Digital Signal Processing Reference
In-Depth Information
one signal operation to a component; it always embodies several signal operations.
As a circuit usually consists of many components, the real behaviour of the circuit
may diverge considerably from the behaviour planned. Every conductor track of a
motherboard also has an ohmic resistance R and an inductance L as a result of the
magnetic field which arises when electricity flows through it. An electrical field exists
between two parallel conductor tracks; they thus form a capacitance. These characte-
ristics of the motherboard are rarely taken into account in the design of the circuit
(except in the high and maximum frequency area).
• As a result of the influences or inteference effects listed here analogue technology
has its limitations especially where the greatest precision in the execution of a
desired behaviour (e.g. filtering) is required. This means that analog circuits cannot
be produced in practice with the quality or characteristics which are theoretically
possible.
• There is, however, a way to go beyond what is possible with analog technology and
enter a field whose absolute limits are defined by physics: signal processing by means
of digital computers. As their computational precision - unlike the analog computer
and the circuits represented by it - can be increased ad infinitum, there is the possibi-
lity of carrying out signal operations with the desired degree of precision which
previously could not be carried out.
• A communications system can also be represented by a program which links up a
number of algorithms of signal operations. In conjunction with a computer or micro-
processor system (hardware) this produces a system for the digital processing of
signals. The program decides what the system can do.
• The limits of this technology with digital computers (microprocessors) in the area
defined by physics are at present defined by the speed of computing and the problems
that arise in the conversion and reconversion of signals (A/D and D/A conversion)
which is necessary for computation. They are constantly displaced to the outside. The
aim of this development is the real-time processing of signals, i.e the arithmetical pro-
cessing of signals at such a high speed that no unwanted loss of information occurs.
• It is already clear: the measurement and control technology processes which are
executed by means of microprocessor circuits are essentially superior to traditional
analogue processes. Thus for example it is not possible with traditional technology to
store data precisely for a longer period of time before they are re-used, even the
precise short-term time delaying of analog signals causes considerable difficulties.
• Analog technology is being pushed more and more to the periphery of microelectro-
nics, to the source and drain of the signal, and the actual transmission path which in
retrospect can be seen as a "crutch" with which it was possible to carry out signal
processes in a very inadequate and faulty fashion which was prone to interference.
The trend is therefore to reduce the analogue part of a system to a minimum by means
of an A/D converter to arrive at numbers as quickly as possible with which it is
possible to compute (Sampel&Hold, quantization and encoding). The precision of
A/D and D/A converters now depends practically only on factors such as the height
and constancy of the quartz frequency reference and/or the constancy of a constant
current source or reference voltage. Any modern digital multimeter is based on this
technology.
