Maximum Signal Level Research Articles

Polarization-agile self-adjusting microstrip antenna

A self-adjusting polarization-agile patch antenna is presented. It allows us to track a linear polarization, if the received field is depolarized, to always obtain the maximum signal level. Two varactor diodes are connected to the patch to produce three states of linear polarization. The depolarization of the incident wave is used to produce the appropriate state of dc voltage biasing, using a conversion circuit of a microwave signal into a dc one, and then to control the independently biased varactors. Unlike a circular polarization antenna, this patch allows us to avoid a 3 dB loss of the received signal magnitude. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 26: 260–262, 2000.

A new CCII-based sinusoidal oscillator providing fully independent control of oscillation condition and frequency

In this paper, a new CCII-based double-resistance controlled sinusoidal oscillator employing grounded resistors and capacitors is presented. The oscillator topology provides fully independent control of oscillation conditions and oscillation frequency, and suitability for VLSI realization due to including only grounded passive elements. The circuit exhibits low active and passive sensitivities; voltage and current tracking error effects on the current conveyors can easily be eliminated with careful design. Moreover, a methodology for determination of linear operation conditions of the oscillator is studied. For the proposed oscillator circuits, the maximum output signal level not causing clipping and the slew-rate-limiting problem is determined using a simple formula. Theoretical results are confirmed with both PSPICE simulations and experimental results.

On the realization of OTA-C oscillators

In this study, six tunable sinusoidal oscillator topologies, two of them known from the literature, are proposed using only CMOS operational transconductance amplifiers (OTAs) and grounded capacitors. The oscillator configurations have the properties of oscillation frequency control using the transconductance gain without affecting the oscillation condition, the suitability for very large scale integration (VLSI) since they are composed of only OTAs and grounded capacitors, and the capability of operation at high frequency. For the proposed topologies, the non-ideality effects of an OTA such as finite output conductance, and finite bandwidth are investigated, and for one of the proposed OTA-C oscillator circuits the maximum output signal level is determined using a simple formula that does not cause clipping and the slew-rate-limiting problem. The theoretical results are verified by SPICE simulation results. The oscillator topologies are simulated with the SPICE computer program and the resulting output voltage waveforms plotted.

Counting of single protein molecules at interfaces and application of this technique in early-stage diagnosis.

The fluorescence-based detection and counting of single protein molecules after specific binding to antibodies at interfaces is presented. A diode laser was used as the excitation source. The unspecific binding at the interface has been reduced to a level of only 0.1% of the maximum signal level. At present, the detection limit of this molecule-counting process is in the range of 10(-17) mol/L, and the dynamic range of the signal corresponds to 7 orders of magnitude of antigen concentration, but these values are not limiting. As a preliminary application in early-stage diagnosis, we have investigated the detection of a single cardiac actin molecule in human plasma, which is of interest in myocardial infarction diagnosis.

S/N Optimized, Programmable 1–10 MHz Bandwidth and 0–20 dB Gain, Precision I-Q Communication Channel for Digital Video Applications

An analog part of a digital-video quadrature demodulation scheme is built using a 7 GHz, 0.8 μm biCMOS process. The scheme provides for 1–10 MHz cutoff frequency and 0–20 dB gain controls and dissipates 250 mW from a power supply of 5 V. The channel filtering is realized by two identical 4th Order Butterworth lowpass filters built with the g_m - C technique. They are equipped with cutoff programming and in-package trim tuning for cutoff adjustment. A programmable gain amplifier is placed in front of each filter for better joint noise and intermodulation performance. Such an arrangement allows to operate the filter at a maximum signal level improving the worst-case channel S/N by 6.5 dB. For the in-band components the worst case S/N is better than 41 dB, whereas THD and IMD are less than - 48 dB. This single-ended channel achieves PSRR of 42 dB.

Method and apparatus for enhancing the quality of sound from electrically powered audio equipment

A silent method of, and apparatus for use in, enhancing the quality of sound from an electrically powered audio equipment assembly. The apparatus includes an electrical signal conducting component which forms a part of a home audio equipment assembly. The method includes the step of applying a pulsed digital signal having a wide and continuous range of frequencies within the audio frequency bandwidth to the electrical signal conducting component. The signal is applied at a signal level which is a substantial fraction of the maximum signal level rating of the component for a prolonged period of time.

Simulated performance of an acoustic modem using phase-modulated signals in a time-varying, shallow-water environment

Underwater acoustic modems using coherent modulation, such as phase-shift keying, have proven to efficiently exploit the bandlimited underwater acoustical communication channel. However, the performance of an acoustic modem, given as maximum range and data and error rate, is limited in the complex and dynamic multipath channel. Multipath arrivals at the receiver cause phase distortion and fading of the signal envelope. Yet, for extreme ratios of range to depth, the delays of multipath arrivals decrease, and the channel impulse response coherently contributes energy to the signal at short delays relative to the first arrival, while longer delays give rise to intersymbol interference. Following this, the signal-to-multipath ratio (SMR) is introduced. It is claimed that the SMR determines the performance rather than the signal-to-noise ratio (SNR). Using a ray model including temporal variations of the shallow-water environment, the performance of the acoustic modem may be estimated. Simulations indicate that optimum performance is not necessarily found at receiver depths yielding the maximum total signal level, since the SMR may correspondingly be low due to strong intersymbol interference. [Work sponsored by the Danish Technical Research Council.]

The double loop sigma delta modulator with unstable filter dynamics: stability analysis and tone behavior

Conventional /spl Sigma//spl Delta/ modulators suffer from idle tones. In order to alleviate the tone problem, /spl Sigma//spl Delta/ modulators with unstable filter dynamics have been proposed. In this paper we present an analysis of the saturation characteristics and tone behavior of the double loop /spl Sigma//spl Delta/ modulator with unstable filter dynamics. We begin by deriving stability boundaries for the double loop /spl Sigma//spl Delta/ modulator with unstable filter dynamics which yield bounds on maximum internal signal levels. We then show via simulations and steady state analysis that while tonal properties are improved by using unstable filter dynamics, idle tones are not completely removed. Specifically, we show that some unstable limit cycles have an attractor region in their neighborhood which results in tones in the spectrum corresponding to the fundamental or harmonics of these limit cycles.

Limitations on input signal level in current-mode active-RC filters using CCIIs

The maximum input signal level that does not cause clipping and slew-rate limiting effects is investigated for current-mode active-RC filters involving second generation current conveyors (CCIIs), and a simple formula is derived for the maximum input signal amplitude that does not cause nonlinearities.

Frequency-Domain Electromagnetic Characteristics of a 26-Kilowatt Ammonia Arcjet

Abstract : Arcjet thrusters employ an arc discharge to heat propellant, which expands through a nozzle to produce thrust Spacecraft designers who desire to exploit the enhanced specific impulse of arcjets have expressed concern about the electromagnetic environment produced by the thrusters. Laboratory tests were performed to investigate the electromagnetic environment produced by a 26-kW ammonia arcjet in the frequency domain from dc to 10 GHz using antennas intended to characterize electric and magnetic fields. Results obtained with a 30-cm monopole antenna exposed to the arcjet plume correspond to those of similar ground tests at lower power. When the antenna was shielded from electrical contact with the plume by a Pyrex(R) cover, signal levels dropped sharply at all frequencies. With a covered 30-cm monopole antenna near the arcjet plume, arcjet-on signals exceeded ambient levels over the frequency range 10 kHz-5 MHz. The maximum signal level typically exceeded the ambient level of 40 dBumV/MHz by approximately 27 dBumV/MHz near 200 kHz. A likely explanation for The sharp reduction in signal level once the antenna electrode is covered is that electrons and ions from the plume are collected on the exposed antenna but not on the covered antenna. Signals on the shielded antenna may be interpreted as the result of propagating electric fields, but considerable uncertainty remains about the field source and the effects of the facility on the measurements. Although the electromagnetic fields produced by an arcjet operating as part of a satellite are probably lower than previously expected, these results raise new concerns about the character and Spacecraft compatibility of the plasma from an arcjet plume.

Theoretical determination of maximum signal levels obtainable with modulation transfer spectroscopy

The maximum signal levels that are possible with modulation transfer spectroscopy using both amplitude modulated and frequency modulated pump fields are theoretically investigated. The results indicate that amplitude modulation produces signals that are larger than those obtained with frequency modulation for modulation frequencies that are suitable for frequency locking applications.

Design techniques for tunable transresistance-C VHF bandpass filters

In this paper, a tunable wideband linear transresistance (R/sub m/) amplifier is proposed and analyzed. Using the tunable R/sub m/ amplifier, a new transresistance-capacitor (R/sub m/-C) differentiator is designed. Considering the intrinsic capacitances of the MOS transistors as filter elements, this R/sub m/-C configuration can he regarded as a very high frequency (VHF) bandpass biquadratic filter. The proposed biquad has a simple structure and thus occupies a small chip area and consumes little power. Moreover, higher-order VHF bandpass filters can be realized by directly cascading the biquads. Experimental results have successfully proven the capability of the proposed new filter implementation method in realizing VHF bandpass filters with the center frequency higher than 100 MHz when C/sub d/=1 pF. The deviations of the measured center frequency f/sub o/ and quality factor Q of the fabricated bandpass filter from the simulated results are less than 8%. The deviation of the center frequency can be post-tuned by adjusting the control voltages V/sub CN/ and V/sub CP/ of the tunable R/sub m/ amplifier. With 1 pF differentiating capacitor, the center frequency of the fabricated VHF R/sub m/-C bandpass filters can be tuned in a wide range larger than 30 MHz. The measured maximum signal level is 25 mV/sub rms/ and the dynamic range is 47 dB. The chip area is 0.05 mm/sup 2/ and power consumption is 5.05 mW with /spl plusmn/2.5 V power supply.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A wide-range tunable BiCMOS transconductor

This paper describes a fully differential BiCMOS operational transconductance amplifier (OTA) with a transconductance parameter G m that is tunable over 1 decade. Another significant feature of this OTA is that the tuning scheme is based on current steering resulting in the maximum input signal level being independent of tuning and a reduction in bias dependencies. The circuit is suitable for implementing adaptive analog OTA-C filters for high-frequency data communication applications where moderate SNR is acceptable.

A methodology for assessment of harmonic impact and compliance with standards for distribution systems

The new IEEE Standard 519 specifies maximum harmonic signal levels at points of common coupling to the electric utility. The authors find these standards to be applicable within industrial and institutional sites. A state estimation methodology is illustrated for the calculation of harmonic current and voltage distortion at all buses in a distribution system. It is recommended that these distortion levels are checked for compliance with Standard 519. The authors also give a calculation of the total harmonic distortion of an ideal converter current. New approximations are also introduced for the bus impedance matrix at frequency h omega /sub 0/. The approximations are developed from power series expansions in either frequency, omega , or inverse complex frequency, (j omega )/sup -1/. The convergence of the series is studied in terms of Banach's lemma.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Characterisation of a 9-mm torch for inductively coupled plasma mass spectrometry

A 9-mm torch and a 40.68-MHz radiofrequency power supply were evaluated for use in inductively coupled plasma mass spectrometry (ICP-MS). With this system, an analytically useful plasma can be supported at 850 W applied r.f. power and 8.7 l min–1 total argon flow-rate. The effects of operating parameters (nebuliser gas flow-rate, r.f. power, sampling depth and ion-lens voltages) on the analyte ion signals were determined. The 9-mm source exhibits greater independence of the ion-optic bias potential on relative atomic mass than do conventional-sized torches. Further, the 9-mm system produced similar sensitivities, detection limits, doubly charged ion ratios and oxide ion ratios to the conventional plasma but with lower power and argon consumption. However, the proper placement of the discharge under the interface was found to be critical to obtain maximum signal levels.

ULF signatures of the polar cusp

Geomagnetic pulsations associated with the polar cusp have been detected at Cape Parry, Northwest Territories, Canada, using flux gate and induction magnetometers. Data from this station show enhanced power almost every day near local noon. It is this enhancement which is taken as the signature of the polar cusp. Maximum signal levels are observed prior to local noon, although the signals are present for several hours on each side of local noon. The spectrum of pulsations near the cusp is broadband, reaching from a few millihertz to above 1 Hz. On average the power spectrum decreases with frequency as f−2.6. Within this general decrease there are often found regions of enhanced power, principally near 5 mHz and near 40 mHz. We have identified the 5‐mHz band with fluctuations in ionospheric currents associated with the cusp boundary and its motions. The 40‐mHz band is presumed to be due to direct penetration of the hydromagnetic radiation in the cusp to the ground. From the measured spectrum we infer an rms fluctuation amplitude of the cusp currents of approximately 3×10³ A, and from this we estimate the total power dissipated by these fluctuations of approximately 4×107 W.

Design and Construction of an Arbitrary Waveform Generator

The purpose of this paper is to describe the design and characteristics of an arbitrary waveform generator, built at the Biophysical and Electronic Engineering Division of the Electrical Engineering Department of the University of Genoa, which exhibits the following features: a) The signal waveform is any band-limited periodic signal, whose frequency content ranges from 0.125 mHz up to 30 MHz. The low-frequency limit has been chosen in order to meet the needs of bioengineering, mechanical, and chemical applications. The high-frequency limit covers, for instance, TV and image processing applications. b) The noise level is at least 66 dB below the maximum signal level. c) Typical distortion is less than -66 dB. d) The generator's performance can be easily improved, depending on the availability of up-to-date solid-state devices, without changing its design.

Switching field distribution and A.C. bias recording parameters

A set of tapes has been prepared for audio recording measurements by mixing cobalt modified iron oxides for equal coercivity and remanence but varying switching field distribution (SFD). At low level recording the optimum high frequency bias current but not the maximum signal level was found to decrease with increasing SFD. The long wavelength output at 5% third harmonic distortion remains unchanged. The decrease of short wavelength saturated signal with increasing SFD was separated into demagnetization and bias current losses.

Bistatic Microwave Probing of a Refractively Perturbed Clear Atmosphere

Abstract Comprehensive calculations are carried out to predict the signal levels to be received by powerful 5- and 10-cm wavelength bistatic scatter systems from vertically thin but horizontally extensive layers of turbulently perturbed refractivity in the clear atmosphere. The results indicate that the model systems can detect regions having only modest refractivity perturbations throughout the entire depth of the troposphere. Although the horizontal coverage and the maximum signal levels decrease with increasing altitude of the scatter layer, the signals are sufficiently strong in the vicinity of the mid-path point to assure the reliable detection of extremely weak scattering layers. In particular, the tropopause should be detected routinely. Hazardous clear air turbulence should also be readily detected, at least in the vicinity of the mid-path. Vertical polarization is superior to horizontal polarization for large horizontal coverage. The shorter wavelength is also slightly superior to the longer, oth...

A Submillimeter Measurement System Using a Harmonic Mixing Superheterodyne Receiver

A measurement system for use in the submillimeter wavelength region has been assembled and evaluated. This system utilizes two 70-Gc klystron sources and operates as high as the sixth harmonic. One of these sources provides the fundamental input power for a crystal harmonic generator which serves as the transmitter. The other klystron serves as a fundamental local oscillator for the harmonic mixing receiver. Incorporation of harmonic mixing techniques provides identification and selection of individual harmonics and simultaneously affords improved sensitivity over crystal video detection. The dynamic range of the measurement system is here defined as the difference (in db) between the maximum signal level at a specified harmonic, and that level for which the signal-to-noise ratio is unity. Dynamic ranges were measured to be 61 db at 210 Gc, 46 db at 280 Gc, 32 db at 350 Gc, and 29 db at 420 Gc, selection of any of these frequencies is accomplished by inserting an appropriate filter in the receiver's IF amplifier. Techniques are described which can be used to improve substantially the dynamic range at the above-mentioned frequencies. The system is suitable for many types of measurements in the short millimeter and the submillimeter region, and has good possibilities for frequency extension by increasing the frequency of the fundamental signal. Some data are included on measured transmission losses of dominant mode, and oversized, overmoded waveguide. The latter type is seen to offer advantages of reasonably low loss and simple construction when transmission over moderate path lengths is needed.