Circuits and Components for System Evaluations and Design - intro

A real RF system or a piece of RF equipment is made of real components or circuits. This chapter tries to introduce some of the fundamental building blocks, which the designer can use, for example, to construct a demonstrator or even sometimes the final system as well. Both passive and active circuits will be highlighted with the exception of antennas and related hardware, which have a chapter of their own later. In this context, a demonstrator is a special piece of equipment or an entire sys­tem that does not necessarily have all the external characteristics of the prototype to come and that might also lack some of the software features. The demonstrator's main purpose is to be a test bed for evaluating the key problems and their solutions. Its main benefits when compared to a real industrial prototype are cost and time savings and the possibility to focus at the essential issues.

Standard or Custom Design?

Sometimes already ar the starting phase of a project we face the question of whether the entire system or at least some parts of it should he tailored to the specific task. Could we base the realization on ordinary commercial-off-the-shelf (COTS) tech­nology? Circuit designers might want to rush to the workshop to pick some bread­board and wire and immediately switch on the soldering iron. Alternatively, if those who are more theory-oriented could click MATLAB or MathCAD or Maple to the screen or perhaps go straight to some electromagnetic simulation package. The real solution for systems engineers is to simplify.

Custom designs, either homemade or ordered from a vendor, tend to have far more risks than benefits. If performance criteria can he met with existing hardware and software, that is the path to take. Often, we can even adjust the overall design so that system specifications will be met, even though the original configuration indi­cated severe constraints. For example, if the initial plan calls for previously unavail­able TX output power in an end-to-end system, wc can sometimes compensate for this by taking more out of antenna gain or by selecting a little hit better RX NF—doing so, of course, assuming that such LNAs are readily available.

Custom designs cannot be avoided, though. Particularly novel military and sci­entific systems are forced to use such designs to be able to comply with their mission requirements. Typical—and often neglected—difficulties appearing with such mod­ules include the following:

·         Severe delays in the schedule and often within the critical path;

·         Budget collapses due to labor and hardware costs;

·         Unexpected technical side effects (e.g., power supply, temperature, and avail­ability of semiconductors);

·         Maintainability problems (only the specialist who designed the module knows it thoroughly);

·         Documentation challenges.

Practical experience indicates that even if the financial and timing estimates are made with the best available professionalism, final conclusions after completing a project show a two- to threefold increase in the use of funding and other resources. Seldom can the designed special component or module be applied in, for example, industrial production without considerable refinements and sometimes even redesign.

Pagina fuente:  http://books.google.co.ve/books?id=63_zqr7w9OoC&pg=PA63&lpg=PA63&dq=Circuits+and+Components+for+system+evaluations&source=bl&ots=wynYdLf_wJ&sig=pYFYYhrXuw-CR9rSUZHIkfW0TdM&hl=es&ei=Z0ZrS8a9Msmj8AaR5-2EBg&sa=X&oi=book_result&ct=result&resnum=9&ved=0CDYQ6AEwCA#v=onepage&q=Circuits%20and%20Components%20for%20system%20evaluations&f=false

Libro:  Circuits and Components for System Evaluations and Design

Autor: Pekka Eskelinen

Nombre: Josmar Eduardo Depablos Rodriguez

Asignatura: Circuitos de Alta Frecuencia