing board has been designed in accordance with a previously presented architecture that contains a master floating point Digital Signal Processor (DSP), a scalable number of slave DSPs and, special purpose trigger, pulse locator and data routing digital circuits. This architecture as well as the data acquisition block has been optimized to accommodate high throughput pulse rates in Nuclear Spectroscopy applications. However, its generality allows for many other signal processing, control and communication applications to be easily implemented using this system.

Determining the effective number of bits of high resolution digitizers

A new testing method has been used to evaluate the dynamic performance of several digitizing systems used in nuclear physics experiments. This method is useful for characterizing high resolution analog to digital converters when a pure enough signal source is not available. The signal to noise ratio of the digitizer, excluding the harmonic components from the noise, is the computed parameter. The use of this method to estimate jitter errors is also studied.