Showing papers on "Linear phase published in 2005"

Power converter line synchronization using a discrete Fourier transform (DFT) based on a variable sample rate

Abstract: Line synchronization of grid connected power converters is a well recognized problem when the grid is weak, or derives from a remote area power supply with poor frequency regulation. Such systems can suffer significant line voltage distortion due to notches caused by power device switching and/or low frequency harmonic content, which can easily corrupt the output of a conventional zero crossing detector. This paper presents a method of filtering the incoming grid voltage using a recursive discrete Fourier transform (DFT). The filter provides a high degree of noise immunity but does produce a phase shift between the incoming grid voltage and the filtered output voltage when the DFT time window does not match the grid period. Two methods of compensating this phase shift are presented, based on tracking the drift in the phase predicted by the recursive DFT. The first method makes a deadbeat adjustment to the time window (thereby changing the sampling rate) while the second approach calculates the phase error based on the linear phase response of the DFT. These compensation algorithms can correct for discrepancies of at least 25% between the DFT time window and the system period, and can track grid frequencies with slew rates as high as 40 Hz/s with negligible phase shift (<2/spl deg/) between the grid voltage input and the filtered output waveforms.

Substrate integrated waveguide (SIW) linear phase filter

Abstract: A planar four-pole linear phase filter centered at 10GHz based on substrate integrated waveguide (SIW) is proposed. The filter is composed of four side-by-side horizontally oriented SIW cavities, which are coupled in turn by evanescent waveguide sections with three direct coupling and one cross coupling between the first and fourth SIW cavities. The SIW cavities are fed by microstrips through coupling slots. A curve-fitting technique is adopted to improve the efficiency of the design process. The measured results are presented and compared with the results simulated by a high-frequency structure simulator. Good agreement between the simulated and measured results is observed.

Linear tunable phase shifter using a left-handed transmission line

Abstract: We demonstrate a compact, linear, and low loss variation hybrid phase shifter using a left-handed (LH) transmission line. For frequencies from 4.3 to 5.6 GHz, this phase shifter gives a nearly linear phase variation with voltage, with a maximum deviation of /spl plusmn/7.5/spl deg/. Within this frequency range, the maximum insertion loss is 3.6 dB, and the minimum insertion loss is 1.8 dB over a continuously adjustable phase range of more than 125/spl deg/, while minimum return loss is only 10.2 dB. Furthermore, this phase shifter requires only one control line, and it consumes almost no power.

Accurate encoding of arbitrary complex fields with amplitude-only liquid crystal spatial light modulators

Abstract: We show that computer generated holograms, implemented with amplitude-only liquid crystal spatial light modulators, allow the synthesis of fully complex fields with high accuracy. Our main discussion considers modified amplitude holograms whose transmittance is obtained by adding an appropriate bias function to the real cosine computer hologram of the encoded signal. We first propose a bias function, given by a soft envelope of the signal modulus, which is appropriate for perfect amplitude modulators. We also consider a second bias term, given by a constant function, which results appropriate for modulators whose amplitude transmittance is coupled with a linear phase modulation. The influence of the finite pixel size of the spatial light modulator is compensated by digital pre-filtering of the encoded complex signal. The performance of the discussed amplitude CGHs is illustrated by means of numerical simulations and the experimental synthesis of high order Bessel beams.

Systematic control of nonlinear optical processes using optimally shaped femtosecond pulses

Abstract: This article reviews experimental efforts to control multiphoton transitions using shaped femtosecond laser pulses, and it lays out the systematic study being followed by us for elucidating the effect of phase on nonlinear optical laser–molecule interactions. Starting with a brief review of nonlinear optics and how nonlinear optical processes depend on the electric field inducing them, a number of conclusions can be drawn directly from analytical solutions of the equations. From a Taylor expansion of the phase in the frequency domain, we learn that nonlinear optical processes are affected only by the second- and higher-order terms. This simple result has significant implications on how pulse-shaping experiments are to be designed. If the phase is allowed to vary arbitrarily as a continuous function, then an infinite redundancy that arises from the addition of a linear phase function across the spectrum with arbitrary offset and slope could prevent us from carrying out a closed-loop optimization experiment. The early results illustrate how the outcome of a nonlinear optical transition depends on the cooperative action of all frequencies in the bandwidth of a laser pulse. Maximum constructive or destructive interference can be achieved by programming the phase using only two phase values, 0 and p. This assertion has been confirmed experimentally, where binary phase shaping (BPS) was shown to outperform other alternative functions, sometimes by at least on order of magnitude, in controlling multiphoton processes. Here we discuss the solution of a number of nonlinear problems that range from narrowing the second harmonic spectrum of a laser pulse to optimizing the competition between two- and three-photon transitions. This Review explores some present and future applications of pulse shaping and coherent control.

Matrix analysis of 2-D microresonator lattice optical filters

Abstract: We present a transfer matrix analysis of a two-dimensional (2-D) filter to study its frequency response functions. The (M/spl times/N) array consists of N independent columns of microring resonators side-coupled to two channel bus waveguides, with equal spacing between columns and each column consisting of M coupled resonators. We show that such a general 2-D lattice network of lossless and symmetric resonators can approximate an ideal bandpass filter characterized by a flat-top box-like amplitude response without out-of-band sidelobes, and a linear phase response. The bandwidth is determined by the coupling factor between resonators. The 2-D periodic structure exhibits nonoverlapping photonic bandgaps arising from the complementary transmission properties of the row and column arrays. The row array behaves as a distributed feedback grating giving rise to narrow bandgaps corresponding to the flat reflection passbands of the filter with out-of-band sidelobes. The column array, on the other hand, acts as a high-order coupled-cavities filter with broad bandgaps that overlap with the sidelobe regions, thereby effectively suppressing the sidelobes. The phase response is linear except near the band edges, where enhanced group delay limits the usable bandwidth of the filter to about 80%. The minimum size of the array required is about 3/spl times/10, but is ultimately limited by waveguide loss.

Linear-phase FIR interpolation, decimation, and mth-band filters utilizing the farrow structure

Abstract: This paper introduces novel linear-phase finite-impulse response (FIR) interpolation, decimation, and Mth-band filters utilizing the Farrow structure. In these new overall filters, each polyphase component (except for one term) is realized using the Farrow structure with a distinct fractional delay. The corresponding interpolation/decimation structures can therefore be implemented using only one set of linear-phase FIR subfilters and one set of multipliers that correspond to the distinct fractional delays. The main advantage of the proposed structures is that they are flexible as to the conversion factors, and this also for an arbitrary set of integer factors, including prime numbers. In particular, they can simultaneously implement several converters at a low cost. The proposed filters can be used to generate both general filters and Mth-band filters for interpolation and decimation by the integer factor M. (In this paper, a general filter for interpolation and decimation by M means a filter having a bandwidth of approximately /spl pi//M without the restriction that /spl pi//M be included in the transition band. This is in contrast to an Mth-band filter whose transition band does include /spl pi//M.) In both cases, the overall filter design problem can be posed as a convex problem, the solution of which is globally optimum. Design examples are included in the paper illustrating the properties and potentials of the proposed filters.

A systematic technique for designing linear-phase FIR prototype filters for perfect-reconstruction cosine-modulated and modified DFT filterbanks

Abstract: This paper describes a systematic technique for designing prototype filters for generating perfect-reconstruction (PR) orthogonal cosine-modulated and modified discrete Fourier transform filterbanks. In the proposed design scheme, the stopband energy of the prototype filter is minimized, and the basic unknowns are the angles of a special lattice structure used for implementing the prototype filter so that the PR property is automatically satisfied independent of the angle values. This selection of the unknowns makes the overall optimization problem unconstrained. Due to the fact that there are several local optima, the design is performed in multiple steps in order to arrive at least at a very good suboptimal solution. First, for the given number of channels, the length of the channel filters, and the stopband edge of the prototype filter, the corresponding two-channel filterbank is designed based on the preoptimized data. Then, after knowing the angles for the optimized two-channel case, the prototype filter for the desired filterbank is generated by gradually increasing the number of channels and by properly using the result of the previous step as a start-up solution for the present step. The main benefit of the proposed design technique is that it enables one to effectively design prototype filters for filterbanks with very high-order analysis and synthesis filters.

Zero Phase Learning Control Using Reversed Time Input Runs

Abstract: Phase lead is introduced to iterative learning control systems. The best phase lead is the one that can exactly compensate the phase lag of a system. A zero phase learning control using reversed time input runs is proposed based on the analysis in frequency domain utilizing a simple phase lead generation method. The plant itself or a nominal model is used to obtain the desired phase lead to ensure the monotonic convergence of tracking errors. The learning controller is robust to large inaccuracies of system models.

Metrological characteristics of dual-tree complex wavelet transform for surface analysis

Abstract: The metrological characteristics of a newly developed dual-tree complex wavelet transform (DT-CWT) for surface analysis are investigated, especially on the aspect of transmission characteristics analysis. The property of zero/linear phase by the DT-CWT ensures filtering results with no distortion and good ability for feature localization. Due to the 'steep transmission curve' property of the amplitude transmission characteristic, the DT-CWT can separate different frequency components efficiently. Both computer simulation and experimental results of practical surface 2D/3D filtering prove that the DT-CWT filter is very suitable for the separation and extraction of frequency components such as surface roughness, waviness and form.

Receiver for a coherent fiber-optic link with high dynamic range and low noise figure

Abstract: Phase modulated coherent fiberoptic links can potentially provide exceptionally high spurious free dynamic range (SFDR) and low noise figure (NF). Critical issue is the development of a strictly linear phase demodulator. In this paper we describe a phase demodulator employing a phase locked loop discriminator. Implementing the PPLL on a single substrate using the state-of-the-art components could yield an SFDR better than 145 dB/Hz2/3 and NF lower than 3dB.

Fractional-n offset phase locked loop

Abstract: A fractional-N offset phase locked loop (FN-OPLL) is provided. The N-OPLL includes a fractional divider, a phase detector, a loop filter, a voltage controlled oscillator (VCO), and feedback circuitry. Combiner circuitry (108) combines an initial fractional divide value and a modulation signal to provide a combined fractional divide value. Based on the combined fractional divide value, the fractional-N divider (96) divides a reference frequency and provides a divided reference frequency to the phase detector. The phase detector (98) compares a phase of the divided reference frequency to a phase of a feedback signal to provide a comparison signal. The comparison signal is filtered by the loop filter (100) to provide a control signal to the VCO, where the control signal controls a frequency of an output signal of the VCO. The output signal is processed by the feedback circuitry to provide the feedback signal to the phase detector.

A 0.25-mm CMOS T/R switch for UWB wireless communications

Abstract: A T/R switch, fabricated using standard 025-/spl mu/m CMOS process, for ultra wide-band (UWB) wireless communications is presented The switch is designed based on the concept of synthetic transmission line, utilizing both CPW and CMOS transistors, to achieve not only an extremely wide bandwidth but also a linear phase response necessary for time-domain UWB applications On-chip measurement is completed in both frequency and time domains Frequency-domain measured results show insertion loss of 22-42 dB, isolation from 34-48 dB, and highly linear transmission phase from 045 MHz to 13 GHz These results are quite consistent with the calculations Particularly, the time-domain pulse measurement shows that the output pulses resemble closely the input pulses with very little reflection, demonstrating the switch's suitability for true time-domain UWB applications The developed switch is ready to be integrated with other CMOS RFICs to form on-chip transceivers for various UWB applications

Complete characterization of systems for simultaneous Lagrangian upsampling and fractional-sample delaying

Abstract: We present a complete formulation and an exact solution to the problem of designing systems for simultaneous sampling rate increase and fractional-sample delay in the Lagrangian sense. The problem may be regarded as that of a linear transformation, i.e., scaling, and/or shifting, of the uniform sampling grid of a discrete-time signal having a Newton series representation. It is proved that the solution forms a three-parameter family of maximally flat finite impulse response digital filters with a variable group-delay at the zero frequency. Various properties of the solution, including Nyquist properties and conditions for a linear phase response are analyzed. The solution, obtained in the closed form, is exact for polynomial inputs. We show that it is also suited for processing discrete-time versions of certain continuous-time bandlimited signals and signals having a rational Laplace transform. We then derive a generalization of the solution by augmenting the family with a fourth parameter that controls the number of multiple zeros at the roots of unity. This four-parameter family contains various types of maximally flat filters including those due to Herrmann and Baher. We list specific conditions on the four parameters to obtain many of the maximally flat filters reported in the literature. A significant part of the family of systems characterized by the solutions has been hitherto unknown. Examples are provided to elucidate this part as well.

A simple design method of linear-phase nonuniform filter banks with integer decimation factors

Abstract: In this paper, we propose a simple method for designing linear-phase (LP) nonuniform filter banks (NUFBs) with integer decimation factors. The NUFBs are constructed in a direct structure. We derive a design criterion for the NUFB. With this criterion, the NUFBs can be designed simply and efficiently. By using the proposed method, near-perfect-reconstruction LP NUFBs with high stopband attenuation are obtained.

Modified linear phase frequency response masking FIR filter

Abstract: This paper proposes a modified frequency response masking (FRM) technique for the synthesis of linear phase, sharp transition, low arithmetic complexity FlR filter. The structure is composed of lowpass and bandpass subfilters which are designed as linear phase, equiripple passband and computationally efficient FIR filters. The frequency response of the subfilters are modeled using trigonometric functions of frequency and the design yields closed form expressions for the impulse response coefficients of the subfilters. The slopes at the edges of the transition region of the subfilter are matched which makes the frequency response a continuous function of frequency and hence reduces the effects due to Gibb's phenomenon thereby reducing passband edge ripple of the subfilters. The bandpass filter eliminates one masking filter and a model filter from the basic FRM approach thereby simplifying the synthesis of the proposed modified FRM FIR filter.

Comparison of the horizontal and the vertical common subexpression elimination methods for realizing digital filters

Abstract: Common subexpression elimination (CSE) techniques address the issue of minimizing the number of adders needed to implement the coefficient multipliers in digital filters. Two classes of common subexpressions (CS) occur in the canonic signed digit (CSD) representation of coefficients, called the horizontal and the vertical CS. Previous works have not addressed the trade-offs in using these two types of CS on the delay and the number of multiplier block adders. We provide a comparison of hardware reductions achieved using the horizontal and the vertical CS in realizing digital filters. We show that the CSE technique employing horizontal CS offers better reductions in the number of adders and critical paths than its vertical CS counterpart in practical linear phase finite impulse response (LPFIR) filter implementations. Our simulation results show that the hardware reductions offered by the vertical CS in implementing infinite impulse response (IIR) filters are improved compared to their LPFIR counterparts.

Uniform FIR filterbank optimization with group delay specifications

Abstract: We characterize the delay properties of uniformly modulated finite impulse response (FIR) filterbanks. Conditions on the permissable delay are developed for this class of filterbanks when the perfect reconstruction condition is relaxed. Accurate linear approximations for the phase and the group delay of the total filterbank are derived. These approximations allow linear phase or group delay constraints to be introduced in the filter optimization problem. A tractable quadratic optimization problem for the design of optimal analysis and synthesis filter prototypes is proposed. The problem involves the minimization of the aliasing distortion while constraining group delay and amplitude distortion. Thus, a new algorithm is presented to solve this optimization problem for the analysis and synthesis filterbanks simultaneously. Numerical examples are presented that confirm the theoretical results and verify that the approximations used are highly accurate.

New approach to the synthesis of sharp transition FIR digital filter

Abstract: A model is proposed for a linear phase, sharp transition, lowpass FIR filter. The filter model is formulated using sinusoidal functions of frequency to evaluate the impulse response coefficients in closed form. Filter transfer function is evolved in frequency and time domain. This design approach is found to be closely comparable to FRM techniques in terms of arithmetic complexity with added advantage of simpler design and having closed form expressions for impulse response coefficients. Approach can be extended to design sharp transition arbitrary passband highpass, bandpass and bandstop filters.

Reconstructing a nonminimum phase response from the far-field power pattern of an electromagnetic system

Abstract: A new technique for reconstructing the nonminimum phase function from magnitude-only data is presented in this paper. The nonminimum phase function is reconstructed by utilizing the fact that the discrete Fourier transform of the far field power pattern is equal to the autocorrelation of the equivalent spatial current distribution on the electromagnetic structure. An all-pass filter representation is also used to reduce the computational load in computing the nonminimum phase function. The solution for the phase is not unique but is up to a linear phase delay between the actual phase function and the phase produced by the current approach. However, we generate a solution which has a spatially causal response, as the antennas are all finite in size. This approach is applied to the synthesis of nonminimum phase functions from the magnitude only antenna pattern. Several examples dealing with single antennas and antenna arrays have been simulated to illustrate the applicability of this approach.

Design of linear phase lead repetitive control for CVCF PWM DC-AC converters

Abstract: A linear phase lead repetitive controller is introduced for the constant-voltage constant-frequency (CVCF) pulse-width modulated (PWM) DC-AC converters The design of the repetitive control (RC) is discussed Since phase lead can compensate the phase lag of feedback control system, more harmonics can he suppressed which leads to a low total harmonic distortion (THD) of the output voltage in the presence of nonlinear load disturbances and parameter uncertainties Simulation results show that this method has a fast response and good tracking accuracy

A 2 V 0.25 /spl mu/m CMOS 250 MHz fully-differential seventh-order equiripple linear phase LF filter

Abstract: A fully-differential seventh-order 0.05/spl deg/ equiripple linear phase low-pass filter based on multiple loop feedback (MLF) leapfrog (LF) topology is presented for read/write channels. The filter is designed and simulated with a fully balanced, highly linear operational transconductance amplifier (OTA). The proposed OTA contains two complementary differential cross-coupled input pairs and a pair of regulated cascode outputs in order to achieve both low-distortion and wide dynamic range in high-frequency operation. Simulations in 0.25 /spl mu/m CMOS show that the cutoff frequency of the low pass filter without and with gain boost ranges from 50 to 150 MHz and 65 to 250 MHz respectively, dynamic-range is over 65 dB and total harmonic distortion is less than 40 dB. The group delay ripple is less than 5% for frequencies up to 1.5 times the cutoff frequency, and for a 2-volt power supply, the maximum power consumption is 216 mW.

Direct synthesis of first order controllers from frequency response measurements

Abstract: This paper gives a constructive algorithm to obtain the entire set of stabilizing first order controllers for a given single-input single-output linear time invariant system. Unlike earlier results, a mathematical model such as the transfer function or a state space model is not required. Instead, only the frequency response (Nyquist-Bode data) and knowledge of the number of RHP poles of the plant are utilized to solve the problem. The method is of practical importance especially when mathematical models are not available or identification is not desirable. We also show that the method can be extended to include various performance requirements such as guaranteed gain and phase margins, and guaranteed H/sub /spl infin// margin. An example is given for illustration.

Compensation for modulation distortion

Abstract: A modulation distortion compensation system for a phase locked loop 109 includes a compensation function (115) that is arranged to be coupled to a tuning voltage signal (117) corresponding to a tuning voltage from the phase locked loop and is configured to select a filter response from a plurality of filter responses, where the filter response corresponds to the tuning voltage. The distortion compensation system further includes a filter 224 that is configured to distort a modulation signal in accordance with the filter response and provide a distorted signal suitable for being coupled to a modulation input 211 of a feedback divider 209 included with the phase locked loop, wherein the distorted signal when used by the feedback divider will facilitate modulation and compensation of a radio frequency signal provided by the phase locked loop. Various environmental measurements in addition to the tuning voltage can also be used in selecting the filter response.

Non-sequential linear CMOS phase detector for CDR applications

Abstract: This paper describes a new non-sequential linear phase detector using a standard 0.18 μm CMOS process for high-speed clock and data recovery applications. The new phase detector avoids using DFFs or D-latches in order to achieve high operating speeds up to 10 Gbit/s. Its circuit structure is much simpler than the existing half-rate 10 Gbit/s phase detectors reported so far. Consisting of 1 delay cell, 2 XOR gates and 1 AND gate, the proposed PD consumes 34.58 mW. It exhibits a linear characteristic for low jitter operation and avoids half-cycle skew problem inherent in the conventional linear phase detectors. The simple structure of the proposed PD also has the advantage of lower power consumption compared with other PDs reported in the literature.

Low-reflection bandpass filters with a flat group delay

Abstract: Recently, low-reflection low-pass RLC filters with a linear phase characteristic have been reported. This paper is an extension of this study on bandpass filters, including their realizations with lumped-element and distributed-parameter networks. A topology particularly suitable for microstrip techniques is proposed. It yields a compact design that enables miniaturization and is easy for manufacturing and tuning.

A Low Power Linear Phase Digital FIR Filter for Wearable ECG Devices

Abstract: In this paper we present a low power linear phase digital FIR filter which is a part of an ECG-on-Chip. The ECG-on-Chip can be embedded into clothing to acquire the electrocardiogram (ECG) signal and send a warning message to a mobile phone or PDA if an abnormal ECG is detected. The proposed new filter structure significantly reduces the arithmetic operations for each sample which in turn lowers the power consumption. The filter is developed based on the interpolated finite impulse filter technique and is very attractive for a low cost and low power VLSI implementation

Oscilloscope having an enhancement filter

Abstract: An enhancement filter for an oscilloscope is disclosed wherein the enhancement filter may be initially calibrated for one or more channels and/or for one or more attenuation settings such as 50 mV per division, 100 mV per division, and/or 200 mV per division, for example In one embodiment, a desired filter response is selected to have a modified Gaussian type filter function having an at least approximately linear phase response, wherein the transfer function of the desired filter response comprises a step response that is be stored in the oscilloscope to be used as a part of calibration system of the oscilloscope