Showing papers on "Pulse-frequency modulation published in 1981"

Apparatus and method for remotely measuring temperature

Abstract: Apparatus and method for remotely measuring temperature in which a transmitter having a temperature sensitive element is placed in close proximity with the environment sought to the measured, with the temperature sensitive element controlling a reference voltage applied to a first terminal of a testing circuit, a second terminal of which receives a constant frequency alternating output of an oscillator. The output signal from the testing circuit is a constant frequency signal having a duty cycle which varies with the temperature of the element. An RF signal carrier is modulated at the transition points of the variable duty cycle signal for transmitting bursts of energy which are received and from which a replica signal corresponding to the variable duty cycle signal is reconstructed. A counter in the receiver counts high frequency pulses over a predetermined period of time during "on times" in duty cycle to obtain a numerical indication of the measured temperature.

Amplitude modulation thresholds for the parakeet (Melopsittacus undulatus)

Abstract: Parakeets were tested for the ability to detect sinusoidal amplitude modulation of broad band noise. Instrumental avoidance conditioning and a psychophysical modified method of limits procedure were used to measure the threshold for detecting amplitude modulation at 10 modulation frequencies between 2 and 2,048 Hz. Below about 40 Hz, modulation threshold is independent of modulation rate and noise level. Above 40 Hz, modulation threshold decreases with modulation frequency at the rate of 3 dB/ octave. These results are somewhat different from amplitude modulation functions in humans suggesting different degrees of temporal resolving power in birds and humans. Thresholds for changes in modulation rate are 1–2 orders of magnitude higher than pure tone frequency difference limens.

Modulation frequency characteristics of directly optical frequency modulated AlGaAs semiconductor laser

Abstract: Optical frequency spectra of directly frequency modulated AlGaAs semiconductor laser in the 0?5.2 GHz range were measured by using a Fabry-Perot interferometer and a birefringent optical filter. The frequency deviation is linearly proportional to the RF modulation current. The measured modulation frequency characteristics for the frequency deviation show that the thermal effect is predominant in the frequency below 10 MHz. It has a resonance peak which behaves just like the peak observed in the modulation. Experimental results agreed well with theoretical values calculated by considering thermal effect and carrier-dependent refractive index variation.

Phase-locked loop frequency synthesizer including compensated phase and frequency modulation

Abstract: A phase-locked loop is disclosed that exhibits flat modulation characteristics over a wide range of carrier frequencies for either frequency or phase modulation at rates that are both within and outside the loop bandwidth. The disclosed arrangement is a programmable divide-by-N phase-locked loop frequency synthesizer wherein the feedback path includes a second phase-locked loop that serves as a tracking filter 20. Modulation is supplied to the main phase-locked loop via a first modulation path that couples the modulating signal to the frequency control terminal 50 of the phase-locked loop voltage-controlled oscillator 12 and via a second modulation path that couples the modulating signal to the phase-locked loop phase detector 22. To configure the system so that flat modulation is attained. the gain factors of the first and second modulation paths are established in accordance with specific relationships and the second modulation path includes a compensator network 44 having a transfer function that at least approximates that of the phase-locked loop 20 which is embedded in the system feedback path. Additionally, the modulation signal coupled to both modulation paths is adjusted on the basis of carrier frequency to compensate for frequency-related variation in the transfer characteristics of the main loop VCO. The transfer characteristic of the main loop phase detector 22 is controlled to maintain a constant loop bandwidth.

PWM Systems in Power Converters: An Extension of the ``Subharmonic'' Method

Abstract: In this paper the extension of the subharmonic method for pulse-width modulation (PWM) systems, in the case in which the ratio between modulating and carrier wave amplitudes can be varied from 0 to ?, is studied in an analytical way. This method allows us to obtain an inverter output waveform variable continuously from a nearly sinusoidal to a square wave and to increase somewhat the amplitude of the fundamental output wave without a significant worsening of the harmonic content, a feature particularly useful for drives with wide speed variations or which need an optimized use of dc power supply.

Microcomputer-based pulse width modulated inverter fed machine drive system

Abstract: Regulation of inverter-machine drive system torque and frequency in accordance with operator commands is achieved by the use of an improved, microcomputer-based, control apparatus. At machine frequencies less than a preselected machine frequency, inverter pulse width modulation signal pulses and half cycle polarity signal pulses are supplied by the control apparatus to the inverter to regulate the duration and conduction sequence, respectively, of inverter switching devices in accordance with pulse width modulation signal data computed by equilateral triangulation and stored half cycle polarity signal data. At frequencies above the preselected machine frequency, when computation of inverter pulse width modulation signal data becomes impractical, inverter pulse width modulation signal pulses are synthesized from stored data. This achieves simplification of control hardware and provides improved machine drive system performance.

Apparatus and method for compressively approximating an analog signal

Abstract: An input analog signal, such as a sound signal, is sampled by a sample-and-hold circuit, while sampling timing is variable in accordance with the amplitude variation of the analog signal. A difference between the amplitude of the analog signal and the amplitude of the output signal of the sample-and-hold circuit is detected, and the detected difference is integrated after passing through a square-law detecter. On the other hand, the average amplitude level of the input analog signal is detected to be compared with the integrated value. The sampling timing will be determined in accordance with the result of the comparison so that frequency of sampling pulses applied to the sample-and-hold circuit varies in accordance with the waveform of the input analog signal. The interval between two adjacent sampling pulses may be detected and stored together with digitally coded signals indicative of varying amplitudes of the input analog signal for recording or writing the analog signal information in a memory.

Optimum Pulse Shaping in Digital Angle Modulation

Abstract: This paper presents a technique for optimizing the baseband pulse shapes in digital angle modulated signals to minimize the fraction of out-of-band power for a given channel bandwidth. As examples of practical interest, the optimization is carried out for channel bandwidths up to three times the bit rate and for the range of modulation indices usually encountered in digital transmission. Results for MSK-type signals appear as a special case.

Dual slope pulse width modulation regulator and control system

Abstract: A dual slope pulse width modulation regulator for separate control of two independently operative power supplies is provided. An oscillator supplies a triangle wave having a period T signal to each of two separate DC comparators each of which also receives an analog error signal related to the difference between a power supply output signal and a predetermined reference level. The outputs of the DC comparators are coupled to a pair of AND gates which are alternately enabled by a digital output signal of the oscillator with the digital output signal having output states corresponding to the duration of first and second rates of change of the triangle wave signal which occur during each period T. The outputs of the AND gates correspond to pulse width modulated drive signals which are utilized to control the excitation of independently operative power supplies having output sensor circuits which sample the output of the power supplies and result in providing the first and second analog error signals. During each period T separate, independently operative pulse width modulation power supply control signals are provided through the alternate use of the first and second rates of change of the triangle wave signal of the oscillator to provide pulse width modulation control signals.

Broad‐band guided‐wave light intensity modulator

Abstract: With a view to realizing a broadband guided-wave light intensity modulator, we fabricated a traveling-wave type guided-wave light intensity modulator. We succeeded in experiments of light intensity modulation over 18 GHz. In this paper, the traveling wave operation is shown to be superior almost always to the conventional lumped element operation in terms of bandwidth and efficiency. As an electric circuit appropriate for the traveling wave operation, the effectiveness of nonsymmetric electrodes is described. Analytical results are shown for the transmission line constants and modulation frequency characteristics. Next, the push-pull optical modulation which is useful to obtain an efficient optical intensity modulator with good optical characteristics is considered. The configuration for the optical circuit is studied and the possibility of obtaining a traveling wave operation is discussed. Further, the result of the prototype development and modulation experiment using a Ti diffused LiNbO3 optical waveguide (c plate) is reported. The device consists of two branches made of a single transverse mode waveguide 5 μm wide, and a differential modulation portion with parallel waveguides. The electrodes are nonsymmetric transmission lines with separation 32 μm, width 20 μm and length 6 mm. The half wavelength voltage was 8.8 V, extinction ratio 98%, 1/√2 bandwidth 11.2 GHz and the modulation input power 130 mW for 88% intensity modulation. The modulation sensitivity was 11.3 μW/MHz, and the frequency characteristics were found to be excellent.

A compact spectrum constant envelope digital phase modulation

Abstract: A digital modulation system with compact spectrum and constant envelope is proposed, based on the results of theoretical and experimental studies. This modulation system is suitable for digital mobile communication, which generally is subject to deep and rapid fading. It is characterized with a possibility of practical and stable instrumentation. In the modulator, modulation signal parameters are read out of the memories, by which precise spectrum and waveform can be realized. For the modulator, an orthogonal phase modulation, whose parameters are stable, can be adopted by pertinent parameter design for the modulating signal stored in the memories. The experimental results agree well with the design.

Single unit responses in the auditory center of the frog mesencephalon to amplitude-modulated tones

Abstract: Responses of most single neurons of the torus semicircularis ofRana ridibunda to stimuli of characteristic frequency and with low (10–30%) sinusoidal amplitude modulation were considerably stronger than those of the same neurons to pure tones. Analysis of phase histograms synchronized with the period of modulation was used to study dependence of the response on the frequency of modulation. In some cells the degree of modulation of the phase histogram fell steadily with an increase in modulation frequency, but in others a maximum was found in the 10–20 Hz region. Usually modulations of the phase histogram were significantly greater than stimulus modulation. The phase angle between the maximum of stimulus amplitude and the maximum of the unit response increased as an approximately linear function of the increase in modulation frequency.

Amplitude modulation detector

Abstract: The amplitude modulation detection device, which is provided with an AM (amplitude modulation) responsive to first and second input signals for maintaining a constant D.C. level output signal, the first signal being the AM signal, and the second signal produced by feedback loop which includes a D.C. voltage comparator connected to the detector for comparing the D.C. output level of the detector with a reference signal level.

A practical procedure for estimation of instantaneous frequency

Abstract: The instantaneous frequency of a frequency-modulated signal may be estimated using the zero crossings of the signal. Furthermore, the procedure is simple and gives good results when only samples of the signals are available and when the signal-to-noise ratio is above about 12 dB. An example is given.

Selecting smoothing pulses for partial-response digital FM

Abstract: In recent years, it has been demonstrated that partial-response continuous-phase modulation (sometimes also referred to as partial-response digital FM) is a spectrally efficient constant-envelope digital-modulation method. If maximum-likelihood sequence detection (e.g. the Viterbi detector) is used, these schemes can also be made power efficient. System complexity grows exponentially with the length of the baseband pulse that introduces the memory in the partial-response scheme. The smoothness and the length of this pulse determines the spectral properties. The paper considers binary systems based on short pulses of length ?2 symbol intervals. New spectrum formulas are given for modulation schemes based on pulses with an increasing number of continuous derivatives. It is demonstrated how the spectral mainlobe and the spectral tails are affected by the shape of the pulse. Comparisons are made with binary full-response systems. The tradeoff between error probability and bandwidth is demonstrated.

Built-in group delay testing arrangement for an fm radio system

Abstract: The baseband input to a frequency modulation transmitter is switchably connectable to a square wave generator, the amplitude of the square wave output being adjusted to provide a predetermined deviation of the FM radio transmitter. The output frequency of a pilot oscillator is also applied to the baseband input and it is subjected to phase modulation because of group delay which exists in the system and which adversely affects the signal during transmission through the system. At the receiving end of the radio system, the receiver output obtains the pilot signal which has been phase modulated by the group delay slope in the system, because of the square wave test signal. This phase modulation is detected in a phase lock loop, amplified, rectified and applied to a meter so as to provide an indication of the group delay slope in the system.

High power class B modulation amplifier for a broadcast transmitter

Abstract: A method for amplifying electric signals, an amplifier circuit and application of this amplifier circuit as the modulator stage of a subsequent amplifier, employing a variable anode voltage for the purpose of improving the efficiency of amplifiers and particularly of high-power modulation amplifiers which are used, for example, in broadcast transmitters for the amplitude modulation of the radio-frequency output stage. From the modulation signal to be amplified, a control signal is derived in a control stage, this control signal being associated with the amplitude of the envelope of this modulation signal and being used for controlling the output voltage of a modulator/rectifier. The control signal is caused to follow the modulation signal within a presettable response time.

Optically frequency modulated GaAs MESFET oscillator

Abstract: A GaAs MESFET X-band oscillator has been frequency modulated by an amplitude modulated optical signal injected on the active device A modulation index of 05 corresponding to MSK modulation has been achieved at 2 Mbit/s without parasitic amplitude modulation It is shown that the FM modulation index variation against frequency is directly related to the drain current response of the FET considered as a photodetector This responsivity has been measured to decrease above 5 MHz, which limits the oscillator FM capability

Simulation of systems involving pulse frequency modulation with special reference to modelling of muscle spindle receptors

Abstract: The pulse frequency modulated form of neural signals can cause significant problems in the application of a system identification approach to the experimental investigation of elements within the neuromuscular control system. The paper describes how computer simulation techniques have been used in the investigation of different methods for the processing of neural signals. The use of an appropriate form of pre-processing method may allow conventional identification techniques to be applied to neurophysiological data.

Parasitic amplitude modulation of stabilized CO2 lasers

Abstract: An experimental investigation was made of parasitic amplitude modulation in a CO2 laser with intracavity frequency modulation. This effect was due to periodic misalignment of the laser cavity during operation of a piezoelectric ceramic modulator. A method for controlling and minimizing the parasitic modulation was developed. Relationships were derived for the shift of the stabilized frequency due to such parasitic amplitude modulation and estimates were obtained for the case of a stabilized CO2/OsO4 laser. It was found that the parasitic modulation could give rise to a dependence of the stabilized frequency on the phase relationships in the case of phase-sensitive detection in an automatic frequency control system of the laser.

New method for generating frequency modulation

Abstract: The paper describes how asynchronons delta sigma modulation can be used to generate frequency modulation. Present FM modulators have an inherent nonlinearity in the voltage/frequency characteristic, and as a consequence they are restricted to small percentage frequency deviations. The ADSM-FM modulator is inherently linear, allowing a wide percentage frequency deviation to be obtained. When incorporating this ADSM-FM modulator in the design of an FM broadcast exciter a system results which has an order of magnitude improvement in both signal/noise ratio and harmonic distortion compared with conventional designs.

A pulse width modulation system

Abstract: A first source (1) of voltage V supplies sufficient rectified power for the carrier to the R.F. stage (7) of a radio transmitter. A second source (9) which exceeds twice the voltage V, powers a pulse width modulation amplifier (8) serving to amplify an incoming audio signal (A). The amplified signal (A) is applied, via a capacitor (16), to the load, thereby modulating the voltage V. Because the voltage of the second power source more than exceeds twice the voltage V, the amplifier can be operated at less than 100% pulse width modulation whilst still obtaining an amplification sufficient to achieve 100% modulation of the voltage V applied to the load.

A new FM modulator using phase unstable PLL (PU-PLL)

Abstract: A phase-locked loop (PLL) with a second-order low-pass filter can oscillate with the frequency nearly equal to the filter cutoff. By modulating the amplitude of the oscillation, a stable frequency modulated signal can be obtained at the output of a voltage-controlled oscillator (VCO).

Mode Locking Of (GaAI)As Injection Lasers

Abstract: The important experimental parameters affecting the mode locking of a variety of (GaAl)As injection lasers operating in an external optical cavity are described. We find that short detector-limited pulses (less than 60 psec) with 100% modulation depth can only be obtained using lasers that exhibit either an anomalous narrowband noise resonance or self pulsations. Little or no mode locking is observed in lasers having the normal broad noise resonance. The maximum frequency of the mode-locked pulses is ≈1 GHz and is limited by the laser and not the external cavity. The observed amplitude, pulse width, and frequency of the mode-locked pulses are correlated to the degree of self-pulsation and the external cavity length. The experimental results are in qualitative agreement with a model that uses the rate equations modified by either electron traps or saturable absorbers and a delayed feedback term. Our results appear to imply that mode locking in (GaAl)As injection lasers is related to saturable absorbing centers and is very similar to passive mode locking in dye lasers.