Butterworth filter

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

Design of grating-assisted waveguide couplers with weighted coupling

Abstract: The design of grating-assisted, channel waveguide codirectional couplers is demonstrated using the Gel'fand-Levitan-Marchenko inverse scattering method. Weighted coupling coefficients are computed from rational expression for the desired wavelength response. Approximate formulas that relate the waveguide and grating geometries to the computed coupling coefficients are derived. The technique is illustrated by designing a directional coupler with a third-order Butterworth filter characteristic and a 130 AA full-width-half-maximum bandwidth. >

Filter and method for filtering baseline wander

Abstract: A linear phase high pass filter having a linear phase low pass filter in parallel with an electronic delay means is disclosed to remove baseline wander from an ECG signal. The linear phase low pass filter is preferably a digital Infinite Impulse Response (IIR) filter. An input ECG signal is simultaneously presented to an IIR low pass filter and an electronic delay. The low pass filter passes the low frequency baseline signal while blocking the ECG signal comprised of higher frequency components than the cutoff frequency of the low pass filter. Thereafter, the outputs from the IIR low pass filter and delay are passed to a summer that subtracts the output of the low pass filter from the output of the delay to produce the output of the filter. The combination of the output of a low pass filter being subtracted from a delayed input signal produces a high pass filter. The resulting high pass filter has a -0.3 dB cutoff frequency of about 0.5 Hertz while providing a virtually constant group delay for the ECG signal passed through the filter.

Programmable surface acoustic wave (SAW) filter

Abstract: A novel programmable SAW filter with switchable multi-element interdigital transducers (IDTs) controlled by a microprocessor or a computer is provided that realizes the tunability of both center frequency and bandwidth of the SAW filter. The filter possesses the feature of the programmability of both center frequency and 3 dB bandwidth. As an example design, the center frequency of the SAW filter ranges from 126.8 MHz to 199.1 MHz while the 3 dB bandwidth ranges from 18.8 MHz to 58.9 MHz. The multi-input configuration increases the programmability of the device and improves insertion loss. A matching network for the programmable SAW filter further improves insertion loss level and stopband attenuation. A resistance weighting method has been applied to improve in band ripple with the passband ripple being reduced from 6.44 dB to 1.37 dB after resistance weighting. The prototype of programmable SAW filter simplifies the device structure and fabrication process by eliminating the tap weighting and summing circuits, resulting in a smaller device and lower costs. Moreover, frequency response shaping is realized without apodization.

Soliton transmission control by Butterworth filters.

Abstract: Butterworth filters of second or higher order periodically inserted along a soliton transmission line, although they are flat at bandpass center, give to first order a nonzero restoring force for frequency and amplitude displacements. The amplified spontaneous emission generated at the filter center frequency is significantly less than that generated with fixed etalons for the same damping strength.

A novel approach for suppression of powerline interference and impulse noise in ECG signals

Abstract: One of the major problems encountered in recording ECG is the appearance of unwanted distortions induced by power line interference in the electrocardiogram. In addition, infections due to impulse noise leads to variations in the amplitudes which represent the abnormalities associated with the heart. This paper proposes a novel approach for addressing both the aforementioned issues in ECG signals employing sub-band decomposition using wavelets analysis. Morphological filtering is applied to the detail sub-bands for removal of impulse noise using one-dimensional structuring element. Further, the powerline interference is removed using IIR Butterworth filter providing significant reduction in power spectral density levels between 50 to 60 Hz. The finally reconstructed ECG signal yields reasonably good impulse noise as well as powerline suppression using the proposed approach.