Signal Generation Techniques Research Articles

Coupling conducting polymers and mediated electrochemical responses for the detection of Listeria

Different signal generation techniques were investigated for the development of a biosensor for Listeria monocytogenes. Conventional amperometry at an antibody-containing polypyrrole film electrode was found to be unsuccessful in detecting levels below 10 6 cells ml −1. More successful was the coupling of a covalently modified film with the use of electron mediators in a single device. This sensor was capable of reproducibly detecting Listeria at levels of 10 5 cells ml −1 in 30 min.

An integration of memory-based analog signal generation into current DFT architectures

One method for the testing of mixed analog/digital integrated circuits involves the digital encoding of analog signals into an aperiodic pulse-density modulated (PDM) serial bit stream and using it to stimulate a device under test (DUT). This paper describes a method for obtaining a short periodic approximation of the PDM pattern and identifies two methods of integrating this analog test scheme into the current digital test environment: RAM- and scan-based storage. Using such design-for-test logic as the 1149.1-1990 JTAG architecture and a typical RAMBIST controller, these analog signal generation techniques can be added to digital integrated circuits (IC's) with minimal additional hardware overhead.

Speech compressor using trellis encoding and linear prediction

A speech compressor utilizing Trellis Encoding and Linear Prediction (TELP). A TELP speech compressor provides improved signal generation and search technique for a code-excited linear prediction (CELP) speech encoder. TELP is a frame oriented coding that breaks the quantized speech signals into frames of prescribed length N and each frame into subframes of prescribed length L, which are processed as dependent units utilizing an analysis-by-synthesis approach. The approach is based on constructing the best mean square linear predicting filter and searching the best exciting sequence for the filter in order to produce synthesized speech. A trellis encoder is used instead of a stochastic code book. The Q-ary analysis of a given subframe and previous excitations is proposed for a fast vector search in an adaptive code book. It simplifies the implementation of digital speech compression.

A precision measurement system for use in underwater acoustics measurements.

A Precision Measurement System (PMS) has been developed at NRL-USRD to serve both as a production measurement system and as a platform for ongoing research in new signal generation and measurement techniques. This system is intended as a single-platform solution to most of USRD’s underwater acoustic test needs. Calibration of transducers and measurements of acoustic coatings are included in the tests performed by the PMS. The precision measurement system offers the following features: wide range in both frequency and amplitude; built-in calibration for traceability to NIST; multiple channels for simultaneous signal measurements; a flexible combination of analog gain and filtering stages; digital technology to allow generation of complex waveforms as well as sophisticated processing of measured data; an integrated programming language interface based on VAX/VMS workstations; a variety of signal processing algorithms for wideband versus narrow band, continuous versus transient, parametric versus nonparametric signal processing techniques. Four copies of the system have been built to insure uniformity of measurements across all USRD measurement facilities. Because the system is based on VAX/VMS, a variety of software is available for plotting and reporting as well as more sophisticated offline mathematical analysis.

Sub-natural absorption resonances on the D 1 line of rubidium induced by coherent population trapping

A narrow (70 kHz fwhm) high-contrast resonance formed due to coherent population trapping (Λ-resonance) has been observed in 87Rb vapour by using two independent laser diodes. The first results on the dependences of its width on magnetic field, laser intensity and divergence are reported. The Λ-resonance is used to stabilize the difference of laser frequencies to the hyperfine splitting of the Rb ground state. A new technique of stable microwave signal generation is proposed. It is based on optical locking of two lasers via Λ-resonance in a cell inserted in an external cavity of a laser diode.

多方向不規則波の造波信号発生法に関する検討

多方向不規則波の造波信号発生法に関する検討

Circuit structures for high-digit-rate bit error ratio measurements

Series-parallel signal generation and processing techniques are identified which may be used to circumvent the speed limitations of available logic devices in realising bit error ratio measurements for high-digit-rate transmission systems. New techniques are proposed which offer advantages in enabling devices to be used near their maximum operating rate while achieving, by virtue of the parallelism inherent in the structures proposed, yet higher data throughout rates. The specific application of these techniques to highspeed line-coded test signal generation and error detection is examined, and the series-parallel generators are shown to be particularly well suited to the economical realisation of mB(m+1)B block-coded test signals.

A harmonic distortion standard

All harmonic distortion analyzer instruments may not give the same reading when measuring a particular audio range signal. A design method is presented that can supply a signal with a precisely determined amount of harmonic distortion. Digital signal generation technique is used. Factors which determine the accuracy of the signal are examined. An instrument was designed using the outlined principles. With it, the operator can control the frequency of operation, the harmonic, and the percentage of distortion. Results from the sample constructed are presented. Performance of a number of distortion analyzers are shown.

An acousto-optic modulator for a CO2 laser rangefinder using heterodyne detection

The ability to superimpose arbitrary modulation waveforms on a CW laser beam makes the acoustooptic modulator suitable for an important task: to apply modern microwave radar electronic signalprocessing and signal-generation techniques to heterodyne CO2 laser radar systems. The fundamental constraints on modulator design are first presented graphically in a novel treatment. The fabrication of 50–70 MHz germanium-lithium niobate modulators for a CO2 laser radar is then described. Experimental measurements of efficiency (about 4% per electrical watt transducer input power) and rise time (∼ 40 ns) are finally presented.