Butterworth filter

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

Current-mode operational transconductance amplifier-capacitor biquad filter structures based on Tarmy-Ghausi Active-RC filter and second-order digital all-pass filters

Abstract: The Tarmy-Ghausi (TG) active resistor-capacitor (RC) filters using op-amps and its modification by Moschytz are well known to active RC filter designers. These use first-order all-pass networks in a negative feedback loop. New current-mode universal operational transconductance amplifier-capacitor (OTA-C) biquad filters based on the TG active RC filter are considered here. These are based on a recently proposed OTA-C based first-order all-pass network. Three different feedback arrangements are investigated in the proposed filter structure so as to reduce the pole-Q sensitivity. The proposed biquad filters are shown to implement all different types of filters like low-pass, high-pass, band-pass, symmetric notch, all-pass, low-pass notch and high-pass notch. The synthesis of the general biquad is carried out in a novel way by invoking the analogy with direct-form digital filter structures. The special case of all-pass filter realisation derived from the proposed universal filter needs additional hardware for realising the feed-forward coefficients. Hence alternative OTA-C based all-pass filter implementations based on Mitra-Hirano and Gray-Markel second-order digital filter structures are derived in which the coefficients that are used to realise the denominator are shared in the realisation of numerator also. All the proposed circuits are compared with the other structures available in the literature. The simulation results of the proposed circuits are also presented.

High-order spline filter and ideal low-pass filter at the limit of its order

Abstract: We propose a method of obtaining a more vertical step-edge-like cut-off characteristic of a low-pass filter, in which a mean line for the roughness profile is extracted and the computation time is significantly reduced. In order to make the cut-off characteristic more step-edge-like, attention is focused on the relationship between the spline filter order and mean line smoothness, and the order is made larger. This filter, i.e., the high-order spline filter, has extremely low end effects because it is an extension of the spline filter. Raising the order of the high-order spline filter to ∞ can also realize an ideal low-pass filter that has a step-edge-shaped cut-off characteristic. In addition, in order to reduce computation time, the high-order spline filter is calculated in the frequency domain. When several thousand data points are used, the spline filter requires a maximum of 1 h, whereas using the proposed high-order spline filter allows computation to be completed in less than 1 s.

Design of hexagonal filter with source-load coupling

Abstract: A method for synthesising a novel hexagonal filter with source-load coupling is presented. The equivalent circuit of the lowpass prototype of a general lossless coupled resonator filter is proposed, and the corresponding transfer function t(s) is derived. A novel quasi-elliptic function microstrip hexagonal filter is designed and fabricated. Simulated and measured results are presented. Compared with the conventional cross-coupling filter, the proposed hexagonal filter acquires more than 27.5% size reduction and provides improved selectivity by a relatively small bandwidth

Optimal Use of Some Classical Approximations in Filter Design

Abstract: The classical Butter worth, Chebyshev and Elliptic (Cauer) low-pass filter approximations can be used in the design of analog and IIR digital filters in such a way as to obtain passband, stopband and transition band optimized filters at no order cost. The exact analytical relationships for such an optimal deployment of these approximations are developed and presented in this paper and their use is demonstrated through design examples.

Surface acoustic wave device and communication apparatus

Abstract: A branching filter is a surface acoustic wave device in which a first filter having a relatively low bandpass frequency and a second filter having a relatively high bandpass frequency are connected to a common terminal. A junction-side resonator that is included in the second filter and that is connected in closest proximity to the common terminal is connected in series. The resonant frequency f sr of the junction-side resonator is higher than the center frequency f 0 , which is the center of the passband, of the second filter, and is more preferably set so as to satisfy the expression: f 0 +BW×0.2≦f sr ≦f 0 +BW×0.7, where BW is the bandwidth of the passband.