Low-pass Infinite Impulse Response Research Articles

The Design and Experiment of IIR Lowpass Digital Filters for Airborne Gravity Data

AbstractWe have designed IIR (Infinite Impulse Response) lowpass digital filters based on Butterworth and Chebyshev approximations, and conducted an experiment research of filtering to GT‐1A airborne gravity data. The result shows that: by selecting proper parameters such as passband and stopband attenuation, these IIR lowpass digital filters for airborne gravity data can get satisfactory filtering effect almost as good as that of GT‐1A filtering result.

The design and implementation of a digital infinite impulse response (IIR) Lowpass Butterworth filter– impulse response (IIR) Lowpass Butterworth filter– A comparison of Matlab and Bilinear transformation methods

This research compares two IIR digital filter design and implementation methods– viz MATLAB direct method and Bilinear transformation method. Programs to design and implement Butterworth IIR lowpass digital filters were developed and executed using both methods. In the design, at Fpass of 1Hz, Fstop of 2.414 Hz, using MATLAB method the 3 dB frequency is at 1.605 Hz while using the Bilinear transformation method the 3 dB frequency is at 1.395 Hz. At Fpass of 0.7839Hz, Fstop of 2.007 Hz, using MATLAB method the 3 dB frequency is at 1.181 Hz while using the Bilinear method the 3 dB frequency is at 1.001 Hz. From the design it was observed that the Butterworth filter has maximally flat passband in its frequency response and a poor roll-off at its bandstop which is in line with predicted theory. The Butterworth filters designed using Bilinear transformation were more stable with a monotonically decreasing gain response due to its poor roll-off which may be associated to discrete component performance. The magnitude of the passband decreases as the order of the filter increases. The designs also show that higher order filters have sharper skirts and may be used in phase modulated wave (PMW) applications. Keywords: Matlab, Bilinear transformation methods, Keywords filter design.

Improved narrowband low-pass IIR filters in fixed-point systems [DSP Tips & Tricks

Due to their resistance to quantized-coefficient errors, traditional second-order infinite impulse response (IIR) filters are the fundamental building blocks in computationally efficient high-order IIR digital filter implementations. However, when used in fixed-point number systems, the inherent properties of quantized-coefficient second-order IIR filters do not readily permit their use in narrowband low-pass filtering applications. Narrowband low- pass IIR filters have traditionally had a bad reputation; for example, MATLAB's Signal Processing Toolbox documentation warns: "All classical IIR low-pass filters are ill conditioned for extremely low cutoff frequencies." This article presents a neat trick that can be used to overcome the shortcomings of narrowband second-order low- pass IIR filters, with no increase in filter coefficient bit widths and no increase in the number of filter multiplies per output sample.

A Compact Single-FPGA Fading-Channel Simulator

This brief presents a novel computationally efficient design and implementation of a Rayleigh flat fading-channel simulator. To generate complex Gaussian variates with the required U-shaped power spectrum, the simulator utilizes an infinite-impulse response (IIR) spectrum shaping filter followed by multistage interpolators and low-pass IIR filters. The new simulator significantly simplifies the characterization of wireless systems by providing a fast and area-efficient field-programmable gate array (FPGA) implementation of the fading channel. Our fixed-point Rayleigh fading-channel simulator utilizes only 4% of the configurable slices, 20% of the dedicated multipliers, and 2% of the available memories on a Xilinx Virtex2P XC2VP100-6 FPGA, while generating 25 million fading variates per second. The parameterized fading-channel simulator can be readily reconfigured to accurately simulate a wide variety of different channel characteristics.

Constant beamwidth IIR lowpass filter for data sampled at nonuniform rate

A simple modification to the algorithm for a first-order infinite impulse response lowpass filter to allow the use of nonuniformly sampled data is described. This real-time algorithm uses measurements of the intersample interval to modify the recursion weight so that the filter cutoff frequency is kept constant.

Design of two-dimensional circularly symmetric low-pass IIR filters using transformation

A technique for designing two-dimensional IIR (infinite-impulse response) filters using a separable transformation function has been reported recently. A modification of this technique is proposed for circularly symmetric filters which gives better results. >