Showing papers on "Sampling (signal processing) published in 1985"

Multirate digital signal processing

Abstract: There has been a great deal of material in the area of discrete-time transforms that has been published in recent years. This book does an excellent job of presenting important aspects of such material in a clear manner. The book has 11 chapters and a very useful appendix. Seven of these chapters are essentially devoted to the Fourier series/transform, discrete Fourier transform, fast Fourier transform (FFT), and applications of the FFT in the area of spectral estimation. Chapters 8 through 10 deal with many other discrete-time transforms and algorithms to compute them. Of these transforms, the KarhunenLoeve, the discrete cosine, and the Walsh-Hadamard transform are perhaps the most well-known. A lucid discussion of number theoretic transforms i5 presented in Chapter 11. This reviewer feels that the authors have done a fine job of compiling the pertinent material and presenting it in a concise and clear manner. There are a number of problems at the end of each chapter, an appreciable number of which are challenging. The authors have included a comprehensive set of references at the end of the book. In brief, this book is a valuable contribution to the general areas of signal processing and communications. It can be used for a graduate level course in perhaps two ways. One would be to cover the first seven chapters in great detail. The other would be to cover the whole book by focussing on different topics in a selective manner. This book by Elliott and Rao is extremely useful to researchers/engineers who are working in the areas of signal processing and communications. It i s also an excellent reference book, and hence a valuable addition to one’s library

Noise and filtration in magnetic resonance imaging.

Abstract: Noise in two-dimensional Fourier transform magnetic resonance images has been investigated using noise power spectra and measurements of standard deviation. The measured effects of averaging, spatial filtering, temporal filtering, and sampling have been compared with theoretical calculations. The noise of unfiltered images is found to be white, as expected, and the choice of the temporal filter and sampling interval affects the noise in a manner predicted by sampling theory. The shapes of the imager's spatial frequency filters are extracted using noise power spectra.

Fiso sampling system

Abstract: A fast-in, slow-out sampling system that operates at a very high sampling frequency at high accuracy. The system includes a parallel processing sampling structure controlled by a precision pulse generation system.

Power converter with duty ratio quantization

Abstract: A discrete proportional-integral-differential controller, driven from a sampling digital error amplifier, is used to penetrate a quantized duty ratio control signal to provide dynamic output voltage regulation for switching dc-to-dc power converters. The sampling frequency of the digital PID controller is equal to the switching frequency of the power converter, so the digital controller may be used at different switching frequencies without recompensation. Digital techniques are also used to provide output current limiting, soft-start, undervoltage lockout, overvoltage shutdown, and power master-clear indications.

Auto focus circuit for video camera

Abstract: An auto focus circuit for a video camera comprises an A-D converting circuit (7) for converting to a digital amount a high frequency component absolute value output of a luminance signal in a sampling area for focusing. The A-D converting circuit (7) is connected so that the high frequency component absolute value output of a luminance signal is directly converted to a digital amount. Then, the signal converted to a digital amount is added in an integrating circuit (12) for each field and the signal amount in one field and the signal amount in the coming one field ahead of it or behind it are compared in a comparing circuit (10) so that the output of comparison serves for control of focusing. Thus, addition processing of the high frequency component of the luminance signal, that is, averaging processing is performed digitally in the integrating circuit (12). Accordingly, as compared with the case of analog averaging processing of a signal, the processing operation is stable and as a result the focusing precision is improved.

Stereoscopic television picture transmission system

Abstract: A stereoscopic television picture transmission system includes a device (14) for obtaining a picture signal with respect to one of right and left pictures in a stereoscopic television, circuitry (22) for obtaining a difference signal between a right picture signal for the right picture and a left picture signal for the left picture, circuitry (27, 28, 29, 30) for effecting sub-Nyquist sampling of the difference signal at a frame period relating to a critical frequency for stereoscopic visual perception in a direction of depth to obtain a sampled difference signal, circuitry (36, 42) for combining one picture signal with the sampled difference signal to form a combined signal and for transmitting the combined signal, circuitry (50) for separating one picture signal and the difference signal from the transmitted combined signal, circuitry (56, 58, 60) for judging a motion between frames of the separated one picture signal, circuitry (62, 64) responsive to the motion judgement result for effecting interframe interpolation of the separated difference signal, and circuitry (66) for combining the separated one picture signal with the interframe interpolated difference signal to obtain the other picture signal of the right and left picture signals. When a frequency band occupied by a motion picture is compressed in accordance with the invention, the high frequency component of the difference signal, which would be difficult to transmit were the difference signal merely compressed, can be transmitted within the frequency band for a conventional one channel television signal.

A 6-Bit/200-MHz Full Nyquist A/D Converter

Abstract: This paper deals with the development of an extremely fast 6-bit flash A/D converter. To gain insight into the nature of speed limitations, the effects arising from operation at very high sampling rates have been investigated. This led to the implementation of an optimized double-stage comparator circuit. The chip has been fabricated in a fast standard oxide isolated bipolar process. At a sampling rate of 200 MHz, measurements show excellent dynamic performance (high signal-to-noise ratio, no error codes) up to input frequencies of 100 MHz.

Digital phase-locked loop and frequency measuring device

Abstract: Method and apparatus are disclosed for providing a sampling signal having a frequency which is maintained in constant proportion to the frequency of an input signal. The input signal is sampled at instants determined by the sampling signal to provide a plurality of data signals associated with one cycle of the input signal. A signal processor is adapted to receive first and second pluralities of data signals associated with first and second cycles of the input signal and to perform two discrete Fourier analyses to provide two phasor signals representing two voltage phasors of respective fundamental frequencies of the discrete Fourier transforms. The phasor signals are used to generate a difference signal indicative of the angle between the two voltage phasors and, therefore, proportional to the difference between the sampling frequency and the input frequency. The difference signal is used to modulate the period of the sampling signal such that the frequency of the sampling signal is maintained in constant proportion to that of the input signal.

Timing Recovery in Digital Subscriber Loops

Abstract: Tradeoffs in the design of the timing recovery functions in a subscriber loop receiver are analyzed. The techniques considered are applicable to both the echo cancellation (EC) and time compression multiplexing (TCM) methods of full duplex transmission. Emphasis is on those techniques that lend themselves to implementation in MOSLSI technology, where the objective requirement is that timing recovery be implemented on a sampled-data signal (with the minimum possible sampling rate where EC is used). The wave difference method (WDM) for timing recovery appears to be the best candidate. A detailed study of its performance is carried out analytically and by computer simulation for the case of binary and alternate mark-inversion (AMI) line coding. A closed form expression describing the binary jitter performance of the WDM and its continuous time counterpart, the spectral line technique, is used to compare the two techniques. Analytical and simulation results for recovered phase and jitter are presented for various cable pulse responses carefully chosen to represent worst-case or nearly worst-case conditions. Two methods for including frequency detection in the WDM, the quadricorrelator and the rotational detector, are also simulated.

Waveform disturbance detection apparatus and method

Abstract: A waveform disturbance detection apparatus for detecting disturbances in alternating current electromagnetic energy waveform, the alternating current electromagnetic energy waveform having a plurality of periodic, substantially similar cycles. The detection apparatus comprises converter means for sampling the electromagnetic energy waveform, generating a plurality of samples, and converting the samples into digital signals. The detection apparatus also comprises processing means for evaluating the digital signals so as to detect disturbances in the electromagnetic energy waveform, wherein the processing means detects the disturbances by comparing a particular one of the digital signals that represents a particular one of the samples in a particular one of the cycles with a corresponding one of the digital signals that represents a corresponding one of the samples from the remaining cycles.

Sampling clock pulse generator

Abstract: A sampling pulse generator receives a plurality of clock signals having the same frequency and phase differences. An additional signal, which may be a clock-run-in signal is also inputted to the generator. Phase relationship data are constructed and assembled and an optimum one of the clock signals is selected and outputted based on the phase data.

Digital phase locked loop synchronizer

Abstract: A phase locked loop (PLL) arrangement comprising a local crystal oscillator (23) and a tapped delay chain (15) of analog delay elements (17). Connected to the delay chain taps are a flash register (25) consisting of latches which store the tap signal values at each data signal transition, and an output multiplexer (37) for selecting one of the tap signals as phase shifted output clock. Contents of the flash register are encoded by an encoder (33) which furnishes a value representing the phase offset between data signal and local clock signal. By a look-up table (41), the phase offset is converted to a phase selection value controlling the output multiplexer. The delay chain serves two purposes: Phase offset detection and clock signal phase shifting. No sampling or control signals are used which have a higher frequency than that of the system clock.

Narrow bandwidth signal transmission

Abstract: A method and apparatus for compressing digital data for transmission and reception in a narrow bandwidth, the method comprising preliminarily smoothing raw data according to a spatial convolution or running average technique, sampling the convoluted or averaged data to produce a subset having information from the full set of raw data, but fewer data points, determining the energy of the subset with a transform coder, encoding the transformed image, predicting the full set of raw data points at and between the points in the subset by means of a prediction algorithm, subtracting the raw data from the thus-predicted values to develop a difference signal, encoding one field of the difference signal and transmitting the encoded transformed data and the encoded difference signal to a receiver employing the same prediction algorithm. The signal is decoded in the receiver to produce both the transformed image and the difference signal. The decoded transformed image is applied to the predictor, and then subsampled and added to the decoded difference signal, thereby recovering the raw data. Statistical techniques are used in encoding to assign the shortest of variable length data words to the most frequent occurrences of given data values. The preliminary convolution or averaging reduces the extent of standard deviation of data values. The apparatus includes video processing hardware adapted to the method, and may include parallel processing for producing the convoluted average, subtraction, encoding, decoding or addition.

Arrangement for receiving digital data comprising an arrangement for adaptive rate recovery

Abstract: "Arrangement for receiving digital data comprising an arrangement for adaptive rate recovery." A digital data receiving arrangement, which adapts itself to channel variations of a transmission system, comprises an adaptive receiver stage (11), having an adaptive equalizer and at least one sampler, and pro-ducing, at a certain rate, complex samples Yk from the input signal x(t), a decision circuit (14) supplying de-tected complex samples ak and an adaptive rate recovery circuit (12) determining the optimal sampling instant by minimizing a quadratic function J which represents the difference between yk and ak. The adaptive rate recovery circuit comprises means (121) for shaping a primary clock signal in accordance with a secondary clock signal, whose period is twice the period of the primary clock and whose consecutive ascending edges are spaced in time by T1 and T2, said secondary clock producing alternately two sampling instants ? and ? + .DELTA.?. By minimizing the function J, on the basis of the difference determined for two instants ? k and ?k + .DELTA.?, the control of the rate recovery is defined for the consecutive sampling instants ?k and ?k+1.

Inertial reference system

Abstract: An inertial sensor assembly (ISA) includes a cluster of three ring laser gyros, each gyro producing an output signal having a pulse repetition rate representative of the rate of angular deviation of the ISA about one of three coordinate axes X, Y, and Z. The ring laser gyros are synchronously dithered at a relatively constant rate. The ISA also includes a triad of three accelerometers, with each accelerometer producing an output signal representative of the rate of velocity deviation of the ISA along one of the X, Y, and Z coordinate axes. A first processor, P1, accumulates the pulses produced by each ring laser gyro over its dither period. The resultant counts are stored in registers for subsequent sampling by the P1 processor at a periodic sampling rate which is greater than the dither rate. The P1 processor then synchronizes each sampled pulse count to a common sampling interval, thereby eliminating errors otherwise caused by using positional data values taken at different times. The P1 processor also compensates the ring laser gyro and accelerometer-produced signals at the sensor and the system level for effects such as temperature, bias offsets, scale factor and misalignment by the use of compensating coefficients stored in electrically erasable, programmable read-only memory. The processed data from the P1 processor are passed to a P2 processor which performs navigational computations to thereby produce computed positional information.

Investigation of basic imaging properties in digital radiography. 3. Effect of pixel size on SNR and threshold contrast.

Abstract: The effect of pixel size on the signal-to-noise ratio (SNR) and threshold detection of low-contrast radiologic patterns was investigated theoretically for digital radiographic systems. The SNR based on the perceived statistical decision theory model, together with the internal noise of the human eye-brain system, was calculated by using two-dimensional displayed digital signal spectra and noise Wiener spectra. Threshold contrasts were predicted from the calculated SNR for various combinations of object size and shape, pixel size, resolution, and noise. Predicted threshold contrasts agreed well with those determined experimentally in an observer performance study. The threshold contrast of small objects increased substantially as the pixel size increased beyond 0.2 mm. For pixel sizes of 0.1 and 0.2 mm, however, the threshold contrasts were similar. Since a digital system is not shift invariant, a range of threshold contrast results for a small object and a large pixel, depending on the alignment of the object position relative to the sampling coordinates.

Effect of sampling frequencies on computation of the maximum velocity of saccadic eye movements

Abstract: The maximum velocity of saccades is widely used in the clinical assessment of topographical diagnoses. Several methodological factors affect the maximum velocity results. The sampling frequency, the resolution of the analog-digital converter, and filtering of the signal are the most important factors. The sampling frequency should preferabel be higher than 300 Hz. Frequencies below 200 Hz severily deform the velocity profile. The resolution of the analog-digital converter should be 10 bits or more. A theoretical model was constructed for maximum velocity computation. A case study of electro-oculographic and photoelectric recordings confirmed the theoretical model.

Converting and decoding receiver for digital data recorded in analog form on magnetic tape

Abstract: Multi-phase/multi-level modulation data signals recorded on tape after conversion from original digital data are first converted to complex digital signals in an analog-to-digital converter in which the sampling rate is set by a pulse generator frequency controlled by the received signals through a control loop which develops a frequency control voltage (A). The complex digital signals have their real and imaginary parts separately filtered by filters of variable propagation time, but of constant bandwidth to produce complex signals to which the nearest permissible output complex signal (reference signal) is selected by a decision circuit (17), for final conversion to binary signals by a decoder (19) and a shift register (20). Timing shift correction is based on comparison of the received signals and reference signals of the decision stage to produce a control signal (φ) which further processed by addition to its previous value to produce a timing correction signal (A) which is applied both to the pulse generator for the sampling frequency of the analog-to-digital converter and to control the propagation time of digital non-recursive filters (14, 15). The timing correction signal (A) control of the filter propagation time makes possible a rapid timing shift correction that overcomes tape jitter effects. It is not necessary to stabilize the received carrier frequency because the tap recording preserves the relation between the sampling/keying frequency and the carrier frequency.

Super resolving partial wave analyzer-transceiver

Abstract: Methods and electronic apparatus for recovering relatively high-resolution information from a partial wave representation of an information signal. According to the invention, there is provided a method of operating on a given partial wave function, or of producing a partial wave representation of an information signal as part of the method. Portions of the partial wave representation of the information signal are synchronously selected as by signal sampling under control of an interpolated high frequency clock. An inverse partial wave representation of the selected portions of the transformed signal is then performed, and the inverse partial wave representation is linearly deconvolved to produce a high resolution equivalent of high-resolution information signal. The invention may include an analytic converter for removing the effects of any dispersion of the partial wave representation. While the concepts involved are universally adaptable to signal processing systems, preferred embodiments of the invention as applied to a modem network and to an interferometer are described.

Infrared detector and imaging system

Abstract: An infrared detector and imaging system responsive to the scanned image from an objective lens and scanner system, the infrared detector and imaging system comprising: a detector substrate; a sparsely populated staggered detector array formed on the detector substrate, the detector substrate having a focal plane surface receiving the scanned image from the objective lens and scanner system. A clock means provides clock signals. A control signal means is responsive to the clock signal for providing a sequence of predetermined scanner position signals. A servo responsive to each scanner position signal commands the scanner means to locate the scanned image at predetermined positions on the focal plane. A detector signal integration means receives and integrates an array of detector signals from the sparsely populated detector array. A sampling means samples the amplitudes of each integrated signal from each image and digitizes each integrated signal amplitude to provide an array of digitized integrated detector signal values for each successive scanned image. A digital memory means stores each successive array of digitized integrated detector signal values in corresponding image position memory locations.

Synchronization of multichannel receiver based on higher quality channels

Abstract: A synchronization of a multichannel receiver based on higher-quality channels capable of establishing and maintaining timing synchronism stably even when the transmission channels deteriorate due to fading. A plurality of power detectors measure the quality of the baseband signals of a plurality of channel lines and generate a quality signal. A plurality of equalizers generate timing phase deviation signals for the channel lines. A selecting circuit selects at least one channel line using the quality signal. A frequency controlling circuit generates a frequency control signal in accordance with at least one timing phase deviation signal from the selected channel line and controls a sampling frequency of a sampling circuit which converts a transmitted signal into digital form. Thus, the sampling frequency for all channel lines is determined by using the timing phase deviation signal obtained from a high quality channel line. As a result, the timing phase control can be established with stability.

Video recorder with a magnetic recording medium in the form of a tape

Abstract: To raise the integration level of a video recorder, and to provide a uniform circuit concept suitable for all three color-television standard (PAL, NTSC, SECAM) which, in particular, requires only slight modifications for adaptation to the respective standard, signal processing is performed by fast digital circuits whose signals are stored on the recording medium not in digital form, but after digital-to-analog conversion. The composite color signal is converted into digital form by a fast analog-to-digital converter (aw) whose sampling signal (fc) has a fixed frequency (Fc) for all three color-television standards. Digital signal processing in the chroma channel is performed at a fixed subcarrier frequency (zt) for all three color-television standards which is an integral subharmonic of the sampling frequency (Fc).

Rotary head type PCM recording and reproduction method and system

Abstract: A data recording/reproducing method and apparatus for' carrying out the method in a rotary head type PCM recording/reproducing apparatus including at least two magnetic heads (10, 11), a rotatable cylinder (9) having mounted thereon the magnetic heads in diametrical opposition at an angle of 180°, an A/D converter (6) for sampling an analog signal such as audio signal and converting it to a digital signal, and a signal processing circuit (7, 14) for adding the digital signal with an error detecting and correcting code, synchronizing signal and control signal, wherein the output of the signal processing circuit is recorded on a magnetic tape (12) or the signal recorded on the magnetic tape is reproduced. In recording operation, the odd-numbered sample data and the even-numbered sample data are discriminatively extracted and stored. The stored data corresponding to an amount of data outputted from the A/D converter (6) and completed within a predetermined time is selectively read out and supplied to the two heads to thereby record the data in such a manner that the odd-numbered data and the even-numbered data are recorded separately on the track basis (24, 25) or alternatively recorded separately on a preceding half (R-ODD, L-ODD) and a succeeding half (L-EVEN, R-EVEN) of each track. The error detecting and correcting code is prepared on the basis of the data to be recorded in each track. In reproduction, upon detection of drop-out of data from one of the two heads, the drop-out data is corrected through interpolation procedure to thereby reconstitute the original analog signal.

Digital sample and hold phase detector

Abstract: The digital sample and hold phase detector to compare the phase relationship between input pulses and a high frequency reference clock comprises a digital counter arrangement coupled to count the high frequency reference clock to produce a digital ramp signal and a digital sampling arrangement coupled to at least the input pulses and an output of the counter arrangement to enable the input pulses to sample the digital ramp signal and produce a digital phase difference signal.

Tone signal processing device

Abstract: A digital filter is provided between a tone signal generation circuit which supplies a digital tone signal in accordance with a first sampling frequency and a sampling circuit which resamples this digital tone signal in accordance with a second sampling frequency which is lower than the first sampling frequency. This digital filter filters the input digital tone signal with such amplitude-frequency characteristics as to be able to substantially remove an aliasing noise produced due to the second sampling frequency (e.g., with low-pass filter characteristics having a cut-off frequency which is 1/2 the second sampling frequency). This removes high frequency components producing an aliasing noise from the digital tone signal before it is applied to the resampling circuit whereby generation of the aliasing noise in resampling is prevented. The resampling is performed for adapting the digital tone signal to an operation clock frequency of an effect imparting circuit provided in a posterior stage for imparting, in digital, a tone effect such as a modulation effect to the digital tone signal.

Method and apparatus for level measurement with microwaves

Abstract: The invention concerns a method and an apparatus for measuring the level of a material with microwave signals. The apparatus consists of a signal processing unit (10) and a transmitter unit (1) of known type. The transmitter unit produces a measuring signal having a frequency (f m ) corresponding to the distance (H) to be measured and a reference signal having a frequency (f r ) corresponding to an accurately known length (L). In the signal processing unit (10) the reference signal is multiplied by a selectable number (AQ) which is proportional to the quotient of an assumed value for the distance divided by the known length (L), after which the frequency is divided by a fixed number (Z) so that the frequency of the signal after multiplication and division becomes equal to the expected frequency of the measuring signal. Thereafter the control signal thus produced is mixed with the measuring signal, for determination of the phase difference between them, which is sampled in each of a succession of regular sampling intervals, and the change in phase difference through the successive sampling intervals is calculated for determining a correction term for the assumed distance.

Digitally Phase Modulated (DPM) Signals

Abstract: Some properties of digitally phase modulated (DPM) signals are presented. Phase modulation with (overlapping) pulses generated by a digital FIR filter belong to this class, which may be considered to be a practical approximation to continuous phase modulated (CPM) signals. The power spectra of DPM signals are derived analytically. The ability of these signals to operate through an additive white Gaussian noise channel is assessed by calculating their minimum Euclidean distance. Their noise and spectral properties are found to be similar to those of CPM signals. Assuming that a Viterbi decoder is used to resolve symbol interference, the out-of-band power tends to decrease as the pulse duration increases, and the noise immunity is enhanced. At the same time the receiver complexity grows exponentially. Hence, noise immunity and spectrum compactness are achieved at the cost of higher received complexity. Modems for DPM signals are believed to be easier to implement than those for CPM signals. This is because filter design is simple and a residual carrier component can be retained to facilitate carrier regeneration. Furthermore, the accumulated carrier phase does not need to be continuously evaluated in order to perform matched filtering. The analytic results derived are supported by measurements and simulations.

Analog-to-digital conversion

Abstract: Analog-to-digital converters are subject to various error inducing factors such as offset errors, scale factor instability, quantisation errors, bit weighting errors, and particularly where samples from two or more multiplexed input signal channels are to be digitized, cross-talk errors in the form of signal residues from one channel which affect subsequent channels. The analog-to-digital conversion apparatus described herein comprises a multiplexer for sampling a series of input channels in a sequence which repeats several times over a predetermined digital value update interval, an analog-to-digital converter which digitizes the samples, and an adder/memory combination for summing the samples of each signal during the update interval. To reduce the scale factor errors, a reference voltage signal is applied as one of the channels so that a digitized value of the reference, the digitization being subject to the same instabilities as occur in relation to the other signals, becomes available for correcting the digital values of the other signals. To ensure that this does not just lead to proper scale factor correction at a single point in the converter range, all the input signal samples are combined with a dither signal in the form of a ramp signal which extends over one half of that range and repeats twice during each update interval. The dither signal also includes a pseudo-random or noise component to reduce the quatisa- tion errors. The dithering also reduces the bit-weighting errors. Offset errors are reduced by an auto-zeroing technique in which half the samples taken in each update interval are inverted prior to digitization and re-inverted after digitization. Preferably, to reduce cross-talk, the auto-zeroing does not just comprise inverting and re-inverting for one complete half of the update interval - rather the auto-zeroing 'on' signal comprises a chosen binary sequence with one bit for each sample. The auto-zero 'on' periods still sum to half the update interval but are distributed over that interval, in effect, so as to decorrelate the channels. By making the update interval equal the period of some dominant noise component which may appear in the input channels, ie the gyro wheel noise in the case of an inertial navigation system, this noise component can be averaged out by the auto-zeroing and sample summation.