Asynchronous Modulation Research Articles

An exercise in the automatic verification of asynchronous designs

This paper illustrates the practical application of an automatic formal verification technique to circuit designs of realistic complexity. The Circal System is presented and a number of asynchronous hardware modules are described and formally verified using it. Asynchronous logic is generally considered hard to design and analyse, and this serves as an appropriate demonstration of the features of a formal description and verification system.

A novel simulation technique for the analysis of digital asynchronous pulse width modulation

A digital simulation technique based on single Fourier series is used to predict the spectra, including the nonintegral harmonics, generated by digital asynchronous pulse width modulation invertors. The results, with an accuracy of 70 dB, are superior to the results obtained with fast Fourier transform techniques, and offer an alternative to the complex methods based on double Fourier integration and Bessel functions. The technique is applicable to any choice of reference waveform. Output distortion with the introduction of minimum pulse and dead time is studied. >

Optimal pulsewidth modulation for AC servos and low-cost industrial drives

An optimal pulsewidth modulation method is described in which the durations of switching subcycles are considered as optimization variables, a subcycle being the time sequence of three consecutive switching state vectors. Operation at variable subcycle duration entails a prediction of the controlling reference voltage vector. It is a special advantage that the optimization and prediction can be carried out off line. The optimal technique exhibits high dynamic performance. It can be used for synchronized and asynchronous modulation in a wide range of switching frequencies. The optimization reduces the harmonic currents at a given switching frequency. The Fourier spectrum lacks dominant carrier frequencies

Digital quasi-random modulated SFAVM PWM in an AC-drive system

A main research topic in PWM-VSI inverter-driven electrical machines is to reduce the generated acoustic noise which often is dominated by a multiple of the switching frequency in the inverter. This paper proposes a modulation scheme for reducing the acoustic noise effect from an AC machine which can be implemented digitally for low and high performance systems. The scheme is based on a stator flux asynchronous vector modulation (SFAVM) imposed by a digital band limited PWM white noise generator for varying the switching frequency randomly. The white noise generator can be used for 8, 16 and 32 bit microcontrollers. The modulation strategy is tested in a 1 kVA high performance 16 bit microprocessor controlled AC drive system. Voltage-spectra on the line-to-line voltage and the acoustic noise spectra are presented and show that the new modulation strategy can decrease the noise effect. The stator-flux-polygon and the line current are measured and demonstrate the random modulation strategy. Finally, the total sound pressure level from the AC machine is investigated with fixed switching frequencies and with different randomly modulated frequency spans. It is concluded that a properly chosen fixed switching frequency has the lowest total sound pressure level. However, the random modulation strategy distributes the noise frequencies and the noise is more comfortable and less annoying. >

Cavity modulation coupled with asynchronous source modulation in a microwave cavity spectrometer

This paper reports a novel modulation technique, namely, cavity modulation coupled with asynchronous source modulation, employed in a simple microwave cavity spectrometer system. The feasibility of the technique was successfully demonstrated by determining the output of the system whilst examining one of the absorption peaks of ethylene oxide gas (with centre frequency F0 = 24.923 GHz for the level transition 202 to 211). The variation in the output signal with frequency was as expected to within a standard error of 8.3%. Also, a good linear correlation was demonstrated between the magnitude of the output signal and the concentration of ethylene oxide gas in the gas cell (to within a standard error of 4%). The operation of this system is such that the microwave source frequency, F, sweeps across a given range (F1 to F2) which contains one of the absorption peaks of the analyte gas whilst the cavity resonant frequency, Fr, is oscillated within the profile of the absorption peak. Signal enhancement is achieved by adding a relatively small magnitude high-frequency 'dither' signal to the source frequency sweep pattern. The salient information of the gas absorption due to the oscillation of the resonant frequency of the cavity is carried by the 'dither' signal and then amplified and extracted by a series of tuned amplifiers and demodulators.

Microwave cavity spectrometer for process monitoring of ethylene oxide sterilization

This article reports a novel and simple cavity spectrometer for process monitoring of ethylene oxide sterilization, in which the source frequency, cavity resonant frequency, and gas absorption center frequency are asynchronous with respect to each other, thus, enabling sophisticated signal enhancement techniques to be employed without the need to engage the Stark effect. The operation of the device is such that the source frequency sweeps across a given range (F1 to F2) which contains one of the absorption peaks of the analyte gas (gases) of interest while the cavity resonant frequency Fr is oscillated within the profile of the absorption peak. Signal enhancement is achieved by adding a relatively small magnitude/high-frequency ‘‘dither’’ signal to the source frequency sweep pattern. The salient information of the gas absorption due to the oscillation of the resonant frequency of the cavity is carried by the ‘‘dither’’ signal and amplified and extracted by a series of tuned amplifiers and demodulators. Although the device is still at the initial design stage, a working prototype has been constructed in order to test the feasibility of the novel asynchronous modulation technique. This was achieved by successfully demonstrating that the device operates in an expected manner to within a standard error of 8.3%. It is believed that this error largely results from mechanical components. The significance of this error is greatly reduced when the spectrometer is operated in a large signal scanning mode as is the case when we apply the ‘‘power saturation’’ technique to measure the concentration of ethylene oxide in the resonant cavity. This measurement showed that there is a good linear correlation between the output signal and the concentration of ethylene oxide gas (to within a standard error of 4%).

Harmonic imbalance in asynchronous PWM schemes

The harmonic content (both integral and nonintegral) of an asynchronous three-phase PWM (pulse width modulated) scheme is analyzed. It is shown that in a three-phase inverter with asynchronous modulation the nonintegral line currents produced form unbalanced sets. The percentage imbalance for a particular order is a function of the harmonic order only. No attempt has been made here to analyze the effect of harmonic imbalance in a load such as an induction motor. However, for practical frequency ratios the absolute amplitude of the current imbalance is small due to the small amplitude of the nonintegral components. More significant changes occur in the balanced integral orders due to small changes in frequency ratio. >

General aspects of an asynchronous delta modulated inverter with RL loads

The application of an asynchronous delta modulation principle to the operation of pulse width modulated inverters with resistive induction loads is presented. The main inverter with its load is within the loop of an asynchronous delta modulator. With this arrangement, the load current can follow the desired input waveform with a predetermined accuracy. General relations are given with associated data curves applicable to fundamental performance characteristics useful for AC induction motor loads. An experimental system was built and the measurements taken are in good agreement with theory.

Field-oriented asynchronous pulse-width modulation for high-performance AC machine drives operating at low switching frequency

A novel pulse-width modulation (PWM) technique is based on the prediction of the trajectory patterns that the stator current vector describes in a field-oriented coordinate system. The method of field-oriented PWM control minimizes the switching frequency at given torque ripple. The harmonics of the field producing current are left to develop freely, permitting operation at values of switching frequency that are lower than those of the optimal schemes known so far. The optimal switching times are computed off line and are called from a memory during operation. Signal processing is performed in a simple hardware structure. >

A Silicon Compiler System Based on Asynchronous Architecture

As one of the most promising approaches for the automatic generation of VLSI chips, the concept of "silicon compilers" was presented. A silicon compiler is a software system which accepts the behavioral or functional description of the chip and directly translates it to the layout patterns of the VLSI masks. In order to realize a design automation aid for full-custom VLSI chips for nonprofessional chip designers such as programmers, we have selected asynchronous architecture as the target model of the compiler and have been developing a silicon compiler system. A VLSI chip based on this architecture model consists of asynchronous modules which hold the control information internally. The behavior of the chip is controlled only by local communication among these modules. The silicon compiler system accepts the purely functional specifications of the chip, written by the hardware specification language ISPC, and directly translates it to the layout patterns in the form of CIF codes. By selecting an effective architecture model, it is possible to realize the silicon compiler system through simple translation programs which analyze the functional description of the chip and extract from it the configuration of components and the control information and through a library of the asynchronous modules which are generally defined with suitable parameters.

A robust layered control system for a mobile robot

A new architecture for controlling mobile robots is described. Layers of control system are built to let the robot operate at increasing levels of competence. Layers are made up of asynchronous modules that communicate over low-bandwidth channels. Each module is an instance of a fairly simple computational machine. Higher-level layers can subsume the roles of lower levels by suppressing their outputs. However, lower levels continue to function as higher levels are added. The result is a robust and flexible robot control system. The system has been used to control a mobile robot wandering around unconstrained laboratory areas and computer machine rooms. Eventually it is intended to control a robot that wanders the office areas of our laboratory, building maps of its surroundings using an onboard arm to perform simple tasks.

On the Design of Three-Valued Asynchronous Modules

The use of three-valued signals in the design of asynchronous speed-independent modules is considered. The three-valued Post algebra is used as the mathematical basis for multivalued logic design. Asynchronous operation in a three-valued system is defined. Basis data/control signal detectors and control primitives are developed. It is shown that the design of the nonbinary modules only requires the use of standard binary design techniques and the detectors and logic primitives that are developed. A general monitoring and control structure that allows the interconnection of both combinational and sequential modules is described.

Towards a Theory of Universal Speed-Independent Modules

Of concern here are asynchronous modules, i.e., those whose activity is regulated by initiation and completion signals with no clocks being present. First a number of operating conditions are described that are deemed essential or useful in a system of asynchronous modules, while retaining an air of independence of particular hardware implementations as much as possible. Second, some results are presented concerning sets of modules that are universal with respect to these conditions. That is, from these sets any arbitrarily complex module may be constructed as a network. It is stipulated that such constructions be speed independent, i.e., independent of the delay time involved in any constituent modules. Furthermore it is required that the constructions be delay insensitive in the sense that an arbitrary number of delay elements may be inserted into or removed from connecting lines without effecting the external behavior of the network.

Duality principle for asynchronous control circuits for directed graphs

The directed graph provides a means of analysing parallel computer structures, whether implemented in hardware or software. This letter discusses the asynchronous circuit modules used to implement the control section of such systems, and indicates a duality principle that permits a wider variety of control functions to be envisaged.

Superposition of excitatory and inhibitory influences in the retina of Limulus: effect of delayed inhibition.

In an optic nerve fiber of the compound eye of the horseshoe crab, Limulus, the time course of a train of nerve impulses discharged in response to illumination reflects the interplay of excitatory and inhibitory influences. Responses to sinusoidally modulated excitation and inhibition, as a function of frequency, were measured separately and in combination. A simple linear superposition of the separate frequency responses properly accounts for the composite frequency response for both synchronous and asynchronous modulation of the excitatory and inhibitory influences. In general, the effect on the frequency response of increasing the delay of the inhibitory influence is progressively to shift the maximum amplitude to lower frequencies and gradually to produce pronounced maxima and minima in both the amplitude and phase.

An Analysis of Inherent Distortion in Asynchronous Frequency-Shift Modulators

In many commonly used frequency-shift modulators, a phase error occurs at the time of switching. If a demodulator is used which utilizes only the zero-crossing information, then this phase error will cause time jitter in the received data transitions. The magnitude of the peak time jitter for various modulators is derived, assuming an ideal zero-crossing detector. The modulators considered include the reactance tube and variable reactance modulators, the basic switched reactance modulators, and the multivibrator modulator. It is found that the switched reactance modulators cause the most jitter, and that the multivibrator modulator may be designed to cause as small a jitter as desired. The theory agrees well with some experimental measurements made on existing data sets, which show that this jitter accounts for most of the back-to-back data distortion in many wideband data systems. Finally, a set of sufficient conditions is derived for jitter-free frequency-shift modulation, and an implementation of a modulator satisfying these conditions is described.