Showing papers on "Linear phase published in 1993"

Linear phase paraunitary filter banks: theory, factorizations and designs

Abstract: M channel maximally decimated filter banks have been used in the past to decompose signals into subbands. The theory of perfect-reconstruction filter banks has also been studied extensively. Nonparaunitary systems with linear phase filters have also been designed. The authors study paraunitary systems in which each individual filter in the analysis synthesis banks has linear phase. Specific instances of this problem have been addressed by other authors, and linear phase paraunitary systems have been shown to exist. This property is often desirable for several applications, particularly in image processing. They begin by answering several theoretical questions pertaining to linear phase paraunitary systems. Next, they develop a minimal factorization for a large class of such systems. This factorization will be proved to be complete for even M. Further, they structurally impose the additional condition that the filters satisfy pairwise mirror-image symmetry in the frequency domain. This significantly reduces the number of parameters to be optimized in the design process. They then demonstrate the use of these filter banks in the generation of M-band orthonormal wavelets. Several design examples are also given to validate the theory. >

Wavelets and recursive filter banks

Abstract: It is shown that infinite impulse response (IIR) filters lead to more general wavelets of infinite support than finite impulse response (FIR) filters. A complete constructive method that yields all orthogonal two channel filter banks, where the filters have rational transfer functions, is given, and it is shown how these can be used to generate orthonormal wavelet bases. A family of orthonormal wavelets that have a maximum number of disappearing moments is shown to be generated by the halfband Butterworth filters. When there is an odd number of zeros at pi it is shown that closed forms for the filters are available without need for factorization. A still larger class of orthonormal wavelet bases having the same moment properties and containing the Daubechies and Butterworth filters as the limiting cases is presented. It is shown that it is possible to have both linear phase and orthogonality in the infinite impulse response case, and a constructive method is given. It is also shown how compactly supported bases may be orthogonalized, and bases for the spline function spaces are constructed. >

400-Hz mechanical scanning optical delay line.

Abstract: We have developed a simple, high-speed, nearly vibration-free, mechanically scanned, optical delay line suitable for femtosecond time-resolved signal-averaging measurements. We demonstrate a 2-ps time window autocorrelator with a display updated at 400 Hz. The delay line uses a dithering planar mirror as a time-varying linear phase ramp in the spectral plane of a modified grating-lens femtosecond pulse shaper. The time delay is linearly proportional to the angular deviation of the mirror. The high speed and low vibration are a result of the extremely small angular changes required to generate a large time delay.

Flexible design of multidimensional perfect reconstruction FIR 2-band filters using transformations of variables

Abstract: An approach to designing multidimensional linear-phase FIR diamond subband filters having the perfect reconstruction property is presented. It is based on a transformation of variables technique and is equivalent to the generalized McClellan transformation. Methods for designing a whole class of transformation are given. The approach consists of two parts; design of the transformation and design of the 1-D filters. The use of Lagrange halfband filters to design the 1-D filters is discussed. The modification of a particular Lagrange halfband filter which gives a pair of simple 1-D filters that are almost similar to each other in their frequency characteristics but still form a perfect reconstruction pair is presented. The design technique is extended to other types of two-channel sampling lattice and subband shapes, in particular, the parallelogram and the diagonally quadrant subband cases. Several numerical design examples are presented to illustrate the flexibility of the design method. >

Applications of complex valued wavelet transforms to subband decomposition

Abstract: A method for constructing complex valued linear phase FIR conjugate quadrature filters and associated wavelet bases is described. Each filter is derived by replating certain zeros of a real valued FIR conjugate quadrature filter by their reciprocal conjugates. The derived filters have the same frequency response magnitudes as the original filters and their linear phase property permits the use of symmetrization in subband decomposition to avoid border discontinuities that result from signal periodization. Subband decomposition and reconstruction using both a length 6 filter associated with a Daubechies (1988) wavelet bases and a related length 6 complex valued linear phase filter are compared to illustrate the reduced border effects. >

Time-varying digital filtering of ECG baseline wander

Abstract: Time-varying filtering techniques are applied to the problem of baseline correction by letting the cut-off frequency of a linear filter be controlled by the low-frequency properties of the ECG signal. The time-varying filter is implemented as a bank of linear low-pass filters, in which each filter has a slightly differing cut-off frequency. Sampling rate decimation and interpolation are employed because the design of a filter for baseline reduction can be treated as a narrowband filtering problem. All filters have a linear phase response to reduce, for example, ST-segment distortion. The performance of the technique presented is studied on ECG signals with different types of simulated baseline wander. The results are compared with the performance of time-invariant linear filtering and cubic spline interpolation. The results show that an improvement in performance can be achieved when using time-varying filtering, especially at low heart rates or during episodes with excessive baseline wander.

Phase locked loop having plural selectable voltage controlled oscillators

Abstract: The invention discloses a PLL formed by a phase detector, a filter, three VCO's (VCO1, VCO2, and VCO3), a multiplexer, and a frequency divider. The VCO1, VCO2, and VCO3 have different mean frequencies, each oscillating at a frequency controlled according to the voltage value of a phase control signal from the filter. The multiplexer selects one of the VCO's which operate in parallel. If a pulse of a digital phase difference signal UP indicating that an internal signal is delayed in phase with respect to a reference signal is output twice in succession, or if a pulse of a digital phase difference signal DOWN indicating that an internal signal is advanced in phase with respect to a reference signal is output twice in succession, a counter makes the multiplexer change its current VCO selection via a shift register. Accordingly, high-speed PLL pulling is achievable even if a PLL frequency variable-range is expanded.

Novel class of digital integrators and differentiators

Abstract: A novel class of digital integrators and differentiators is presented. These first-order filters are very convenient for real-time applications. Every integrator is expressed as a weighted sum of the classical rectangular and trapezoidal integrators, with the additional constraint of a minimum phase. The corresponding differentiator is obtained by inverting the transfer function of the integrator. The filter class depends on a parameter. Properties of the filters are derived and the filter parameter is determined according to different chosen criteria. The capability of these filters to approximate the ideal linear phase integrator and differentiator with good accuracy and over a large frequency band is shown.

The achievable accuracy in estimating the instantaneous phase and frequency of a constant amplitude signal

Abstract: The approach is based on modeling the signal phase by a polynomial function of time on a finite interval. The phase polynomial is expressed as a linear combination of the Legendre basis polynomials. First, the Cramer-Rao bound (CRB) of the instantaneous phase and frequency of constant-amplitude polynomial-phase signals is derived. Then some properties of the CRBs are used to estimate the order of magnitude of the bounds. The analysis is extended to signals whose phase and frequency are continuous but not polynomial. The CRB can be achieved asymptotically if the estimation of the phase coefficients is done by maximum likelihood. The maximum-likelihood estimates are used to show that the achievable accuracy in phase and frequency estimation is determined by the CRB of the polynomial coefficients and the deviation of true phase and frequency from the polynomial approximations. >

A linear phase two-channel filter bank allowing perfect reconstruction

Abstract: Describes a perfect-reconstruction two-channel QMF (quadrature mirror filter) bank, in which the analysis and synthesis filters have linear phases. First, a technique for designing filter banks is presented. Next, the results of two examples demonstrate that the method can lead to good filters although its procedure is very simple; also, this yields filters without multipliers such as the SSKF (symmetric short kernel filter) bank.<>

Fast locking phase locked loop frequency synthesizer

Abstract: A radio apparatus with a phase locked loop is disclosed. The apparatus contains a phase detector with first and second inputs, where the first input receiving a reference frequency signal and the second input receives a controllable frequency signal that is controlled by a tuning voltage. Also included is, a loop filter for filtering the output of the phase detector, circuitry for decoding when a phase difference at the inputs of the phase detector exceeds a predetermined value, and a filter bypass circuit. This circuit bypasses operation of the loop filter when the difference at the inputs of the phase detector exceeds a predetermined value, allowing fast voltage changes of the tuning voltage, and providing a short lock time for the phase locked loop.

Phase alignment methods and apparatus

Abstract: In methods and apparatus for controlling a phase relationship of two signals, a supplementary phase adjustment signal is generated. The supplementary phase adjustment signal has a zero value when an actual phase relationship of the two signals deviates from a desired phase relationship by less than a threshold phase deviation, and has a non-zero value when the actual phase relationship deviates from the desired phase relationship by more than the threshold phase deviation. The phase relationship of the two signals is adjusted in response to a sum of the supplementary phase adjustment signal and a phase adjustment signal which is proportional to the deviation of the actual phase relationship from the desired phase relationship. The methods and apparatus are particularly applicable to alignment of clock signals with data signals.

Current, luminosity, and X-ray emission in the early phase of dielectric surface flashover in vacuum

Abstract: With high-speed electrical and optical diagnostics, an attempt is made to elucidate the physical mechanisms leading to surface flashover. The experimental device uses a cable discharge to study self-breakdown along the surface of an insulator in vacuum. Preflashover current, breakdown voltage, luminosity, and soft X-ray emission are measured in temporal correlation with a resolution of 1 ns. The results show a linearly increasing current in the subampere range, and a corresponding linearly increasing luminosity, before an exponential increase of both signals takes over. The linear phase is accompanied by X-ray emission which ceases at the onset of the exponential phase. The strong influence of externally applied magnetic fields on the linear phase points to the existence of free electrons above the surface during the early phase of flashover. A linear current rise without magnetic field and the formation of a current plateau with an insulating magnetic field indicate a saturation of the current amplification mechanism in the early phase. >

Emission in the Early Phase of Dielectric Surface Flashover in Vacuum

Abstract: Abstruct-With high-speed electrical and optical diagnostics, an attempt is made to elucidate the physical mechanisms leading to surface flashover. The experimental device uses a cable discharge to study self-breakdown along the surface of an insulator in vacuum. Preflashover current, breakdown voltage, luminosity, and soft X-ray emission are measured in temporal correlation with a resolution of one nanosecond. The results show a linearly increasing current in the sub-ampere range, and a corresponding linearly increasing luminosity, before an exponential increase of both signals takes over. The linear phase is accompanied by Xray emission which ceases at the onset of the exponential phase. The strong influence of externally applied magnetic fields, on the linear phase, points to the existence of free electrons above the surface during the early phase of flashover. A linear current rise without magnetic field, and plateau formation of the current with an insulating magnetic field, indicates a saturation of the current amplification mechanism in the early phase.

Digital frequency and phase modulator for radio transmission

Abstract: For digital transitions from one binary logic level to another by frequency or phase shift of an electric carrier wave the modulation sidebands are reduced by performing each transition by means of several phase steps at small intervals. Equal phase steps at varying intervals are preferred over equal intervals between varying phase steps although both procedures can provide a low-bandwidth transition. This procedure is readily incorporated at low cost in frequency synthesizers. The use of a higher-frequency master oscillator (16) followed by a fixed-ratio frequency divider (17) ahead of a variable-ratio frequency divider (18) makes it easy to shift phase or frequency digitally by small quick steps. Another variable-ratio frequency divider (13) is desirable but not essential in the final PLL between a ultimately controlled oscillator (10) and a loop filter (12) connected to a phase discriminator (11). The discriminator (11) and the two variable-ratio frequency dividers (17, 13) require simultaneous or coordinated initialization (line 20). A binary digital signal produces GMSK modulation by means of a processor in which the divider ratios and their timings and sequence are stored. The steps are small enough for the loop filter to provide adequate bandwidth reduction. Steps each produced by a divisor one unit higher than the divisor which keeps the phase constant for the nominal frequency are produced by one cycle of the reference frequency, which corresponds to a number equal to the overall divisor of cycles of the master oscillator.

Open-loop phase estimation methods and apparatus for coherent demodulation of phase modulated carriers in mobile channels

Abstract: Open-loop phase estimation methods and apparatus for coherent demodulation on mobile channels is disclosed. A PSK RF modulated signal is received, RF demodulated to obtain inphase and quadrature components thereof, and the inphase and quadrature components sampled and digitized periodically to provide inphase and quadrature components of the signal vector. A phase estimator strips the data contribution from each vector, leaving only a phase error measurement related to the true phase error. That phase error indication is averaged over a fixed window of time to determine an average phase estimate applicable to the signal vector at the middle of the window. Resulting one hundred eighty degree ambiguities are resolved, and then the applicable signal vector is phase corrected by the average phase estimate and result of the ambiguity resolution, with the following demodulation being responsive to the phase of the phase corrected signal vector.

Nonlinear phase portrait models for oriented textures

Abstract: Nonlinear differential equations in Taylor series form are employed to model oriented textures. These models build upon the linear phase portrait description. Inclusion of higher order nonlinear terms provides a more accurate description in critical point regions. Nonlinear models containing multiple critical points are generated from linear phase portrait descriptions. The resulting models are highly compact descriptors, in that the flow-like textures of complex patterns are described by a single nonlinear system of differential equations. >

Method and apparatus for digital automatic frequency control of TDM communications systems

Abstract: An automatic frequency control method re-modulates a binary data sequence output from an equalizer using the convolution of an estimated channel characteristic value function and a transfer function of the modulator in the transmitter of a communication system, to obtain a reference phase. The reference phase then is compared with a receiving phase to produce a phase error value. The phase error value is converted into a frequency error value, which is then converted into an analog control voltage and applied to a voltage controlled oscillator. Apparatus for performing the method includes an equalizer, a channel characteristic estimator, a re-modulator, a phase comparator, a frequency error estimator and a digital-to-analog converter, to thus improve the receiving performance of a receiver by digital implementation.

Two-dimensional anisotropic scattering in a semi-infinite cylindrical medium exposed to a laser beam

Abstract: A modification of Ambarzumian's method is used to develop the integro-differential equations for the source function, flux, and intensity at the boundary of a two-dimensional, semi-infinite cylindrical medium which scatters linearly. The incident radiation is collimated, normal to the top surface of the medium, and is dependent only on the radial coordinate. The radial variation is assumed to be a Bessel function or a Gaussian distribution. The Gaussian boundary condition is used to simulate a laser beam. Numerical results are presented in graphical and tabular forms for both boundary conditions. Results for forward and backward scattering phase functions are compared with those for isotropic scattering. A method is presented for extending these results to the problem of a strongly anisotropic phase function which is made up of a spike in the forward direction superimposed on a linear phase function.

Mode locking with linear and nonlinear phase shifts

Abstract: The mode locking of a cw Nd:YAG laser by translation of one of the cavity mirrors is reported. The mode-locking effect is greatly enhanced when an intracavity nonlinear KTP crystal is used. Stable pulse trains with a 60-ps average pulse width are obtained. Theoretical analysis shows that the combined effect of linear phase shift imposed by the moving mirror and the nonlinear phase shift in the Kerr medium gives rise to a saturable-absorber-like behavior in a homogeneously broadened laser. The theory agrees well with the experimental results as well as with results obtained with a Ti:sapphire laser.

Group delay estimate system using least square fit to phase response ramp

Abstract: The phase response of a network is measured at uniform frequency intervals. A linear regression analysis is performed on samples of the phase response measured at frequencies within an aperture centered on a group delay frequency to obtain an estimate of the group delay of the network at that frequency. The process is repeated for a sequence of group delay frequencies to determine a trace of the group delay of the network across a range of frequencies.

Analysis of digital tanlock loop with adaptive filtering

Abstract: The authors consider the discrete-time analysis of adaptive filtering in a digital tanlock loop (DTLL) for tracking a wide variety of input signals. The detection circuit (DTLL) uses a linear phase error detector which is the tan function with in-phase and quadrature samples of the received signal. Using a uniform multisampling structure gives a wide pull-in range and fast acquisition performance. In order to maintain optimum detection, adjustments in the filter coefficients are needed. The problem is solved when the performance is increased by using a least mean square adaptive detection filter. >

Decision feedback demodulator with phase and frequency estimation

Abstract: A data communication receiver (10) uses a decision feedback demodulator (32) to remove data from a received signal. Quadrature components of the received signal define a received phase. The received phase is rotated (46) by an amount predicted to compensate for phase and frequency errors. After this rotation, a decision circuit (52) determines the modulation phase for a current symbol. A phase rotator (64) compares the modulation phase with the received phase to generate a measured phase error for the symbol. This measured phase error and measured phase errors from past symbols are averaged in a combination circuit (80) to produce a phase estimate. The past measured phase errors are also processed to determine the amount of change in measured phase error that has occurred over a number of symbols. This processing yields a frequency estimate. A phase rotator (94) merges the frequency and phase estimates for use in compensating a current received phase.

Phase error detector for a phase locked loop

Abstract: A phase lock loop (PLL) arrangement includes a voltage controlled ring oscillator (VCRO) including delay elements whose delay is controlled by a control voltage produced by the PLL. A phase error detector is provided which compares pulses of a PLL feedback frequency with pulses of a delayed reference signal, the delay being provided by further delay elements controlled by the same control voltage. The phase error detector produces an output signal which indicates when phase error exceeds a predetermined tolerance, and also indicates an absence of frequency lock.

A prototype filter design approach to pyramid generation

Abstract: This paper presents a technique for image pyramid generation, in which the reduction (expansion) factor between layers is any rational number M/L. The image pyramid generation is modeled as an interpolation and filtering followed by a decimation. The model enables frequency domain analysis of the image pyramid, as well as convenient design of the generating kernels. L(M) generating kernels are necessary to produce an image pyramid with reduction (expansion) factor M/L(L/M). A polyphase filter network scheme is used where the L(M) generating kernels can be produced by sampling one prototype low-pass filter with cutoff frequency at omega = pi /max(M,L). Using these polyphase filters, the frequency content of pyramid image decompositions can be adjusted with great flexibility. A systematic procedure is presented here for specifying the relative positions of spatial samples in successive pyramid levels-a complication that arises when generalizing from integer reduction factors to rational factors. Two types of low-pass filters are employed in this work for the prototype filter design: a binomial filter and an FIR linear phase filter. Illustrative examples are presented. >

High-speed D/A conversion with linear phase sin x/x compensation

Abstract: A design technique is described for the realization of a digital-to-analog (D/A) conversion system with an embedded finite impulse response (FIR) filtering function suitable for the compensation of the sin x/x distortion introduced by fully sampled-and-held signals and which is attractive for integrated circuit implementation from the viewpoints of area and power consumption. This is demonstrated for an 8-b D/A conversion prototype system with an associated 3-tap 5-b precision FIR filtering function that has been fabricated using a 1.2-/spl mu/m digital CMOS technology. >

FM stereo decoder and method using digital signal processing

Abstract: A digital FM stereo decoder uses the phase characteristics of linear phase FIR filters, together with a trignometric operation, to generate a 38 kHz subcarrier signal from a 19 kHz pilot. The subcarrier signal is mixed with the input composite signal from which the pilot has been removed to shift its L-R component to baseband; the linear phase FIR filters also maintain phase coherence between the subcarrier and the composite signals. A low distortion output is obtained without the use of a phase locked loop for the regeneration of the subcarrier signal.

Linear phase orthonormal filter banks

Abstract: Paraunitary systems in which each individual filter in the analysis and synthesis banks has linear phase are studied This property is often desirable for several applications, particularly in image processing Several theoretical questions pertaining to linear phase paraunitary systems are answered Next, a factorization for such systems is developed which is proved to be minimal as well as complete The number of parameters in the optimization process is reduced by structurally imposing the additional condition that the filters satisfy pairwise mirror-image symmetry in the frequency domain Examples of M-band linear phase orthonormal wavelets are presented >

Second order phase locked loop

Abstract: A phase locked loop using an oscillating circuit for controlling the frequency by a digital signal according to the present invention comprises a loop filter. The loop filter includes a random walk filter 3, a counter 4, a register 5 and an adder 6. The oscillating circuit 7 emits a signal having a frequency corresponding to the output of the adder 6. Further, a phase/frequency detector 2 emits a phase lag signal LAG and a phase lead signal LEAD according to the phase difference between a signal IN provided to an input terminal 1 and a signal REF provided from the oscillating circuit 7 to thereby increase the degree of freedom for determining a loop constant while avoiding generation of the steady phase error relative to the frequency offset.