Showing papers on "Sampling (signal processing) published in 1970"

Adaptive delta modulation with a one-bit memory

Abstract: We propose a delta modulator which, at every sampling instant r, adapts its step-size (for a staircase approximation to the input signal) on the basis of a comparison between the two latest channel symbols, C r and C r-1 Specifically, the ratio of the modified step-size m r to the previous step size m r-1 is either +P or — Q depending on whether C r and C r-1 are equal or not (We recall that, in delta modulation, C r represents the polarity of the difference, at the sampling instant r, between the input signal X r and the latest staircase approximation to it, Y r-1 ) A simulation of the delta modulator with a band-limited speech input has revealed that PQ = 1 and P ⋍ 15 represent optimal adaptation characteristics, on the basis of signal-to-error ratios, over an important range of sampling frequencies; and that at 60 kHz, delta modulation with these adaptation parameters compares favorably with 7-bit logarithmic PCM, which reproduces speech with good telephone quality We present several graphical results from this simulation, and include an evaluation of the effect of independent channel errors on the adaptive delta modulator We proceed to suggest a heuristic theory of the delta modulator which explains the optimality of the condition PQ = 1, and develops an upper bound of 2 for the optimum value of P We conclude with a summary of results from a video simulation which revealed that aforementioned optima for P and Q apply to a video signal

Signal processing and transmission by means of walsh functions

Abstract: In the transmission by carrier waves a plurality of signals are produced and each multiplied by one of 12 Paley functions derived from a Hadamard matrix of rank 12. The resulting signals are added to form a multiplexed signal. The multiplexed signal is frequency limited by sampling it with a trigger function and passing the samples through a bandpass filter. Reconversion of the multiplex signal is accomplished at the receiver.

Analog signal to discrete time interval converter (asdtic)

Abstract: An electronic signal conversion device is disclosed. The concept of pulse modulation includes in the sense of this invention the process of sampling a source of electric energy by one or several switches, and the electronic function that controls this switch or switches; any utilization of averaging devices to smooth the ensuing pulses such as filters are excluded as part of this process, except that a filter may be inserted ahead of a lead to be energized. The device is particularly useful wherever conversion of analog signals to discrete time signal intervals for purpose of pulse modulation is required. However, the invention has general utility and is presently being used with specific power supplies in the space program and communication technology. In addition, the device lends itself to incorporate a reference source and feedback network as used with power amplifiers and direct current pulse modulated power converters. The device maintains its accuracy of expected operation notwithstanding variations in its component characteristics, variations of applied voltage waveforms and supply voltages.

Apparatus for deriving synchronizing pulses from pulses in a single channel pcm communications system

Abstract: A method and apparatus is disclosed for bit synchronization of a received PCM communications signal, without requiring a separate synchronization channel in the communications signal by digital correlation of the received square-wave signal with a predetermined number of phase displaced replicas of its expected form. Each phase displaced replica is correlated with the input signal to determine which phase displaced replica produces the largest correlation signal. In carrying out the correlation of the square-wave signal with a given phased displaced replica, the two levels of the replica corresponding to the +1 and -1 binary values of the input signal are employed as sign signals to control the arithmetic addition or subtraction of the input signal binary values to the contents of an accumulator. The binary values of the input signal are produced by means for sampling and converting the input signal into +1 and -1 values. A plurality of samples of the input signal are thus accumulated during each cycle of a number of input signal cycles to develop a correlation value.

Discrete adaptive delta modulator

Abstract: A discrete adaptive delta modulator (DADM) comprising a comparator, a quantizer and a sampling pulse generator operating at the rate f2 is characterized in that complex analog feedback circuitry is replaced by a programmable pulse generator operating at the rate ft, which provides a controlled number of pulses k during each sampling period 1/f2 to a single step-size analog feedback integrator. The number of pulses k provided by the programmable generator multiplied by the basic step size sigma o of the feedback integrator determines the step-size sigma k in the feedback signal. This DADM is readily implemented in integrated circuit form and retains such advantages of the nonadaptive delta modulator as circuit simplicity and the requirement of only a single adjustable basic step size sigma o. The number n of available step sizes sigma k, which is determined by the ratio of the generator rates ft and fs, can be several hundred compared to a maximum of ten in a conventional DADM.

Mass flow monitoring system and method

Abstract: A densitometer has an acoustically shielded, temperature insensitive, tuning fork-type density sensing element which incorporates certain design factors and is driven at its natural frequency by a regenerative drive circuit employing piezoelectric drive and pickup crystals. A mass flow rate computing method is embodied in a computing system having electronic multiplication means which operates in dependency upon volume flow rate information in a digital signal and which is controlled by the output from a signal sampling and density computing circuit that operates in dependency upon a digital signal having a frequency that varies as an inverse linear function of the sensed density condition. During a sampling period, the latter circuit gates a clock signal to a counter preset to provide a registered count proportional to the density condition during the sampling period and the registered count is transferred to a memory having an output that controls the output of the electronic multiplication means between successive count transfers.

Sampling and Averaging Techniques in the Analysis of Fast Random Signals

Abstract: Problems arising when averaging fast signals random in shape and occurrence time are systematically examined. A setup is described, comprising a sampling oscilloscope and a memory unit, allowing high speed random operation. The system logic, which insures one‐to‐one delay‐channel correspondence under the most stringent conditions, allows averaging signals satisfying various specified conditions and optimizes the statistical accuracy of the results. An add‐subtract method allows elimination of synchronous transient noise, either external or arising from the sampling unit itself. Signals of 30 μV were averaged out in this way with a 0.1 nsec instrumental risetime. Applications are shown to a broad range of problems which include fast signal enhancement, optical signal measurements, photomultiplier single electron response studies, illumination function measurements for fast organic and slow scintillators, and semiconductor detector risetime observation. Two‐dimensional representation of random signal proper...

Adaptive Delta Modulation of Speech with a One‐Bit Memory

Abstract: We define an adaptive delta modulator in which the adaptation of the step size mr at the rth sampling instant depends on the comparison of two channel symbols—the bits Cr and Cr−1 corresponding to the rth and (r−1)st sampling instants. Specifically, the ratio of mr to the previous step size mr−1 is +P or −Q depending on whether Cr and Cr−1 are equal or not. We indicate the step response of the delta modulator and present results on the simulation of the adaptation logic on a speech sample that was band limited to 3.3 kHz. On the basis of signal‐to‐error ratios, we note that the equations PQ = 1 and P = 1.5 define optimal adaptation characteristics for sampling frequencies of 20, 40, and 60 kHz, and also that PQ⩽1+e(e≪1) represents a strong condition for stability. Finally, we comment on the relative performance of the adaptive delta modulator and of logarithmic PCM, and find that at a 60‐kHz sampling rate, the delta modulator achieves a 7 log‐bit PCM quality.

Real time serial fourier transformation circuit

Abstract: Circuitry for sampling a time varying waveform, converting each sample to a complex digital number representative of a predetermined parameter and then analyzing each one of such complex digital numbers in a plurality of stages serially to derive the Fourier transform of the original signal. The disclosed circuitry is adapted to analyzing N samples of a complex waveform, where N is an integral power of 2, but may be adapted to analyze any number of samples or any radix other than 2. Successive pairs of stages in the analyzing section of the circuitry are arranged to time-share a single digital multiplier, referred to as a productor, so as to reduce the complexity of the circuitry required to carry out the multiplication necessary in the transformation process.

Process for measuring the sampled amplitude of a seismic signal

Abstract: A process for measuring the sampled amplitude of a seismic signal received by a sensing device after the said signal has travelled through a continuous medium, in which the content of an adding counter for each basic unit of time is compared in turn with the contents of each of a first series of memories, containing, in digital form, the instants of emission of a sequence of energy impulses, in which the sampled digital value of the signal supplied by the sensor is received in another series of memories, the elements of which are identified in relation to the time, and in which each sample is given a number of addresses determined by the instant of sampling and the various instants of prior emissions preceding the instant of sampling, with a period shorter than the maximum time taken for the mechanical waves to travel through the ground.

Apparatus to measure fluorescence decay curves

Abstract: A pulse fluorimeter is described which allows measurements of fluorescence decays in the range 1 ns to 1 μs. The system is built from a modified Hundley light source with 1 kHz repetition frequency and a commercially available sampling oscilloscope combined with a signal averager. The signal is digitized at 254 discrete time positions with a 10 bit resolution. Up to 256 scans can be summed and the data can be read out either analogue or on punched tape for digital processing. Both the shape of exitation pulse and the fluorescence decay curve are measured and individually corrected for spurious signals.

Method and apparatus for storing and retrieving information by analog waveform correlation techniques

Abstract: A high-density storage and retrieval system is disclosed in which information is divided into a succession of groups of binary digits and stored as patterns of representations in an associated plurality of storage cells in a record medium. Upon scanning each recorded pattern of representations, a transducer generates an electrical signal having one discrete analog waveform uniquely corresponding to each of the recorded patterns of representations. A set of sample signals is then generated by sampling each discrete analog waveform at critical points. Each such set of sample signals is summed by correlation techniques requiring the adding and subtracting of the various individual sample signals to generate a sum signal. The magnitude of the sum signal is correlated to, or related with, a reference magnitude which is representative of a sum signal corresponding to a known analog waveform. As a result of this correlation, the magnitude of each sum signal is recognized as being indicative of a particular group of binary digits. The use of correlation techniques allows for the cancellation and averaging of analog waveform imperfections, and results in a sum signal which more accurately corresponds to the analog waveform detected.

Track and hold apparatus

Abstract: Track and hold apparatus for sampling a video analog input signal including input buffer means having a constant power dissipation for a varying input signal and including a diode switching bridge coupled to a holding capacitor which is switched off at a common level by turn off clamps whose turn off level is varied by the stored amplitude level of the holding capacitor.

Feed-forward amplifier having arbitrary gain-frequency characteristic

Abstract: Frequency-shaping of the gain characteristic of a feed-forward, error-corrected amplifier using main and error amplifiers having essentially flat, or frequency-independent gain characteristics, is achieved by tapering the power division characteristics of: the input coupler, which extracts a reference signal component from the input signal; the sampling coupler, which compares the output from the main amplifier with the reference signal to form an error signal; and the error injection coupler, which injects the error signal into the main signal path. In a second embodiment of the invention, the band-shaping burden is shared between the amplifiers and the couplers.

Digital threshold detector

Abstract: A METHOD OF, AND CIRCUITRY FOR, CONVERTING PCM CODE GROUPS GENERATED BY SAMPLING THE ANALOGUE SIGNAL LEVEL ON A LINE INTO A SET OF SIGNALS REPRESENTING DISCRETE ANALOGUE AMPLITUDE LEVELS PRESENT IN THE SAMPLED SIGNAL IS DISCLOSED. EACH NEWLY GENERATED CODE GROUP IS APPLIED TO A OMPARATOR WHICH COMPARES ITS ABSOLUTE VALUE WITH A STORED CODE. THE STORED CODE IS SIMULTANEOUSLY APPLIED TO A CODE TRANSLATOR WHICH CONVERTS IT INTO A SET OF DISCRETE AMPLITUDE SIGNALS. WHEN THE COMPARISON INDICATES THAT A SELECTED RELATION HAS EXISTED BETWEEN THE CODE GROUPS GENERATED BY SAMPLES OF THE LINE AND THE STORED CODE FOR A SELECTED INTERVAL, THE CURRENT CODE GROUP REPLACES THE STORED CODE TO INDICATE THE CHANGES IN SIGNAL MAGNITUDE ON THE SAMPLIED LINE.

Fourier analysis of cardiovascular events

Abstract: The theory and application of the method of Fourier analysis has been reviewed with specific reference to the applications of this technique to analysis of signals related to cardiovascular functions. Mathematics have been developed that relate the sampling rate of a function to the accuracy of harmonic amplitude resolution of the function. Specifically, the mathematical scheme was developed for the purpose of designing criteria for determining the minimum sampling rate of a function without introducing aliasing errors, and for elucidating the basis for the false indications resulting from selecting too few ordinates for the Fourier analysis. The application of Fourier methods to the analysis of cardiovascular functions has been studied. A thoracic aorta pressure pulse, the coronary artery flow pulse, and the electrocardiogram of a normal anesthesized mongrel dog have been examined in terms of the maximum sampling frequency required to yield the most dependable results. It was found that by sampling the arterial pressure pulse from 6 to 96 times/cycle, the absolute value of each harmonic amplitude for the first ten harmonics approaches asymptotically constant value at the higher sampling rates, suggesting that little or no further frequency information can be obtained by increasing the sampling rate >96 per second. At the lower sample rates (6–12 per cycle) the harmonic values were generally larger than the final steady value. The same type of asymptotic behavior is observed for the phase angle of each harmonic component as a function of the sample rate. The normal arterial pressure pulses appear to be fit adequately with ten harmonics. Sampling rates of about four times the largest significant frequency component in the wave form appear to produce the best analytical results. For the arterial pressure pulse, coronary flow pulse, and electrocardiogram, this turned out to be about 100 per second.

Automatic gain control utilizing controlled sampling

Abstract: Automatic gain control for burst signals is achieved by converting a burst signal into a pulsating signal having a duty cycle proportional to the amplitude of the burst signal, and by integrating the pulse signal to obtain a direct current control voltage. To prevent unwanted variations in the control voltage during no-signal intervals, adjustment of the control voltage amplitude takes place on a cycle-by-cycle basis of the burst signal by providing a discharge path for the integrator circuit for a predetermined interval only after each pulse of the pulsating signal.

Repetitive sampling weighted function converter

Abstract: An electrical signal is sampled repeatedly and the samples are integrated in analog or digital form to effect active filtering of the signal. Preferably the samples are weighted differently or the inter-sample interval is varied in accordance with a weighting function chosen to improve noise rejection at one or more frequencies.

Acceleration control system for vehicles

Abstract: Train acceleration indicating arrangement wherein a sample circuit samples a vehicle velocity signal for a brief interval during each sampling period and produces a sampling signal whose amplitude during each sample period is substantially constant and a function of the sampled velocity signal. Means are provided for algebraically adding an AC signal and the sampling and velocity signals to produce an AC output signal solely during sampling periods when the difference between the sampling and velocity signals exceeds a predetermined magnitude. A relay circuit actuated in response to the AC output signal provides an indication of satisfactory vehicle deceleration. The relay circuit is connected in an emergency circuit of the type applying full service brakes upon detection of an abnormal indication. Actuation of the relay circuit holds off additional actuation of emergency brakes in the event the vehicle decelerates adequately subsequent to detection of an abnormal indication.

Sample, hold, and subtract circuit

Abstract: To correct the drifting baseline of a chromatographic signal, a sampling, holding, and subtracting circuit of a baseline correction apparatus samples the signals during clock pulses from a timing source and stores the values of the signals across a capacitor. When a slope detector in the baseline correction circuit senses that the slope of the signal starts to deviate from the baseline and form a peak, the sample, hold and subtract circuit stops sampling and storing new values and subtracts the last stored value from the signal.

Low level conversion system

Abstract: Multiplexed analog signals are applied to the input of a sampling amplifier having a digitally controlled gain. The signals at the output of the sampling amplifier are applied to an analog to digital integrating converter. A phase lock oscillator is connected to a clock which controls the operation of the converter in such a manner that the integration time of the converter is equal to one or more cycles of the power line frequency, whereby maximum common mode rejection occurs at the power line frequency.

Method and apparatus for high-resolution spectral analysis

Abstract: A method and apparatus for high-resolution power spectral analysis employing a digital computer is provided without stringent stability requirements on the sampling rate by using a pair of balanced mixers to combine one signal directly and in quadrature with a second signal, and alternately sampling the outputs of the mixers through an analog-to-digital converter. The computer then carries out computations of a convolution spectrum from two autocorrelation and two cross-correlation functions which can be computed from the two sequences of samples with compensation for variations in gain of the signal channels by normalizing correlation functions, and known deviation from 90* in the quadrature mixing of signals by using phi in place of - 90* in the analysis and dividing the sum of the crosscorrelation functions by - sin phi .

Drift correcting servo

Abstract: This invention is an error correcting circuit to cancel the drift of a drifting electronic or electromechanical system by periodically sampling the output of the drifting electronic or electromechanical system for output signal error due to drift and then introducing a feedback signal to cancel out the drift error thereby providing a corrected output. The invention encompasses a short and a long term memory and functions by periodically setting the drifting electronic or electromechanical system input to zero for a short time sampling interval, sensing the output of the drifting system, developing a feedback correction signal and then adding or subtracting the feedback signal from the drifting system output to effectively cancel out the error portion of the drifting system output signal. The short term memory provides an almost instantaneous feedback correction signal value and very quickly brings the drifting system output to its corrected signal amplitude while simultaneously initiating a change in the output of the long term memory to bring the output of the long term memory into coincidence with the output of the short term memory. The short term memory holds the correction signal after the expiration of the short sampling period, long enough for the long term memory signal output to become equal to the short term memory correction signal. Then the short term memory is taken out of circuit and the stable long term memory signal is introduced to provide the corrected signal for the electronic system over a relatively long time interval, until the next sampling period. Additionally, during the sampling period when the drifting system input is set to zero, a holding circuit having the signal value of the drifting system immediately before the sampling period, is introduced in place of the drifting system and during the sampling period provides an output signal in place of the drifting system.

Echo simulation means

Abstract: Synthetic sonar echoes are generated in response to a sonar signal by utilizing a delay line, time compression technique to generate a reconstructed waveform which is then sampled to provide a pulsed input to a shift register means having taps spaced therealong corresponding to structural highlight positions along a target. The shift register is caused to serve as a variable delay line by varying the sampling and shift rate in response to aspect angle as determined by phase-sensitive logic means. The taps feed a network of attenuators and filters which produce across an output resistor an electrical signal which can be amplified and used to drive a sound projector to produce the desired simulated echo.

Triple-sample a/d converter

Abstract: An analog-to-digital converter that eliminates dynamic coupling errors in a system where the measured signal and the reference signal are subject to such variations. This device sequentially samples an analog unknown voltage and a reference voltage and converts the sampled signals into digital information representative of the unknown voltage. Sampling and conversion is achieved in a three step process which alternates the reference and unknown signal inputs to an integrator and level holding circuits. The integrator output controls the duration of a digital counter which runs until the integrator output crosses a zero value. The result in the digital counter provides the binary value representative of the analog unknown signal. Dynamic coupling errors which occur during the reference and unknown signal sample times are eliminated by dividing the sample time of the unknown signal in two segments, a first sampling segment prior to sampling the reference signal, and a second sampling segment after the reference signal.

Reexamination of the prefiltering problem in a state-variable formulation (Corresp.)

Abstract: Optimal (least-mean-square linear) filtering of random signals prior to sampling may be represented as a Wiener-Kalman state-variable filter followed by a coder that synthesizes the signal to be sampled as a linear combination of the estimated states. Although the prefilter doubles the number of states of the overall presampling signal process, the postsampling reconstruction filter need only model the original signal generator and the coder. Overall optimization involves selecting the parameters of the coder to minimize a weighted time-averaged error criterion.

Multiplexed, sequential dot interlaced television system

Abstract: A multiplexed sequential dot interlaced television system having a plurality of television cameras at the transmitting station with a common source of line and frame synchronizing signals supplying all of the cameras. A clock pulse generator is provided for generating a train of clock pulses having a frequency fc fen2 WHERE FE IS THE SAMPLING SIGNAL FREQUENCY FE FV (LD)/(n1n2) WHERE FV IS THE FREQUENCY OF THE FRAME SYNCHRONIZING SIGNALS, L is the number of lines in one frame, D is the number of clock pulses occurring during one line, n1 is the vertical interlace ratio (if any), and n2 is a predetermined dot interlace ratio, it being required that the quotient LD/n1n2 be irreducible and that there are no more cameras than the dot interlace ratio. A shift register is provided coupled to the clock pulse generator and having n2 output channels, the shift register thus sequentially switching successive ones of the clock pulses to successive ones of its output channels so that a train of sampling pulses having a frequency fe is provided in each output channel of the shift register, these trains of sampling pulses being respective phasedisplaced by the period of the clock pulse frequency fc. A plurality of sampling gates is provided respectively coupling the output circuits of the cameras to a video signal transmission facility, each of the sampling gates having a sampling signal output circuit which is coupled to a different output channel of the shift register. Each of the sampling gates thus passes a train of sampled video signals from the respective camera to the transmission facility, the trains of sampled video signals being multiplexed in the transmission facility by reason of the phasedisplacement of the trains of sampling signals. The line and frame synchronizing signals are also applied to the transmission facility. At the receiving station, a plurality of video monitors is provided equal in number to the cameras and each having line and frame sweep means and a video signal input circuit. A synchronizing signal detector circuit is coupled to the transmission facility for separating the line and frame synchronizing signals which are applied to all of the video monitors. Another clock pulse generator is provided which generates a train of clock pulses having a frequency fc, this receiving station clock pulse generator being coupled to the synchronizing signal detector and synchronized with the clock pulse generator at the transmitting station by the separated line synchronizing signals. Another shift register is provided coupled to the receiving station clock pulse generator and also having n2 channels. Another plurality of sampling gates is provided equal in number to the video monitors and respectively coupling the monitors to the transmission facility. Each of the receiving stations sampling gates has a sampling signal input circuit which is couplEd to a different one of the receiving station output channels.

Nonlinearly sampled differential quantizer for variable length encoding

Abstract: A differential quantizer for predictive PCM transmission systems in which difference signals are quantized at the Nyquist rate when they are below a predetermined level but are quantized at twice the Nyquist rate when they exceed that level. The difference signals are encoded for transmission but an extra bit follows each code word representing a level above the predetermined threshold to indicate to the receiver whether that sample is to be inserted by the receiver at a Nyquist interval or one-half a Nyquist interval from the preceding sample. Where the difference signal to be encoded is large due to a substantial change in the input signal, several such samples taken at twice the Nyquist rate serve to rapidly reduce the difference signal and provide a better approximation of the input signal to the receiver.

Limit-cycle constraints for recursive-digital-filter design

Abstract: Quantisation errors can cause nonlinear oscillations in recursive digital filters if the input signal is low or constant. Limit-cycle constraints are derived in terms of the feedback coefficients, the gain and the sampling ratio. These represent convenient ways of reducing nonlinear effects in the realisation of the recursive digital filter.

Analog signal selective-peak sampler system for blood pressure signals

Abstract: A system for sampling selected peak values of an analog signal. A system is disclosed for detecting peak occurrences of a signal and for triggering a device which operates on the signal. One such device described herein is a numerical display device. The system includes means for limiting the repetition rate of peak-indicating trigger pulses to a rate between upper and lower predetermined rate-limits. The system can be used in various applications and is particularly useful in the numerical display of systolic pressure as disclosed herein. The repetition rate limits employed herein are compatible with the ability of the human eye and brain to sense and absorb visual numerical information.