Showing papers on "Digital signal published in 1982"

AC-DC Converter having an improved power factor

Abstract: An AC to DC converter utilizes a first power converter for converting an AC signal to a DC signal under the control of a control signal. The control signal is generated by a control circuit that includes a first analog generator that provides a first signal that is analogous to the voltage of the AC signal that is to be converted. A second analog generator generates a second signal that is analogous to the current of the AC signal that is to be converted and a third analog generator generates a third signal that is analogous to the voltage of the DC output signal. The third signal and the first signal are multiplied together to obtain a fourth signal. The control signal is generated from the fourth signal and the second signal and is used to control the power converter such that the waveform of the current of the AC signal is limited to a sinusoidal waveform of the same frequency and phase as the AC signal.

State of charge indicator

Abstract: A method and apparatus for producing a visual signal of the state of charge of a battery selectively connected and disconnected from an external load. A test load is connected to the battery for a predetermined period of time to draw a current pulse from the battery when the battery is disconnected from the external load. Simultaneously, the voltage of the battery is measured. The measured voltage is converted to a digital signal, and the digital signal is transmitted to a storage means. The stored signal is then transmitted to a visual display device.

Digital radio system

Abstract: Frequency diversity is employed to counter selective fadings as a result of multi-path propagation for troposcatter and short-wave connections for digital useful signals employing frequency modulation. For this purpose, the digital useful signal is supported on a frequency arrangement comprising at least three radio frequencies in that the digital useful signal, together with at least one additional oscillation, and, in fact, an additional fundamental oscillation which determines the frequency of the spacing in radio-frequency frequency arrangement, is fed to the input of a frequency modulator. At the input end, the radio-frequency carriers of the frequency arrangement, which are each modulated with the useful signal, are all converted by coherent mixing into the same frequency level, from which, by way of a combiner, a sum signal is obtained which is the optimum in respect of signal-to-noise ratio.

Power-line baseband communication system

Abstract: A communication system for transmitting baseband digital signals (16) on an electrical power line (12). A pulse generator (14) produces digital signals which are limited to a frequency spectrum of 30 kHz to 300 kHz and applied directly, i.e., without modulation, to an electrical power line. At the receiving terminal (25) an amplifier (32) compensates for attenuation characteristics of the electrical power line and the received signal is then sampled (34) to extract the information from it. To avoid interference when both a transmitting and receiving link are located at a substation, the baseband system incorporates a mimic network to mimic the interference signal erroneously picked up by the receiving link from the transmitting link located at the same substation. The mimic signal is then subtracted from the interference signal to neutralize the effect of the latter. When both a baseband digital communication system and a carrier communication system utilize the same electrical power lines, provision is made for interrupting the baseband digital signal to allow communications via the carrier system.

Signal sampling system

Abstract: A signal sampling system includes a combined digital and analog acquisition time base for accurately sampling and displaying an extremely short duration electrical event superimposed on a long time duration signal. The signal sampling system of the present invention is intended for use in stimulus-response situations, and both stimulus and response signals are synchronized with the clock of the digital portion of the time base. The system may be operated under microprocessor control, providing both flexibility and programmability, in turn permitting not only acquisition of waveforms that start and stop at arbitrary points with extreme precision, but signal averaging or smoothing as well.

Analog and digital signal apparatus

Abstract: In order to reduce the effect of modulation of the quantizing error (noise) by the signal in an adaptive digital audio system and to increase the dynamic range of the system, the adaptive analog to digital converter is preceded by a frequency dependent network that changes the shape of its characteristic in response to a control signal. The control signal is derived from the variable scaling factor in the adaptive converter. After transmission via a transmission channel or record/playback process, complementary operations are performed by a digital to analog converter followed by a further frequency dependent variable response network.

Enhanced delta modulation encoder

Abstract: An improved analog-to-digital encoder comprising an enhanced delta modulation encoder. The enhanced delta modulation encoder includes a spectrum tilter, a 1 bit analog-to-digital converter, a sampling circuit and an internal decoder. An analog input signal and an internal analog signal from the internal decoder are summed to provide an analog dither which is essentially an internal error signal. The analog dither signal is tilted by the spectrum tilter and is provided to the 1 bit analog-to-digital converter which generates a digital signal. The sampling circuit receives the digital signal from the analog-to-digital converter and generates a digital output which is fed back to the internal decoder. The spectrum tilter comprises at least three integrator circuits and a clipping circuit connected in parallel to two of the three integrator circuits. The three integrator circuits tilt the frequency spectrum of noise above the maximum frequency of interest, and the clipping circuit prevents the encoder from becoming unstable. A digital filter may be connected to the output of the sampling circuit in order to filter the digital output to make it compatible with systems commonly employed to process the digital output.

Constrained adaptive equalizer

Abstract: Disclosed is a constrained adaptive equalizer (10) for use in a digital communication system receiver combining transversal and decision feedback equalization techniques. The constrained adaptive equalizer (10) uses a constraint on the taps of the transversal section (13) of the equalizer which has both leading and lagging taps. These constraints force the transversal equalizer (13) to correct only the leading echoes of a received digital signal (12) in a communication system and treat them as if they resulted only from phase distortion. The constrained adaptive equalizer (10) provides a means for equalization that minimizes noise amplification while reducing inter-symbol interference. The transversal segment (13) of the constrained adaptive equalizer (10) approximate the phase equalizer by constraining its multiplying coefficients in accordance with the symmetry of the differential delay characteristic of the transmission medium around a signal carrier frequency. This constrained transversal decision feedback equalizer combination can be used for either passband or baseband equalization and for either complex signals, such as CAM signals, or real signals, such as baseband single side band signal.

Optimal Detection of Digitally Modulated Signals

Abstract: In this paper optimal detectors are derived and analyzed for the general class of digitally modulated signals in which the sequence of symbols is unknown a priori and information data are not of interest. The detectors test the signal present condition in background white Gaussian noise versus the null condition of noise alone. Particular attention is focused upon cases in which the SNR per symbol is low compared to unity. The models employed herein are sufficiently general to include most forms of spread-spectrum signals as well as other digital type communication signals.

Two wire voice and data subscriber loop

Abstract: A circuit for transmitting both voice and data at the same time between a subscriber's set and a switching exchange via a bidirectional two wire link The invention is comprised of a subscriber's set adapted to generate and receive baseband voice signals and data signals, a circuit for 100% amplitude modulating the generated data signal on a carrier signal having its lowest sideband after filtering above the voice signal base band, a circuit for applying the voice signals and modulated carrier to a two-wire subscriber's line, a circuit for separating the voice signals and modulated carrier, and a circuit for demodulating the digital signal and applying the digital signal to control circuits of a switching exchange Voice signals are applied to voice handling circuits such as the voice switching circuits of the switching machine

Apparatus for detecting pick-up at a remote telephone set

Abstract: An improved combination of a hardware and digital signal processing filter for detecting pick-up of a telephone call, solely through audio information on the telephone line, is disclosed. The apparatus employs a high gain band pass filter (28) with no automatic gain control, the output of which goes to a window comparator (30). The output from the window comparator (31) goes to a digital high pass filter (32) and from there to an integrator 37 for providing a digital output signal (40) indicative of the presence or absence on the telephone line of a signal exceeding a predetermined magnitude within the filter pass band. The digital signal is then processed by an intelligent digital filter having a set of predetermined threshold values of durations for states of the digital output signal, by which determinations of pick-up are made. The digital filter is adaptive and learns the durations high and low states of the digital output signal as they occur, subsequently checking for deviations from previously learned valid values. The digital filter includes a digital phase lock loop which will lock onto a periodic but asymmetric pattern in the digital output signal and declare pick-up when lock is lost.

Digital to analog converter

Abstract: A digital to analog converter having an improved conversion linearity is disclosed The digital to analog converter comprises means for receiving an input digital signal (1), means for dividing the first digital signal to a plurality of digital signals (2, 3), a plurality of conversion means (8, 9) for converting the divided digital signals to analog signals, respectively, and means (10) for summing the analog signals to produce a summed analog signal corresponding to the input digital signal

A microcomputer with digital signal processing capability

Abstract: A single microcomputer for realtime digital signal processing and high-speed controller applications, with a 200ns instruction cycle, 16 × 16 parallel multiplier, 32b arithmetic unit, 144 by 16 data memory, a 1536 by 16 program and coefficient memory, will be discussed.

Digital signal transmission system

Abstract: A signal transmission system which allows digital signals to be transmitted over twisted pair transmission lines. Master and slave transmission circuits are located at the switching system and terminal ends, respectively, of the transmission line. Both circuits include transmit and receive circuitry. The transmit circuitry includes a summing circuit connected to a constant current generator and the receive circuit includes an adaptive equalization/automatic gain control circuit connected between a differential amplifier and a slicer circuit.

Digital loop transceiver having a power up/down circuit

Abstract: In a digital telephone system, a digital private automatic branch exchange (PABX) has a plurality of digital line cards for coupling the PABX to respective digital subscriber sets via subscriber lines. In each digital line card, a digital loop transceiver operates in a master mode to couple the digital data bus of the PABX to the subscriber line via a subscriber line interface circuit in response to control signals provided by the PABX on the control bus thereof. In each digital subscriber set, a digital loop transceiver operates in a slave mode to couple the subscriber set to the subscriber line via a subscriber line interface circuit and to provide the several control signals required by the other components thereof. The digital loop transceivers may provide communication on each of two communication channels, with the digital data words of the first channel being treated the same as the digital data words of the second channel. In each digital loop transceiver, a power up/ power down circuit powers down all circuitry associated with each digital loop transceiver except for enough circuitry to detect an incoming data burst. Power up of each digital loop transceiver is accomplished via a power control portion which controls a data transmission controller in response to a detect signal and a power enable signal. A data control portion controls the transmission of bursted data to guarantee the avoidance of data collisions in a two-wire full duplex communication system.

Direct digital loudspeaker

Abstract: A method of and apparatus for converting a digital signal to sound, the digital signal being encoded in a sequence of code words at a signal encoding frequency, the code words representing the analog sound pressure of an original audio signal, with decoding of the digital signal occurring after electro-acoustic transduction through mechanical rectification and characteristics of a listener's ear, includes utilizing a plurality of substantially identical sound pressure generating elements each having an individual driver associated therewith, and selectively energizing the drivers in a pulsed manner at the signal encoding frequency in combination in response to a respective order of the bits of each code word of a digital signal from a most significant bit to a least significant bit. The sum of the air pressures produced by the sound pressure generating elements in response to each of the successive code words of the digital signal has a magnitude corresponding to the analog value of the respective code word, and the auditory system of the listener has the characteristics of a low pass filter whereby the listener receives the sum of the air pressures as the analog sound pressure of the original audio signal.

Digital signal repeating system

Abstract: A communication system includes a plurality of digital signal transmission systems each connected to the next by a repeater installation. Signal packets travelling from a station in one system to a station in another adjacent system are picked out by a repeater station and stored in a buffer memory. The contents of the memory are compiled into a packet for transmission to the other system, with an address designating the station of the other system, and are inserted into an empty block or blocks of a periodically repeated frame of the other system with a waiting time of less than one complete frame.

Interface circuit for digital signal transmission system

Abstract: A signal transmission system which allows digital signals to be transmitted over twisted pair transmission lines. Master and slave transmission circuits are located at the switching system and terminal ends, respectively, of the transmission line. Both circuits include transmit and receive circuitry. The transmit circuitry includes a summing circuit connected to a constant current generator and the receive circuit includes a differential amplifier connected to a slicer circuit.

Signature analysis system for testing digital circuits

Abstract: A signature analyzer for testing digital circuits includes a memory which is initially programmed with a set of signatures characterizing the digital signals on the nodes of a correctly operating circuit. The nodes of a test circuit are then sequentially applied to a signature generator formed by a multi-stage shift register having the outputs of selected stages fed back to a gate to which the digital signal is applied. The signature generated by the shift register is compared to each of the signatures stored in memory until a signature match is found, thus indicating that the digital circuit, at least as far as the test node is concerned, is operating correctly. The signature generated by the shift register consists of twenty-four bits to provide a probability of error which is comparable to the probability of error in comparing a sixteen-bit signature with the signature from a specifically identified node. At the conclusion of a gate period. sixteen bits of the signature are displayed as four hexedecimal digits In order to minimize the probability of error, the analyzer also counts the number of transitions of the digital signal during the gate period and compares the count to transition counts stored in memory for the digital signals on the nodes of a correctly operating circuit. A comparison is then made of the transition count at the test node with each of the transition counts stored in memory. The analyzer thus ensures a transition count match as well as a signature match.

Telephone answering and message recording system

Abstract: A telephone answering and message recording system comprises a microphone (4), an analog-digital converter (6) for converting the analog speech signal of the microphone (4) to a digital signal, a digital memory (M 1 , M 2 , M 3 , M 4 , MEM,-MEM n ) for storing the digital speech signal from the converter (6), a digital-analog converter (7) for re-converting the digital signal of the output of the memory to an analog signal, and a speaker (5) coupled to the output of the digital-analog converter (7). The system also comprises a PB (push button) code receiver (40) for detecting a PB code which is the combination of two frequencies. The operational mode and/or the memory to record or reproduce speech is switched by the particular PB code. The system may operate in a first, fixed answering, mode in which a fixed answer recorded in the memory is transmitted to a remote subscriber or in a second, adaptive oral communication, mode in which speech recorded in the memory can be revised and/or transmitted to a remote subscriber through a telephone line. In the latter mode, two remote persons may communicate with each other through the system even when those two persons do not call the system simultaneously.

Method and apparatus for identifying sound recordings

Abstract: In an installation comprising a master assembly for reading the sound information signals and the end-of-program sequence signals recorded on a master tape, and at least one slave assembly to record a second time the read out signals, the slave assembly comprises circuits for detecting and regenerating end-of-sequence signals, which circuits are connected to the output of the said recording amplifier, digital coding circuits by derivation from a pilot frequency for producing a coded auxiliary digital signal, means to modify the digital coding at each new detection of end-of-sequence signals and an adder circuit to add the coded auxiliary digital signal with the sound information signal before re-recording the latter.

Method and apparatus for concealing errors in a digital television signal

Abstract: The digital signals representing successive picture points of a digital television video signal is caused to pass through, in succession, two delay circuits each providing a delay of one television line interval. This makes three places available where shift registers may be connected for stepping the digital signals at picture point intervals, so that a two-dimensional array of neighboring picture points located on adjacent portions of three television lines can be made simultaneously available for correcting the signal of the central picture point if it is found to be defective. A defective picture point is caused to be represented by a null value of digital signals by an error-correcting circuit. Thus, at the same places where the video signal shift registers are connected, gates for detecting null signals may be connected, each of which is followed by one-bit shift registers for addressing a read-only memory for controlling the choice of digital signal pairs from the picture point array which will be averaged in an averaging circuit to provide the output signal. If the digital signal of the central point of the picture point array is not defective, duplicates of this signal are provided to the averaging circuit under control of the read-only memory so that the original signal will proceed to the output of the circuit. If this signal is defective, however, the read-only memory selects a pair of signals corresponding to picture points bracketing the central point to provide the average signal, in accordance with a program that takes account of which points in the picture point array are defective. If no bracketing pair of points provides nondefective signals, the memory causes a medium gray signal to be substituted for the defective center point signal. This system has the advantage that the same stages are used and the same operating times occur in the processing of every picture point, whether the signal for that point is defective or not.

Tailings monitor for combine harvester

Abstract: A combine harvester vehicle having threshing, separating and cleaning stages for cut crop material and a tailings return elevator for conveying tailings to one of the stages for recycling, is provided with a tailings monitor including a photodiode for transmitting a radiant energy beam across the path of tailings being conveyed in the elevator, an electrical circuit including a photodetector for deriving digital signals indicative of whether the beam is impinging on the photodetector or is being interrupted by the tailings, and an RC circuit which charges a capacitor through a resistance when the digital signal is present indicating that the beam is interrupted and discharges it when the opposite digital signal is present to thereby develop an average voltage across the capacitor which is an analog of the percentage of time that the beam is interrupted by the tailings being conveyed in the elevator and can be visually displayed on a voltmeter to the combine operator as a measure of tailings volume. In an alternative embodiment the digital signals are coupled to a microprocessor for processing of the signals and display to the operator.

A 2-channel, 16-bit digital sampling frequency converter for professional digital audio

Abstract: A digital sampling frequency converter for arbitrary ratios of sampling frequencies is presented. It is based on a multistage interpolating filter, and on a novel time-domain control of the filter stages by signals derived from the sampling frequency clocks. Time-domain resolution of ±300 picoseconds is obtained, compatible with digital audio of 16-bit resolution. In addition to the filter design and implementation, measurement results are presented. They indicate that 16-bit accuracy is indeed achieved, even with asynchronous, drifting and time-varying sampling frequencies. A number of applications (digital mastering, program transfer between conflicting digital audio formats, pitch control with constant sampling frequency in digital recorders, error concealment, interfaces in digital transmission) are presented.

Method and apparatus for the digital control of the phase of the system clock of a digital signal processing system

Abstract: Method for digitally controlling the phase of the system clock frequency of a digital signal processing system which processes an analog signal containing a reference signal, wherein a fixed phase relation exists between the digitalized reference signal and the system clock frequency, which includes digitalizing the reference signal by sampling the analog reference signal, weighting the scanning values of the digitalized reference signal for obtaining a digital phase comparison variable, feeding the phase comparison variable through a digital PLL filter to a digitally controlled oscillator, and deriving the system clock frequency from the output signal of the digitally controlled oscillator, and an apparatus for carrying out the method.

Apparatus for electronically determining postage in response to weight

Abstract: An electronic scale electronically determines postage or shipping rates and displays also actual weight in chosen increments of items weighed by a platform atop an enclosure of the scale. A weight sensor provides an analog signal representing item weight. This signal is converted to a digital signal and provided to a computing circuit having a microprocessor for computing weight and rate signals corresponding to the digital signal. Separate weight and rate displays display total weight digitally and display also the actual cost of shipping or postage. An encoded rate selection device is readily and selectively usable with, and replaceable with respect to, the enclosure allowing the user to select a desired predetermined postage or shipping rate schedule, or structure. This device may be a rate selection card carried upon a front panel of the enclosure or a circuit board received within the enclosure. Detectors decode the rate selection device encoding for computing of weight and rate signals only according to this predetermined schedule.

Optical transmission system for high frequency digital signals

Abstract: A desire exists in the optical transmission of optical signals to co-transmit a service channel or telemetry signals in the form of an additional low frequency signal over the light conductor, since a remote feed line or a service channel is not always installed parallel to the light conductor length. The requirement exists for the transmission of the additional signal that, in addition to a low additional expense, no disruption of the actual useful signal can occur. To this end, the control signal of a laser diode transmitter is modulated with the signal to be additionally transmitted and this light component is coupled out at the receiving side. The structure is particularly useful in optical transmission systems for very high frequency digital signals with bit rates above 100 Mbit/s.

Phase programmable signal generator means

Abstract: A phase controlled signal generator using a cyclical counter with preset and reset control terminals to provide a continually advancing digital signal. This digital signal is converted in a sine table PROM and D to A converter to a sine wave signal which signal has a phase shift with respect to a reference in accordance with a phase control preset input and which signal can be periodically synchronized to a given starting phase to maintain signal stability or Doppler frequency shift.