An accurate center frequency tuning scheme for 450-KHz CMOS Gm-C bandpass filters

This paper describes a center frequency tuning technique for a second intermediate-frequency (IF) bandpass filter. The utilization of the step signal response ensures the direct measurement of the center frequency. This tuning technique guarantees the accuracy of the design. A 450-kHz G_m-C bandpass filter tuned using this technique has been developed to integrate the IF module for personal digital cellular (PDC) handsets for use in 0.35-μm CMOS. The filter with the tuning scheme achieves a center frequency accuracy of ±0.5%     

Digital bandpass and bandstop filters with variable center frequency and bandwidth

This paper presents a method of designing wave digital bandpass (BP) and bandstop (BS) filters whereby the center frequency and bandwidth can be independently controlled by simply changing the multiplier values. Also given are the canonic realizations for the BP and BS wave digital filters. This method of designing BP and BS wave digital filter results in a saving of coefficient registers.     

New high-Q discrete-time LC bandpass filter design with center frequency broadband tuning

Discrete-time switched-capacitor filters have been in wide-spread used for a few years, for the realization of stable, accurate and high quality filters. This paper describes the design of a new 8-path pseudo switched-capacitor LC bandpass filter and its command circuit made up by a ring voltage controlled oscillator (VCO) with ‘XOR’ gates. The proposed architecture presents the possibility of tuning over a frequency broadband allowing to sweep different channels with a high quality factor. This circuit is intended to replace the surface acoustic wave (SAW) filters in broadband wireless applications. Experimental results carried out on a prototype show quality factors up to 200, and a tunable center frequency range of 300 MHz [250–550 MHz]. Ahmed El Oualkadi received the PhD. degree in electronics from the University of Poitiers, France, in 2004. Since 2001, he has been with the LAII-ESIP laboratory, Electronics & Electrostatics Research Unit, University of Poitiers, France. In 2004, he was an assistant lecturer of Electronics Engineering at the University Institute of Technology, Angoulême, France. During this period he worked on various projects which concern the nonlinear analysis & design of switched-capacitor filters for radio-communication systems. Currently, he is a senior research engineer at the Université Catholique de Louvain, Microelectronics Laboratory, Louvain-la-Neuve, Belgium. His main interest of research is the design of low power high temperature circuits and systems for low cost wireless communications especially for ZigBee applications. Jean-Marie Paillot received a Ph.D in Electronics form the University of Limoges, in 1990. His thesis on the design of non-linear analog circuits and the study of the noise spectral of integrated oscillators was prepared at the Institute of Research for Optical Communications and Microwaves, Limoges. After graduation, he joined the Electronics Laboratory of PHILIPS Microwave, at Limeil, as R&D engineer in charge of the design of analogical and numerical microwave monolithic integrated circuits. Since October 1992, J.M. Paillot is at the University Institute of Technology, Angoulême, where he currently is Professor of Electronics Engineering. In charge of several contracts with industry, and author of papers published in scientific journals, J.M. Paillot is at present interested in phase noise reduction techniques for microwave oscillators, as well as in the research and development of switched capacitor filters in RF domain. Rachid Allam received the Dipl. Eng. Degree from the Université des Sciences et Technologies dran, Algeria, in 1980. He joined the Centre Hyperfréquences et Semiconducteurs, University of Lille 1,Villeneuve d’Ascq, France, in 1980. He received the Docteur-Ingénieur degree in 1984 from the University of Lille 1. In 1988, he joined the Institut d’Electronique et de Microélectronique du Nord and received the Habilitation à Diriger les Recherches en Sciences Physiques degree, in 1996. Currently, he is Assistant Professor at the University of Poitiers (IUT Angoulême), France. In 1997, he joined the Equipe Electronique et Electrostatique at the Laboratoire d’Automatique et d’Informatique Industrielle (LAII - UPRESS - EA 1219). Research work concerns microwaves devices and circuits, FET nonlinear modeling, microwaves mixers, non linear CAD, millimeter wave MMIC’s and non linear noise analysis.     

The design of CMOS continuous-time VHF current and voltage-modelowpass filters with Q-enhancement circuits

In this paper, very high frequency (VHF) current and voltage biquadratic lowpass filters implemented directly by the linear wideband finite-gain current and voltage amplifiers, respectively, are proposed and analyzed. A new Q-enhancement circuit which consists of a finite-gain wideband tunable voltage amplifier and a Miller capacitor is also proposed. It can increase the maximum-gain frequency f_M, and enhance the maximum-gain quality factor Q_M of the VHF lowpass filters. Experimental results have successfully verified the capability of the proposed new filter implementation method in realizing both VHF current and voltage lowpass filters with maximum-gain frequency f_M tunable in the range of 148 MHz to 92 MHz. It is also shown from experimental results that the VHF current lowpass biquad with the Q-enhancement circuit has the maximum-gain frequency f_M near 185 MHz and the maximum-gain quality factor Q_M up to 18.5. A fourth-order Chebyshev current lowpass filter with the cut-off frequency of 190 MHz has been successfully designed by using the current biquads with Q-enhancement circuits     

Dual-mode quasi-elliptic-function bandpass filters using ringresonators with enhanced-coupling tuning stubs

A novel microwave dual-mode quasi-elliptic-function bandpass filter structure has been designed and fabricated. The filter uses L-shaped coupling arms for enhanced coupling and dual-mode excitation. The effects of varying the length of tuning stubs and gap size between tuning stubs and ring resonator have been studied. Filters using multiple cascaded ring resonators with high rejection band are presented. The new filters have been verified by simulation and measurement with good agreement     

A highly linear CMOS Gm-C bandpass filter with on-chipfrequency tuning

A fourteenth-order CMOS transconductance-C (G_m-C) bandpass filter with on-chip automatic frequency tuning is described. By using highly linear G_m-C integrators, the filter achieves 75 dB dynamic range over 700 kHz noise bandwidth. The measured intermodulation distortion (IM3) @ 600 kHz for a 4 V_pp input signal is only -61 dB. On-chip automatic frequency tuning provides more than 300% center frequency range (i.e., 165-505 kHz) of the filter with ±1% frequency accuracy. The 0.7-μm CMOS filter measures 4.8 mm ² and consumes 70 mW from a single 5 V power supply     

Cascaded frequency domain bandpass filters for multivernier spectra

Passive sonar processing generally consists of many concurrent verniers on each beam or channel which are very narrow bands centered at widely separated, independent frequencies sparsely placed across the total search band. Each is analyzed by a fast Fourier transform (FFT) with extremely narrow coefficients. A cascaded frequency domain filter structure that provides such verniers with fewer computations than other methods is described     

Zolotarev bandpass filters

Zolotarev rational functions may be used in certain bandpass filter applications for which two narrower passbands are required. Coupled-resonator low-pass prototypes for narrow bandpass filters based on even- and odd-degree Zolotarev functions are synthesized using a transformed variable. Compared to other filters, those with Zolotarev responses have sharper skirt selectivity, resulting in lower passband distortion     

Inductorless bandpass filters

The technique of designing inductorless filters by replacing the inductors in conventional LC filters with gyrators and capacitors is considered for the special case of the high-quality channel bandpass filters used in multiplex telephony. One particular gyrator circuit, which has been found to be very satisfactory, using two operational amplifiers and four resistors, is analyzed in some detail. The difficulties of simulating floating inductors are discussed, and ways of designing filters to avoid the necessity of such simulations are proposed. The dynamic range of a filter is defined and the factors controlling it are described. Detailed measured results of two specific channel filter designs are included.     

Synthesis of dual-band bandpass filters using successive frequency transformations and circuit conversions

A novel method is proposed to synthesize dual-band bandpass filters (BPFs) from a prototype low-pass filter. By implementing successive frequency transformations and circuit conversions, a new filter topology is obtained which consists of only admittance inverters and series resonators, and is thereby easy to be realized by using conventional distributed elements. A dual-band BPF with center frequencies of 1.8GHz and 2.4GHz is designed and fabricated using microstrip lines and stubs. The simulated and measured results show a good agreement and validate the proposed theory.     

Stripline bandpass filters with step-impedance resonators

Research results for stripline bandpass filters with step-impedance resonators formed on Al₂O₃ (Alumina, polycor) and operating in the frequency band 1500–2500 MHz are presented in this article. Use of step-impedance resonators breaks repetition factor in frequency positioning of passbands in such filters. This allows suppressing harmonics of output signal in transmitters and widening stopband for parasitic signals in receivers.     

On the use of Nauta's transconductor in low-frequency CMOS gm-C bandpass filters

This paper discusses the use of a transconductor, first proposed by Nauta for high frequency applications, in low frequency CMOS g_m -C bandpass filters. The behavior of the transconductor is examined in detail, showing that the robust implementation of higher-order low-voltage filters is possible for center frequencies in the lower megahertz region. The experimental results are presented of the realization of two prototypes, a 0.6-μm CMOS 18th-order real bandpass filter and a 0.35-μm CMOS 7th-order complex (14th-order bandpass) filter, both with a center frequency of 3 MHz and a passband of 1 MHz. These filters comply with the specifications for the channel-select stage of the Bluetooth short-range radio receiver     

Stripline bandpass filters with alternating coupling coefficients

This article shows the possibility in principle to design stripline comb filters with alternating signs of the coupling coefficients. The new feature of the stepped-impedance resonators of the quarterwave type was established. They provide the opposite sings of the electromagnetic coupling with adjacent resonators. Such resonators are asymmetric relative to the vertical axes, which is drawn through their middle part. The stripline passband filters with alternating signs of coupling coefficients have attenuation poles that are located to the left and to the right of the passband. Those poles improve the selectivity of such filters. The articles provide the measured characteristics of the stripline comb filter of the forth order with alternating coupling, which has the central frequency of f ₀ = 1835 MHz and the passband width of 90 MHz. The filter is constructed using a dielectric material with relative permittivity of ε_r = 92 and has the dimensions of 7.4×4.2×2 mm.     

Two bandpass active filters with reduced sensitivities

A current-controlled current source and a voltage-controlled voltage source are used in conjunction with four passive components to implement second-order bandpass filters. The circuits, which exhibit reduced values for their active and passive sensitivities, can be used in a very large frequency range when the active elements are designed from high-performance bipolar arrays. Simulated results using SPICE, which confirm the theoretical analysis, are reported and discussed for active elements implemented in a translinear form. Experimental results are given indicating that the implementation compares favorably with conventional ones     

Millimiter-wave stripline bandpass filters

The possibility to use thin (1 mm or less) pseudocombline structures of λ/2 resonators made of sections of symmetric transmission strip lines from a dielectric material with ε _r = 2.2 as millimeter-wave bandpass filters is shown. It is established that the relative bandwidth of such filters can reach FBW = 0.1. Designs of stripline pseudocombline filters with alternating signs of the coupling coefficients, which are characterized by improved selectivity due to the attenuation poles located on both sides of the passband, are proposed; the filters contain stepped-impedance “half-wave” resonators with a new feature. The results of the computer simulation of the frequency characteristics of the filters in the frequency band of 31–122 GHz and the comparison of them with the characteristics of other filters are presented.     

Millimeter-wave tune-all bandpass filters

Distributed microelectromechanical varactors on a coplanar waveguide have been used to design a two- and four-pole bandpass tune-all filters. The two-pole initial bandwidth is 6.4% at 44.05 GHz with a mid-band insertion loss of 3.2 dB and with matching better than 15 dB. The four-pole initial bandwidth is 6.1% at 43.25 GHz with a mid-band insertion loss of 6.5 dB and with matching better than 10 dB. The use of microelectromechanical system bridges allows a continuous tuning for both center frequency and bandwidth. The varactors biasing network has been designed so that the center frequency and bandwidth can be tuned separately. The two-pole filter center frequency can be changed from 44.05 to 41.55 GHz (5.6% tuning range), while the bandwidth can be independently changed from 2.8 to 2.05 GHz. The four-pole filter center frequency can be changed from 43.25 to 40.95 GHz (5.3% tuning range) and the bandwidth can be changed from 2.65 to 1.9 GHz.     

An analytical procedure for critical frequency tuning of FIR filters

A novel analytical procedure for the tuning of finite-impulse response (FIR) filters is introduced. The tuning procedure adjusts a single frequency of the frequency response to the desired value while preserving the nature of the filter. The impulse responses of the original and of the final filter are related by the transformation matrix. Two examples in the analytical design of notch FIR filters demonstrate the usefulness of the proposed tuning procedure.     

Realisability of bandpass filters

The traditional method of realising attenuation poles by resonant circuits is questioned. It is shown that, under some conditions, it is possible to depart from the conventional solution.     

Optimized E-plane bandpass filters with improved stopbandperformance

A computer-aided synthesis technique for E-plane bandpass filters with improved stopband performance is developed. An optimization procedure based on equal ripple optimization is adopted. The design of a symmetrical E-plane bandpass filter with improved stopband performance is considered; higher order mode interaction between E-plane discontinuities is included in the design. The predicted filter performance shows improved stopband performance and reduced filter dimensions compared with conventional E-plane bandpass filters. The validity of the method is confirmed by the measurement of a fabricated five resonator E-plane bandpass filter with improved stopband performance     

Planar three-resonator bandpass filters with cross coupling

New designs of planar three-resonator bandpass filters with cross coupling having a large variety of frequency characteristics are considered. In addition to better one-sided selectivity, such filters implement symmetric amplitude–frequency characteristics with an attenuation pole at each side of the passband. These filters can also have constant delay time in the passband. Concatenation of the proposed three-resonator filters leads to multiresonator filters with high selectivity determined by two attenuation poles at each side of the passband. It is found that the type of connection of the middle resonator in the circuit of a three-resonator filter with cross coupling results in substantial differences in amplitude–frequency characteristics. The results of modeling of different frequency characteristics are presented. It is shown that filters have small dimensions, which are comparable to overall dimensions of microwave ceramic filters. For example, dimensions of a three-resonator stripline filter designed for a frequency of 1.9 GHz are 9.4 × 5 × 2 mm for the permittivity of the filter material ε_r = 92 and dimensions of a six-resonator filter are 10 × 9.4 × 2 mm.