Showing papers on "Digital signal published in 1975"

Theory and application of digital signal processing

Abstract: sprightly style and is interesting from cover to cover. The comments, critiques, and summaries that accompany the chapters are very helpful in crystalizing the ideas and answering questions that may arise, particularly to the self-learner. The transparency in the presentation of the material in the book equips the reader to proceed quickly to a wealth of problems included at the end of each chapter. These problems ranging from elementary to research-level are very valuable in that a solid working knowledge of the invariant imbedding techniques is acquired as well as good insight in attacking problems in various applied areas. Furthermore, a useful selection of references is given at the end of each chapter. This book may not appeal to those mathematicians who are interested primarily in the sophistication of mathematical theory, because the authors have deliberately avoided all pseudo-sophistication in attaining transparency of exposition. Precisely for the same reason the majority of the intended readers who are applications-oriented and are eager to use the techniques quickly in their own fields will welcome and appreciate the efforts put into writing this book. From a purely mathematical point of view, some of the invariant imbedding results may be considered to be generalizations of the classical theory of first-order partial differential equations, and a part of the analysis of invariant imbedding is still at a somewhat heuristic stage despite successes in many computational applications. However, those who are concerned with mathematical rigor will find opportunities to explore the foundations of the invariant imbedding method. In conclusion, let me quote the following: "What is the best method to obtain the solution to a problem'? The answer is, any way that works." (Richard P. Feyman, Engineering and Science, March 1965, Vol. XXVIII, no. 6, p. 9.) In this well-written book, Bellman and Wing have indeed accomplished the task of introducing the simplicity of the invariant imbedding method to tackle various problems of interest to engineers, physicists, applied mathematicians, and numerical analysts.

Digital signal analysis

Abstract: Review of least squares, orthogonality and the Fourier series review of continuous transforms transfer functions and convolution sampling and measurement of signals the discrete Fourier transform the fast Fourier transform the z-transform non-recursive digital systems digital and continuous systems simulation of continuous systems analogue and digital filter design review of random functions correlation and power spectra least-squares system design random sequences and spectral estimation.

Suppression of parasitic oscillations in wave digital filters

Abstract: Parasitic oscillations can occur in digital filters due to the granularity of the signal and to overflow. It is shown that for wave digital filters, the earlier concept of pseudopower leads to a function called stored pseudopower, from which a simple criterion guaranteeing absence of parasitic oscillations can be derived. For fixed-point two's-complement arithmetic, this criterion can be taken into account by particularly simple requirements for the adaptor output signals. A special type of calculus is developed which makes it possible to derive the corresponding simple requirements for the chopping operations at the various stages of the signal processing in the adaptors. The method is extended to cover scaling.

Modulation and filtering device

Abstract: A digital data transmitter is described, whose line carrier frequency need not be an integral multiple of one half the clock frequency of the digital input signal. Use is made of a digital filter for increasing the sampling frequency to a value which is twice the modulator carrier wave frequency.

On-line verification system for identification card or the like

Abstract: In an on-line banking system including a central computer and at least one remote terminal, a method of an apparatus for verifying that a holder of an identification card is authorized to complete a transaction at the terminal is disclosed. Account number data are machine read from the card, scrambled, and then compared to secret alphanumeric data, keyboard entered by the card holder at the terminal. The secret alphanumeric data are converted to a digital signal, and the signal is converted into first and second signal portions. The first signal portion is compared to the scrambled account number data. If the comparison is positive, the second signal portion, along with keyboard-entered transaction data and account number data, is transmitted to the central computer. Since only the second signal portion of the keyboard-entered secret data is transmitted on-line to the central computer, it is impossible to determine the entire secret data for gaining unauthorized use of the terminal by monitoring the line between the terminal and the central computer. At the central computer, the second signal portion is compared with a reference signal stored on the authorized holder's account and addressed by the account number data. In response to a positive comparison, the central computer authorizes the remote terminal to complete the requested transaction.

Polar coordinate format to a cartesian coordinate format scan converter

Abstract: A slow scan radar signal is converted from a polar coordinate format to a cartesian coordinate format to permit the radar signal to be displayed on a television type display device. The radar signal, in analog form, is converted to a digital signal, placed in a memory to permit readout of the data in a cartesian coordinate format and converted from a digital to analog signal which may then be applied to the television type display device.

Automatic gain controlled amplifier apparatus

Abstract: In an analog data acquisition system, used for digital treatment, analog signals of different levels received from remote locations are amplified with a selected gain before being converted by a common A/D converter. A discretely variable gain amplifier is used in which a series of programmed predetermined ranges are sequentially tested against the capability of the A/D converter in relation to the particular input analog signal. The first acceptable gain is selected and a code can be used to identify the selected gain for digital treatment of the derived corresponding digital signal.

Digital time-division multiplexing system

Abstract: Disclosed is a digital multiplexer which combines N parallel bit-synchronized digital signals, each of bit rate f 1 , into a single composite line signal of bit rate f 2 , where f 2 > Nf 1 . Before the individual bits are interleaved, each digital signal is converted to a submultiple of the line frequency, f 2 . By inserting gaps having a predetermined duration and occurring at a fixed rate into each of the N digital signals, the bit rate f 1 of each bit stream is increased to f 2 /N. This is done without sampling any bit more than once. A multiplexer sequentially interleaves each bit from the N converted bit streams along with the gaps in each bit stream, forming the composite signal of bit rate f 2 . The interleaved gaps form empty time slots in the composite signal into which one or more signaling bits are added. Some of the added signaling bits carry framing information to lock the transmitter and receiver together. Thus, a composite higher-rate digital line signal consisting of interleaved information bits and signaling bits forms the time-division multiplex signal suitable for transmission over a single digital transmission path.

Real-time speech analyzer

Abstract: Apparatus for the real-time analysis of speech signals in which a digital signal representative of the speech signal is adaptive threshold center-clipped and infinite peak-clipped to form a signal comprising three logic states (+1,0,-1). The autocorrelation function of this signal is determined by a circuit which employs simple combinational logic and an updown counter circuit. Pitch period and voiced-unvoiced indication are determined from the location and magnitude of the peak value of the autocorrelation function. Additionally, a signal representative of the speech energy is provided by summing the digital speech signals over a predetermined time interval and intervals of silence are detected by comparing the speech energy in an interval of time with a predetermined or adaptively determined threshold energy.

Demodulator for combined digital amplitude and phase keyed modulation signals

Abstract: A digital carrier signal demodulation circuit is used in the carrier digital transmission system utilizing a 16-ary APK (Amplitude and Phase Keying) signal produced by the vector superposition of a second path signal consisting of a four-phase shift keying signal upon each phase of a first path signal consisting of a four-phase shift keying signal, the level of the second path signal being lower than that of the first path signal. The received 16-ary APK signal is detected with the reference carrier extracted from the received signal, regenerated to reproduce the base band pulses of the first path signal. The recovered base band pulses remodulate the reference carrier to produce the first path signal. The phases of the recovered first path signal and received signal are compared to phase lock a voltage controlled oscillator thereby producing the reference character.

Servo system employing a tracking digital angle encoder

Abstract: An absolute positioning servo for positioning a shaft in response to a digital command input which utilizes a resolver, for providing an analog position indication of the shaft, an analog to digital converter, which provides a digital indication of the shaft position, a comparator for comparing the digital command input signal with the digital indication signal and providing a differential digital error signal which is converted to an analog signal and fed back to position the shaft so that the differential digital error is 0. An analog fine control positioning means is provided which positions and maintains the shaft near the center point of the position represented by the digital command input signal when the digital differential error is 0. A signal representing the difference between the exact analog position of the shaft and the digital approximate position of the shaft is provided at the output of the translator. This is utilized to position the shaft within an angle equivalent of the least significant digital bit. The digital positioning system is utilized to move the shaft to a position within ± 1/2 bit of the desired position, then the analog positioning system takes over and positions and maintains the shaft within a lesser fractional portion of a bit to the absolute desired position. A short path positioning means is provided for selecting the shortest path to move the shaft to a new position indicated by the digital command input signal. That is, whenever the shaft is to be rotated to a position more than 180° away, it is rotated in the opposite direction over an angle which then is necessarily less than 180°. A square root function generator is provided following the digital to analog converter for the digital error signal which permits minimum positioning time for the servo system.

Automatic patient weighing system

Abstract: A patient weighing system for automatically providing a visual display of stantaneous patient weight includes a bed assembly for receiving the patient which is supported by weight responsive means producing analog signals as a function of instantaneous total weight. The analog signals are converted to commensurate digital signals. A first storage register stores the digital signal representative of the weight of the bed assembly without the patient. A second storage register stores the digital signals representative of the total weight of the bed assembly including the patient. A difference digital signal is developed which is representative of the difference between the digital signals stored in the first and second storage registers, providing a net or remainder digital signal which is a function of patient weight. A suitable means responsive to the difference digital signal is provided for visually displaying the patient weight, preferably on a repetitive cyclic basis so that the patient weight visual data is constantly updated. In a preferred embodiment, a manually adjustable input is provided to compensate for additions to the bed weight not attributable to change in patient weight such as pillows, blankets, medical equipment, etc. Additionally, by storing the difference digital signal and comparing it with the next sequentially developed difference digital signal, a suitable change of patient weight visual display can be provided.

Digital signal generator

Abstract: Digital signal generator for producing digital signalling codes employed in a digital telephone communication system including several tone generators for providing presynthesized digital tone signals which are convertible to audible tones. Permutable digital codewords are produced by a codeword generator. Some of the tone signals and codewords are combined by FSK and switching circuitry. Tone signals, codeword signals, and combination signals are stored in storage registers and read out by a multiplexer to provide a continuous TDM bit stream of 60 channels of digital signalling codes.

Correlative timing recovery in digital data transmission systems

Abstract: A sample timing recovery arrangement for synchronous amplitude and phase modulated digital data transmission systems correlates present and delayed samples of received digital data signals to obtain a spectral line at the sampling rate using digital techniques. Conventional methods of timing recovery generally perform analog operations on the envelope of a received data signal.

Logic level decoding circuit

Abstract: In a digital system wherein digital data having two operating logic voltage levels corresponding to two different logic states is transmitted from one unit and received at another separate unit, circuitry is provided for determining the mean voltage value of the received logic voltage levels and for comparing the mean voltage value to the received data to provide decoding of the correct logic state of the individual signal bits.

Pattern generating system

Abstract: Pattern information for production of a Jacquard pattern by a knitting or a weaving machine is automatically and quickly obtained. A pattern drawn on a sheet by a designer is converted to an analog type electrical signal by a television camera, and said analog signal is converted to a digital signal according to each color of each picture element. Said digital signal is stored in a digital memory. After the edition of said digital signal in the memory, the digital signal which defines the color of each picture element is applied to a knitting or a weaving machine.

A Special-Purpose Computer for Digital Signal Processing

Abstract: This paper describes a special-purpose processor for use in performing various operations on sampled signals. The system is fast, flexible, and programmable for performing, in real time, operations such as fast Fourier transformation (FFT) and digital filtering of acoustically derived signals.

Method and arrangement for the avoidance of errors during the reproduction of an image pattern

Abstract: A method for the reproduction of an image pattern disposed on a substantially nonuniformly driven scanning drum, wherein the image pattern is photo-electrically scanned point-by-point and line-by-line to generate an image pattern signal having an analog relationship to the image pattern and the image pattern signal is used to record on at least one recording drum driven substantially nonuniformly and independently of the scanning drum, features generating a scanning timing signal in synchronism with the rotational movement of the scanning drum, converting the image pattern signal to a digital signal in synchronism with the scanning timing signal, storing the digital signal in a storage unit measure-by-measure in synchronism with the scanning timing signal, generating a recording timing signal in synchronism with the rotational movement of the recording drum, reading out the digital signal from the storage unit measure-by-measure in synchronism with the recording timing signal, and, thereafter, driving at least one recording member with the digital signal to produce an image reproduction on the recording drum.

Video special effects generator

Abstract: A digital special effects generator combines two or more video signals under the control of a control lever or programmable hardware. Forward and reverse horizontal, vertical and corner wipes as well as a QUAD effect where four video signals may be simultaneously displayed are among the effects obtainable. An improved analog-to-digital converter is utilized to generate a digital signal representative of the position of the control lever, and a digital quantizer is used in conjunction with the analog-to-digital converter to eliminate jitter in the digital signal. The transition between video signals is controlled by comparing the digital lever position representative signal with a digital signal representative of the scanning beam position, and providing a video transition signal when a predetermined relationship between the two digital signals is reached. Border video switching circuitry utilizing a digital counter to control border width is used to generate a variable width, variable pattern border between the video displays.

Self contained electronic digital thermometer

Abstract: A self-contained electronic digital thermometer is in the form of an elongated probe has a temperature transducing thermistor at a front end and an electronic digital display at a rear end. Circuitry housed within the probe converts the voltage across the thermistor to a digital signal for driving the display. The circuitry includes an operational amplifier fed by the thermistor voltage via a pair of selectable input resistors for providing different gains for the amplifier and fed by a voltage source via a different pair of selectable input resistors for providing different biases to the amplifier. The different gains and biases are selected by a switch for enabling readout in either degree Fahrenheit or degrees Centigrade. A differentiator and comparators are also provided to drive a series of lights indicative of whether the temperature is increasing, decreasing or stable.

Digital firing pulse generator for thyristor power converters

Abstract: A digital pulse generator for firing thyristors in a polyphase converter system is described in an hybrid analog-digital and in an all digital form. A phase locked oscillator associated with a digital counter generates timing waveforms synchronized with the phase lines to establish firing angles in relation to a reference signal. Each firing pulse triggers the logic circuit of a distributor and a multiplexer is coupled with such logic circuitry in order to insure that the proper timing waveform is selected so as to match the selection of the next thyristor to be fired.

Bar graph digital interface circuit

Abstract: A circuit for controlling the height of a bar graph display in response to a digital input signal. A first count, representing the particular cathode segment of the bar graph under energization, is developed by a counter which monitors the clock signal driving the bar graph display. A second count is developed by a counter stepped by a clock when the digital input signal is in a selected logic state. At the end of a selected interval, the counters contents are transferred to a register for supply to a digital comparator, which compares the first and second counts and produces a control signal upon their equality.

Automatic crop inventory system

Abstract: In an automatic inventory system for crops, especially tree-borne crops, an airborne television camera views the area being surveyed and delivers an analogue video signal which is converted into a series binary digital signal by a level detector. The serial digital signal is received in a shift register that delivers a parallel digital output to a computer. The shift register is controlled by shift pulses derived from a pulse generator that has the video signal applied to it to maintain the pulses in synchronism with the camera operation. The computer receives the information from the shift register a frame at a time and determines from it parameters such as the average size, and spacing of crop-bearing trees and their numbers.

Waveform comparing phasemeter

Abstract: An electrical circuit for measuring the phase difference between a pair ofnput signals by uniformly limiting selected properties of the waveforms describing the input signals and modulating an output signal in dependence upon the duration of contrariety between the unlimited properties of the input signals whereby error in the output signal due to "jitter" (i.e., abrupt, spurious variations in pulse amplitude or duration caused by superimposition of noise) is substantially eliminated. Various output means produce either a continuous wave analog signal or a digital bit signal in dependence upon the modulation of the output signal. Coupled ancillary circuitry monitors one input signal in comparison with the other input signal and provides an output signal signifying which input signal has a leading phase angle.

Numerical control system having a digitized phase loop

Abstract: A numerical control system having a digitized phase loop comprising a motor for moving an object being controlled, a servo amplifier for driving the motor, feedback means coupled to the motor for generating a first signal indicative of the actual position of the object, and means for converting the first signal to a digital signal indicative of a change in the actual position of the object. Further provided is means for comparing a command digital signal indicative of the desired change in position of the object with the digital signal indicative of the actual change in position of the object to generate an error digital signal and for converting the error signal to an analog signal for driving the servo amplifier.

Variable rate clock signal recovery circuit

Abstract: A circuit for use in a digital data receiver to recover a clock signal, of variable rate, from the signal received by the receiver. A typical digital data receiver includes demodulating or other means for converting the received signal to a binary data signal having a characteristic which changes in a manner corresponding to transition in the digital data received. The invention provides circuit means for recovering a clock signal from the binary data signal where the data rate may vary over a substantial range. The clock signal recovery circuit utilizes a logic transition detector to produce a narrow pulse at each data transition in the binary data signal. The pulses, which contain harmonic frequencies at the clock rate of the binary data signal, are up-converted or mixed with an electrical signal from a frequency synthesizer. The signal resulting from this up-conversion is filtered by a narrow-band filter to produce an electrical signal at a predetermined intermediate frequency. The output signal from the frequency synthesizer is mixed with the signal from the narrow-band filter, in a down-converter circuit, to produce a reference signal having a frequency proportional to the clock frequency of the binary data signal. The frequency synthesizer has a variable frequency output determined by the setting of a data rate selector. An electronically controlled oscillator produces a signal having a frequency proportional to the binary-data-signal clock rate. The oscillator is in a phase-lock loop including a phase detector supplied with the reference signal having a frequency proportional to the clock rate of the binary data signal.

System for digitizing and interfacing analog data for a digital computer

Abstract: A system for digitizing and interfacing analog data from a plurality of amplitude modulated periodic signals with a computer in which an alternating reference signal is identified and sampled input data to be digitized is synchronized at the same time reference point of the waveform of the reference signal. Pulses from a real time clock are counted and synchronized with the reference signal and this synchronized signal is delayed and fed to a timing circuit which starts the multiplexing of the input signals and also activates an address counter to initialize the address locations in the computer. The analog data from the multiplexer is converted to digital values by an analog-to-digital converter and fed to the computer at the given address.

Digital altitude encoder

Abstract: In one exemplar embodiment, a digital altitude encoder is provided that utilizes a conventional altimeter responsive to atmospheric pressure for rotationally driving an indicator shaft. Attached to the shaft is a disc having repetitive, alternate, regularly disposed solid portions and slots. A light source and a pair of light detectors for receiving light from the source are spaced adjacent the disc to permit one of the detectors to generate a first signal and the other detector to generate a second signal having a relative time of occurrence dependent on the direction of the rotation of the disc. A counting means that is presettable to a predetermined digital count representative of a preselected altitude function receives the first and second signals and increments or decrements the predetermined count in response to changes in altitude. A code conversion circuit receives the digital signal output from the counter and converts the digital signal to a parallel digital code acceptable for transmission of aeronautical altitude information.

Differential sense amplifier

Abstract: An amplifier for sensing two signals at differing voltages which has a translated differential output at standard MOS digital signal levels. The amplifier is particularly well suited for sensing the logic state of a plurality of binary static electronic memory cells each of which is selectively connectable to a pair of sense lines.