Showing papers on "Pulse-frequency modulation published in 1982"

Encoding of rapid amplitude fluctuations by cochlear-nerve fibres in the guinea-pig

Abstract: Responses of cochlear nerve fibres in the guinea-pig were measured to sinusoidally amplitude-modulated tones at fibre characteristic frequency. The modulation depth was ± 3 dB and the modulation rate was varied between 6.25 and 6400 Hz keeping the mean level of the tone constant. The resultant period histogram (locked to the modulation cycle) was used to determine the depth of modulated neural discharge. The functions showing the variation of discharge modulation with modulation frequency were, in general, low-pass. The cut-off of these functions appears to be primarily determined by the filtering properties of the fibres.

An investigation into the origin of frequency sweeping in a hybrid TEA CO2 laser

Abstract: An analysis of the sources of the intrapulse frequency modulation in the hybrid TEA CO2 laser is presented. Two principal effects predominate: the falling frequency at the start of the pulse is shown to be due to plasma effects, while the increasing frequency during the remainder of the pulse arises from a laser induced refractive index perturbation. The significance of these results to the design of high stability pulsed lasers is discussed.

Optical phase modulation in an injection locked AlGaAs semiconductor laser

Abstract: Optical phase modulation by injecting coherent CW light into a directly frequency modulated semiconductor laser is reported. Phase modulation was obtained at up to 800 MHz modulation frequency without distortion for a 1.6 GHz full locking bandwidth. A static phase shift of π took place with a 0.48 mA bias current change in the injection locked laser. Experimental and theoretical results showed that the product of the normalised phase deviation by the frequency deviation and the cutoff modulation frequency is constant.

A Novel Three-Phase Reference Sine-Wave Generator for PWM Inverters

Abstract: A hybrid circuit for producing a three-phase reference sine wave required with PWM inverters is described in this paper. The principle of the circuit is simple and the implementation of the circuit is easy. The circuit has all the features discussed in the literature. The unit built has, apart from the three-phase sine waves, balanced three-phase square and triangular waves. A high-frequency triangular wave already available in the circuit can be used for the PWM control circuitry. The scheme can easily be extended to generate sine waves of any number of phases.

Gated asynchronous carrier modulation

Abstract: A motor pulse width modulation control technique employing gated asynchronous carrier modulation including establishing a repetitive modulation signal along with the generation of a carrier frequency signal at a frequency greater than the frequency of the modulation signal. The carrier frequency signal is gated at a gating rate less than the frequency of the carrier frequency signal so as to provide the gated carrier frequency signal. Means are provided for modulating the gated carrier frequency signal by the aforementioned repetitive modulation signal so as to provide cyclic pulse width modulation drive signal for motor control.

Fast frequency measuring system

Abstract: Disclosed is a high resolution frequency measuring system which uses a frequency counter for a coarse reading and a frequency to voltage converter for a vernier reading, which readings are combined. Two types of converters are disclosed. One embodiment comprises an input terminal for receiving an input signal frequency and a pulse shaper for converting the input signal to a first train of pulses. The pulses are applied to a delay means to produce a second train of pulses delayed with respect to the first train of pulses and the first and second trains of pulses are applied to first and second inputs of a phase detector, e.g. a flip-flop. In another embodiment, delayed and undelayed versions of the input signal are fed to separate pulse shapers and then to the inputs of the phase detector. The phase detector has an output connected to operate a switch between two voltage levels to produce a third train of pulses having a duty ratio depending on the phase difference between the first and second trains of pulses. The third train of pulses is time averaged to produce an output voltage, the output voltage being proportional to the phase difference between the first and second trains of pulses and varying with changes in the frequency of the input signal. An analog to digital converter converts the output voltage to a digital reading for combining with the output of the frequency counter. The invention provides a unique, fast frequency measuring system allowing high resolution, not obtainable with a counter.

Method of converting a digital signal into an analog signal and a converter therefor

Abstract: This invention relates to a method of converting a digital signal into an analog signal and a digital-to-analog converter therefor. In the invention, a digital signal having varying pulse width values is converted into a first pulse width signal, with each pulse varying in its pulse width in response to its respective data values and with the center of each pulse width being at a fixed time position within a respective sampling period, while a complement of the digital signal is converted into a second pulse width signal with each pulse varying in its pulse width in response to its respective data value and relative to said center of each respective pulse width. The first and second pulse width signals, after one of them is inverted, are mixed and pass through a smoothing filter to demodulate the digital signal into the analog signal.

Analog-to-digital converter for seismic exploration using delta modulation

Abstract: An analog-to-digital converter for use in seismic data processing applications is disclosed which features variants on delta modulation and delta-sigma modulation methods. A series of single bits is output by an analog-to-digital converter based on comparison of a predicted analog signal with the actual analog signal. A low pass filter and subsampling operation is applied to the output digital bits to provide digital words corresponding to the analog signal amplitude. Plural integrator stages are shown which allow reduction of quantization error.

Frequency modulation transmitter

Abstract: A frequency modulation transmitter has a frequency synthesizer (8) comprised of a voltage controlled oscillator (1) for operating a transmitter section (33) of the modulation transmitter. The output center frequency of the voltage controlled oscillator (1) is determined by channel designation information. The level of a modulation input signal (11) applied to the voltage controlled oscillator (1) for modulating the center frequency is changed in accordance with the channel designation information.

Property measuring apparatus for analog/digital converter

Abstract: PURPOSE:To examine a property of an A/D converter at a high frequency with the operation of a D/A converter in a high range of accuracy by feeding a high frequency test signal converted to a differential frequency between a test signal frequency and a clock signal frequency. CONSTITUTION:The waveform A is for a sine wave test signal Fs from a test signal generator 10 and the waveform B for a clock signal Fc=Fs-Fp from a frequency converter 20. An A/D converter 12 converts the test signal A to a digital signal each time the clock signal B is generated. This digital signal is converted to an analog signal C with a standard D/A converter 16. As the signal to be converted with the D/A converter 16 is low in the frequency, the converter 16 operates in a high range of accuracy even when the signal tested with the A/D converter 12 is a high frequency signal. Therefore, the property of the A/D converter 12 for any high frequency signal can be measured accurately with a measuring device 18.

Electronic musical instrument of frequency modulation tone synthesis type

Abstract: An electronic musical instrument using FM tone synthesis technology produces a musical tone signal e(t) expressed as e(t)=A·sin[ωct+I·sin ωmt], where A I, ωct and ωmt represent an amplitude information, a modulation index information, a carrier frequency information and a modulation frequency information, respectively. The carrier frequency information ωct and the modulation frequency information ωmt are related to a pitch of a depressed key of the electronic musical instrument. A modulation ratio controller is further provided in the instrument. The modulation ratio controller varies the modulation ratio ωc:ωm of the carrier frequency information ωct to the modulation frequency information ωmt in accordance with the pitch of the depressed key. Such a musical tone having different harmonic constructions according to the tone pitches as that of a pipe organ is implemented by this variation of the modulation ratio.

Output noise spectrum from demodulator in an optical PFM system

Abstract: An expression relating the input and output noise spectra of a PFM demodulator used in an optical transmission system has been derived and confirmed experimentally.

Refinements of the polar motion frequency modulation hypothesis

Abstract: In a previous paper (Carter, 1981) I suggested that the Chandler component of polar motion may be frequency modulated, as a function of the instantaneous polar motion magnitude. A composite of observational records compiled by S. C. Chandler and the International Latitude Service series suggests a variation in the magnitude at a frequency of approximately 0.0118 cycles per year (cpy). The spectrum produced by the resulting frequency modulation would depend on the modulation index. Comparison of spectra synthesized with various degrees of frequency modulation and those derived from observational data, suggest a frequency increase of 0.15 to 0.30 cpy/arc sec decrease in the polar motion magnitude. This degree of frequency modulation would cause ‘splitting’ of the Chandler component, producing dual spectral peaks at periods of 427 and 439 days, similar to that reported by several investigators beginning with Chandler (1901a, b).

Discrimination of modulation depth of SAM noise

Abstract: Difference limens (DLs) for modulation depth of sinusoidally amplitude modulated (SAM) wideband noise were measured as a function of the modulation depth of the standard, the frequency of modulation (25, 100, 400 Hz), and the spectrum level of the noise (0, 20, 40 dB SPL). Preliminary results for one subject show that psychometric functions are linear and parallel in Log d′ and 10 Log(m12 − m02), where m1 and m0 are the modulation depths of the variable and standard stimuli, respectively. In the main study, three subjects were tested using a 2IFC adaptive procedure. The DL [10 Log(m12 − m02)] is at, or slightly above, the modulation detection threshold when m0 is small. For m0 above modulation threshold, the DL is a positively accelerating function of 20 Log(m0). Weber's Law does not describe the discrimination of modulation depth over any appreciable range. Across all conditions, DLs tend to converge to values around −9 dB when the level of the standard is −5 dB (m0 = 56%) and generally cannot be measure...

Analog recording system

Abstract: An arrangement for recording an analog signal onto magnetic tape in which the analog signal modulates a square wave bias field by moving the negative-going transition of the square wave so that the average of the positive portion and negative portion of the square wave, equals the instantaneous value of the analog signal. The period of the total square wave, is maintained constant. The analog signal is compared to a periodic triangular-shaped wave, in a comparator, and the output of the comparator becomes switched in polarity whenever the analog modulating signal is equal in value to the instantaneous value of the triangular wave. The point at which polarity is switched corresponds to an intersection of the analog signal superimposed on the triangular wave. The resultant modulated square wave is applied to a recording head.

Vector summation power amplifier

Abstract: A time sequence of square waves is summed to provide minimum distortion h power voltage sinusoids. The phase difference of two identical sinusoids is varied to control the resultant summed amplitude. Amplitude modulation of the sum sinusoid is achieved through varying the phase relationship between the two identical sinusoids. Frequency and phase modulation is achieved through digital control of the individual square waves.

Simultaneous amplitude and angle modulation using detection of complex zeroes

Abstract: Modulation of a carrier signal using both amplitude and angle modulation increases the information capacity of transmission without increasing bandwidth. Complex zeros in an amplitude modulating signal are detected and a conjugation function dependent on the time of occurrence and imaginary root values of the zeros is generated. The conjugation function is inverted or not inverted in accordance with a binary data signal and used to control the frequency of an oscillator whose output is an angle modulated carrier signal which is then amplitude modulated. On reception the amplitude modulating signal is recovered by an envelope detector and the data signal by a phase locked loop.

Adjustable signal frequency limiting device - filters frequency transponder input signal and varies transponder modulation frequency to adjust limit frequency

Abstract: The device uses a variable modulation frequency (F) to provide a frequency transposed signal (f2) from the input signal (f1). The transposed signal (f2) is fed through a filter (FI1) to obtain a frequency limited signal (f3) before being fed to a further transporter (DM1) providing an output signal (f4) which comprises a frequency limited version of the input signal (f1). Pref. the modulation frequency (F) is higher than the highest frequency component in the input signal (f1), with the filter (FI1) eliminating the upper side band, the output signal (f4) being identical to the input signal (f1) except that the higher frequency components have been removed. The cut-off frequency for the device is easily adjusted by varying the modulation frequency.

Four-Level Pulse Width Modulation for Fiber Optic Communications

Abstract: The performance of a digital fiber optical system employing four-level pulse width modulation (PWM) is considered. It is shown that PWM may be an attractive alternative to pulse amplitude modulation (PAM), especially if a wide band channel is used. The probability density function (pdf) of the timing error is obtained in terms of the pdf of the noise amplitude, taking into account the thermal noise of the amplifier and the signal-dependent shot noise introduced by the photodiode detector. Near-Gaussian optical pulse edges at the receiver are assumed. Using typical system parameters, the variation of bit error rate (BER) with power level, and the effects of different bit rates, mean photodetector gain, and system bandwidths are calculated. It is observed that minimum BER's are achieved at moderate values of mean photodetector gain and that increased system bandwidth results in increased receiver sensitivity.

Sampling and Pulse Code Modulation

Abstract: In the previous three chapters, we have discussed the modulation of a sinusoidal carrier of a suitably high frequency by means of an analogue baseband-signal such as a speech or music waveform. The object of modulation was primarily to achieve a relocation of baseband information at a carrier frequency that was suitable for electromagnetic propagation.

Linear digital phase-locked loops using integrators in a pulse frequency-modulation system

Abstract: The conventional digital phase-locked loop (DPLL) has a number of problems which need to be solved: the pull-in and lock ranges are very restricted by the phase detector and are dependent on the noise bandwidth, and their operation is not linear. In the paper, DPLLs free from such disadvantages are proposed. These DPLLs are realised by a new method, i.e. by use of integrators in a pulse frequency-modulation system, and the higher-order DPLL is systematically designed by controlling the free-running frequency of one VCO with the error of the other DPLLs. The operation of the DPLL is similar to that of an analogue PLL (APLL). However, the former operates linearly in a wider region than does the latter; unlike the APLL, the pull-in and lock ranges of the first-order and imperfect second-order DPLL are the same as those of the perfect second- order APLL in the range from zero to almost the maximum frequency of the VCO and are independent of the noise bandwidth. Excellent agreement is obtained between theory and experiments.

Perpendicular magnetic recording of analog signals by means of pulse width modulation

Abstract: A pulse width modulation (PWM) recording, which effectively utilizes the perpendicular recording feature, is proposed to record analog signals on perpendicular media. Experimentally obtained PWM recording results showed a good linearity in a wide signal frequency range, even at high modulation levels. Frequency response curve for a double-layer (Co-Cr/Fe-Ni) medium differs from that for a single-layer (Co-Cr) medium. This difference is explained by the backlayer (Fe-Ni) flux-sink effect in the double-layer medium.

Correlation type flicker flamon

Abstract: A device and method is disclosed which determines the presence and absence of a burner flame by injecting a pressure modulated signal into the burner which modulates a flame at a selected frequency. Light emitted from the flame is modulated at the same frequency. An optical sensor is provided for sensing the light amplitude modulation frequency and connected to a correlator circuit for correlating the light amplitude modulation signal with the pressure modulation signal. If the signals correlate, a flame is assumed to be present and a flame on signal generated. The pressure modulation signal can be discontinued periodically. If a corresponding discontinuation of the light amplitude modulation signal is sensed this is indicative of the continued presence of the flame whereas a continuation of the light amplitude modulation signal indicates a flame out condition.

Micropower Pulse Frequency Modulator for Use in an Optically Isolated Catheter System

Abstract: A micropower pulse frequency modulator (PFM) has been developed for implementing an opticaily isolated system capable of making sensor voltage measurements. The PFM circuit is powered with an array of solar cells which converts light energy into electrical energy. An input port receives the sensor voltage. The PFM signal generated by the circuit drives an infrared emitting diode which provides the frequency-modulated output signal. The PFM circuit can accept sensor output voltages in the range ±500 mV and has a minimum bandwidth of 500Hz.

Video signal modulation circuit

Abstract: PURPOSE:To improve the general purpose properties of an RF modulator IC and to obtain inexpensive product, by adjusting externally the modulation of a video mdulation circuit of a VTR, so as to cope easily with different modulating modes such as positive and negative modulation CONSTITUTION:A video signal is clamped to a sink chip level at a clamp circuit 4 and applied to a base of a transistor (TR)8 of a balanced modulation circuit 6 A bias input voltage determined by a position of a variable terminal of a variable resistor 24 is impressed to the base of a TR10 When a carrier input is given from a signal source 33 between a base of TRs 26, 32 and a base of TRs 28, 30, a modulation output having a modulation determined by said bias input is extracted from a terminal 38 The output having a desired modulation is obtained by changing the variable resistor 24

Demodulator for frequency modulated signal accompanied by reference signal

Abstract: The demodulator is especially adapted for a data signal (F'c) that was recorded on tape in the form of a frequency modulated signal together with a reference signal (F'R) of frequency greater than the greatest frequency of the data signal, so that both signals are subject to the same proportional frequency errors. During each cycle of the data signal, a representation of the period of one cycle of the reference signal is measured and stored. Then at the end of each following cycle of the data signal, there is produced a pulse of area dependent on the representation. A filter (LPF) produces a signal representing the area of each pulse averaged over one cycle of the data signal.