Abstract
The paper presents proposal of a fully-differential (1 + α)-order low-pass filter. The order of the filter and its cut-off frequency can be controlled electronically. The filter is proposed using operational transconductance amplifiers (OTAs), adjustable current amplifiers (ACAs) and fully-differential current follower (FD-CF). The circuit structure is based on well-known Inverse Follow-the-Leader Feedback (IFLF) topology. Design correctness of the proposed filter is supported by PSpice simulations with transistor-level simulation models. The ability of the electronic control of the order has been tested for five individual values of parameter α. Furthermore, the ability of the electronic control of the cut-off frequency of the filter has been also tested for five different values. Additionally, the simulation results of the proposed fully-differential (F-D) filter are compared with the results of the single-ended (S-E) equivalent of the presented filter.DOI: http://dx.doi.org/10.5755/j01.eie.23.3.18332
Highlights
Regardless of the fact that technology is working mainly with digital signals nowadays, analog frequency filters are a vital part of electronic circuits which are required in cases when digital filters cannot be used e. g. the preprocessing of the analog signals before the digitalization, etc
The design procedure which leads to a creation of a (1 + α)-order fractional low-pass filter using an approximation of Laplacian operator of fractional-order sα is described
The presented filter is a fully-differential form of the S-E (1 + α)-order low-pass filter proposed in [37]
Summary
Regardless of the fact that technology is working mainly with digital signals nowadays, analog frequency filters are a vital part of electronic circuits which are required in cases when digital filters cannot be used e. g. the preprocessing of the analog signals before the digitalization, etc. A cascade combination of an integer-order and fractional 1 + α filter is used in order to create a fractional filter of higher order than 1 + α [4] The advantage of this approach is that the structures are constructed by commercially available active and passive elements. The filter was proposed in its fully-differential form which brings the advantages of the FD structures in comparison to the single-ended (S-E) circuits such as greater dynamic range of the processed signals, better power supply rejection ratio, lower harmonic distortion and greater attenuation of common-mode signal [31]. The other disadvantage of some of these structures ([5], [13], [15], [16], [18]) is that they do not provide the electronic control of some of the filter parameters and they are not working in the current mode
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