scispace - formally typeset
Search or ask a question

Showing papers on "Sampling (signal processing) published in 1981"


Journal ArticleDOI
TL;DR: A method is presented for correcting the gain and phase imbalances and the bias errors of the in-phase and quadrature channels of a coherent signal processor by means of coefficients which are derived from measurements of a test signal.
Abstract: A method is presented for correcting the gain and phase imbalances and the bias errors of the in-phase and quadrature channels of a coherent signal processor [1] by means of coefficients which are derived from measurements of a test signal. The residual errors after correction depend upon the signal-to-noise ratio (S/N) of the test signal and the degree of filtering used in deriving the correction coefficients.

175 citations


Journal ArticleDOI
TL;DR: In this paper, a back projection of filtered projection (BKFIL) reconstruction algorithm is presented that is applicable to single-photon emission computed tomography (ECT) in the presence of a constant attenuating medium such as the brain.
Abstract: A back projection of filtered projection (BKFIL) reconstruction algorithm is presented that is applicable to single-photon emission computed tomography (ECT) in the presence of a constant attenuating medium such as the brain. The filters used in transmission computed tomography (TCT)-comprised of a ramp multiplied by window functions?are modified so that the single-photon ECT filter is a function of the constant attenuation coefficient. The filters give good reconstruction results with sufficient angular and lateral sampling. With continuous samples the BKFIL algorithm has a point spread function that is the Hankel transform of the window function. The resolution and statistical properties of the filters are demonstrated by various simulations which assume an ideal detector response. Statistical formulas for the reconstructed image show that the square of the percent-root-mean-square (percent-rms) uncertainty of the reconstruction is inversely proportional to the total measured counts. The results indicate that constant attenuation can be compensated for by using an attenuation-dependent filter that reconstructs the transverse section reliably. Computer time requirements are two times that of conventional TCT or positron ECT and there is no increase in memory requirements.

158 citations


Journal ArticleDOI
TL;DR: Oversampling and digital filtering have been used to design a per-channel voiceband codec with resolution that exceeds the typical transmission system requirement by more than 15 dB and the response of the codec is described mathematically and the results are confirmed by measurements of experimental breadboard models.
Abstract: Oversampling and digital filtering have been used to design a per-channel voiceband codec with resolution that exceeds the typical transmission system requirement by more than 15 dB. This extended dynamic range will allow for the use of digital processing in the management of signal levels and system characteristics in many telecommunication applications. Digital filtering contained in the codec provides rejection of out-of-band inputs and smoothing of the analog output that is sufficient to eliminate the need for analog filtering in most telephone applications. Some analog filtering may be required only to maintain the expanded dynamic range in cases where there is a danger of large amounts of out-of-band energy on the analog input impairing the dynamic range of the modulator. The encoder portion of the oversampled codec comprises an interpolating modulator that samples at 256 kHz followed by digital filtering that produces a 16-bit PCM code at a sample rate of 8 kHz. In the decoder, digital processing is used to raise the sampling rate to 1 MHz prior to demodulation in a 17-level interpolating demodulator. The circuits in the codec are designed to be suitable for large-scale integration. Component matching tolerances required in the analog circuits are of the order of only ± 1 percent, While the digital circuits can be implemented with fewer than 5000 gates with delays on the order of 0.1 μs. In this paper the response of the codec is described mathematically and the results are confirmed by measurements of experimental breadboard models.

79 citations


Patent
11 Feb 1981
TL;DR: In this paper, the characteristics of the surface acoustic wave transversal filter are chosen to be such that each elementary pulse in the original waveform is transformed into an oscillatory waveform, the zero crossings of the different oscillator waveforms coinciding with one another and defining the sampling times.
Abstract: System for extracting timing information from a digital waveform supplied to the system in which the waveform is modulated by a modulator, passed through a surface acoustic wave transversal filter and demodulated by a demodulator. Zero crossings in the resultant transformed waveform are detected by a detector and used to determine the times at which another version of the original waveform is sampled by a sampling circuit. The characteristics of the surface acoustic wave transversal filter are chosen to be such that each elementary pulse in the original waveform is transformed into an oscillatory waveform, the zero crossings of the different oscillatory waveforms coinciding with one another and defining the sampling times.

62 citations


Journal ArticleDOI
TL;DR: The results indicate that constant attenuation can be compensated for by using an attenuation-dependent filter that reconstructs the transverse section reliably and Computer time requirements are two times that of conventional TCT or positron ECT and there is no increase in memory requirements.
Abstract: A back projection of filtered projection (BKFIL) reconstruction algorithm is presented that is applicable to single-photon emission computed tomography (ECT) in the presence of a constant attenuating medium such as the brain. The filters used in transmission computed tomography (TCT)-comprised of a ramp multiplied by window functions?are modified so that the single-photon ECT filter is a function of the constant attenuation coefficient. The filters give good reconstruction results with sufficient angular and lateral sampling. With continuous samples the BKFIL algorithm has a point spread function that is the Hankel transform of the window function. The resolution and statistical properties of the filters are demonstrated by various simulations which assume an ideal detector response. Statistical formulas for the reconstructed image show that the square of the percent-root-mean-square (percent-rms) uncertainty of the reconstruction is inversely proportional to the total measured counts. The results indicate that constant attenuation can be compensated for by using an attenuation-dependent filter that reconstructs the transverse section reliably. Computer time requirements are two times that of conventional TCT or positron ECT and there is no increase in memory requirements.

54 citations


Patent
29 Jun 1981
TL;DR: In this paper, a phase corrected clock signal recovery circuit (150) for multilevel digital signals includes a transition marker generator (200) for generating a narrow width pulse each time a received multi-level digital signal crosses one of the threshold levels between the adjacent logic levels of multileal signal.
Abstract: As shown in Fig. 4 a phase corrected clock signal recovery circuit (150) for multilevel digital signals includes a transition marker generator (200) for generating a narrow width pulse each time a received multilevel digital signal crosses one of the threshold levels between the adjacent logic levels of multilevel signal. Picket fence-like pulse trains are thus formed, the pulses (transition markers) of which correspond to the threshold crossings of the received digital signal. The pulse trains are interspersed with spaces or eye intervals which correspond to the absence of any threshold crossings. Each eye interval additionally corresponds to the time during which each respective bit of digital signal information is transmitted. The rate of occurrence of the pulse trains is substantially equal to the clock frequency of the received digital signal. A phase error detection circuit (400) is operatively coupled to the output of the transition marker generator (200) and to an electronically tune bandpass filter (300) capable of adjusting the phase of the pulse trains. More specifically, the phase error detection circuit (400) includes an up/down counter (410, 411) and adjusts the phase of the clock signal recovered from the pulse trains such that the number of transition markers generated during the high portion of the clock signal equals the number of transition markers generated during the low portion of the clock signal. Thus, selected transitory edges of the pulses of the recovered clock signal are centered at the middles of the respective eye intervals, that is, at the points in time when each respective bit of multilevel digital signal information occurs. This phase corrected recovered clock signal is conveniently applied to appropriate sampling circuitry to enable sampling of the multilevel digital signal at optimum times, that is, at the center of the eye intervals.

54 citations


Patent
23 Oct 1981
TL;DR: In this article, a light beam emitted from a laser light source is made incident upon a video disc by means of an objective lens and a light flux reflected by the disc is made incidents upon a light detector arranged in a far field of an information track of the disc.
Abstract: A light beam emitted from a laser light source is made incident upon a video disc by means of an objective lens and a light flux reflected by the disc is made incident upon a light detector arranged in a far field of an information track of the disc. The light detector includes four light receiving regions divided in a track direction and a direction perpendicular to the track direction. A first sum of output signals from diagonally aligned two light receiving regions and a second sum of the remaining two light receiving regions are derived and then a sum signal and a difference signal of the first and second sums are formed. The difference signals are sampled by sampling pulses generated at positive going and/or negative going zero cross points of the sum signal to generate sampled values. A tracking error signal is obtained from sampled values.

45 citations


Journal ArticleDOI
TL;DR: The processor incorporates a 16/spl times/16-bit full hardware multiplier and a sophisticated bus structure to minimize bus conflicts, thus attaining the capability to implement 55 second-order filters at a sampling rate of 8 kHz with sufficient dynamic range to process PCM encoded signals.
Abstract: A single-chip, software-programmable digital signal processor, intended for telecommunication applications, has been developed. The processor, fabricated with the most advanced 3 /spl mu/m n-channel E/D MOS technology, incorporates a 16/spl times/16-bit full hardware multiplier and a sophisticated bus structure to minimize bus conflicts, thus attaining the capability to implement 55 second-order filters at a sampling rate of 8 kHz with sufficient dynamic range to process PCM encoded signals. The authors describe the design concept, architecture, instructions, device design, and application techniques.

44 citations


Journal ArticleDOI
M.M Tropper1
TL;DR: A rigorous theoretical analysis of the echo-planar imaging technique is presented, as a result of which a general reconstruction algorithm, applicable to any form of periodic gradient modulation, is derived.

39 citations


Patent
Robert Warren Mortonson1
29 Apr 1981
TL;DR: A detector monitoring the operational status of the field coil circuit in a multiphase alternator and voltage regulator battery charging system is disclosed in this paper, where a first signal at a first terminal is monitored during sampling intervals at a second terminal.
Abstract: A detector monitoring the operational status of the field coil circuit in a multiphase alternator and voltage regulator battery charging system is disclosed Circuit means monitor a first signal at a first terminal of the field coil circuit Means generate sampling intervals on a repetitive basis Circuit means interrupt the excitation signal supplied to the field coil by the voltage regulator during the sampling intervals A second signal is measured during sampling intervals at a second terminal of the field coil circuit Comparator means compare the first and second signals and produce an output signal when the comparison varies from a predetermined value

31 citations


Patent
03 Jun 1981
TL;DR: In this paper, a generalized interpolative procedure was proposed for effecting digital to analog conversion of PCM signals by using generalized interpolation procedure, by sampling the PCM signal at a first sampling rate and supplying each sampled word in succession to a first input of a digital adder; dividing each word at the output of the adder into a first part representing the higher value portion of adder output word and having a length shorter than that of the input word, and a second part representing lower value part of the output word.
Abstract: A method for effecting digital to analog conversion of PCM signals by a generalized interpolative procedure, by sampling the PCM signals at a first sampling rate and supplying each sampled word in succession to a first input of a digital adder; dividing each word at the output of the adder into a first part representing the higher value portion of the adder output word and having a length shorter than that of the adder input word, and a second part representing the lower value part of the adder output word; conducting the second part of each adder output word through a digital, nonrecursive counter feedback filter having a degree greater than one at a clock pulse rate which is an integral multiple of the sampling rate, and supplying each resulting word at the filter output to a second input of the digital adder where it is added to the stored word at the first adder input; converting the first part of each adder output word into an analog signal in a digital/analog converter having a small number of available output values; and passing the analog signal at the output of the converter through an analog lowpass filter.

PatentDOI
TL;DR: A transmitting section periodically radiates a signal wave, and a receiving section receives the signal wave radiated from the transmitting section and reflected from the monitored region to produce the received signal.
Abstract: A transmitting section periodically radiates a signal wave. A receiving section receives the signal wave radiated from the transmitting section and reflected from the monitored region to produce the received signal. A sampling circuit samples the output signal from the receiving section at given time intervals. A memory stores the output signal from the sampling circuit at the time of one period of transmission, and a judging circuit compares the output signal from the sampling circuit at each transmission with the signal previously stored in the memory to detect a change in a state of an object to be detected.

Patent
17 Jun 1981
TL;DR: In this article, a thermovision pyrometer for measuring the temperature of an object t.v. is presented, which is based on the ratio of the flux densities of the respective spectral components detected at the point of observation.
Abstract: A thermovision pyrometer for measuring the temperature of an object t.v. camera for focusing thermal radiation, an optical switch for alternately passing at least two spectral components of the radiation, a detector for sensing each spectral component and for generating respective video signals proportional to the density of the spectral components. The synchronizing signal of the t.v. camera controls the optical switch. The pyrometer also includes a gating circuit for generating a gating marker signal which control the position of the point of observation. The gating circuit also is controlled by the t.v. synchronizing signal. Further, the pyrometer includes a sampling circuit for sampling and measuring the amplitudes of the video signals from both the t.v. camera and the gating circuit, as well as circuitry for determining the temperature of the object based upon the ratio of the flux densities of the respective spectral components detected at the point of observation. This ratio information is transferred to a computer via an information signal transfer switch which switches the information path between the gating circuit and the raster scanning circuit to drive a character generator which displays on a t.v. monitor temperature information relative to an object under investigation. The result achieved is to minimize temperature measurement error due to nonuniformity in surface emissivity of the object or raster sensitivity of the vidicon tube used in the t.v. camera.

Proceedings ArticleDOI
01 Apr 1981
TL;DR: A novel approach to digital sampling frequency conversion based on a single, multistage filter and adapted to conversion between arbitrary, a priori unknown sampling frequency ratios is presented.
Abstract: Digital Audio requires high-quality signal conversion between a variety of sampling frequencies, often in non-trivial integer ratios. In such applications, conventional methods based on analog processing or classical FIR filter rate-changing are not adequate. A novel approach to digital sampling frequency conversion based on a single, multistage filter and adapted to conversion between arbitrary, a priori unknown sampling frequency ratios is presented. Its design, implementation and control are discussed in some detail.

Patent
29 Jan 1981
TL;DR: In this paper, a digital color encoder for a television camera is presented, in which during digitally modulating a carrier of 3fsc (fsc is a color subcarrier frequency) with a digital signal which is obtained by sampling input video information data at a sampling pulse rate having a frequency of 3(n/m)fsc with m and n being relatively small integers, at N line the digital signal is amplitude modulated by 3-phase modulation vectors each having a phase difference of 2/3π from each other.
Abstract: A digital color encoder for a television camera in which during digitally modulating a carrier of 3fsc (fsc is a color subcarrier frequency) with a digital color signal which is obtained by sampling input video information data at a sampling pulse rate having a frequency of 3(n/m)fsc (with m and n being relatively small integers) at N line the digital color signal is amplitude modulated by 3-phase modulation vectors each having a phase difference of 2/3π from each other so as to produce a digitally modulated color signal. At N+1 line, the digital color signal is amplitude modulated by the 3-phase modulation vectors each having a phase opposite to that at the N line so as to produce an output of N+1 line which is then phase inverted to provide a digital modulated color signal. Thus, a digital color television signal with color phase having the standard television signal format is obtained.

Patent
30 Mar 1981
TL;DR: In this paper, a codeword digital data stream, in digitized form, is shaped so that the bit transitions have the form of a portion of a sine waveform and then is applied to a D/A converter.
Abstract: Digital method and apparatus for generation of a digital data stream with the bit transitions shaped to reduce splatter, and minimize droop and overshoot in a radio communications system utilizing digital coded squelch. A codeword digital data stream, in digitized form, is shaped so that the bit transitions have the form of a portion of a sine waveform and then is applied to a D/A converter. A simple filter follows the D/A converter to attenuate sampling noise.

Journal ArticleDOI
TL;DR: A three-dimensional analysis of sampling structures suitable for sampling NTSC signals at twice the color subcarrier frequency is presented, and a method for designing the reconstruction filters is described.
Abstract: Methods for sampling and reconstruction of NTSC video signals at twice the color subcarrier frequency are described and evaluated. A scheme for sampling NTSC signals is characterized by the horizontal sampling frequency and the spatiotemporal sampling structure. For a given sampling frequency, the sampling structure should be chosen to permit the best subjective reconstruction of the analog signal. This paper presents a three-dimensional analysis of sampling structures suitable for sampling NTSC signals at twice the color subcarrier frequency, and describes a method for designing the reconstruction filters. Three sampling schemes were simulated on a number of sequences of NTSC video, and evaluated in a subjective test. The field quincunx (QT) sampling structure was found to give best results. There was no detectable subjective difference between the original and reconstructed sequences in most cases. Minor degradations were detected for some critical images, upon close inspection.

Patent
19 Feb 1981
TL;DR: In this article, the relationship of the duty cycle of the transmitter and the sampling and reset periods of the receiver was investigated to reduce the potentially adverse influences of spurious signals on the receiver.
Abstract: Tracing and identifying electrical conductors in a power distribution network is achieved by use of a transmitter operating on a duty cycle of delivering or absorbing current pulses at a predetermined frequency from the power distribution network, and by use of a remotely located receiver which detects the electromagnetic field signals resulting from the current pulses in a predetermined cyclic manner of operation defined by a sample period and a reset period. During the sample period the receiver supplies an indication of the maximum received strength of the transmitter signal. The relationship of the duty cycle of the transmitter and the sampling and reset periods of the receiver reduce the potentially adverse influences of spurious signals on the receiver. The transmitter may include means for delivering constant energy content pulses to the power distribution network, thereby rendering the signals detected by the receiver insensitive to variations in voltage on the power distribution network. Improved signal filtering is achieved in the receiver by connecting a plurality of relatively low Q filters in series to reduce the effects of ringing and increase the damping factor, or by employing a digital capacitive filter switching technique for precise filtering by phase discrimination.

Patent
06 Jul 1981
TL;DR: In this paper, a microprocessor is provided in a television receiver which is responsive to a clock signal phase locked to a recurrent signal component of a composite video signal, such as a horizontal line rate signal component.
Abstract: A microprocessor is provided in a television receiver which is responsive to a clock signal phase locked to a recurrent signal component of a composite video signal, such as a horizontal line rate signal component. The clock signal frequency is chosen to be an integer multiple of the recurrent signal component and to enable the microprocessor to execute an integer number of uniform instruction cycles during an integer number of periods of the recurrent signal component. The execution of the instruction cycles is brought into a real time phase alignment with the recurrent signal component by causing the microprocessor to execute an instruction during a time interval which is greater than the time required to execute one of the uniform insturction cycles. The phase of subsequently executed uniform instruction cycles is shifted in this manner until signal sampling indicates that the desired phase relationship has been achieved.

Book
01 Jan 1981
TL;DR: In this paper, the authors present some principles of signal recovery: basic mathematical concepts and their physical implementation filtering signal recovery by autocorrelation phase-sensitive detection signal recovery and multipoint correlation by digital technique warehouse recovery multichannel averager the "box-car" detector computer-aided signal recovery.
Abstract: Part 1 Modern semiconductor devices: physical basis of semiconductor device operation single junction devices optoelectronic devices and displays bulk semiconductor mechanisms Part 2 Microelectrical device technology: the planar technique preparation of a pure silicon slice and controlled oxidation preparation of masks and photolithography selective doping thin-film deposition, isolation, interconnection and encapsulation microcircuit functions and limits of circuit integration Part 3 Linear circuit design and building blocks of analogue circuiting: black box representation equivalent circuits interrelation between the various parameters analysis of commonly used linear circuits high frequency circuits in general large - signal circuit design criteria building blocks of analogue circuiting Part 4 Logic design and building blocks of digital circuiting: Boolean algebra and the physical implementation of its concepts minimisation of Boolean expressions binary numbers and codes digital IC terminology families of digital IC's combinational logic circuits and some commonly used MSI functional circuits assemblies sequential logic systems monastable circuits and clock pulse generators digital memories microprocessors Part 5 Principles of digital-to-analogue converters and analogue-to-digital converters: digital to analogue - types of converters - converter terminology - conversion with magnitude and sign analogue to digital - types of converters - converter terminology appropriate choice of converters for certain applications Part 6 Feedback theory and its applications: basic mathematical concepts in feedback theory flow diagrams and linear feedback systems feedback and its consequences instability of linear feedback systems stabilisation techniques practical applications Part 7 Transducers: transducer terminology types of transducers conversion of optical signals into electrical ones modern digital transducers Part 8 Frequency analysis: some properties of Fourier transforms and their applications spectral representation of signals some statistical techniques in signal analysis 2-transforms and sampled signals the time domain and frequency domain convultion, correlation and power spectra of waveforms sampling and reconstitution of electronic signals filters references Part 9 Noise: sources of fundamental noise environmental noise - sources and minimisation noise measurements some commonly encountered experimental situations Part 10 Principles of signal recovery: basic mathematical concepts and their physical implementation filtering signal recovery by autocorrelation phase-sensitive detection signal recovery by autocorrelation multipoint correlation by digital technique warehouse recovery multichannel averager the "box-car" detector computer-aided signal recovery

Patent
26 Jun 1981
TL;DR: In this article, the burst signal of a color television signal is sampled at a rate which is a multiple of burst signal frequency, and the phase of the sampling pulses which are used to sample the burst signals, are adjusted in accordance with the determination, such that burst signals are sampled at the predetermined phase angle.
Abstract: The burst signal of a color television signal is sampled at a rate which is a multiple of the burst signal frequency. A theoretical sample level of the burst signal is determined as a function of at least two of the actual sample levels thereof, the theoretical sample level representing a sample level that would be obtained if the burst signal is sampled at a predetermined phase angle. Based on the theoretical sample level and a predetermined one of the actual sample levels, a determination is made as to whether the burst signal actually is sampled at the predetermined phase angle. The phase of the sampling pulses which are used to sample the burst signal, is adjusted in accordance with the determination, such that the burst signal is sampled at the predetermined phase angle.

Patent
25 Sep 1981
TL;DR: In this paper, the echo cancellation (100) algorithm is proposed to eliminate undesirable echo appearing in a long-distance telephone network having a four-wire circuit (120) and a two-wire (3) at the junction (5) of the fourwire circuit and the twowire circuit, and is particularly suited for a long distance digitized telephone network where the incoming and outgoing digital signals have mutually different sampling rates.
Abstract: The echo canceller (100) eliminates undesirable echo appearing in a long-distance telephone network having a four-wire circuit (120) and a two-wire circuit (3) at the junction (5) of the four-wire circuit (120) and the two-wire circuit (3) and is particularly suited for a long-distance digitized telephone network where the incoming and outgoing digital signals have mutually different sampling rates. The echo canceller (100) comprises a sample interpolator (10) for converting the incoming digital signal into a digital signal having the same sampling rate as that of the outgoing digital signal on the basis of relative positions of the sampling timings for corresponding imaginary envelopes of the incoming and outgoing digital signals, an echo estimator (11) responsive to the output of the sample interpolator (10) for producing an estimated echo signal to cancel said echo signal, and means (12) for subtracting the estimated echo signal from the unprocessed digital signal to produce an echo cancelled digital signal.

Patent
Labedz Gerald P1
08 Jan 1981
TL;DR: In this paper, a digital pseudo continuous correlation tone detection method was proposed for continuous tone controlled squelch systems, which utilizes sample matrix limiting (26 and 28) to provide rapid reverse burst turnoff, as well as background detection to avoid adjacent channel reverse burst turning off falsing.
Abstract: Method and apparatus (Fig. 1) for sampling input signals (20) of different frequencies and providing a detect signal when the input frequency has a predetermined value suitable for use as a tone decoder for continuous tone controlled squelch systems. The method utilizes digital pseudo continuous correlation tone detection, and includes sample matrix limiting (26 and 28) to provide rapid reverse burst turnoff, as well as background detection to avoid adjacent channel reverse burst turnoff falsing.

Patent
30 Mar 1981
TL;DR: In this paper, a method for monitoring the bit error rate of digital signals according to the pseudo error rate technique is proposed, which includes effecting an optimal regeneration of the signal elements in a main signal path by sampling each signal element in that path, and effecting a degraded regeneration in a secondary path.
Abstract: A method for monitoring the bit error rate of digital signals according to the pseudo error rate technique which includes effecting an optimal regeneration of the signal elements in a main signal path by sampling each signal element in that path, and effecting a degraded regeneration of the signal elements in a secondary path. Regeneration in the secondary signal path is carried out by sampling each signal element twice to determine its value, once a fraction of half the element period before the midpoint of the element period and once the same fraction of half the element period after the midpoint of the element period, the two sampling moments being rigidly coupled together in time, comparing the result of each of the two samplings of one element in the secondary signal path with the result of the sampling of the same element in the main signal path, and utilizing the number of disagreements occurring over a given time interval as a measure for the bit error rate in the main signal path.

Journal ArticleDOI
TL;DR: It is shown, however, that to approximately minimize the mean-square error of these estimates, one should sample at twice the Nyquist rate.
Abstract: In power spectral estimation of a continuous band-limited random process, one must usually estimate the continuous autocorrelation function at lags which are multiples of the Nyquist interval. This is done by sampling the random process at the Nyquist rate and basing the autocorrelation lag estimates on these samples. It is shown, however, that to approximately minimize the mean-square error of these estimates, one should sample at twice the Nyquist rate. The resultant decrease in mean-square error is most pronounced for short data records. For longer data records, the use of Nyquist rate sampling proves to be adequate.

Journal ArticleDOI
TL;DR: An experimental GPS receiver/digital processing system that has been operating for two years, and an improved engineering development model that is now in test are described, providing a basis for realization of the high degree of very large-scale integration (VLSI) potential for development of small economical GPS sets.
Abstract: THIS PAPER describes all-digital baseband correlation processing of GPS signals. The features of this highly digital mechanization are its (1) potential for improved anti-jamming (AJ) performance, (2) fast acquisition by a digital matched filter, (3) reduction of adjustment, (4) increased system reliability, and (5) provision of a basis for realization of the high degree of very large-scale integration (VLSI) potential for development of small economical GPS sets. Described are an experimental GPS receiver/digital processing system that has been operating for two years, and an improved engineering development model that is now in test. The basic technical approach consists of a broadband, fix-tuned RF converter followed by a digitizer, digital-matched-filter acquisition section; phase-and delay-lock tracking via baseband digital correlation; software acquisition logic and loop filter implementation; and all-digital implementation of the feedback numerically controlled oscillators (NCOs) and code generator. Baseband in-phase (I) and quadrature (Q) tracking is performed by an arctangent angle detector followed by a phaseunwrapping algorithm that eliminates false locks induced by sampling and data bit transitions, and yields a wide pull-in frequency range approaching one-fourth of the loop iteration frequency. Test data from the experimental unit includes basic resolution and computation noise of the digital processing, pseudorange and range-rate errors, and acquisition times for the digital matched filter.

Patent
11 Mar 1981
TL;DR: In this article, an analog synthesized signal is produced throughout the first portion of each period of the analog noisy test signal by means of the digital value of samples memorizing in a random access memory and a digital-to-analog converter.
Abstract: In the error signal feature sensor of the device, an analog synthesized signal is produced throughout the first portion of each period of the analog noisy test signal to be acquired by means of the digital value of samples memorizing in a random access memory and a digital-to-analog converter. The noisy signal and the synthesized signal are compared therebetween at predetermined sampling times in predetermined number. The sign and modulus of the error signal in relation to a predetermined threshold voltage are written in the memory. During the second portion of the period without the noisy signal, a processing unit as a microprocessor calculates the new digital values of the samples in term of comparison results and the preceding digital values of the samples in accordance with a particular algorithm. A new comparison and calculation cycle is performed and so on. After acquisition in steady working, the synthesized signal coincides with the average value of the noisy signal at the predetermined sampling times.

Patent
07 Apr 1981
TL;DR: In this paper, the radiated signal of an instrument landing system (ILS) has several monitor probes for the radiation, and the RF signal is demodulated to obtain a composite signal, from which information is extracted by sampling at specific points of one cycle.
Abstract: The radiated signal of an instrument landing system (ILS) has several monitor probes for the radiation. For each probe the RF signal is demodulated to obtain a composite signal, from which information is extracted by sampling at specific points of one cycle. Sample voltages are combined by addition, subtraction, and division to obtain relative RF level, total percentage modulation, and difference of the depth of modulation (DMM). A digital monitor is the preferred embodiment, utilizing a microprocessor for converting the sampled voltage into binary data. The monitor accepts inputs from eight probes and is self synchronized. Data is compared with established limits to indicate an alarm condition. In another embodiment, an analog monitor has a processor board for each input to be monitored, and a common control board.

Patent
01 Jun 1981
TL;DR: In this article, the authors proposed a scan converter circuit for use in a imaging system that uses a sinusoidally oscillating scanning reflector for scanning an object and a constant rate scanned display monitor for displaying an image of the object.
Abstract: A scan converter circuit for use in a imaging system that uses a sinusoidally oscillating scanning reflector for scanning an object and a constant rate scanned display monitor for displaying an image of the object The circuit enables a variable time rate of sampling of picture elements in the object field to match a desired constant display rate of picture elements in the CRT display monitor The circuit comprises a constant rate VCO clock and a sampling clock that produces periodically variable rate pulses, the periodicity of which being phase locked with zero crossings of the oscillating reflector and wherein the pulses are derived from the constant rate VCO clock The sampling clock enables an image sensor to sample the radiance levels at a rate which varies with the sinusoidal sweep speed of the oscillating reflector The circuit further includes a memory circuit for buffering and reversing the order of picture element information during at least one sweep direction, and a transfer control circuit for alternately supplying to the CRT display monitor picture element representations from the sensor and the temporary memory so that picture elements obtained during a right-to-left sweep and a succeeding left-to-right sweep are accurately aligned with each other and bear a one-to-one correspondence with picture elements in the image field

Patent
29 Apr 1981
TL;DR: In this article, the high frequency pulses are outputted so as to be distributed substantially in equal numbers on either side of the center of each sampling period for each value of the sampled input signal.
Abstract: A laser recorder in which pictures with gradations at equal density intervals are reproduced with a high accuracy. An input analog video signal is sampled with a sampling pulse at a predetermined sampling rate. For each value of the sampled input signal, a number of high frequency pulses are outputted to modulate a semiconductor laser. The high frequency pulses are outputted so as to be distributed substantially in equal numbers on either side of the center of each sampling period.