Butterworth filter

About: Butterworth filter is a research topic. Over the lifetime, 6187 publications have been published within this topic receiving 69070 citations.

Compact wideband balanced bandpass filter with high common-mode suppression based on cascade parallel coupled lines

Abstract: A novel differential bandpass filter based on the cascaded parallel coupled lines is proposed, which takes the features of wide passband, high common-mode suppression and compact size. Six transmission zeros are created and located at the frequency range of 0-2f 0 ( f 0 is centre frequency of the passband), which helps realise the wide passband performances. The balanced bandpass filter consists of the four-stage parallel coupled lines, and the even- and odd- mode characteristic impedances can be adjusted to achieve the desired bandwidth of the passband while the positions of four transmission zeros can be conveniently adjusted by changing the impedance ratio of the asymmetrical stepped impedance resonator (SIR) structures in the proposed filter. By applying the differential and common modes analysis method, the two-port bisections of the filter become a bandpass and all-stop filter topologies under differential- and common-mode excitations, respectively. For performance demonstration of the proposed differential filter, a prototype operating at the frequency band of 2.15-3.85 GHz (with fractional bandwidth of 56.7%) was designed and fabricated on a commercial printed circuit board (PCB) substrate. The insertion loss and return losses of the differential-mode filter are 15 dB in the passband and the common-mode suppression is higher than 30 dB. Good agreements between the simulated and measured results have been observed.

Voltage-mode multifunction biquadratic filter based on simple CMOS OTAs

Abstract: A voltage-mode versatile multifunction filter with four inputs and three outputs biquadratic filter based on simple CMOS operational transconductance amplifiers (OTAs) is presented. By appropriately connecting the input and output terminals, the proposed circuit can work as either a single-input multiple-output (SIMO) or a multiple-input single-output (MISO) filter without changing the circuit topology. When the circuit functions as a SIMO filter, it provides bandpass (BP), lowpass (LP) and bandstop (BS) voltage responses with grounded capacitors. When it functions as a MISO filter, the circuit can realize all the standard non-inverting and inverting second-order filter functions. The parameters ω 0 and Q can be set orthogonally by adjusting the circuit components. For realizing all the filter responses, no critical matching condition is required, no inverting-type input signal is imposed and all the incremental parameter sensitivities are low. The simulation results confirm the theoretical analysis.

Cut-off frequency automatic adjusting filter

Abstract: A cut-off frequency automatic adjusting filter includes a plurality of filters, one of them being a reference filter, and a feedback circuit for the reference filter. The feedback circuit is formed by a subtracter, a full-wave rectifier, an integrator and an error amplifier. A square wave signal is inputted to the reference filter as a reference signal instead of a sine wave signal in the conventional filter. The feedback circuit generates an electrical signal which causes the cut-off frequency of the reference filter and another filter to be constant.

Analog Integrated Polyphase Filters

Abstract: When it comes to integratability, the zero-IF receiver is an alternative for the heterodyne or IF receiver. In recent years it has been introduced in several applications, but its performance can not be compared to that of the IF receiver yet. In this paper the principle of the low-IF receiver is introduced. The low-IF receiver has a topology which is closely related to the zero-IF receiver. Like the zero-IF receiver, the implementation of a low-IF receiver can be done with a high degree of integration. Its performance can however be better. The low-IF receiver is not sensitive to DC-offsets or LO to RF crosstalk. The principle of the low-IF receiver is based on the replacement of the LF lowpass filter of a zero-IF receiver with an analog integrated active polyphase filter. An active polyphase filter can perform a lowpass filter operation shifted on to a center frequency. In this paper the realization of a 5th order lowpass Butterworth filter centered around a low IF of 250 kHz is presented. This polyphase filter is designed for a low-IF receiver for high quality applications. The filter is implemented with the active-RC technique in a standard 1.2 μm CMOS process.

Reconfigurable cascaded coupled line filter with four distinct bandwidth states

Abstract: This study presents a cascaded coupled line filtering structure for the development of high-order reconfigurable microwave filters. A reconfigurable bandpass filter of this type that is capable of switching between four distinct bandwidth states ranging from around 20 to 50% 3 dB fractional bandwidth centred at 2 GHz, is described. The filter exhibits insertion losses ranging from 0.47 to 5.5 dB. The circuit is designed from a filter building block proposed previously in earlier literature. The publication enhances the understanding of this building block and shows why such a filter topology is used in order to develop higher order filters. This is done through mathematical modelling of the filter building block and theoretical simulation. The modelling shows that the centre frequency is only dependent on the set of even- and odd-mode impedances, which makes tuning the bandwidth easy. It also shows that changing the characteristic impedance of short-circuit stubs changes the bandwidth. The fabricated filter shows good agreement with electromagnetic simulated results.