Digital Signal Processing Reference
In-Depth Information
Clarification of Objectives
Up until now, we have described the
methods
to be used in this introductory course. It is
now time to focus on content. Here too, a kind of preview will show the reader what
awaits him and enable him to get his bearings.
To use another image: imagine the content as a kind of platform which is supported and
fenced in. The railing is described by the technical framework conditions that exist at
present.
The basic phenomena and basic concepts and their definitions form the supports of the
platform. Beyond the railing the horizon can be seen more or less clearly. It extends to the
boundaries defined by natural laws - i.e. by physics.
The platform is roughly as follows:
• Signals can be defined as (physical) oscillations or waves which are carriers of
information.
• Information exists in the form of agreed patterns which constitute meaning which the
recipient must know and recognise. Data are informative patterns. The essential task
of communications technology or signal technology is thus the recognition of
patterns.
• All the measurable signals of the real physical world - even if they are bit patterns -
are present in analog continuous form. They are usually transformed into electric
signals by sensors (converters) and are present at the measuring points usually in the
form of AC voltage.
• (Storage) oscilloscopes are instruments which can display the chronological course of
AC voltages in the form of a graph on the screen.
• Every signal technology process (e.g. filtering, modulation and demodulation) can in
general be described in mathematical terms (theory!) and subsequently be carried out
by means of the appropriate algorithms or programs on a purely arithmetic level.
Thus, from the theoretical point of view an analog system - created by the combina-
tion of several individual circuits/ processes/ algorithms - represents an analog
computer which works through a sequence of algorithms in real time. This aspect is
often overlooked. For example, this is also true of conventional radio receivers.
•
Real time processing
of (frequency band limited) signals is understood as the capacity
to record the flow of desired information without gaps or to retrieve it from the signal.
• Analog components are above all resistors, spools, capacitors and, of course, diodes,
transistors etc. Their fundamental disadvantages are inaccuracy (tolerance), noise
features, lack of long-term consistency (aging), temperature dependence, non-
linearity (where it is desired) and above all their combined behaviour. Thus, a real
spool behaves like a combination of (ideal) inductance L and resistance R. A real
resistance has the same equivalent circuit, when current flows through a magnetic
field forms around it and therefore inductance exists in addition to the resistance.
Every diode is not only a rectifier, it also distorts in a nonlinear fashion in an unwan-
ted way. This combined behaviour is the reason why it is not possible to ascribe only
