New class of time-varying filters

A new class of time-varying lowpass and highpass filters is described in which the stopband attenuation is obtained by outphasing in a quadrature-modulation arrangement, the undesired associated frequency translation or inversion being cancelled by a suitably chosen second step of quadrature demodulation or both; bandpass and bandstop filters can be obtained as combinations of lowpass and highpass filters.     

An Ultra-Broadband Coplanar-Waveguide Bandpass Filter With Sharp Skirt Selectivity

An ultra-broadband coplanar-waveguide (CPW) bandpass filter (BPF) is demonstrated. The proposed CPW BPF is designed via cascading CPW lowpass and bandpass structures. As compared to the classical CPW BPFs, the ultra broadband is realized relatively easily by separately adjusting the cutoff frequencies of the CPW lowpass and bandpass structures. The cascaded CPW BPF is of greater than 120% 3-dB fractional bandwidth, very sharp skirt selectivity, good stopband rejection, and no repeated passbands     

Current-Mode Active RC Filters Using Current Followers

In this letter, a realization of current-mode active filter using current followers as active element is described. We show the constructions of second-order lowpass, highpass and bandpass filters. The high-order filters can be realized by a cascade connection of these second filters. As examples, the second-order lowpass and highpass filters are designed for frequency of 5 MHz. The effectiveness of the proposed method is demonstrated through SPICE simulation.     

Planar microstrip UWB bandpass filter using U-shaped slot coupling structure

A compact planar microstrip UWB bandpass filter is proposed. It is realised by cascading a lowpass filter and a highpass filter. A transmission line with U-shaped slots coupled with two DGS units on the back of the circuit board has the characteristic of highpass, while a periodic uniform DGS array has the characteristic of lowpass. Combining these two structures, a new UWB bandpass filter (BPF) is fabricated and measured. Measured results show that the proposed BPF has wide bandwidth from 3.0 to 10.9 GHz, all the measured return loss less than 13 dB in the passband. The BPF achieves a wide stopband with 18 dB attenuation up to 18.0 GHz     

M-band biorthogonal interpolating wavelets via lifting scheme

Recently, the lifting scheme was generalized to the multidimensional and multiband cases and was used to design M-band interpolating scaling filters and their duals. Based on this idea, we develop a new lifting pattern, namely, the progressive lifting pattern. This pattern allows us to pairwise generate M-band interpolating filterbanks and wavelets by the order from lowpass to highpass filters. A complete lifting procedure is divided into M - 1 simple steps, in each step, a pair of filters (the l'th filter and its dual) are generated. In this way, an M -band biorthogonal interpolating filterbank/wavelet is determined by M(M - 1) lifting filters. The first 2(M 1) lifting filters completely characterize the two scaling filters as well as the vanishing moments of bandpass and highpass filters; the residual (M - 1) (M - 2) lifting filters are used to pairwise optimize the bandpass and highpass filters in terms of the criterion of stopband energy minimization. The obtained M-band biorthogonal interpolating filterbanks and wavelets provide excellent frequency characteristics, in particular, low stopband sidelobes. Furthermore, the pattern is also utilized to design signal-adapted interpolating filterbanks and their rational coefficient counterparts in terms of subband coding gain. The obtained filterbanks achieve large subband coding gains. The rational coefficient filterbanks preserve the biorthogonality and allow wavelet transforms from integers to integers and a unifying lossy/lossless coding framework at the cost of a slight degradation in subband coding gain.     

Current-mode universal filters using unity-gain cells

Two new current-mode universal filters are presented. The proposed filters use unity gain current and voltage followers. The first filter has three inputs and one output and can realise lowpass, highpass and bandpass responses without any changes in the circuit topology. Realisation of notch and allpass responses can be easily achieved without adding any additional active elements. The second filter has three inputs and one output and can simultaneously realise lowpass, highpass and bandpass responses without any changes in the circuit topology. Realisation of notch and allpass responses can be easily achieved without adding any additional active elements. The proposed circuits enjoy low active and passive sensitivities     

一种用CFA实现的通用高阶滤波器

以信号流图为基础,用CFA设计了一种通用高阶滤波电路。这种电路结构由CFA和电阻、电容组成,具有通用性,只需调整接地阻抗的值,就能实现高阶低通、带通、高通及带阻几种不同的滤波功能。列举了四阶带通和五阶高通两种滤波器,并对两种滤波器进行了仿真,PSpice仿真结果与理论分析一致。     

High input impedance voltage-mode lowpass, bandpass and highpassfilter using current-feedback amplifiers

A new configuration for realising high input impedance lowpass, bandpass and highpass filters simultaneously by using three current-feedback amplifiers, three grounded capacitors, three grounded resistors and one floating resistor is presented. The proposed circuit offers the following features: realisation of lowpass, bandpass and highpass signals from the same configuration, no requirements for component matching conditions, orthogonal control of ω₀ and Q, the use of grounded capacitors, low active and passive sensitivities and low output impedance     

Voltage-mode highpass,bandpass and lowpass filters using two DDCCs

A new configuration for realizing voltage-mode highpass, bandpass and lowpass filters, simultaneously, using two differential difference current conveyors (DDCCs), two grounded capacitors and two grounded resistors is presented. The proposed circuit offers the following features: realization of highpass, bandpass and lowpass signals from the same configuration, no requirements for component matching conditions, the use of only grounded capacitors and resistors, high input impedance, low active and passive sensitivities and simpler configuration due to the use of only two DDCCs and four passive components.     

Synthesis of fiber-optic delay line filters

This paper deals with the synthesis of fiber-optic delay line filters and is organized as follows. We show how filters with negative coefficients can be implemented using positive structures and differential detection at the optoelectronic conversion. This possibility implies that not only lowpass, but bandpass and highpass filters with arbitrary transfer functions may be implemented. Synthesis methods for positive filters based on modified versions of well-known time and frequency domain techniques are presented which take into account the restriction on the positive nature of the filter coefficients. We make use of these results to describe the synthesis procedure for arbitrary filters using fiber-optic structures. Some designs of lowpass, bandpass and highpass filters are presented as examples, and a possible implementation of these structures with a view of future optoelectronic integration is presented     

MOCCII电流模式二阶滤波器的系统设计

本文提出一种MOCCⅡ电流模式二阶滤波器的一般电路模型和设计理论。根据该电路模型和理论可以产生多种滤波器结构。每一种结构可以实现低通、带通、高通、带阻及全通滤波器或其中的多种滤波器。所有滤波器的无源元件均接地，且具有很低的灵敏度。最后对所产生的滤波器进行了PSPICE模拟。     

New current-mode current-controlled universal filter with single input and three outputs

In this study, a new current-mode current-controlled universal filter with single input and three outputs is presented. The proposed circuit uses single-output current controlled conveyors (CCCIIs) and can simultaneously realize lowpass, bandpass and highpass filter functions all at high impedance outputs. Realization of notch and allpass responses does not require additional active elements. The circuit enjoys independent current-control of the parameters ω₀ and ω₀/Q without disturbing the gains of the lowpass, bandpass and highpass filters. Both its active and passive sensitivities are low.     

Novel coplanar-waveguide bandpass filters using loaded air-bridge enhanced capacitors and broadside-coupled transition structures for wideband spurious suppression

Novel inline coplanar-waveguide (CPW) bandpass filters composed of quarter-wavelength stepped-impedance resonators are proposed, using loaded air-bridge enhanced capacitors and broadside-coupled microstrip-to-CPW transition structures for both wideband spurious suppression and size miniaturization. First, by suitably designing the loaded capacitor implemented by enhancing the air bridges printed over the CPW structure and the resonator parameters, the lower order spurious passbands of the proposed filter may effectively be suppressed. Next, by adopting the broadside-coupled microstrip-to-CPW transitions as the fed structures to provide required input and output coupling capacitances and high attenuation level in the upper stopband, the filter with suppressed higher order spurious responses may be achieved. In this study, two second- and fourth-order inline bandpass filters with wide rejection band are implemented and thoughtfully examined. Specifically, the proposed second-order filter has its stopband extended up to 13.3f/sub 0/, where f/sub 0/ stands for the passband center frequency, and the fourth-order filter even possesses better stopband up to 19.04f/sub 0/ with a satisfactory rejection greater than 30 dB.     

Bandstop monolithic crystal filters having allpass response outside stopband

A dual-resonator monolithic crystal filter (MCF) is basically a narrowband bandpass filter. It is well known that a narrowband bandstop response can be obtained by connecting an inductor in parallel to an MCF element, however, it yields a lowpass response outside the stopband with a cutoff frequency about square root (2) times the stopband frequency. Ideally, outside the stopband, it should have an allpass characteristic. The author shows a simple method of designing a bandstop MCF filter having an allpass response outside the stopband by adding a series-connection inductor. The series inductor together with two capacitors provide the required highpass structure that complements the lowpass response to yield an allpass response.<>     

采用单个四端浮地零器的电压模式滤波器

文中提出了电压模式单ＦＴＦＮ滤波器新通用电路结构，它能实现二阶低通、高通、带通、全通（陷波）和一阶低通、高通、全通滤波功能。给出了二阶带通和一阶低通的ＰＳＰＩＣＥ仿真频响，进一步证实了理论分析的正确性，各滤波电路的增益与极点角频率（或品质因素）独立可调，且有低的无源灵敏度。     

Insensitive current/voltage-mode filters using FTFNs

A new configuration for realising insensitive current/voltage-mode filters using two four-terminal floating nullors (FTFNs) is presented. It can provide the curren/voltage-mode filters with reduced sensitivities. Moreover, the current-mode filters can have high output impedance and only grounded capacitors. The proposed universal voltage-mode filter with dual outputs can realise lowpass, bandpass, highpass, notch and allpass filtering functions. Simulation results are given to verify the theoretical analysis     

High input impedance voltage-mode universal biquadratic filters with three inputs using plus-type CCIIs

Two new configurations for realizing high input impedance voltage-mode universal biquadratic filters are presented. Each proposed universal biquadratic filter with three inputs is composed of three plus-type CCIIs and can realize all the standard filter functions, that is, highpass, bandpass, lowpass, notch and allpass filters. In spite of the active components, the first proposed configuration uses five passive components, the second proposed configuration uses three capacitors and three resistors. The use of only plus-type CCIIs simplifies the configurations.     

Three-channel variable filter-bank for digital hearing aids

This study proposes a three-channel (3-channel) variable filter-bank (VFB) that consists of variable lowpass, variable bandpass and variable highpass digital filters. The three variable digital filters are obtained from a normalised analog prototype Chebyshev type-I lowpass filter using analog frequency transformations along with a modified bilinear transformation. Since both the magnitudes (gains) and band edge frequencies of the three variable digital filters are independently adjustable, the 3-channel VFB is considerably flexible, and can be successfully applied for compensating various hearing loss patterns in digital hearing aids. Various audiograms have been used to verify that high-accuracy fittings can be achieved with low order variable filters. Moreover, the authors reveal and theoretically prove the numerator coefficient-symmetries of the variable lowpass, variable bandpass and variable highpass filters, and show that each variable filter requires only one multiplication for its numerator filtering operations, so the total number of multiplications can be significantly reduced. More specifically, only 11 multiplications and 14 additions are required in the whole 3-channel VFB. Therefore the 3-channel VFB has extremely simple structure and high tuning flexibility for hearing aids.     

New analogue inverse filters realised with current feedback op-amps

This article presents new configurations for realising analogue inverse lowpass, inverse bandpass, inverse highpass and inverse bandreject filters using commercially available current feedback op-amps (CFOA) with an accessible z-terminal (such as AD844). The workability of the proposed circuits has been confirmed by experimental results by employing AD844-type CFOAs.     

New universal biquad filters using only two unity-gain cells

New current-mode and voltage-mode universal biquad filters are presented using only two unity-gain cells (one current follower and one voltage follower) in each configuration. The proposed filters employ one less follower than in the literature to date. The filters can realize highpass, bandpass, lowpass, notch and allpass responses without any changes in the circuit topology. The circuits enjoy the following advantages: minimum number of active elements, no component-matching condition and low active and passive sensitivities.