Showing papers on "Modulation published in 1986"

Modulation system capable of improving a transmission system

Abstract: In a modulation system responsive to a system input signal for supplying an amplifier having nonlinearities with a modulated analog signal to make the amplifier produce an amplified output signal, the system input signal conveys a baseband signal having a predetermined sampling rate for reproduction and is sampled into a sequence of sampled signals having a specific rate higher than the predetermined sampling rate. The sampled signal sequence is converted by a random access memory into a sequence of predistorted signals which compensate for the nonlinearities and which are modulated into the modulated analog signal. Each predistorted signal is adaptively modified at the specific rate with reference to the sampled signals and an additional input signal derived from the amplified output signal. When the sampled signal sequence is sampled at the predetermined sampling rate, the predistorted signal sequence may be produced by interpolating each of the sampled signals at the specific rate. The baseband signal may be either a digital signal or an analog one.

Phase modulation to amplitude modulation conversion of CW laser light in optical fibres

Abstract: We have measured the induced amplitude modulation of sinusoidally phase-modulated CW 1.5 ?m laser light propagating in a single-mode fibre. Amplitude modulation approaching 100% was observed for light phase-modulated at 4 GHz and transmitted through 50 km of fibre. PM-AM conversion produces a power penalty in coherent transmission systems.

Maximum Likelihood Carrier Phase Recovery for Linear Suppressed-Carrier Digital Data Modulations

Abstract: The problem of ML estimation of the Phase of a general data-modulated carrier is considered. The shortcomings of current iterative approaches to the problem are pointed out, and the correct conceptual approach is proposed. The true ML estimator is then obtained and found to be nonimplementable. However, by specializing to limits of high and low SNR, the general ML estimator is shown to reduce to implementable DA and NDA ML estimators, respectively. The DA receiver's performance in terms of phase tracking and symbol error probability can be analyzed, and even the effects of past decision errors on current system performance can be assessed. For circular signal constellations, the DA receiver has a simple and totally linear structure which is easy to implement. The NDA ML estimator is shown to be equivalent to the common carrier loops. Our emphasis here on explicit computation of the ML phase estimate from the past received signal leads to detection strategies which do not require a carrier loop and a VCO for coherent detection.

Average Efficiency of Class-G Power Amplifiers

Abstract: Class-G operation is an inexpensive and yet effective means of increasing the efficiency of audio power amplifiers (PAs) and amplitude modulators A class-G PA consists of two or more parallel-connected class-B PAs with different supply voltages Low-voltage segments of the signal are amplified by the low-voltage component of the amplifier, thus reducing power dissipation and increasing efficiency The average efficiency of a class-G PA depends upon both the supply-voltage transition point and the amplitude distribution of the signal Average efficiencies are computed for a number of signals that occur in AF amplification, full- carrier amplitude modulation, and envelope modulation of a linear RF PA For typical peak-to-average ratios, an ideal, two-voltage class-G PA has average efficiencies in the range of 60 to 70 percent, in contrast to the 35 to 40 percent of an analogous class-B PA

Method and means for optical detection of charge density modulation in a semiconductor

Abstract: Disclosed is a technique for probing dynamic sheet charge density variations in integrated semiconductor devices. Using a specially designed non-invasive Nomarski phase contrast interferometer a sheet charge density sensitivity of 2.6×108 e/cm2 / √Hz is extracted from experimental data for 1 mA of detected photocurrent. The charge density sensitivity makes possible μV signal level detection in an active device, and with digital signals the corresponding signal/noise level is sufficiently high that multi-mega-baud data can be captured in real time.

Digital communication systems

Abstract: Digital communication systems , Digital communication systems , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Calibration of vector modulators using a scalar detector

Abstract: Calibration of a vector modulator is done using a scalar detector to measure the amplitude of the RF output signal, phase shifters to adjust the relative phases of the I and Q components of the RF carrier, and variable attenuators in the I and Q modulation signal input lines to adjust the relative amplitude of the modulation signals. DC signal sources provide reference signals for the I and Q modulation inputs, carrier leak compensation signals, and calibration signals for balancing the amplitude of the I and Q modulation signals. An iterative four step calibration process is followed until no change in the results is observed. The quadrature phase error is minimized by adjusting the phase shifters. The carrier leakage is minimized by adjusting the carrier leak compensation sources to minimize RF output with the modulation inputs grounded. The amplitudes of the I and Q modulation signals are balanced by adjusting the attenuators until the output amplitudes are equal. Finally, the quadrature calibration signal sources are adjusted until the output amplitudes they produce are balanced.

Transmitter/responder systems

Abstract: A memory suitable for use as a responder, comprising: (a) receiver means for receiving a transmitted signal S1; (b) generator means (76) for generating a carrier component of a transmittable signal S2; (c) logic means (L2) for enabling signal S2 to be in mathematical relationship with signal S1, said logic means comprising: (i) at least one memory means (60) for storing code; (ii) at least one modulation means (65) for modulating said carrier component of signal S2, the modulating being under control of at least a portion of said stored code, such that signal S2 is in coded mathematical relationship with signal S1; and (d) transmitter means (T2) for transmitting signal S2.

Persistent photoconductivity in AlGaAs/GaAs modulation doped layers and field effect transistors: a review

Abstract: The phenomenon of persistent photoconductivity in AlGaAs/GaAs modulation-doped layers and transistors is reviewed. Experimental observations, mechanisms which are responsible for it and structures for its elimination are discussed.

Modulation Classification based on Statistical Moments

Abstract: The ability to identify the modulation of an arbitrary signal is desirable for a number of reasons, including signal confirmation, interference identification, and the selection of proper demodulators A modulation classification algorithm using statistical pattern recognition techniques has been developed and tested on numerically simulated signals This algorithm uses statistical moments of both the demodulated signal and the signal spectrum as the modulation identifying parameters The basis for the classification routine is a set of formulated probability distributions which were developed by generating and statistically analyzing a large set of numerically simulated signals The resulting classification equations were tested on an independent set of numerically simulated signals

Trapezoidal Modulating Signal for Three-Phase PWM Inverter

Abstract: Trapezoidal wave is suitable for the modulating signal of the microcomputer-based pulsewidth modulation (PWM) inverter for the use of motor drives because the switching patterns can be generated by means of on-line computation. The waveform is changed from a rectangular to a triangular wave.

Theory and implementation of a Raman active fiber delay line

Abstract: In an optical delay line made of a single-mode reentrant fiber loop, Raman amplification is used to compensate for recirculating signal losses. Concurrent Stokes noise amplification limits the system performances. A theoretical model shows that the signal-to-noise ratio decays as the reciprocal of the number of signal recirculations. Experimental results obtained with a 760-m-long fiber loop operated at \lambda = 1.12 \mu m are presented. A new pump modulation technique resulting in improved output signal stability is reported whereupon optical delays up to 3 ms were achieved.

High-frequency-modulation spectroscopy with a lead-salt diode laser

Abstract: High frequency modulation (FM) spectroscopy, (1,2,3) is a promising tool for high speed and ultrasensitive atmospheric trace gas monitoring. Based on a measured wideband noise characteristics (4) of a lead-salt diode-laser emitting in the mid IR a sensitivity improvement of 2 orders of magnitude in comparison to conventional derivative (2f) spectroscopy is expected. This improvement can be achieved by moving in modulation and detection frequency space from the 1/f noise dominated region (10 kHz) into a shot noise limited frequency domain above 100 MHz. Optical densities of 10−4 were measured on a µsec timescale with a 200 kHz detection bandwidth. Using digital averaging techniques (5) a detection limit of 2.5.10−6 has been demonstrated with the actual measurement bandwidth of 1.5 kHz. Up to this sensitivity no limitations due to etalons or laser intrinsic parameters could be observed. Further bandwidth reduction is currently being investigated and requires digital background subtraction techniques as well as etalon suppression schemes.

Simulation studies of bifurcation and chaos in semiconductor lasers

Abstract: We apply the phase portrait analysis for photon density and carrier density to analyze simulation results obtained from the rate equations for semiconductor lasers. On the two‐dimensional bifurcation diagram of modulation depth and modulation frequency, there are six regions: periodic pulse, continuous oscillation wave, chaos, period doubling of single period, period multiplying of single period, and period doubling of two period. The region of chaos is located below the region of periodic pulse. By properly choosing the modulation frequency, chaotic behavior can be avoided. A normalized two‐dimensional bifurcation diagram defining the periodic pulse region is presented for the purpose of locating the suitable region for modulation of a semiconductor laser.

Measurement of Loop Gain with the Digital Modulator

Abstract: A loop gain measurement technique for switching regulators using a digital modulator is introduced. While the conventional technique injects and measures the analog signals, the proposed digital modulator injects a digital perturbation and measures the resultant duty cycle modulation. Since the duty cycle signal, derived from all feedback loops, provides the ultimate control of a switching regulator, the loop gain defined at the duty cycle modulator is unique. Employing the digital modulator, this loop gain can be measured even with a switching regulator employing the current injected control. Furthermore, this new technique overcomes false measurement problems found in the conventional technique when the feedback signal at the point where the loop gain is measured contains a pulsating nature.

Light/Dark Modulation of Enzyme Activity in Plants1

Abstract: Publisher Summary It is now widely accepted that light/dark modulation of enzyme activity in green plants is an important regulatory process that directs metabolism toward synthesis of sugars and storage products in the light and toward the breakdown of these compounds in the dark. This chapter discusses the extent and distribution of what is thought to be light-dependent posttranslational modification of chloroplastic and cytosolic enzymes. Various mechanisms have been proposed for this kind of light modulation, and functions have been suggested for this process. Since it has not yet been demonstrated that the light-activated and light-inactivated enzymes are actually covalently modified, the chapter refers to this process by the more general (and more ambiguous) term light modulation. Light modulation is used to refer to those effects which clearly do not involve covalent modification, that is, pH effects, Mg2+ effects, metabolite effects. Light does, of course, also control enzyme activity through the alteration of stromal pH, and ion and metabolite levels.

Electronic sound synthesizer

Abstract: An electronic source synthesizer that employs frequency modulation. Wave-form data of both a fundamental wave and a modulated wave are stored in a RAM as 6-bit digital data. A sine wave signal is produced by modulation wave frequency data and the wave-form data from the RAM. The sine wave signal is multiplied with amplitude data of the modulation wave to obtain the modulation index data (J(t)). The frequency data (w c ) of the fundamental wave and the modulation index data are multiplied. A result of the multiplication provides a read out address of the RAM for storing the wave-form data of the fundamental wave, thereby changing the read out speed of the RAM. The digital data read out from the RAM is converted to an analog sound signal by a D/A converter. Amplitude data (A) of the fundamental wave is pulse-width modulated, and the digital data from the RAM is gated by the modulated pulse. Thus the output of the D/A converter is activated and, forms a sound signal represented by the equation e=A sin J(t) w c t.

Dynamic spectral width of an InGaAsP/InP electroabsorption light modulator under high-frequency large-signal modulation

Abstract: The first measurements of dynamic spectra of an InGaAsP/InP electroabsorption light modulator under high-frequency large-signal modulation are reported. A spectral broadening factor ? was determined from the relative sideband strength to the carrier, and it decreased with increasing operating electric field in the modulator. The estimated ?-value for full modulation was |?| = 2.3, which can be reduced by designing a modulator to give a more effective change of electro-absorption.

Optical recording method

Abstract: In an optical recording system wherein the intensity of a laser beam is modulated with an input modulation signal so as to record information on a recording medium, the intensity modulation of the laser beam is performed after the pulse waveform of the input modulation signal is converted into two pulses which express the front edge and rear edge of the pulse waveform respectively.

Method of digital signal transmission

Abstract: A modulation method capable of high-speed or high-quality digital data transmission under a multipath fading transmission line such as a radio transmission in an urban area is a type of differential coding phase modulation and residues in the fact that the rate of change of phase varies, or the phase is discrete, but does not employ a phase transition waveform of a constant value in a time slot which is a smallest unit for transmitting one symbol of data as in conventional methods Phase transition waveforms in respective time slots which are spaced apart from each other by prescribed time slots are identical varying waveforms or discrete waveforms, and entirely shifted from each other by an amount according to the data transmitted A detecting method employed is a differential detection method using a delay line for delaying a signal for a time corresponding to the prescribed time slots In the presence of multipath propagation, a plurality of kinds of detected outputs are produced according to the multipath propagation, and the detected outputs are combined by a filter after the differential detection, producing a diversity effect for improving bit error rate characteristics This digital signal transmission method is capable of multiphase transmission and can increase spectrum utilization efficiency

A serial data highway system

Abstract: A serial data local area network system comprising a serial data highway (10) interconnecting a plurality of transmitting/receiving nodes having transmitters and/or receivers (12) connected thereto characterised in that each transmitter includes means (22), (23) to spread-spectrum modulate digital data signals (21) and address said data signals and means (24) to connect the baseband modulated signal to the highway and each receiver includes means (26)-(29) to selectively demodulate the respective addressed signals from the received signal to reconstitute the data signals, the arrangement being such that multiple simultaneous data signals can be connected to the highway. Direct sequence spread spectrum modulation is preferably employed using a selected code from a family of orthogonal codes. Each code then forms a node or area address, enabling a variety of communications to be achieved eg point-to-point, broadcast, selected area, priority etc. The received signal is oversampled (110), (113) and converted to a binary signal to derive the received sequence and synchronise receiver clocks. Each receiver may include a stack (53) of address codes which are sequentially placed in a sliding polarity correlator (114) through which the received sequence is passed. Means may be provided to change the length of the code sequences in dependence on the number of current users.

Optimum conditions for the high frequency noise reduction method in optical videodisc players.

Abstract: In a previous paper, the authors demonstrated the usefulness of the high frequency (HF) current superposition noise reduction method. This paper discusses optimum conditions for the HF method. The main results obtained are that modulation current frequency must be higher than 600 MHz and modulation depth must be >120%. The optical path length between laser and disk and the removal for interference in the signal detectors must also be taken into consideration.

Two-port synthesizer modulation system employing an improved reference phase modulator

Abstract: An improved frequency modulator apparatus for use in phase-locked loop (PLL) frequency synthesizers is disclosed which makes possible high deviation, low distortion, FM signals for a wide range of modulating signals, such as digital data or low frequency tone modulation. In a first embodiment having the improved frequency modulator, this apparatus advantageously injects the modulation signal into two ports, one at the VCO and the other provided in an unmodulated reference source signal chain. By properly balancing the levels into each of these two ports, a cancellation effect occurs which nulls the modulation signal at the output of the phase detector. In a second embodiment, the improved frequency modulator is incorporated in a PLL frequency synthesizer with an offset mixer to achieve relatively wide percentage deviation at a low frequency RF carrier. In a third embodiment, the improved frequency modulator is incorporated in a PLL synthesizer in its feedback loop so as to cancel the modulation components before they reach the phase detector. Thus, in the first two embodiments, the added phase modulator is inserted in the reference source signal path to the phase detector, while in the alternate third embodiment, the phase modulator is inserted into the feedback path and includes a phase inverter stage to correct for the inherent modulation polarity reversal.

A matched nonlinearity for phase estimation of a PSK- modulated carrier (Corresp.)

Abstract: A nonlinear phase estimator for a phase-shift keyed (PSK)-modulated carrier has been developed by Viterbi and Viterbi. Their analysis is extended, and an optimal or "matched" nonlinearity is derived for the estimator.

Suppression of stimulated brillouin backscattering by psk modulation for high-power optical transmission

Abstract: High-power optical fibre transmission combined with coherent detection offers a significant advantage in terms of length between repeaters. However, nonlinear optical effects limit the level of power into a fibre to a few milliwatts. The paper reports on the initiation and suppression of stimulated Brillouin scattering using phase shift keying at 1320 nm, discusses the effect of signal statistics on the level at which the nonlinear effect appears, and introduces and experimentally confirms an upper bound on the digital sum variation of codes. It emerges that the code requirements for high power, high bit rate, coherent systems can easily be met.

Propagation delays and transition times in pulse-modulated semiconductor lasers

Abstract: An experimental and theoretical study of large‐signal switching transients in directly modulated semiconductor lasers shows that the main parameters affecting high‐speed switching are the small‐signal relaxation oscillation frequency and the optical on/off ratio of the pulses. Simple expressions agree well with measured data and can be used to obtain an estimate of the maximum achievable modulation bit rate.

A model of a diode laser actively mode-locked by gain modulation

Abstract: A rate-equation analysis of a diode laser in an external resonator which is actively mode-locked by periodic modulation of the injection current is presented. A computer simulation of the transient process of pulse generation is developed. The coupled rate equations for electron and photon densities as functions of time and position within the diode are solved numerically. The effects of sinusoidal and pulsed injection current, spatial and temporal gain saturation, various resonator configurations, mismatch between modulation frequency and round-trip frequency, and varying laser parameter values are considered. A comparison of results with those of previous theories is presented. Optimum conditions for mode-locking are stated.