Showing papers on "Pulse-frequency modulation published in 1988"

A DC to DC PWM series resonant converter operated at resonant frequency

Abstract: Resonant DC-DC converters that are usually operated using frequency modulation to achieve regulation have the disadvantage of wideband frequency modulation. An alternate regulation scheme that uses fixed-frequency pulse width modulation (PWM) is proposed. This control scheme is applied to a series-loaded, series-resonant converter. When operated in a full-bridge configuration and with a variation of PWM that can be described as a phase shift modulation between the two sets of switches, the converter presents low switching stresses. Analytical results presented include VA rating and stresses on critical active and passive components as a function of input voltage variation. A 200 kHz, 700 W, 48 V output offline converter was realized using this concept, and some experimental results are presented to corroborate the analysis. >

Voltage to pulse-width conversion circuit

Abstract: A voltage to pulse-width conversion circuit includes a counter which counts a reference frequency signal and produces a multi-bit digital value; a digital/analog converter which converts the digital value into an analog signal; and a voltage comparator which compares an output of the digital/analog converter with a control signal and produces a pulse width modulated output signal which has a predetermined duty cycle ratio.

Adaptive-filter single-bit digital encoder and decoder and adaptation control circuit responsive to bit-stream loading

Abstract: An adaptive single-bit encoder and decoder has its adaptive function determined by dynamically dividing the message frequency band into delta-sigma and delta modulation regimes of operation. In a practical embodiment this is accomplished by varying the corner frequency of a variable-frequency low-pass filter (14, 14′) in a leaky integrator so that below the corner frequency the operation is that of delta-sigma modulation and above the corner frequency the operation is that of delta modulation. An adaptation control circuit (18, 18′) removes the clock signal component from the encoded bit stream to provide an analog signal representative of bit stream information or loading for use in generating the control signal. The analog signal is peak rectified (22, 22′), smoothed (24, 24′), and (optionally) non-linearly processed (26, 26′) to provide the control signal.

Medical stimulator with stimulation signal characteristics modulated as a function of stimulation signal frequency

Abstract: A transcutaneous electrical nerve stimulation (TENS) apparatus includes first, second, and third oscillators. The first oscillator produces a first train of pulses at a main frequency. The second oscillator produces a second train of pulses at a modulation frequency. Output levels of the second train of pulses vary as a function of the modulation frequency. A frequency control simultaneously controls both the main and modulation frequencies. The third oscillator is responsive to the first and second oscillators and produces a third train of pulses at the main frequency. Intensity and frequency of the pulses of the third pulse train are modulated as a function of the output levels of the second train of pulses. An output driver responsive to the third oscillator converts the third train of pulses into a train of stimulation pulses having electrical characteristics adapted to be applied to a human body to suppress pain.

Frequency modulating circuit for video tape recorder

Abstract: A frequency modulating circuit comprising a circuit for separating a synchronizing signal from an input signal, a circuit for generating a sampling pulse in accordance with the synchronizing signal, a circuit for producing a frequency modulated signal out of the input signal, and a circuit for detecting the phase of the frequency modulated signal at the timing of the sampling pulse. The level of the input signal is corrected in accordance with the output of the detecting circuit, so that the phase of the frequency modulated signal is locked to a predetermined phase at the timing of the sampling pulse. Consequently, despite frequency modulation of the wide-band input signal, the invention is capable of preventing occurrence of any moire pattern that may otherwise be caused in displaying the demodulated signal.

Video transmission in optical fiber communication systems using pulse frequency modulation

Abstract: A design procedure has been developed to determine the required operating conditions for a pulse-frequency modulation (PFM) system (modulation index, required system bandwidth, and receiver carrier-to-noise ratio (CNR) for a specified receiver SNR (signal-to-noise ratio) and number of clicks per second. The PFM processing gain (=SNR/CNR) was measured to be 40 dB for a modulation index of beta =2.5, which agrees closely with the theory. The theoretical processing gain advantage of PFM over FM is 15.9 dB for a modulation index of beta =2.5 with receiver bandwidth B/sub rx/=50 MHz. >

A single-chip microprocessor-based PWM technique for sinusoidal inverters

Abstract: A sinusoidal pulsewidth-modulation (PWM) technique suitable for single-chip-microprocessor-based control is described. The scheme can be considered as a digital alternative to the analog subharmonic method (SHM) in the sense that online real-time PWM control is possible, synchronization between carrier wave and signal wave is unnecessary, and low-order harmonics in the output voltage are well suppressed. The maximum output voltage is 15% larger than that obtained by the subharmonic modulation method at the same carrier frequency. >

Measurement of intrinsic frequency response of semiconductor lasers using optical modulation

Abstract: For the first time, optical modulation is used to determine the intrinsic frequency response of a laser diode. It is shown that the shape of the measured frequency response agrees very well with the predicted intrinsic response of semiconductor lasers. As anticipated, the measured frequency response lacks the frequency rolloff that occurs with direct RF current modulation. The resonant frequencies measured are shown to be proportional to the square root of the probe laser bias power and the damping rates are found to be linear in power, in agreement with expectations.

Pulse width distortion correction circuit

Abstract: A pulse width distortion correction circuit in which a digital input signal has its leading and trailing edges smoothed, is added to an analog pulse width control signal and compared to a reference voltage to provide a digital output signal with a corrected duty ratio. A duty ratio detection circuit detects the duty ratio of the digital output signal and provides the corresponding pulse width control signal so as to cause the duty ratio to assume a value of 50%.

A computative decision of pulse width in three-phase PWM inverter

Abstract: A novel PWM (pulsewidth modulation) technique is proposed for a three-phase sine-wave PWM inverter. The pulse width is designed to produce a sine-wave output voltage by numerical calculation based on a geometrical technique. The accuracy of output voltage and the harmonics in an output voltage waveform are discussed and compared with the results of the conventional triangulation method. A modified method is introduced for obtaining a PWM inverter with fluctuating input voltage. The validity of the method is verified in an experiment using a microprocessor-based control system. >

Impact Of Modulation Induced Signal Instabilities On Fiber Gyro Performance

Abstract: The impact of modulation parameters on signal performance of fiber gyroscopes has been investigated. Amplitude modulation (a.m.) causing bias drift and instabilities of phase modulation index causing scaling problems will be discussed and compared to experimental test results.

Frequency or phase modulation

Abstract: A frequency or phase modulator, in particular a DC-­coupled frequency modulation synthesizer, comprises a voltage-controlled oscillator (1) in series with a divider (2) in a phase-locked loop, and an analogue-to-digital converter (17) connected to control the divider in accordance with an input analogue modulation signal. The converter (17), preferably a one-bit charge-balanced converter, has a noise-shaped frequency response to reduce noise at frequencies below the loop-bandwidth.

On system identification using pulse-frequency modulated signals

Abstract: i ON SYSTEM IDENTIFICATION USING PULSE-FREQUENCY MODULATED SIGNALS Nonperiodic time quantization has proved very useful for the improvement of measurement and control systems. Very often nonperiodic time quantization is connected with pulse frequency modulation (PFM). In the present report some aspects of continuous system identification using PFM signals have been studied. Two possibilities for application of PFM signals in system identification are considered. In accordance with these possibilities either the system is excited by PFM signals or the system output is observed with the help of a pulse-frequency converter. For both these cases effective computational schemes for estimation of the transfer function and the weighting function have been obtained. For the case of the weighting function estimate, the relationship with previously obtained estimates has been established. The utility of the suggested estimates is illustrated by computer simulation. For this purpose, several programs are given in the appendix.

Method for the automatic detection and classification of digital quadrature-amplitude-modulated signals having unknown parameters

Abstract: This method is intended for monitoring the radio traffic, for example by the post office. The received signal is digitised and, with prior knowledge of the frequency bandwidth in one or otherwise in a number of parallel channels of different frequency bandwidth, is separately processed further. In each channel, the signal element timing is extracted and the instantaneous values of amplitude, frequency and phase are sampled at the signal element timing points. Mean values and variances of the amplitude and frequency values are determined. Using the amplitude values, the frequency values and the differences of successive phase values, histograms are formed. The histogram forms typical of the wanted signal types are automatically detected by cross correlation with predetermined reference function sets which are typical of the modulation. To increase the reliability of decision, the mean values and variances between amplitude and frequency are simultaneously checked for the maintenance of predetermined value ranges. The classification of the signal type is obtained from the reference function set which leads to the highest correlation results in the histogram analysis. The signal element rate is estimated from the frequency bandwidth of the associated channel.

Phase locked frequency synthesizer with single input wideband modulation system

Abstract: A single input wideband modulation system for a phase locked loop is achieved by interposing the inverse analogue of the closed phase locked loop transfer function between the modulation source and the VCO modulation input. A first branch of the interposed circuit directly passes high frequency signals from the modulation source to a summing device tied to an input of the VCO. A second branch of the interposed circuit boosts low frequency signals and blocks high frequency signals recieved from the modulation source and passes such signal to the summing device where signals from the first and second branches are summed to permit wideband modulation of the VCO. All the modulation processing is performed outside the phase locked loop.

Pseudo-random signal synthesizer with smooth, flat power spectrum

Abstract: Apparatus and a method are disclosed for synthesizing a pseudorandom communications signal having a smooth, flat, power spectrum. The system comprises frequency modulation circuitry for deriving a first analog signal from a digital encoding signal. The first analog signal is derived to have a substantially constant amplitude and a frequency varying in response to the amplitude of the digital encoding signal. Fourier transform circuitry is connected to the modulation circuitry and is operative to derive a second analog signal from the first analog signal. The resulting second analog signal is the fourier transform of the first analog signal, having a substantially constant power spectral density over the bandwidth of said second analog signal, and having an amplitude that varies in response to the amplitude of the digital encoding signal.

Harmonic currents and torque pulsations with pulse width modulation methods in AC motor drives

Abstract: The pulse width modulation (PWM) method used in AC motor drives influences the harmonic current content and the torque pulsations. To investigate this, two PWM methods are compared by means of computer calculations and measurements on an 11 kW squirrel-caged induction motor fed by a transistor inverter. The investigated drive, with a deep-bar squirrel-caged standard induction machine which has frequency dependent rotor parameters, introduces some discrepancies between the measurements and the simulations. The PWM methods investigated are the natural sinusoidal modulation and the staircase modulation, which is a new uncomplicated and efficient modulation method. The same pulse number is used in both methods. To present a reference case, results with a quasi-square wave voltage are also being given.< >

Hybrid frequency shift keying modulator and method

Abstract: A hybrid frequency shift keying modulator and method produces binary FSK by simultaneously applying a digital modulating signal to the DDS section of a frequency synthesizer along with a coordinated analog modulating signal as direct frequency modulation of the accompanying PLL section. Low frequency performance is derived from the characteristics of the DDS modulation and the high frequency performance and accurate wave shape reproduction are derived from the modulation of the direct FM section.

Constant width pulse distribution in a digital to analog converter for serial digital data

Abstract: A digital-to-analog converter comprising: a distributing circuit (2, 3, 4, 5; 2, 13, 14-26) for distributing data pulses, which are bit-serially supplied at constant time intervals, into a plurality of routes and for providing them as pulses having a constant width; and a converting circuit (12) for adding together the pulses from the distributing circuit and thereby for converting them to an analog output. Such a circuit arrangement can provide pulses for conversion to analog form which all have an identical waveform and an identical area, and errors caused by the difference between the rise and fall times of the pulses can be eliminated and therefore D/A conversion characteristics can be improved.

Phase locked frequency synthesizer with single input gain compensated wideband modulation system

Abstract: Several embodiments are disclosed of a modulation equalization network associated with a phase locked loop to achieve frequency independent modulation of the VCO. The equalization network is disposed to introduce the modulation signal into the control loop ahead of the loop filter but after the phase detector output. The interposed equalization network requires only a single input port to achieve a flat modulation response thereby lending itself to a modular implementation. The modulation processing is performed totally outside the phase locked loop. The network serves to provide a boost to low frequency signals from the modulation source using an integrator network while providing a high frequency response that is essentially the inverse of the phase locked loop filter response.

Frequency counter for counting a frequency and partly varied frequencies of a signal in real time

Abstract: A frequency of a signal, particularly a frequency, partly varied as time passes, of a signal is counted in real time by producing a delay signal by delaying the signal as much as a predetermined time, detecting delayed zero-cross pulses from the delayed signal, detecting zero-cross pulses from the non-delayed signal, counting a first number of the delayed zero-cross pulses after the predetermined time is over, counting a second number of the zero-cross pulses during and after the predetermined time, producing a number difference between the first number and the second number by subtracting the first number from the second number and halving the number difference. The predetermined time is designated longer than a half period of the signal frequency to be counted. When the predetermined time is set long, the average frequency of the signal is counted, and when that is set short comparing with the partly varied interval of the signal frequency, the partly varied frequency of the signal is counted in real time.

A digital system for generating dynamic sinusoidal gas concentration signals

Abstract: A computer-controlled gas-mixing system is presented. It is capable of mixing four gases, the concentration of three of which will follow a path to be determined by the user. For our purposes the output O2 fraction is maintained constant and the levels of Ar and N2O vary sinusoidally and independently, with periods between 0.25 and 30 min. A fourth gas, N2 is necessary to make the sum of the individual fractions 100%. The system uses banks of between one and four solenoid valves each linked via a sonic choke to a common mixing chamber. A regime of pulse frequency modulation is employed. All calculations and timing of valve switching are performed by a dedicated microcomputer built for the purpose. The device has been used to provide respiratory gas forcing functions for a program of research in respiratory monitoring.

Principles of modulation

Abstract: This chapter discusses the principles of modulation. The process of modulation is that of modifying some feature of an otherwise regularly recurring quantity in accordance with the signal. Transmission then takes place by means of the modulated high-frequency wave. The high-frequency unmodulated wave is referred to as the carrier wave; after modulation, it is called a modulated carrier. If the carrier frequency is maintained constant and its amplitude is varied in accordance with the modulating signal, the carrier is amplitude modulated. If, on the other hand, the amplitude of the carrier is kept constant and its frequency is varied in accordance with the modulating signal, the carrier is frequency (or angle) modulated. In amplitude modulation, the amplitude of a high-frequency wave is varied in accordance with the signal to be transmitted. This variation may, in the most simple case (which is, in fact, a quite complicated case), consist of an on and off condition of the carrier, representing the transmission of a code such as Morse. In both amplitude and frequency modulation, the carrier wave is continuously present. There are the methods of modulation where the carrier wave is made discontinuous in the form of a train of rectangular pulses. The modulation process is then to vary some characteristic of the pulses in accordance with the modulating signal.

A constant frequency series-resonant DC-DC converter with PWM controlled output

Abstract: A converter composed of a pulsewidth-modulated (PWM) regulator and a resonant converter that operates at a constant frequency is proposed. The output voltage is regulated by a PWM control technique. In contrast to the usual frequency-control technique, this converter has relatively simple control circuits and high conversion efficiency. >

Arrangement for controlling the amplitude of an electric signal for a digital electronic apparatus and corresponding method of control

Abstract: The logical signal at acoustic frequency provided by a sound generator (17) is modulated in a coincidence circuit (25) by means of an ultrasonic signal, the duty-cycle of which can be varied by means of a program. More particularly, the modulating signal is generated by a cyclic counter (29). The duty-cycle is programmed by writing the corresponding numerical value to a register (31) with a capacity equal to that of the counter. An adder (36), adding the value of the counter each time to that of the register, generates a carry signal which gives consent to the acoustic signal only for a part of the relative cycle of the modulating signal. The modulated signal is applied via an amplified (20) to a loudspeaker (21) with a smoothing capacitor (22).

Harmonic analysis of PWM inverter modulation strategies

Abstract: This paper presents the harmonic analysis of various pulse width modulation strategies used for the DC-AC converters. An efficient harmonics computation algorithm for piecewise continuous periodic waveforms has been derived. Fourier coefficients of experimentally obtained waveforms or simulation results can be calculated efficiently. Harmonic performance analysis of natural sampling, modified subharmonic control, symmetric/asymmetric uniform, sinusoidal pulse width modulation, and pulse position modulation strategies have been studied. Results can be used as guidelines for the modulation strategies selection in the PWM inverter design.

A new 'slope-modulated' PWM strategy for implementation in a single chip gate array

Abstract: The task of designing a gate-array-based, dedicated, three-phase PWM (pulsewidth-modulated) modulator for electric drive control is addressed. A novel slope-modulated PWM strategy is presented. Sine-wave and square-wave signal references, under several operating modes, are used to demonstrate the modulation properties. Performance parameters, such as reliable inverter switching, minimum on/off times, peak inverter switching frequency, total harmonic distortion, and pulse dropping are described. The modulator is shown to generate high-resolution PWM waveforms, with excellent performance when a variable-frequency ratio strategy is used with a sine-wave reference signal. The square-wave reference signal uses less complex digital circuitry, with a reliable operation of the inverter bridge. >