Showing papers on "Sampling (signal processing) published in 1996"

Improving an OFDM reception using an adaptive Nyquist windowing

Abstract: This paper explains how a windowing of the OFDM-signal in the time domain contributes to its improved reception. The windowing uses the part of the guard interval that is not disturbed by multipath reception. The length of the window adapts to the transmission conditions. This window may be realized with a raised cosine or other kind of function that fulfils the Nyquist criterion. An easy way to implement the windowing while keeping the FFT complexity low is also shown. The impact of windowing for discrete sine spurious, white noise, phase noise and frequency deviations is also given. OFDM is of interest in terrestrial broadcasting.

Method for generating real time degree of focus signal for handheld imaging device

Abstract: A method for generating, substantially in real time, a user perceptible indication of the degree to which the distance between a handheld imaging device and a target object approximates the in-focus distance therebetween. A stored image of the target object is sampled, in accordance with a pattern of sampling addresses, to determine the magnitude of the slopes of the transitions of the stored image. The stored image is also sampled to determine the contrast value of the stored image. The highest magnitude slope values and the image contrast value are combined to produce a focus metric signal that is indicative of the degree to which the imaging device approximates an in-focus condition. The focus metric signal is then used to generate a user perceptible signal that can be utilized by an operator to move the imaging device toward its in-focus distance.

Signal processing system

Abstract: A CMOS integrated signal processing system for a sampling receiver includes a timing recovery circuit, wherein an on-chip numerically controlled oscillator is operative at periods T that are initially equal to the nominal baud rate of the signals controls a sinc interpolator receiving samples at the sampling rate. A loop filter is coupled to the sinc interpolator and to the numerically controlled oscillator. The arrangement is capable of handling various symbol rates. The system includes a circuit for carrier recovery, having a second on-chip numerically controlled oscillator, a digital derotation circuit responsive to the second numerically controlled oscillator, accepting an in phase component and a quadrature component of the sampled signals. An adaptive phase error estimation circuit is coupled in a feedback loop.

A comparison of adaptive and nonadaptive filters for reduction of power line interference in the ECG

Abstract: We have investigated the relative performance of an adaptive and nonadaptive 60-Hz notch filter applied to an ECG signal. We evaluated the performance of the two implementations with respect to adaptation rate (or transient response time), signal distortion, and implementation complexity. We also investigated the relative effect of adaptive and nonadaptive 60-Hz filtering on ECG data compression. With a 360 Hz sample rate and an adaptation time of approximately 0.3 s for a 1 mV 60-Hz signal, the adaptive implementation is less complex and introduces less noise, particularly in the ST-segment, into a typical ECG signal. When applied to ECG signals, prior to data compression by average beat subtraction and residual differencing, the residual signal resulting from the adaptively filtered signal had an average entropy 0.31 bits per sample (bps) lower than the unfiltered signal. The nonadaptive 60-Hz filter produced an average entropy decrease of 0.08 bps relative to the unfiltered ECG.

Interpolating operation method and apparatus for image signals

Abstract: An original image signal, which represents an original image and are composed of original image signal components representing a plurality of sampling points, that are arrayed at predetermined intervals and in a lattice-like form, is obtained. A judgment is made as to whether an interpolation point belongs to an image edge portion, at which the change in the original image signal is sharp, or belongs to a flat portion, at which the change in the original image signal is unsharp. Interpolating operation processes, one of which is to be employed for the interpolation point, is changed over to each other in accordance with the results of the judgment. Interpolated image signal components corresponding to interpolation points are thereby obtained from the interpolating operation processes such that a visible image, in which a character pattern and an image edge portion are free from any step-like pattern and are sharp and a flat portion has an appropriate level of sharpness, can be reproduced from the interpolated image signal components.

Sampling in digital signal processing and control

Abstract: Fourier analysis sampling and reconstruction analysis of discrete-time systems discrete-time models of continuous deterministic systems optimal linear estimation with finite impulse response filters optimal linear estimation with state-space filters periodic and multirate filtering discrete time control sampled data control generalized sample-hold functions periodic control of linear time-invariant systems multirate control optimal control of periodic systems

FIR filter design for frequency invariant beamformers

Abstract: Two methods of implementing FIR filters for a frequency invariant beamformer are presented. Each of these methods uses a single underlying set of filter coefficients obtained directly from the desired beamformer response. One method uses multirate processing, and the other is based on a single sampling rate.

Frequency domain signal reconstruction compensating for phase adjustments to a sampling signal

Abstract: In a digital communications system, a sampled signal is precisely reconstructed (rather than approximated) even in situations where the phase of the sampling signal is adjusted. More particularly, the sampled signal is compensated in the frequency domain for phase adjustments to the sampling instance in the time domain. In the context of echo cancellation, an echo transfer function is generated representing the echo channel impulse response. Aliased components present in the echo impulse response are specifically identified and compensated for in the frequency domain by treating each spectral filter coefficient of the echo transfer function as the sum of a baseband component and an aliased component. In addition to accurately compensating for sampling phase adjustments, this technique considerably relaxes traditional sampling constraints.

Analysis of noise in phase contrast MR imaging.

Abstract: In this work we analyze the effects of inherent random noise on the detectability of low‐contrast vessel structures that possess slow flow. When flow is encoded in more than one direction, the number of independent noise contributions increases in addition to the scan time. In a fast‐flow scenario, only the noise contribution from sampling along the direction of flow is of any significance. At slow flow rates, however, it becomes necessary to account for the noise in each encoded Cartesian direction. The degree to which noise affects low‐contrast detectability also depends on the method of phase contrastimage processing employed. A theoreticalanalysis of the statistical properties of signal and noise in processed phase contrast magnitude images is presented and verified from experimental MR image data. Results show a progressively increased bias in the processed phase contrastimage magnitude at slow flow rates due to contributions from inherent random noise. The amount of this bias increases with the number of physical directions in which flow is encoded and is larger for complex difference processed images than for phase difference processing. Correspondingly, the output signal‐to‐noise ratio associated with flow is compromised.

Wavelength and direction filtering by magnetic measurements at satellite arrays: Generalized minimum variance analysis

Abstract: The main goal of the Cluster mission, consisting of four identical spacecraft, is the spatial resolution of plasma structures. For the determination of the wave vectors of a wave field from four positions, classical Fourier analysis is inappropriate. We develop a generalized minimum variance technique which gives a high wave vector resolution though the spatial grid is restricted to only a few sampling positions. This technique uses the amplitude and phase information of the magnetic field from the four satellite positions and determines the optimum wave field corresponding to the measured data. The components of the magnetic field are assumed to be normally distributed. The divergence-free nature of the magnetic field is used as a constraint. Using the magnetic data measured at four positions allows up to seven different wave vectors at one frequency to be uniquely resolved.

Data detection for partial response channels

Abstract: A data detector is disclosed which includes a source of a data signal (5) representing a sequence of symbols. A maximum likelihood sequence detector (50), is coupled to the data signal source, and produces a most likely survivor sequence, which includes a plurality of symbols. A decision feedback equalizer (60) and a phase detector (70), controlling the timing of the sampling of the data signal, are made responsive to the most likely survivor sequence.

Fingerprint detector using ridge resistance sensing array

Abstract: A fingerprint detector that uses a skin resistance sensing array for producing a sample trajectory signal when a fingertip is moved across the sensing array surface. The sample trajectory signal represents the electrical conductance changes in the resistance of ridges and valleys of the fingertip. The fingerprint detector also includes a sampling circuit coupled to a processor. In addition, a technique is disclosed for detecting and verifying a fingerprint by moving a fingertip relative to the skin resistance sensing array. The sample trajectory signal produced is translated into a digital signal by the sampling circuit. The processor receives the digital sample trajectory signal for comparison with a known reference trajectory signal. The processor produces a verification signal if a threshold probability that the same fingertip generated both signals is exceeded. The reference trajectory signal is stored in a memory integrated into the device, or is provided from an external storage device through a data interface.

Narrow field electromagnetic sensor system and method

Abstract: A narrow field electromagnetic sensor system and method of sensing a characterisitc of an object such as density, thickness, or presence, for any desired coordinate position on the object. The sensor employs a transmitter (120) for transmitting a sequence of electromagnetic signals in response to a transmit timing signal, a receiver (110) for sampling only the initial direct RF path of the electromagnetic signal while excluding all other electromagnetic signals in response to a receive timing signal, and a signal processor (181) for processing the sampled direct RF path electromagnetic signal and providing an indication of the characteristic of an object. Usually, the electromagnetic signal is a short RF burst and the obstruction must provide a substantially complete eclipse of the direct RF path.

Digital automatic gain control employing two-stage gain-determination process

Abstract: For use in an automatic gain control that receives a digital signal from a digital circuit having a given dynamic range and develops therefrom a gain signal to be applied to a variable gain amplifier, an analyzing circuit for, and method of, determining a magnitude of the gain signal. The analyzing circuit includes: (1) a peak sampling subcircuit that determines an average peak value of the digital signal over variable periods of time and (2) a gain signal adjustment subcircuit, coupled to the peak sampling subcircuit, that operates in a selected one of: (a) a search mode in which the gain signal adjustment subcircuit decreases the periods of time and adjusts the gain signal at a first rate until the average peak value falls within the dynamic range of the digital circuit and (b) a direct step mode in which the gain signal adjustment subcircuit increases the periods of time and adjusts the gain signal at a second rate as a function of a deviation of the average peak value from a target average peak value, the first rate being faster than the second rate, the analyzing circuit thereby applying a two-stage gain determination process to the digital signal to approach the target average peak value.

Method and apparatus for oversampled, noise-shaping, mixed-signal processing

Abstract: A signal processing circuit is provided which includes a frequency selective network in a feedback loop for noise shaping purposes. A sampling analog-to-digital converter in the feedback loop operates at a sample frequency substantially above the Nyquist frequency. A switching device is driven by the sampling analog-to-digital converter and produces a continuous-time output signal which is continuously monitored by and fed back to the frequency selective network for noise and distortion correction in the feedback loop. This is in contrast to traditional techniques which employ only state feedback. State feedback (i.e., digital or sampled) of the output of the analog-to-digital converter may also be employed in combination with the continuous-time feedback of the switching device output.

Method and apparatus for automatic pixel clock phase and frequency correction in analog to digital video signal conversion

Abstract: A method for producing a digital video signal from an analog video signal, the analog video signal including an analog video data signal that is raster scanned in lines across a CRT screen to form consecutive frames of video information, the raster scanning controlled by use of a horizontal synchronizing signal (H snyc ) that controls a line scan rate, and a vertical synchronizing signal (V snyc ) that controls a frame refresh rate, to produce consecutive frames of video information, wherein the digital video signal is produced by generating a pixel clock signal with pixel clocks for repetitively sampling instantaneous values of the analog video data signal, and digitizing the analog video data signal based on the pixel clock sampling. An expected width E, measured in number of pixel clocks, of a video image producible by the analog video signal is estimated, and an actual width W, measured in number of pixel clocks, of the video image producible by the analog video signal is calculated. The actual width W is compared with the expected width E. When E does not equal W, at least one of a frequency component and a phase component of the pixel clock signal is adjusted until E equals W.

Bit error correction algorithm

Abstract: A corrected digital response signal is generated from a corrupted transponder response signal by receiving the response signal an odd number of times, greater than one, and sampling each received response signal a predetermined number of times Then, the sample values from each transponder response signal are compared to one another and a majority sample value is obtained The majority sample value is the value ordained by the majority and therefore represents the corrected response signal value Alternatively, if time does not permit reception of more than one transponder response signal, additional response signals may be generated from the originally received response signal by shifting the received response by a predetermined number of samples to the right and by shifting the received response by a predetermined number of samples to the left to generate second and third response signals Then, as similarly described, the first second and third signals are compared sample by sample with the majority sample value yielding the corrected sample value In this way, a corrected response signal is generated

Envelope detector including sample-and-hold circuit controlled by preceding carrier pulse peak(s)

Abstract: A sampling synchronous envelope detector adopts a specialized sample-and-hold ("S&H") approach, basing a detected output on instantaneous values of the carrier waveform which are sampled at specially chosen instants. Non-linear distortion is avoided by timing the sampling instants to occur at or near a carrier wave peak which is subsequent to an earlier carrier wave peak which serves as a time base. Sampling instants occur only at or near positive carrier peaks (or only at or near negative peaks) in a half-wave embodiment, and sampling instants occur at or near both positive and negative carrier peaks in a full wave embodiment. Another aspect of the detector provides means, such as a phase locked loop, for ensuring that the phase of the sampling instants is maintained continuously, even in the event of carrier pinch-off or other event which distorts or minimizes the carrier waveform from which the timing instants would otherwise be determined. Still another aspect of the detector provides for low pass filtering, and group delay equalization of the filtered signal, before it is output.

Sampling requirements for Volterra system identification

Abstract: Volterra systems generally produce-due to nonlinearity-an output signal with a higher frequency range when compared with the input signal. Hence, it seems necessary to sample the input and output signals at twice the maximum frequency of the output signal. The article shows that it is sufficient to sample at twice the maximum frequency of the input signal. A discrete-time Volterra system also produces the additional frequency components that appear-due to aliasing-at the sampled output of a continuous-time Volterra system with an equivalent transfer function.

Method for in-chip testing of digital circuits of a synchronously sampled data detection channel

Abstract: An on-chip self-test circuit for testing digital elements of a synchronous sampling data detection channel chip, such as a PRML channel of a hard disk drive, with digital pseudo samples representative of samples coming from an analog channel section, includes a sample generator generating idealized digital pseudo samples in accordance with a predetermined spectrum response, a digital noise generator generating digital noise values, a first combining circuit combining the idealized digital pseudo samples with the digital noise values to produce noisy pseudo samples, a bias injection circuit connected to the sample generator and adding a predetermined bias to the idealized digital pseudo samples to produce biased pseudo samples, and a second combining circuit for combining the noisy pseudo samples with the biased pseudo samples to put out biased noisy pseudo samples to test digital data processing and channel control elements of the channel chip.

A stereo multi-bit /spl Sigma//spl Delta/ D/A with asynchronous master-clock interface

Abstract: An oversampling DAC that generates low-jitter, synchronous and oversampled clock internally uses an on-chip digital phase-locked loop (DPLL) and a digital sample-rate converter to decouple the DAC conversion rate from the audio sample rate. This allows the DAC to be driven by an independent low-jitter clock source that minimizes jitter-induced amplitude errors. The DAC uses a second-order /spl Sigma//spl Delta/ modulator in combination with a 17-level quantizer to achieve greater than 110 dB theoretical SNR and reduced out-of-band noise relative to higher-order 1b modulators. The problem of severe element matching in multi-bit DACs is addressed by applying a data-directed scrambling technique on the thermometer-decoded modulator output that modulates DAC element mismatch errors out of band.

Electrical contact probe for sampling high frequency electrical signals

Abstract: An all-electrical high frequency contact sampling probe provides sub-micron spatial resolution and picosecond or sub-picosecond temporal resolution. In a preferred embodiment, the probe is a monolithic integration of a sampling circuit with a cantilever and probe tip, where the distance between the circuit and the tip is less than a wavelength of interest in an RF signal VRF !. The sampling circuit 44! uses Schottky diodes SD! for sampling the RF signal VRF ! from a device under test at a rate determined by local oscillator signals 50, 52!. An IF signal VIF ! produced by the sampling probe is an equivalent time representation of the RF signal. Applications include testing signals at interior nodes of high speed integrated circuits.

Light beam range finder

Abstract: A 'laser tape measure' for measuring distance which includes a transmitter such as a laser diode (43) which transmits a sequence of electromagnetic pulses in response to a transmit timing signal. A receiver samples reflections from objects within the field of the sequence of visible electromagnetic pulses with controlled timing, in response to a receive timing signal (42). The receiver generates a sample signal in response to the samples which indicates distance to the object causing the reflections. The timing circuit supplies the transmit timing signal to the transmitter and supplies the receive timing signal to the receiver. The receive timing signal causes the receiver to sample (50) the reflection such that the time between transmission of pulses in the sequence in sampling by the receiver sweeps over a range of delays.

Gain calibration circuitry for an analog to digital converter

Abstract: A method, and apparatus, for calibrating a delta sigma modulator. The delta sigma modulator includes an integrating amplifier circuit with an integrating capacitor for producing an output indicative of an amount of charge held on the integration capacitor. During the calibration mode, a feedback signal sampling section samples a feedback signal and transfers packets of charge corresponding to such sampled feedback signal to the integrating capacitor in each modulator cycle and an input signal section samples a calibration signal and transfers packets of charge corresponding to a portion of the calibration signal to the integrating capacitor in each modulator cycle. With such an arrangement, some charge is transferred to the integration capacitor in each modulator cycle thus reducing idle-tones.

A magnetic disk sampled amplitude read channel employing interpolated timing recovery for synchronous detection of embedded servo data

Abstract: A sampled amplitude read channel reads user data and embedded servo data stored on a magnetic medium by detecting digital data from a sequence of discrete time interpolated sample values. A write frequency synthesizer generates a write clock for writing digital data to the magnetic medium at a predetermined baud rate for a selected zone, and upon read back, a read frequency synthesizer generates a fixed sampling clock at a frequency slightly higher than the write frequency at the outer zone. A sampling device samples the analog read signal at this fixed sampling rate across the data zones and servo wedges to generate a sequence of discrete time channel samples that are not synchronized to the baud rate. Before sampling, an analog receive filter processes the read signal to attenuate aliasing noise without having to adjust its spectrum across data zones or servo wedges. A discrete time equalizing filter equalizes the channel samples according to a predetermined partial response (PR4, EPR4, EEPR4, etc.). An interpolating timing recovery circuit, responsive to the equalized channel samples, computes an interpolation interval τ and, in response thereto, generates interpolated sample values substantially synchronized to the baud rate. The timing recovery circuit also generates a synchronous data clock for clocking a discrete time sequence detector and pulse detector which detect the digital user and servo data from the interpolated sample values.

Method and apparatus for timing recovery

Abstract: A method and apparatus for recovering a timing phase and frequency of a sampling clock signal in a receiver are disclosed for determining a desired timing phase by minimizing a mean squared error due to uncancelled precursor intersymbol interference. A detected symbol error is correlated with a signal obtained from the received signal. This correlation function provides an approximate of the time instant where the mean squared error approaches its minimum at which point an unambiguous zero crossing of the correlation function signal is obtained. From such an unambiguous zero crossing, e.g., only one zero crossing, a desired sampling timing instant is determined.

Pseudorandom-noise receiver having automatic switching between regular and anti-jamming modes

Abstract: A receiver for pseudorandom noise (PRN) encoded signals consisting of a sampling circuit, multiple carrier and code synchronizing circuits, and multiple digital autocorrelators. The sampling circuit provides digital samples of a received composite signal to each of the several receiver channel circuits. The synchronizing circuits are preferably non-coherent, in the sense that they track any phase shifts in the received signal and adjust the frequency and phase of a locally generated carrier reference signal accordingly, even in the presence of Doppler or ionospheric distortion. The antocorrelators in each channel form a delay lock loop (DLL) which correlates the digital samples of the composite signal with locally generated PRN code values to produce a plurality of (early, late), or (punctual, early-minus-late) correlation signals. The time delay spacing between the (early, late), and (punctual, early-minus-late) correlation signals are dynamically adjusted, such that in an initial acquisition mode, the delay spacing is relatively wide, on the order of approximately one PRN code chip time; once PRN code lock is achieved, the code delay spacing is narrowed to a fraction of a PRN code chip time.

Aliasing sampler for plasma probe detection

Abstract: An aliasing sampler probe (22, Fig 1) for detecting plasma RF voltage and current employs a sampling signal with a sampling rate slower that the RF fundamental frequency selected to produce an aliasing waveform at an aliasing frequency that is several orders of magnitude below the RF fundamental frequency In one embodiment, the RF power is applied at 1356 MHz (Fig 3A), and sampling pulses have a sampling rate of 2732 MHz (Fig 3B) to produce replicas of the RF voltage and current waveforms (Fig 4) at an aliasing frequency of about 100 KHz The aliasing replicas preserve phase and harmonic information with an accuracy that is not available from other sampling techniques

Method and system for removing and/or measuring aliased signals

Abstract: A system and method for separating aliased signals from non-aliased signals in a sampling system and method wherein the input signal includes frequency components above the Nyquist limit wherein the input signal is sampled at a first sampling rate to provide a first sampled signal, the input is sampled at a second sampling rate different from the first rate to provide a second sampled signal, and the spectral patterns of the first and second sampled signals are compared to separate the aliased signals from the real or non-aliased signals. The aliased signals can be eliminated by removing any spectral component which is not present with both of the sampling rates. While the difference in the sampling rates can be arbitrary, it also can be optimized. Additional samplings at different rates can increase the degree of the correction.