Pulse-frequency modulation

About: Pulse-frequency modulation is a research topic. Over the lifetime, 4151 publications have been published within this topic receiving 53039 citations. The topic is also known as: PFM.

Image processing apparatus in which the minimum and maximum widths of a pulse-width modulated signal can be independently adjusted in accordance with predetermined data signals

Abstract: An image processing apparatus includes a D/A converter for generating an analog image signal, a variable resistor for changing an output range of the analog image signal generated by the D/A converter, and a comparator for processing the analog image signal generated by the variable resistor by using an analog pattern signal and for outputting a pulse width modulated signal. The analog pattern signal may be a triangular wave signal, a saw-tooth wave signal, a sine wave signal, or a trapezoidal wave signal. In another version, selection is performed between predetermined data and a generated image signal and the selected signal is processed using an analog pattern signal (e.g., a triangle wave) to output a pulse width modulated signal. A D/A converter may be used to convert the output of the selection. The output range of the DAC may be variable.

Frequency Modulation Propagation Characteristics

Abstract: Early work on frequency modulation is described wherein the propagation characteristics of frequency modulation were determined for frequencies between 9000 and 18,000 kilocycles. Oscilloscopic wave form and aural program observations, taken on a circuit between California and New York, showed that frequency modulation is much more distorted by the effects of multipath transmission than is amplitude modulation. The distortion is greatest at the lower modulation frequencies and higher depths of modulation where the side frequencies are most numerous. Oscilloscopic observations of the Lissajou figures formed by placing the outputs of receivers connected to spaced antennas on opposite oscilloscope plates showed that the diversity characteristics of frequency modulation are similar to those of amplitude modulation. That is, the detected outputs of the receivers tend to remain in phase for the lower modulation frequencies and become more phase random as the modulation frequency is increased. However, this tendency is almost obliterated on the lower modulation frequencies of frequency modulation by the presence of unequal harmonic distortion in the two receiver outputs. Theory is given analyzing the distortion encountered in a two-path transmission medium under various path amplitude and phase relation conditions. The theory explains phenomena observed in the tests and points out the extreme distortion that can be encountered.

Method and apparatus for frequency modulation

Abstract: A voltage controlled oscillator (1), a variable frequency divider (2), a phase comparator (3), and a loop filter (4) form a Phase Locked Loop (PLL). A sigma-delta modulator 5 sigma-delta modulates data obtained by adding a fractional part (M2) of the frequency division factor data with modulation data (X) by using an output signal of the variable frequency divider (2) as a clock. An output signal of the sigma-delta modulator (5) is added to an integral part (M1) of the frequency division factor data, and the resultant data becomes effective frequency division factor data (13) of the variable frequency divider (2). An output signal of the sigma-delta modulator (5) also becomes control data (14) after passing through a D/A converter (6), a low-pass filter (7), and an amplitude adjustment circuit (8). The control data (14) is inputted into a frequency modulation terminal of the voltage controlled oscillator (1). Therefore, it is possible to provide a frequency modulator that can use a reference signal source having no frequency modulation function, and perform modulation over a wide range of frequencies based on a digital modulation signal.

Noise radar using random phase and frequency modulation

Abstract: Pulse compression radar is used in a great number of radar applications. Excellent range resolution and high ECCM performance can be achieved by wide-band modulated long pulses, which spread out the transmitted energy in frequency and time. By using random noise as waveform, the range ambiguity can be suppressed as well. The same limit in Doppler resolution is achieved as for a coherent Doppler radar when the time compression of the reference is tuned to that of the target. Mostly, the random signal is transmitted directly from a noise generating HF-source. A sine wave, which is phase or frequency modulated by random noise, is an alternative giving similar performance but higher transmitted mean power when peak-limited transmitters are applied. A narrower modulation noise bandwidth can also be applied to generate the same output bandwidth. For phase modulation, the bandwidth amplifying factor is simply the rms value of the phase modulation, and for a frequency modulating waveform, the output rms bandwidth equals the rms-value of the frequency modulation. The results also show that the range sidelobes can be highly suppressed compared with the sidelobes of the modulating signal. The mean and variance of the correlation integral are derived in terms of the autocorrelation function of the modulation. The combined effects of low range sidelobes and enhanced range resolution make frequency and phase modulation attractive.

Control voltage means in pulse receiver

Abstract: This invention relates to electric wave modifying circuits and more particularly to wave modifying circuits of the type in which the low frequency modulation content in a signal wave comprising a multiplicity of short pulses of varying amplitude spaced by intervals longer than the duration...