SHAKTOUR, M. Nekonvenční obvodové prvky pro návrh příčkových filtrů [online]. Brno: Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií. 2011.
There are two main aims of the Ph.D. thesis under review: 1) Defining/developing various types of active building blocks for effective synthesis of active filters simulating passive RCL ladder structures. 2) Performing such a synthesis. In order to solve the first problem, the author used the following methodology: He focused on hitherto designed building blocks (current conveyors, OTAs, CDBAs, CDTAs, and others) and analyzed them from the point of view of their prospective utilization in the simuation of ladder structures. As a result, he designed novel buiding blocks called VDTA and VDVTA which enable economical synthesis of floating inductors. As a second step, he proposed an IC topology of VDTA and VDVTA in CMOS technology. In order to prefer low-voltage low-power design, he utilized bulk-driven OTA as a basic building block. Then VDTA and VDVTA were assembled from two OTAs, the second one with special arrangment for external adjustment of its transconductance, providing also linearization of the output stage and an increase of the dynamic range of designed elements. As a result of this stage of research, VDTA/VDVTA, and OTA bulk-driven blocks and their SPICE models were available for the subsequent synthesis. In the second stage, the above building blocks were used for the synthesis of frequency filters. In addition to the ladder structures, other filter structures were also studied, particularly universal biquads and all-pass filters. Some of the filters were constructed also by means of off-the-shelf integrated circuits (diamond transistors and OTA amplifiers). These analyses were accompanied by formulating useful rules which are helpful for filter optimization. The above results can be considered, from my point of view, as most valuable, representing concrete contribution of the author. The main parts of the work were already published in Conference Proceedings and Journals indexed in the Government Council for Research and Science. In July 2011, the Ing. Shaktour's H-index according to Web of Science was 1. The work fulfills the common Ph.D. theses requirements and I recommend it for subsequent processing.
viz soubor pdf
Review of the doctoral thesis “Unconventional circuit elements for ladder filter design” Author: Ing. Mahmoud Shaktour Supervisor: Prof. Ing. Dalibor Biolek, CSc. Thematically, the submitted doctoral thesis is divided into 6 chapters and contains all the required formal components. Also submitted have been reprints of the candidate’s fundamental publications and a printout of the points-based evaluation of publications and the respective responses. The whole work has 108 pages, inclusive of appendices. The introductory part of the thesis is devoted primarily to the state of the art in the given field. The author is here concerned with generally known facts in the given field. This is what is here expected of the author but I believe that the analysis should have been more extensive and better founded. Chapter 2 sets out the goals of the thesis. The author focuses his work on two areas. The first part is focused on designing a high-linearity wideband bulk-driven OTA with tuneable transconductance. The OTA element is the main active building block for CDTA, VDTA, VDVTA and DVCC elements. The other area of the thesis is focused on the application of MAX435 elements and the super-transistor (S-T) represented by elements such as OPA615, OPA860, etc., in the design of the “floating” inductor. The goals are clearly defined and developed in the thesis. What I miss here is a clearly defined contribution of the author to the given problematics. To define the goals as obtaining a high linearity of appropriate control is too general. Chapter 3 gives an introduction to the given problematic; here, the basic building blocks and their basic circuits inclusive of internal circuit structures are given. This part is presented very well, in a clear manner, being a summary of well- or less-known facts. Some simulations of the above internal structures are also given. The results obtained could have been analysed in greater detail even if these results were in most cases expected and the simulations only confirm the assumption. In this chapter, the author is also concerned with various versions of transconductance amplifiers such as difference, current, voltage, and other outputs. Chapter 3 is comparatively extensive and devoted, among other things, to VDTA (Voltage Differencing Transconductance Amplifier) elements in low-voltage and low-input applications. I do not consider this chapter as the very fundamental part of the thesis. The author’s main contribution is in Chapter 4, dealing primarily with applications containing commercially available elements. Here, I appreciate the contribution of the simulations made and, obviously, also of the experimental measurements made, which confirm the expected conclusions as obtained by simulation. I regard this part as pivotal: it is thoroughly prepared, methodologically correct and can be seen as a solid contribution to the problematics in question. The development of the synthesis and analysis is logical and the simulations performed yield interesting results. In conclusion, Spice models of NMOS are given. Here, a discussion of the nature of the model would be worth considering: whether the author himself created the model, what properties the models possess, etc. This is important mainly because simulated structures, analyzed by means of these models, might carry certain simplifications or other errors. For this reason, the author might, in the course of the defence of the thesis, elaborate on the above models. Were other models suitable for computer simulation also considered? Why are the above computer models suitable for the simulation of these circuits? As regards the formal aspect, the thesis has been prepared in a standard way. The main deficiency is the writing of constants and variables, which is not uniform throughout the thesis. A variable is sometimes written in roman and then in italics. Indices are also written incorrectly. I have found a few typing errors. I do not know whether it is meaningful to follow the module of frequency response up to a frequency that is outside the region of interest (p. 93). In my opinion, the thesis submitted satisfies the conditions for being accepted as a dissertation thesis and the candidate has demonstrated sufficient knowledge to be awarded the PhD degree. Brno, June 8, 2011 Reviewer: doc. Ing. Jiří Mišurec, CSc
eVSKP id 41266