Butterworth filter

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

Frequency Response Control in Frequency-Tunable Bandstop Filters

Abstract: This letter presents a tunable bandstop filter with the capability of controlling the shape of the frequency response. The proposed filter structure can be tuned to have either a Butterworth or a Chebyshev response. The filter can also be tuned to have different center frequencies. Both the frequency response and the center frequency of the filter can be tuned by only adjusting the resonant frequency of each resonator without controlling inter-resonator coupling. Since the proposed filter structure has non-zero inter-resonator coupling, it can find its future application in reconfigurable filters which can be tuned to exhibit either a bandstop or a bandpass response.

Quadrature mirror filter banks and method

Abstract: M-channel pseudo-quadrature-mirror-filter (QMF) banks using a prototype filter having a linear-phase spectral-factor of a 2Mth band filter. The overall transfer function of the analysis filter/synthesis filter system is a delay, and the aliasing cancellation has all the significant aliasing terms canceled. Consequently, the aliasing level at the output of the pseudo-QMF banks is comparable to the stopband attenuation of the prototype filter, with the error at the output of the analysis filter/synthesis filter system approximately equal to the aliasing error at the level of the stopband attenuation. The pseudo-QMF banks have the stopband attenuation of the analysis filters and thus synthesis filters of -100 dB. The resulting reconstruction error is also on the order of -100 dB. Optimization of the pseudo-QMF banks by a quadratic-constrained least-squares formulation converges very fast as both a cost function and constraints are quadratic functions with respect to unknown parameters, providing a much higher stopband attenuation compared to previous filter banks.

Sliding-window transform with integrated windowing

Abstract: A system for a sliding-window transform with integrated windowing is described. The system provides a Direct Fourier Transform kernel with an integrated windowing filter having a desired number of stages. In one embodiment, the windowing filter is a lowpass filter. In one embodiment, the lowpass filter has a rectangular filter transfer characteristic. The DFT includes a complex multiplier. A first portion of the windowing filter is provided before the complex multiplier and can be implemented using real arithmetic. A second portion of the windowing filter is provided after the complex multiplier and is implemented using complex arithmetic. In one embodiment, the filter weights of the second portion of the windowing filter are unity and thus no multiplier is needed for the filter weights in the second portion of the windowing filter.

Design Techniques for Continuous-Time ΔΣ Modulators With Embedded Active Filtering

Abstract: Continuous-time ΔΣ modulators (CTDSM) used in wireless systems need to process signals in the presence of interferers. Peaking in the Signal Transfer Function of a conventional design necessitates a higher in-band dynamic range to accommodate interferers. A filter up front solves this problem at the expense of increased power dissipation and degraded linearity of the signal chain. Embedding the filter in the modulator achieves the same objective in a power efficient manner, while improving out-of-band linearity and reducing active area. However, having the filter inside a ΔΣ loop can be problematic with respect to stability. We show that such a system can be stabilized in a robust manner without extra hardware. Measurements of a CTDSM (signal BW = 2 MHz), with a built-in VGA (0 to 18 dB) and a second order Butterworth filter (4 MHz cutoff), show that the in-band/out-of-band IIP 3 improves by about 3/10 dB when compared to the filter-CTDSM cascade, and achieves a similar dynamic range and consumes 25% lower power.