Showing papers on "Pulse-frequency modulation published in 1995"

Voltage regulator that operates in either PWM or PFM mode

Abstract: A switching voltage regulator achieves high efficiency by automatically switching between a pulse frequency modulation (PFM) mode and a pulse-width modulation (PWM) mode. Switching between the modes of voltage regulation is accomplished by monitoring the output voltage and the output current, wherein the regulator operates in PFM mode at small output currents and in PWM mode at moderate to large output currents. PFM mode maintains a constant output voltage by forcing the switching device to skip cycles when the output voltage exceeds its nominal value. In PWM mode, a PWM signal having a variable duty cycle controls the switching device. A constant output voltage is maintained by feedback circuitry which alters the duty cycle of the PWM signal according to fluctuations in the output voltage.

A communication scheme for analog VLSI perceptive systems

Abstract: A communication architecture tailored for analog VLSI perceptive systems is proposed. Information is generated on a transmitter array of cells each driving a pulse generator. The resulting pulse-frequency modulated signals are transmitted through the nonarbitered, asynchronous access of pulses to a common bus. Pulses are decoded and accumulated in a receiver chip and the mapping of the activity distribution of the transmitter onto the receiver is achieved. One possible implementation of these principles is presented. The circuit description of all blocks is given and experimental results are shown: they satisfactorily support the theoretical basis upon which the system was constructed. Extensions to the communication architecture are finally presented. >

Frequency conversion circuit and radio communication apparatus with the same

Abstract: A frequency conversion apparatus comprising a sampling circuit for receiving a first intermediate frequency signal extracted from an input signal and having a predetermined intermediate frequency and a predetermined band width and sampling the first intermediate frequency signal in accordance with a predetermined sampling frequency signal, to output a second intermediate frequency signal, and a sampling signal generator for outputting the sampling frequency signal to the sampling circuit, the sampling frequency signal having a frequency determined so that an integer multiple of not less than three times the sampling frequency is outside a frequency range of the input signal.

Effects of carrier frequency, modulation rate, and modulation waveform on the detection of modulation and the discrimination of modulation type (amplitude modulation versus frequency modulation).

Abstract: Initially, psychometric functions were measured for the detection of amplitude modulation (AM) or frequency modulation (FM), using a two-alternative forced-choice (2AFC) task. Carrier frequencies were 125, 1000, and 6000 Hz, and modulation rates were 2, 5, and 10 Hz. For the two lower carrier frequencies, FM detection tended to be best at the lowest modulation rate while AM detection was best at the highest rate. For the 6000-Hz carrier, both AM and FM detection tended to be poorest at the lowest modulation rate. Then, pairs of values of AM and FM were selected that would be equally detectable, and psychometric functions were measured for the discrimination of AM from FM, again in a 2AFC task. For carrier frequencies of 125 and 1000 Hz, the ability to discriminate AM from FM was always poorest at the highest modulation rate (10 Hz); at this rate some subjects were essentially unable to discriminate AM from FM when the detectability of the modulation was relatively low (d' of 1.16 and below). For a modulation rate of 2 Hz, and when the detectability of the modulation was moderate (d' up to about 2), some subjects discriminated the type of modulation rate varied across subjects, but there was still a trend for poorer discrimination of modulation type at the highest modulation rate. It is suggested that FM detection at a 10-Hz modulation rate is based largely on changes in excitation level for all carrier frequencies. For a 2-Hz modulation rate, and for the two lowest carrier frequencies, an extra mechanism, possibly based on phase locking, may play a role in the detection and discrimination of FM. This mechanism may be ineffective at modulation rates above about 5 Hz because the stimuli spend insufficient time at frequency extremes. To check on this, psychometric functions were measured for the detection of FM and AM using quasitrapezoidal modulation with a rate of five periods per second and carriers of 250, 1000, and 6000 Hz. This produced improvements in performance relative to that obtained with 5-Hz sinusoidal modulation and, for the two lower carrier frequencies only, the improvements were markedly greater for FM than for AM detection. This is consistent with the idea that the use of of phase-locking information depends on the time that the stimuli spend at frequency extremes.

Tunable Multiterahertz Beat Signal Generation from a Two-wavelength Laser-diode Array

Abstract: We report, for the first time to our knowledge, generation of a tunable miltiterahertz modulation signal on an optical carrier directly from a single laser source The modulation frequency, which can be tuned from 015 THz to more than 7 THz, is the beat note obtained by varying the spectral separation between the coaxial two-color output of a two-wavelength laser-diode array from 032 to 17 nm The frequency characteristics of the terahertz beat note are determined with a noncollinear intensity autocorrelator

Instantaneous frequency and time-frequency distributions

Abstract: It is generally stated that the conditional mean frequency of a time-frequency distribution (TFD) should equal the instantaneous frequency of the signal. The commonly accepted definition of instantaneous frequency as the derivative of the phase of the analytic signal sometimes leads to curious results. Although it is commonly held that positivity of the TFD and satisfaction of the so-called "instantaneous frequency constraint" are generally incompatible, we show that one can always find a complex signal, the real part of which is the given signal, for which the derivative of the phase is consistent with the marginals and positivity. Furthermore, for the cases considered, the derivative of the phase of this signal, which by design equals the conditional mean frequency of a positive TFD, is a reasonable, readily interpretable choice for instantaneous frequency.

Recovery of data from amplitude modulated signals with self-coherent demodulation

Abstract: A demodulation system extracts data from an input amplitude modulated signal electromagnetic wave with a signal multiplying means that has two input terminals both of which are coupled to receive the input amplitude modulated signal. An output terminal of the multiplying means provides an output signal which is the instantaneous square of the input amplitude modulated signal. A lowpass filter is coupled to the output terminal of the signal multiplying means to reject at least twice the carrier frequency 2(ωc) and higher frequency components, and to pass the second harmonic and lower frequencies of the modulation signal 2(ωm(max)) to provide a filtered signal that is representative of the square of the amplitude modulation of the input signal. This demodulation method approaches ideal square law detection with power measurement of the input amplitude modulated signal. The filtered signal is supplied to an analog-to-digital converter to supply a digital data output. The signal may optionally be coupled from the lowpass filter through a square root circuit.

Use of a chopper and a sigma-delta modulator for downconverting and digitizing an analog signal including information modulated by a carrier

Abstract: To demodulate an analog signal having information modulated by a carrier, the analog signal is chopped by a chopper, the chopped signal is digitized by a sigma-delta analog-to-digital converter to produce a series of digital samples at a sampling frequency, the digital samples are filtered in a digital decimating filter to produce data words, and the data words are modulated by an intermediate frequency signal to produce a detected information signal. The various frequency signals are generated by a phase-lock loop so that the intermediate frequency is the difference between the carrier frequency and the chopping frequency, and both the chopping frequency and the intermediate frequency are sub-multiples of the sampling frequency. Therefore aliases and artifacts caused by the chopper are either cancelled or fall on multiples of the output sampling frequency, and the intermediate frequency signal can be a square wave without generating artifacts that need be removed by filtering of the detected information signal. Preferably the chopper is placed in an analog portion of a feedback loop of the sigma-delta modulator, and an exclusive-OR gate is placed in the digital portion of the feedback loop, so that the gain of the demodulation process becomes independent of the gain of the chopper. The detection process is especially suited for detecting an angular-rate signal from a vibrating quartz angular rate sensor, because the detection process has very high accuracy, resolution, and linearity.

High frequency sinusoidal generation using delta-sigma modulation techniques

Abstract: An analog sine wave generator based on a digital resonator and a bandpass delta-sigma (/spl Delta//spl Sigma/) modulator is presented Except for a 1-bit D/A, this design is entirely digital allowing precise control over the amplitude and frequency of oscillation Furthermore, it is area efficient as it does not require a ROM or a multiplier Unlike previous designs, this circuit is capable of operating at any ratio of the clock frequency We envision that this device will be used in communications circuits or as a test stimulus for mixed-signal ICs

Digital signal modulation analysis device

Abstract: A digital signal modulation analysis device is to shorten the time for modulation analysis, and at the same time to structure a measurement device that is small in scale and inexpensive. A digital signal modulation analysis device includes a frequency converter which converts a signal from a device under test to a first intermediate frequency signal, a sampling part which converts the first intermediate frequency signal to a second intermediate-frequency signal whose frequency is lower than that of the first intermediate frequency to store the second intermediate frequency signal in a memory, a Hilbert converter which converts an incoming signal into orthogonal component signals through a quadrant-modulate detection process, an initial synchronization part which determines a carrier center frequency, a symbol-demodulation/parameter-estimation part which determines optimal parameters to minimize a modulation error and demodulates all symbol data to determine reference data for the all symbol data, and a modulation-precision calculation component which calculates modulation-precision data and modulation-error data for each symbol.

Method for investigating a scattering medium with intensity-modulated light

Abstract: The invention concerns a method for investigating a scattering medium, especially a biological matrix, with intensity-modulated light. In order, in such a frequency-domain measuring procedure, to reduce the expenditure on electronics without restricting accuracy of measurement, a method is proposed, in which, in order to investigate a scattering medium, especially a biological matrix, with intensity-modulated light, a high-frequency modulation signal is generated by a frequency generator (18), the intensity of a light emitter (10) is modulated with a modulation signal and the light from the light emitter (10) is radiated into the medium, the modulation signal includes frequency chirps during which the modulation frequency is tuned from an initial frequency to a final frequency, the modulation signal is delivered from the frequency generator (18) via at least two different signal paths (23A, 24) to a signal mixer (31), so that during a frequency chirp the input signals of the signal mixer (31) differ by a differential frequency whose magnitude is a function of the difference between the signal transit times over the at least two signal paths (23A, 24) and of the rate of change of the modulation frequency, wherein at least one of the signal paths includes a light path section (20A) passing through the medium as a measurement signal path (23A), and the output signal of the signal mixer (31) is further processed to produce information relating to the scattering medium (FIG. 2).

Random carrier frequency modulation of PWM waveforms to ease EMC problems in switched mode power supplies

Abstract: Electromagnetic compatibility (EMC) remains an issue which can present many problems to designers of high frequency power converter circuits. Usual techniques for alleviating the problems of interference generation by power converters involve the use of screening materials and filters. However, the effectiveness of such measures depends on the frequency of the interference and the power density at each frequency of interest. As pulse width modulation (PWM) generates high frequency harmonics at multiples of the switching frequency, modulation of the switching frequency may be used to spread the spectral power density present at these harmonic frequencies. This paper presents a technique of frequency-hopping spread-spectrum modulation which may be applied to switched-mode power converters to reduce the spectral power density at harmonics of the switching frequency. The influence of the peak frequency deviation and the modulation sequence length on the resultant spectrum are discussed. These predictions have been broadly confirmed in practice. >

Detection of sinusoidal amplitude modulation at unexpected rates

Abstract: The detectability of sinusoidal amplitude modulation at unexpected modulation rates was assessed using a probe-signal method. With this method, three listeners were led to expect a target modulation rate (4, 32, or 256 Hz) by presenting the signal most often at that rate, and sensitivity to modulation at six other unexpected rates between 4 and 256 Hz was measured via occasionally presented probe modulation rates. The modulation phase was random on each two-interval forced-choice trial and the overall level of the 500-ms broadband carrier was randomly varied between 55 and 75 dB SPL across intervals. The modulation depth at each rate was set so that the modulation was detected on about 90% of the trials when only that rate was presented. Performance at the unexpected rates depended upon the target rate. For the 4-Hz target, modulation at all rates was detected on about 80% of the trials. For the 32- and 256-Hz targets, unexpected modulation rates of 16 Hz and above were detected on 80%–90% of the trials, but modulation rates below 16 Hz were detected nearly at chance. The influence of expectation of modulation rate on the detection of sinusoidal amplitude modulation is not readily predicted by current models of modulation detection.

Apparatus and method for optically transmitting electrical signals in the 20-300 gigahertz frequency range

Abstract: The invention discloses a method and an apparatus for optically transmitting a narrow-band optical signal beam having a sub-carrier frequency in the 20 to 300 GHz range. The apparatus has a semiconductor laser with a lasing cavity of length L. The length L preferably ranges from less than 1 mm to 10 mm, thereby defining the round-trip resonance frequency according to the following equation c/2 nL. The apparatus has a signal source for generating an electrical modulating signal having a modulation frequency contained in a narrow band containing the round-trip resonance frequency. An in-coupling means delivers the electrical modulating signal to the semiconductor laser which produces a sub-carrier modulated signal beam whose sub-carrier modulation frequency lies within a response band and corresponds to the modulation frequency. The apparatus further includes a biasing device for providing a biasing voltage for tuning the response band and the sub-carrier modulated signal beam. According to the method of the invention the biasing voltage is used to set the width of the response band and to set a phase shift in the sub-carrier modulated optical signal beam. Varying the biasing voltage thus allows to phase-modulate the sub-carrier modulated optical signal beam.

Compensation of NRZ signal distortion by initial frequency shifting

Abstract: The authors derive an analytical condition for the compensation of the distortion of an intensity-modulated square pulse in a nonlinear dispersive fibre link by means of initial periodic frequency modulation. We confirm the validity of the method by means of numerical simulations.

Statistical properties of the spectrum of light pulses in fast pseudorandom word modulation of a single-mode semiconductor laser

Abstract: The spectrum of single-mode laser pulses generated by fast pseudorandom word modulation is studied numerically for return-to-zero and nonreturn-to-zero control signals. We analyze both statistics and the worst cases for the frequency chirp during each optical pulse, and we study the connection between these frequency chirps and the turn-on times. We show that patterns in the modulation signal sequences contribute to chirp noise. The worst case values of the turn-on time and the chirp range are very similar in the two modulation schemes, hence, the optimum choice depends mainly on the characteristics of the decision circuit and on the driver and detector bandwidths. >

Method for correcting distortion of modulation wave and transmitter

Abstract: PURPOSE: To correct the distortion of a modulation wave. CONSTITUTION: A signal processing section 3 applies digital signal processing to transmission information to provide the output of two couples of base band signals, a quadrature modulation section 7 converts a carrier into two signals with a prescribed phase difference and they are respectively multiplied with a couple of the above base band signals and the products are added and a modulation wave is outputted. In this case, a branching section 4 provided between the quadrature modulation section 7 and an output section 5 provides properly a modulation wave outputted from the quadrature modulation section 7 to the output section 5 and a detection section 6. Then the detection section 6 detects the modulation wave to provide the output of an envelope signal being a signal of the envelope of the modulation wave and a control section 32 provides the output of a distortion correction signal to a signal processing section 3 so as to minimize the amplitude fluctuation of the envelope signal thereby correcting distortion of the modulation wave.

Phase modulator capable of individually defining modulation degree and modulation frequency

Abstract: An FM signal generator generates an FM signal obtained by frequency-modulating a reference frequency signal with a modulating frequency signal. A first mixer mixes the FM signal and an input signal having a predetermined carrier frequency and outputs a pair of frequency signals having sum and difference frequencies thereof. A first signal extracting unit extracts one of the pair of frequency signals as an intermediate frequency signal. A delay circuit delays the extracted intermediate frequency signal by a predetermined time. A second mixer mixes the delayed intermediate frequency signal and the FM signal and outputs a pair of frequency signals having sum and difference frequencies. A second signal extracting unit extracts the frequency signal of the pair of frequency signals which corresponds to the carrier frequency component as a phase-modulated signal. The modulation degree and modulation frequency in phase modulation for the phase-modulated signal can be set in wide ranges.

The response of nonlinear systems to modulated high-frequency input

Abstract: We study the response of a single-degree-of-freedom system with cubic nonlinearities to an amplitude-modulated excitation whose carrier frequency is much higher than the natural frequency of the system. The only restriction on the amplitude modulation is that it contain frequencies much lower than the carrier frequency of the excitation. We apply the theory to different types of amplitude modulation and find that resonant excitation of the system may occur under some conditions.

Device for continuous phase modulation by frequency synthesizer with phase-locked loop

Abstract: Device for continuous phase modulation, produced from a frequency synthesizer including a variable oscillator and a phase-locked loop with, in series, a frequency division circuit, a phase comparator and a low-pass filter. In order to reduce modulation in the loop, the modulation is applied not only to the input of the synthesizer but also, in compensation, in the loop. In order to eliminate the modulation residue in the loop, a control signal for the oscillator is derived by a circuit which performs a correlation between the residue of the modulation and the output signal from a filter producing the same filtering effect as the loop, and which receives the modulation signal from the input of the synthesizer.

Reducing the effect of interrogation phase noise on the frequency stability in passive frequency standards: experimental results and new investigation means

Abstract: It is known that the local oscillator phase noise limits the frequency stability in passive frequency standards. When the probe signal is permanently applied to the atomic resonator, this limitation is due to an intermodulation effect. We have established that, with a square wave frequency modulation, a proper signal processing using a notch filter in the synthesis chain and a peculiar demodulation waveform significantly reduces the limiting effect. Experimental tests confirm the optimization of the performance by the theoretical demodulation waveforms. The previous State of the Art is improved by a factor of 4.5. At last, in order to determine the optimum signal processing for different modulation conditions, we have realized an automatic system. It compares the frequency stabilities obtained for various signal processing conditions, it increases the number of harmonics involved in the demodulation and changes their rates. This system makes it possible to determine the minimum limiting effect on frequency stability, in passive frequency standards where atoms have a permanent interaction with the probe signal.

Super-resonant converter with switched resonant inductor with PFM-PWM control

Abstract: The efficiency of the series-resonant power converters is proved to increase with the improvement of the current form factor of the resonant current. The application of "soft-switching" reduces the switching losses. The maximum value for the pulse frequency in a super-resonant converter is limited by the introduction of a method of pulse width modulation. To improve the current form factor a second inductance is placed in the output side of the converter. This inductance is alternately included in the resonant circuit. The paper offers graphical presentation of the characteristics made to select the choice of the best suitable relationship between the resonant and output inductances and to support the design. The role of the parasitic elements of a transformer is specified. >

Laser intensity modulation as a clipped Gaussian process

Abstract: An attractive application of lightwave technology is cable television (CATV) transmission. In an important lightwave application known as subcarrier multiplexing, a broadband analog signal, consisting of the sum of amplitude modulated subcarriers, is used to intensity modulate a laser to produce an optical signal for transmission by optical fiber. It has been determined that the large negative excursions of the broadband signal lead to nonlinear distortion of the optical signal which also distorts the information bearing modulation on the subcarriers. The purpose of this paper is to present a general result concerning the average power of a clipped Gaussian process and apply this result to analyze the nonlinear distortion resulting from intensity modulation of a laser. In particular, a general formula for computing the average power of a stationary Gaussian process that is clipped at two arbitrary levels is applied to develop an approximation for the carrier-to-nonlinear distortion ratio (C/NLD) per channel as a function of the dynamic range of the clipping levels of the broadband analog signal, and the total RMS modulation index /spl mu/. 2/spl mu//sup 2/ equals the product of the number of channels being multiplexed and the square of the optical modulation index per channel. The approximation stems from an exact result and is especially useful because the conservative version of the approximation is independent of the bandwidth or spectral location of the broadband analog signal. Results are presented in graphical form and they are in reasonable agreement with earlier theoretical and experimental works. >

A 12-transistor PFM demodulator for analog neural networks communication

Abstract: Pulse frequency modulation (PFM) provides robust long-distance communication and event-driven access to the communication channel. A PFM demodulator small and simple enough to equip every cell of a large analog neural network is analyzed. The circuit can demodulate PFM signals with pulse rates as low as 1 kHz using the switched-capacitor technique. Measurement results from integrated demodulators are presented. >

A mathematical model of myoelectric signals obtained during locomotion

Abstract: An analytical expression for the myoelectric signal was derived using the integral pulse frequency and amplitude modulation (IPFAM) approach. The results indicate that, in the frequency domain, the general envelope of the EMG spectrum is affected primarily by the motor unit action potential (MUAP) and its interaction with the pulse amplitude modulation (PAM) and pulse frequency modulation (PFM) processes. Furthermore, the component associated with force modulation co-exists at its modulating frequency with factors related to the MUAP. Therefore, the conventional low-pass filtering is not adequate for reconstructing dynamic muscular force signals from nonstationary myoelectric signals obtained during locomotion.

Modulation amplification system

Abstract: PURPOSE: To amplify an amplitude-modulating signal without distortion by using a power amplifier which has amplitude distortion by converting an inputted digital signal into plural phase-modulating signals, and amplifying and adding the respective output signals together. CONSTITUTION: The 4-bit digital signal inputted from an input terminal 100 is converted by a modulating signal generator 110 into the four phase signals. Respective modulators 120-123 impose phase modulation on the basis of the signals outputted by the modulating signal generator 110. Even when input/ output characteristics of the amplifier 130 are nonlinear, the input signal to the amplifier 130 shifts only in phase and is constant in amplitude, so distortion originating from the nonlinear characteristics never appears. Further, the phase modulation is imposed by the modulators 120-123, so the frequency spectrum of a modulated signal is wider than the frequency spectrum of an input signal, but the phase shift by the modulation is <=±45 deg., so the spread of the spectrum can nearly be ignored and then nearly the same frequency characteristics with linear modulation can be obtained.

Digital pulse interval and width modulation for optical fiber communications

Abstract: This paper investigates the implementation of a new digital pulse time modulation technique based on digital pulse interval and width modulation scheme. Original expressions are presented for power spectral density, code characterization and channel capacity, illustrating the advantages of this technique compared with conventional pulse code modulation. Both theoretical and practical results are given showing close agreement.

Radar apparatus for detecting distance and speed

Abstract: PROBLEM TO BE SOLVED: To detect a distance to a target object and a relative speed even with limited transmission power by removing an FM-AM (re-) conversion noise effectively with a simple structure. SOLUTION: This radar apparatus has a transmitting system to transmit a signal frequency modulated by a signal for modulation with a specified repeated frequency and a receiving system to receive a reflection wave signal as obtained when the modulation signal transmitted from the transmitting system is reflected on a target object 5 while mixing the reflection wave signal and the transmitted modulation signal from the transmitting system to detect a beat wave signal. A highpass filter 6 is provided to interrupt a signal having a modulation frequency component below a specified order modulation frequency component of the transmitted modulation signal for the beat wave signal detected in the receiving system and a distance/speed computation processing section 7 to determine a distance to the target object 5 and the relative speed by computation based on frequency information in the beat wave signal filtered by the high pass filter 6.