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Showing papers on "Stopband published in 1992"


Proceedings ArticleDOI
Osamu Ikata1, Tsutomu Miyashita1, Takashi Matsuda1, Tokihiro Nishihara1, Y. Satoh1 
20 Oct 1992
TL;DR: In this article, a bandpass filter using surface acoustic wave (SAW) resonators in a ladder circuit structure for portable telephone systems is reported, where a simulation tool is used to consider the effects of electrodes (their apertures, the number of paired elements, thickness, and bulk wave radiation). Filter input and output impedance conditions are designed by the resonator capacitance to match the line impedance.
Abstract: A bandpass filter using surface acoustic wave (SAW) resonators in a ladder circuit structure for portable telephone systems is reported. For filter design, a simulation tool is used to consider the effects of electrodes (their apertures, the number of paired elements, thickness, and bulk wave radiation). Filter input and output impedance conditions are designed by the resonator capacitance to match the line impedance. The insertion loss and stopband rejection values are traded off against each other and are controlled by the ratio of capacitances between the parallel arm and series arm resonators, 800-MHz and 1.9-GHz band filters mounted in 3.8 mm*3.8-mm*1.5-mm ceramic packages were fabricated. They are suitable for surface mount technology (SMT). Typical frequency response characteristics are 2.5-dB maximum insertion loss in the 25-MHz passband and a stopband rejection of 25 dB. >

123 citations


Journal ArticleDOI
TL;DR: In this paper, waveguide couplers are combined with lambda /4 shifted distributed feedback (DFB) resonators to produce narrowband channel dropping filters, where the bandwidth of the filter can be made much narrower than the stopband of the grating.
Abstract: Waveguide couplers are combined with lambda /4 shifted distributed feedback (DFB) resonators to produce narrowband channel dropping filters. The bandwidth of the filter can be made much narrower than the stopband of the grating. It is possible to remove the spurious responses of the grating filter by appropriate dispersion characteristics for the coupled waveguides. However, in some practical applications it may not be necessary to do this, if all channels can be accommodated within half the grating bandwidth of the filters. >

109 citations


Journal ArticleDOI
TL;DR: The authors propose the use of transition bands and transition functions in the ideal amplitude frequency response to allow the analytical design of optimal least-squared-error FIR digital filters with an explicit control of the transition band edges.
Abstract: The authors propose the use of transition bands and transition functions in the ideal amplitude frequency response to allow the analytical design of optimal least-squared-error FIR digital filters with an explicit control of the transition band edges. Design formulas are derived for approximations to ideal frequency responses which use pth-order spline transition functions. A mixed analytical and numerical method for zero-error weight in the transition bands and passband and stopband error weighting functions with an integral squared error approximation are derived. A variable-order spline transition function is developed, and a method for choosing the optimal order to minimize the integral squared approximation error is given. >

79 citations


Journal ArticleDOI
TL;DR: In this paper, a birefringent filter was proposed for femtosecond (F2C) laser with a steeply diving optic axis, which achieved two-octave tunability with negligible deterioration of the stopband rejection.
Abstract: A design for a birefringent filter is described, which is suitable for tunable femtosecond lasers. Using a single plate, which has a steeply diving optic axis, two-octave tunability is attained with negligible deterioration of the stopband rejection. For a specific wavelength region, it means that the filter's bandwidth can be changed by a factor of four. Another characteristic of the design is that, for the same bandwidth, the proposed plate is five times thicker than a conventional plate in which the optic axis is parallel to the surface. Thus, etalon effects can be avoided. Tuning characteristics of color center lasers utilizing the new filter are also presented. >

53 citations


Journal ArticleDOI
TL;DR: In this paper, the problem of achieving a wide stopband is reduced to the problems of realizing the resonating capacitance required in an evanescent bandpass filter and computing the junction susceptance occurring at the interface between a larger evanescence section (the resonator enclosure) and the smaller iris opening.
Abstract: Dielectric resonators used in filter networks present a model spectrum with undesired, or spurious, resonances in close proximity to the desired one Through the use of evanescent mode bandpass irises tuned to the filter center frequency, the resonator spurious modes are suppressed, resulting in N-section filters with stopbands clean to at least (N-1) times the individual iris stopband levels The problem of achieving a wide stopband is reduced to the problems of realizing the resonating capacitance required in an evanescent bandpass filter and computing the junction susceptance occurring at the interface between a larger evanescent section (the resonator enclosure) and the smaller iris opening The technique results in high-Q resonator filters with stopbands clean to at least -55 dBc, out to at least 17 times the filter center frequency >

45 citations


Patent
11 Jun 1992
TL;DR: In this paper, the authors proposed a pseudo-quadrature-mirror-filter (QMF) bank using a prototype filter having a linear-phase spectral-factor of a 2Mth band filter.
Abstract: M-channel pseudo-quadrature-mirror-filter (QMF) banks using a prototype filter having a linear-phase spectral-factor of a 2Mth band filter. The overall transfer function of the analysis filter/synthesis filter system is a delay, and the aliasing cancellation has all the significant aliasing terms canceled. Consequently, the aliasing level at the output of the pseudo-QMF banks is comparable to the stopband attenuation of the prototype filter, with the error at the output of the analysis filter/synthesis filter system approximately equal to the aliasing error at the level of the stopband attenuation. The pseudo-QMF banks have the stopband attenuation of the analysis filters and thus synthesis filters of -100 dB. The resulting reconstruction error is also on the order of -100 dB. Optimization of the pseudo-QMF banks by a quadratic-constrained least-squares formulation converges very fast as both a cost function and constraints are quadratic functions with respect to unknown parameters, providing a much higher stopband attenuation compared to previous filter banks.

44 citations


Journal ArticleDOI
TL;DR: Laterally resonant modes of infinite arrays were described for the first time in this paper, where the Bloch-function method was used to provide a simple, yet accurate treatment of the leaky modes of finite-extent antiguided arrays.
Abstract: The Bloch‐function method is used to provide a simple, yet accurate treatment of the leaky modes of infinite‐extent antiguided arrays. Laterally resonant modes of infinite arrays are described for the first time. Bloch‐function solutions for infinite arrays are used to explain key characteristics of the modes of finite‐extent antiguided arrays. It is found that the resonant modes of antiguided arrays satisfy the second‐order lateral Bragg condition, and consequently are analogous to the modes of second‐order distributed‐feedback (DFB) lasers. In effect, the resonant‐optical‐waveguide (ROW) array is a second‐order lateral DFB structure with the radiative component along the longitudinal device axis, and zero stopband.

42 citations


Proceedings ArticleDOI
J. Machui1, W. Ruile
20 Oct 1992
TL;DR: In this article, the propagation path of the SAW was folded in order to make better use of the total chip length and the use of two slightly inclined reflectors results in a Z-shaped filter which conserves the temperature stability of quartz substrate.
Abstract: IF-filters for channel selection in mobile phone systems must offer narrow bandwidths together with very steep skirts and excellent stopband rejection. Surface acoustic wave (SAW) filters fulfill these requirements. But if conventional transversal design techniques are used chip sizes become too large. The propagation path of the SAW was folded in order to make better use of the total chip length. The use of two slightly inclined reflectors results in a Z-shaped filter which conserves the temperature stability of quartz substrate. At a center frequency of 45 MHz, filters were developed on small chips with good passband characteristics and an insertion loss better than 10 dB. A filter with signal suppression of 20 dB and an ultimate relative stopband rejection of 60 dB is shown. >

30 citations


Proceedings ArticleDOI
W. Schwab1, W. Menzel1
01 Jun 1992
TL;DR: Using multilayer structures, very compact planar bandpass filters can be designed with improved stop-band characteristics taking full advantage of the additional degrees of freedom given by the arrangement as mentioned in this paper.
Abstract: Using multilayer structures, very compact planar bandpass filters can be designed with improved stop-band characteristics taking full advantage of the additional degrees of freedom given by the arrangement. As examples, a suspended stripline filter with suppression of the first harmonic frequency and a finline filter with improved attenuation close to the pass-band are presented. >

23 citations


Journal ArticleDOI
TL;DR: A general theory for the synthesis of low-passband-sensitivity switched capacitor (SC) filters using a similar technique and the design of stray-insensitive structurally allpass SC sections is emphasized, ensuring the passivity property for the overall filter.
Abstract: The low-sensitivity property of IIR digital filters designed using a parallel connection of two allpass sections has already been demonstrated in the past few years. This property is closely related to the use of a particular type of allpass structures, called structurally lossless networks, which remain allpass regardless of the coefficient quantization. In this paper we provide a general theory for the synthesis of low-passband-sensitivity switched capacitor (SC) filters using a similar technique. the design of stray-insensitive structurally allpass SC sections is emphasized, ensuring the passivity property for the overall filter. Design examples are presented with computer simulations and experimental results to compare the performance of the different proposed structures. Analytical sensitivity calculations are also derived yielding useful formulae for the prediction of the filter sensitivities with respect to capacitor ratios, particularly in the stopband.

22 citations


Proceedings ArticleDOI
20 Oct 1992
TL;DR: In this paper, the dispersion curves and attenuation coefficients for Rayleigh waves propagating in a periodic system of thin electrodes on a piezeoelectric surface were calculated using periodic Green's functions with a propagation factor exp(i beta chi ) that is not known in advance.
Abstract: A new method of calculating the dispersion curves and attenuation coefficients for Rayleigh waves propagating in a periodic system of thin electrodes on a piezeoelectric surface is proposed. This method uses periodic Green's functions with a propagation factor exp(i beta chi ) that is not known in advance. To describe the charge distribution on the electrodes, both a step approximation and Chebyshev polynomials are used, the latter being more adequate in most cases. Numerically determined values of the Green's function are used and interpolated either linearly or using a modified variant of Ingebrigtsen's formula. Such basic parameters as stopband width, stopband center frequency, wave velocity, and attenuation in the stopband are found. These parameters can be used in a coupling-of-modes (COM) analysis for the design of surface acoustic wave (SAW) devices. The analysis includes the bulk wave radiation and scattering. The corresponding attenuation coefficient dependence on frequency is determined. Numerical results for Rayleigh waves on YZ-LiNbO/sub 3/ and leaky waves on 36 degrees YX-LiTaO/sub 3/ substrates are presented. >

Proceedings ArticleDOI
06 Dec 1992
TL;DR: Different types of digital pulse-shaping filters providing zero intersymbol interference (ISI) in digital transmission systems are examined and it is shown that this filter class includes matched pairs in which both the transmit filter alone and the pair have very low ISI.
Abstract: Different types of digital pulse-shaping filters providing zero intersymbol interference (ISI) in digital transmission systems are examined. The emphasis is on matched transmit-receive filter pairs satisfying the Nyquist criterion. Several finite impulse response (FIR) filter design techniques are discussed. Depending on the application, the stopband attenuation can be minimized either in the minimax or in the least-mean-square sense. A class of transmit-receive filter pairs based on the use of a special type of infinite impulse response (IIR) filters is introduced. It is shown that this filter class includes matched pairs in which both the transmit filter alone and the pair have very low ISI. Computationally efficient multistage designs are considered. Different FIR and IIR Nyquist filter designs are illustrated. >

Journal ArticleDOI
TL;DR: Physical effects causing distortions of the transfer function of a broadband (36% fractional bandwidth) spectrum shaping filter for digital radio with 16 quadrature amplitude modulation (QAM) are analyzed separately and connected with the modular two-dimensional (2-D) model, demonstrating the importance of every single effect.
Abstract: For pt.I see ibid vol.39, no.1, pp.61-72 (1992). Physical effects causing distortions of the transfer function of a broadband (36% fractional bandwidth) spectrum shaping filter for digital radio with 16 quadrature amplitude modulation (QAM) are analyzed separately and connected with the modular two-dimensional (2-D) model described in Part I, demonstrating the importance of every single effect. A compensation of the second-order effects is performed, yielding an agreement between simulation and measurement in amplitude and phase of more than +or-0.1 dB and +or-1 degrees all over the passband. The stopband is also predicted with high accuracy. >

Journal ArticleDOI
TL;DR: In this article, a method using periodic Green functions is developed and used to calculate dispersion curves and attenuation coefficients for Rayleigh waves and for leaky waves propagating in periodic systems of thin electrodes on piezoelectric substrates.
Abstract: A new method using periodic Green functions is developed and used to calculate dispersion curves and attenuation coefficients for Rayleigh waves and for leaky waves propagating in periodic systems of thin electrodes on piezoelectric substrates. Such basic parameters as stopband width, centre frequency of the stopband, attenuation in the stopband and resulting bulk-wave scattering are found for Rayleigh waves in YZ-LiNbO/sub 3/ and leaky waves on 36 degrees YX-LiTaO/sub 3/ substrate with shorted or open electrodes.

Proceedings ArticleDOI
20 Oct 1992
TL;DR: In this article, an 878-MHz IIDT-type surface acoustic wave (SAW) filter with suppressed sidelobes and reduced insertion losses is described. But the insertion losses are less than 3 dB.
Abstract: Interdigitated interdigital transducer (IIDT)-type surface acoustic wave (SAW) filters with suppressed sidelobes and reduced insertion losses are described. The filters are composed of multiple withdrawal-weighted IDTs in different withdrawal positions. An 878-MHz filter composed of 13 IDTs was designed by this method. This filter has a minimum insertion loss of 1.6 dB and a stopband rejection of about 30 dB. Three filters with center frequencies of 0.9 GHz, 1.5 GHz, and 1.9 GHz were fabricated using the lift-off process. Their frequency responses are almost the same, and the insertion losses are less than 3 dB. >

Journal ArticleDOI
TL;DR: Coupled-mode theory is used for the analysis of surface transverse waves (STWs) propagating under metal-strip gratings in the YZ plane of quartz and a quadratic dependence of the stopband width on the height-to-period ratio of the electrodes is found.
Abstract: Coupled-mode theory is used for the analysis of surface transverse waves (STWs) propagating under metal-strip gratings in the YZ plane of quartz. Analytical expressions are obtained for the reflection and transmission coefficients of waves propagating on rotated Y-cut substrates of weakly piezoelectric trigonal, tetragonal, or hexagonal crystals. A quadratic dependence of the stopband width on the height-to-period ratio of the electrodes is found. This is an agreement with stopband width measurements. The results can be used in the analysis of STW grating structures, particularly the two-port resonator filter. >

Proceedings ArticleDOI
20 Oct 1992
TL;DR: In this paper, the results of 50% wideband surface acoustic wave (SAW) filters with 70MHz central frequency and multichannel filters with weighted tapered interdigital transducers (TIDTs) are presented.
Abstract: Results of the investigations of 50% wideband surface acoustic wave (SAW) filters with 70-MHz central frequency and multichannel filters with weighted tapered interdigital transducers (TIDTs) are presented. Computer results are given for different constructions of SAW filters with TIDTs to which variable metallization ratio, apodization, capacitance, or withdrawal weighting techniques are applied. In tested filters stopband rejection from 31 to 42 dB is obtained with relative accuracy of 1 dB within passband. Frequency responses of reflected signals and SAW amplitude profiles launched by TIDTs as a function of frequency and distance are given. Computer and experimental results of a 10-channel filter are presented. >

Proceedings ArticleDOI
01 Jun 1992
TL;DR: In this article, a new type of YIG film filter that consists of a microstrip line with a substrate of yIG films sandwiched between two dielectric slabs is proposed.
Abstract: A new type of YIG film filter that consists of a microstrip line with a substrate of YIG films sandwiched between two dielectric slabs is proposed. The dispersion and transmission characteristics are calculated numerically. Sharp stopband characteristics were observed experimentally with a half-power bandwidth of 16.4 MHz. Alternatively, in the same line with an air gap a bandpass characteristic was observed with a quality factor of 430. These experimental results are compared with theory. >

Proceedings ArticleDOI
23 Mar 1992
TL;DR: A new method for quantizing cascaded subfilters to produce an overall filter that improves upon or compares favorably with the optimal quantized direct-form implementation is introduced, which enhances performance in designs requiring deep stopband suppression, which is very common in applications.
Abstract: The design of finite/wordlength finite impulse response, (FIR) digital filters is of much interest and importance in practical digital systems. In fixed-point implementations of digital filters, the designer is allowed only a finite number of bits for each coefficient. In general, the best choice for the finite wordlength coefficients is neither the truncated nor rounded infinite-precision values. A new method for quantizing cascaded subfilters to produce an overall filter that improves upon or compares favorably with the optimal quantized direct-form implementation is introduced. In particular, this method enhances performance in designs requiring deep stopband suppression, which is very common in applications. By cascading subfilters, it is possible to improve the stopband suppression. A difficulty with designing cascaded subfilters is the nonlinearity of the problem. A Taylor series approximation is used to develop a linear integer program for the optimal cascaded coefficients, improving the stopband suppression with no additional loss in the passband deviation. >

Proceedings ArticleDOI
01 Jun 1992
TL;DR: In this article, the authors describe a six-pole, 12-GHz, pseudoelliptic 76-MHz bandpass filter which achieves a stopband attenuation of greater than 50 dB up to 25 GHz.
Abstract: The authors describe a six-pole, 12-GHz, pseudoelliptic 76-MHz bandpass filter which achieves a stopband attenuation of greater than 50 dB up to 25 GHz. This design eliminates the need for a separate low-pass filter in applications such as output multiplexers of satellite transponders. Equivalent loss performance can be achieved for substantial savings in mass and volume. >

Journal ArticleDOI
TL;DR: In this paper, asymmetric stripline Y-junction circulators have been fabricated and tested over the frequency range of 0.05 to 18 GHz and the insertion loss was approximately 2 dB.
Abstract: Filters incorporating asymmetric stripline Y-junction circulators have been fabricated and tested over the frequency range of 0.05 to 18 GHz. The passband frequency was near 2 GHz. The insertion loss was approximately 2 dB and the stopband extended from 4.5 to 18 GHz with transmission >

Proceedings ArticleDOI
20 Oct 1992
TL;DR: In this paper, a self-resonant SAW filter with reflecting multistrip couplers (RMSC) and unidirectional IDTs was proposed.
Abstract: Low loss high selectivity surface acoustic wave (SAW) filters realized on the basis of the self-resonance approach without the use of matching LC-networks are presented. This approach is based on input interdigital transducer (IDT) static capacitance compensation by radiation susceptance and the choice of a definite number of finger pairs. Self-resonant SAW filters are developed on the basis of a ring configuration with reflecting multistrip couplers (RMSC) and unidirectional IDTs with U-shaped multistrip couplers. The optimization of filter topologies is achieved using computer programs based on the equivalent circuit model. At 45 MHz the ring filters show insertion loss below 2 dB, 2-5% fractional bandwidth, and stopband attenuation over 50 dB. >

Proceedings ArticleDOI
K.C. Wagner1, O. Manner
20 Oct 1992
TL;DR: In this paper, the phase velocity of a straight crested wave propagating with an arbitrary propagation angle in an interdigital transducers (IDTs) array is determined for all frequencies, including the stopbands, and allows the determination of stopband frequencies for obliquely propagating waves.
Abstract: In many surface acoustic wave (SAW) filters, the diffraction of the surface wave occurring in the interdigital transducers (IDTs) is as important as the diffraction on the free surface. The accurate simulation of diffraction effects requires knowledge of the slowness curves for waves propagating in the IDTs. The transducer is modeled as a periodic array of massless, infinitely long metal strips. The task is the determination of the phase velocity of the straight crested wave, which propagates with an arbitrary propagation angle in this array. The method of solution employed is valid for all frequencies, including the stopbands, and allows the determination of stopband frequencies for obliquely propagating waves. The substrate material is characterized by the numerically computed effective permittivity. Examples of slowness diagrams as well as dispersion diagrams are presented. The results of SAW device simulations using models for the SAW slowness curves are compared with each other and with measurements. >

Journal ArticleDOI
TL;DR: In this paper, a procedure for the generation of CMOS, continuous-time, high-frequency g m -C filters with finite tranmission zeros is presented, which can be generalised to arbitrary high-order prototypes and higher-frequency filters derived from LC ladders.
Abstract: A procedure for the generation of CMOS, continuous-time, high-frequency g m -C filters with finite tranmission zeros is presented. A third-order elliptic filter with 0.5 dB equiripple passband, 15 MHz cutoff frequency and -23 dB attenuation in the stopband is given as an example. The automatic generation method can be generalised to arbitrary high-order prototypes and higher-frequency filters derived from LC ladders

Proceedings ArticleDOI
10 May 1992
TL;DR: A design process is described which starts with a prototype resonator-based uniform filter-bank, whose bandpass outputs have poor stopband characteristics, and applies the concept of Lerner grouping of adjacent channels to develop a uniformfilter-bank with much better bandpass characteristics.
Abstract: A design process is described which starts with a prototype resonator-based uniform filter-bank, whose bandpass outputs have poor stopband characteristics, and applies the concept of Lerner grouping of adjacent channels to develop a uniform filter-bank with much better bandpass characteristics. For applications requiring the lower frequencies of the input signal to be resolved more accurately than the higher frequencies, the Lerner based uniform filter-bank may be converted to a nonuniform one by applying an allpass transformation; the merit of using such a transformation is that it retains the good magnitude characteristics of the bandpass channels. The main difference between the present design procedure and that of G. Doblinger (1991) is the manner in which the allpass transformation is applied. Further, unlike previous work, the filter-bank designed here has the property that the sum of the bandpass channels is an allpass function. The implementation of the filter-bank is also considered. The primary additional application of the nonuniform channel-bank examined here is frequency-domain adaptive filtering. >

Journal ArticleDOI
TL;DR: In this paper, a ceramic bandpass filter with increased selectivity on the lower side of the passband is presented, where the circuit was constructed with four coaxial ceramic resonators capacitively coupled using a microstrip PCB.
Abstract: A ceramic bandpass filter with increased selectivity on the lower side of the passband is presented. One application is the receive filter of a mobile radio transceiver operating in the 1.8-GHz bands. Finite transmission zeros have been introduced by using a network with additional cross couplings. The circuit was constructed with four coaxial ceramic resonators capacitively coupled using a microstrip PCB. For a 75-MHz passband filter, a stopband attenuation of 37 dB was attained at 20-MHz offset from the passband. A midband insertion loss of 1.2 dB and bandedge loss of 3 dB were achieved. >

Journal ArticleDOI
TL;DR: In this article, a general procedure is described for the approximation in the Chebychev sense of an arbitrary attenuation curve in the passband and in the stopband by an analog or digital transfer function.
Abstract: A general procedure is described for the approximation in the Chebychev sense of an arbitrary attenuation curve in the passband(s) and in the stopband(s), by an analog or digital transfer function. Both the analog and digital cases are reduced to a common optimization problem which is solved by the efficient Remez algorithm working with the transmission zeros and attenuation zeros. Some of the transmission or attenuation zeros can be fixed by the user at prescribed frequencies. Digital filters with a numerator of lower degree than the denominator can also be designed. The method has been implemented on a PC and is illustrated by some examples. >

Patent
16 Sep 1992
TL;DR: In this article, a high-pass filter with an IF trap was proposed to improve the FM interference ratio by arranging a capacitor in series with a first or second coil and setting the parts constant of this series circuit as an IF frequency to constitute a high pass filter including anIF trap.
Abstract: PURPOSE:To improve the FM interference ratio by arranging a capacitor in series with a first or second coil and setting the parts constant of this series circuit as an IF frequency to constitute a high-pass filter including an IF trap. CONSTITUTION:A first coil 5 is connected between a low-pass filter 2 and the earth, and a first capacitor 6 is connected to one end of the first coil 5, and a second capacitor 14 is connected to the first capacitor 6, and a second coil 7 is connected in series to the second capacitor 14, and the other end of the second coil 7 is connected to the earth, and they constitute the high-pass filter. The series resonance frequency of the coil 7 and the capacitor 14 is set as the IF frequency of the high-pass filter. Thus, the high-pass filter is operated to have not only an extreme point in the stop band but also an attenuation pole in the IF frequency as a maximum attenuation point.

Journal ArticleDOI
TL;DR: In this article, a computer-aided technique for designing FIR digital filters with close to linear phase property is presented, based on a constrained optimisation problem designed to minimise the mean square error between a desired response and the filter response over a passband of interest subject to a mean square stopband constraint.
Abstract: A computer-aided technique for designing FIR digital filters with close to linear phase property is presented. The approach is based on a constrained optimisation problem designed to minimise the mean-square error between a desired response and the filter response over a passband ofinterest subject to a mean-square stopband constraint. Numerical results are presented to illustrate the performance achievable.

Proceedings ArticleDOI
10 May 1992
TL;DR: In this paper, the design of lattice all-pass subfilters approximating linear phase in passband and stopband is studied and the problem is reduced to a nonlinear optimization inside a hypercube in the lattice parameters space and solved using the Fletcher-Powell algorithm.
Abstract: The design of lattice allpass subfilters approximating linear phase in passband and stopband is studied. The problem is reduced to a nonlinear optimization inside a hypercube in the lattice parameters space and solved using Fletcher-Powell algorithm. Using the recursive expressions for the phase response of lattice allpass filters, the authors also illustrate a simple method for fast design. This method uses one-variable optimization techniques and enables one to acquire initial values of lattice parameters for the optimization algorithm. It is shown that the method results in filters that are close to the optimum solution, from various design examples. >