Showing papers on "Pulse-frequency modulation published in 1967"

A nonlinear discrete system equivalence of integral pulse frequency modulation systems

Abstract: In this paper a study of the effect of integral pulse frequency modulation (IPFM) on single-input single-output feedback control is attempted. For zero input such systems can be reduced to a nonlinear discrete system. Lagrange stability concepts are used for the stability study of such systems. A step-by-step procedure is devised for the construction of the state trajectories of the IPFM system. This has been applied to a second-order plant where it is shown that instability, asymptotic stability in the large, and asymptotic stability in the Lagrange sense are exhibited by such systems. It is also shown that in IPFM systems, the periodic oscillation that exists depends on the initial state. The equivalence concepts of such systems are reviewed critically, and the limitations of the method are pointed out. Further research in this area of feedback modulation is proposed and discussed.

Frequency multiplication and displacement

Abstract: A circuit for displacing a signal 90° comprising a frequency doubler wherein an input square wave is differentiated and clipped. The frequency doubler also inverts the square wave, differentiates the inverted square wave and clips the differentiated inverted square wave. The two clipped signals are then added to provide a signal having a frequency twice that of the input square wave. This signal is applied to a sawtooth generator which provides an output signal to actuate a Schmitt trigger. The Schmitt trigger generates a square wave having a frequency twice that of the input square wave for actuating a bistable vibrator. The output of the bistable vibrator is a square wave displaced 90° from the input square wave.

A push-pull optical amplitude modulator

Abstract: A push-pull optical amplitude modulator is described, and some experimental results are presented. The modulator is an interferometer with phase modulators in each arm. The design gives good temperature stability and allows a reduced modulating voltage by using a transverse modulating field. The use of a Koster's beamsplitting prism provided a compact practical design for the experimental KDP modulator. The modulator held a null in the output of 20 dB below the input for periods of one hour. The frequency response out to 30 MHz and the pulse response of the modulator were measured. Strong piezoelectric resonances were observed. The advantages of the push-pull modulator design for use with LiNbO 3 or LiTaO 3 are pointed out.

Effects of phase locking on modulation characteristics

Abstract: An advanced differential equation for phase angle of output voltage, when an unmodulated or modulated oscillator is locked to a modulated or unmodulated external driving signal, respectively, is solved by analog computer. Suppression of the modulation rate is verified experimentally and applied to noise reduction of an avalanche oscillator.

Magnetic analog memory elements of a single core

Abstract: The behavior of an analog memory element using a single toroidal magnetic core with rectangular hysteresis loop is presented. In this element, flux levels stored in the core as analog information can be nondestructively and continuously read out. With the application of a slight, amplitude-modulated, radio frequency (RF) field, the modulation frequency component of the induced voltage waveform is detected as an analog output signal. The principle of operation requires only one core per memory element, so that problems of mismatching of two cores, which appear in a second-harmonic type element, are completely eliminated. Experimental results show that this is suitable as an analog memory element, and that the eddy-current effect enhances the output signals.

Advanced threshold reduction techniques study

Abstract: Threshold improvement capabilities of feedback and band dividing demodulation methods for phase and frequency modulation signals

Frequency modulation-demodulation circuit

Abstract: The frequency modulation (FM) signal received by an FM receiver contains the basic signal frequency, noise in the form of amplitude disturbances, and the audio signal as the frequency modulator. The receiver, by means such as a limiter circuit, produces a series of square wave pulses whose repetition rate is dependent upon the frequency deviation, i.e., the modulation signal. Then, in a discriminator counter detector circuit, the square wave pulse is differentiated to the form of a sharp pulse by means such as a differential network. The pulse may then be amplified by means such as a pulse amplifier; the width of the pulse- but not its height- is expanded by an expanding circuit; and then the pulse may be integrated by an integrating circuit. The output of the integrating circuit is the demodulated audio signal.

A modified integral pulse frequency modulator in control systems

Abstract: Many recent works are concerned with theoretical problems and engineering applications of integral pulse frequency modulation in control systems. It has been shown that a control system in which an integral pulse frequency modulator (IPFM) acts as an error modulator is not, in general, asymptotically stable, and the ultimate motion takes the form of irregular oscillations. By appropriate setting of modulator parameters it is possible to decrease the amplitude of limit oscillations, buthis results in poor system dynamics. Here, a modified IPFM is proposed in which the threshold level is a function of the time interval between succeeding pulses. This modulator retains the noise immunity of a usual IPFM with improved dynamic performance.

Frequency responsive electrical circuit

Abstract: This disclosure deals with an electrical circuit designed to receive a train of input signals and produce an output signal that is indicative of the frequency at which the input signals are received. When the frequency of the input signals is below a critical value, the output signal is in the form of pulses having a width which is proportional to the input signal frequency, and when the input signal frequency is above this critical value, the output signal is zero.

A High-Speed Wideband L-Band Tunnel Diode Frequency Deviator

Abstract: An L-band tunnel diode frequency deviator which can be tuned over an octave bandwidth by a 160-millivolt change in input voltage is described. By using a nonreactive input circuit, a low-frequency prototype deviator has been tuned over a 50-percent frequency range in less than one RF cycle and an L-band deviator has had its frequency shifted and returned to its original value so that the output phase was shifted by ±90 degrees in 4.25 ± 0.25 cycles (3.27 ns).

A new method of measuring amplitude modulation-phase modulation conversion in microwave amplifiers

Abstract: A system is described which directly measures the amplitude modulation to phase modulation conversion in a microwave amplifier. The system is of particular use for testing microwave amplifiers operating in the almost linear regime. It has a useful advantage over similar microwave measurement systems in that it is insensitive to low frequency jitter of phase shift or gain of the amplifier under test, in spite of its high sensitivity to a.m.-ph.m. conversion. A carrier frequency is modulated between two levels of amplitude before it is fed into the amplifier under test. The higher level signal is directly compared in phase with the lower level signal by temporarily storing the signal at one level in a delay line of appropriate length so that the two levels of signal arrive simultaneously at a sensitive phase bridge. Fast p-i-n diode switches enable this technique to be used successfully by providing pure amplitude modulation and switching the arms of the phase bridge alternately into a single detector to improve the accuracy of the bridge. This last technique is of interest for all types of microwave bridge. The modulation imposed on the carrier into the amplifier can also be used to measure the gain compression or distortion. The bridge successfully measured down to 0.1° phase shift, and 0.1 dB change in gain, per dB change in power level.

Desirable bandwidths for optimal frequency-modulated pulses

Abstract: In a paper on radar frequency modulations, Schweppe (IEEE Trans. Military Electronics, vol. MIL-9, pp. 25-32, Jan. 1965) developed a simple design principle: "The target's position is obtained from the modulation while the target's motion (velocity and acceleration) is obtained from the RF phase." It was also pointed out that the modulation should be selected to be orthogonal to the target motion so the modulation will not interfere with the motion estimates. Having satisfied the orthogonality constraint, that modulation is selected that provides the best range estimate. The "best" estimate sought was that which minimized the variance of the range estimate. Designing a radar pulse so as to minimize the variance of an estimate corresponds to the designing of an ambiguity function with a sharp central peak at the true values of the parameters with no regard to the rest of its shape. This analysis was carried out (the solutions in each case are nonunique), the function is plotted for five and seven switching points, as well as 3 and 3. It is shown from these results that an optimal frequency-modulated pulse for an accelerating target with three switching points yields the most desirable ambiguity function.

Nonlinear characteristics of pulse-duration modulation

Abstract: Pulse duration and pulse code modulations compared for input power and output signal to noise ratio at high and low signal strength