Essential Information & explanations, latest texts & monographs on
Analog.
Design of Analog CMOS Integrated Circuits by Behzad Razavi
Analysis and Design of Analog Integrated Circuits (4th Edition) by Paul R. Gray
The Art of Analog Layout by Alan Hastings
Troubleshooting Analog Circuits by Robert Pease
Analog Days : The Invention and Impact of the Moog Synthesizer by Frank Trocco
Design with Operational Amplifiers and Analog Integrated Circuits by Sergio Franco
The Art and Science of Analog Circuit Design by Jim Williams
CMOS Analog Circuit Design by Allen
Design of Analog Filters by Rolf Schaumann
Schaum's Outline of Theory and Problems of Analog and Digital Communications by Hwei P. Hsu
Telling Time: How to Tell Time on Digital and Analog Clocks! by Jules Older
Analog Integrated Circuit Design by David Johns
Modern Digital and Analog Communications Systems by B. P. Lathi
Software Radio Architecture: Object-Oriented Approaches to Wireless Systems Engineering by Joseph Mitola
Analog Interfacing to Embedded Microprocessors : Real World Design by Stuart Ball
Analog
For Analog Science Fiction and Science Fact publication, see Astounding Magazine
An analog (or analogue, non-US spelling) signal is any continuously variable signal. It differs from a digital signal in that small fluctuations in the signal are meaningful. Analog is usually thought of in an electrical context, however mechanical, pneumatic, hydraulic and other systems also use analog signals.
An analog signal uses some property of the medium to convey the signal's information. For example an aneroid barometer uses rotary position as the signal to convey pressure information. Electrically, the property most commonly used is voltage followed closely by current and charge.
Another method of conveying an analog signal is to use modulation. In this, some base signal (e.g., a sinusoidal carrier wave) has one of its properties altered: amplitude modulation involves altering the amplitude of a sinusoidal voltage waveform by the source information, frequency modulation changes the frequency. Other techniques, such as changing the phase of the base signal also work.
Any information may be conveyed by an analog signal, often such a signal is a measured response to changes in physical phenomena, such as sound, light, temperature, position, or pressure and is achieved using a transducer.
Analog circuits do not involve quantisation of information into digital format. The concept being measured over the circuit, whether sound, light, pressure, temperature or an exceeded limit, remains from end to end.
Clocks with hands are called analog, those that display digits digital. However, many analog clocks are actually digital since the hands do not move in a smooth continuous motion, but in small steps every second or half a second.
The word "analog" implies an analogy between cause and effect, voltage in and voltage out, current in and current out, sound in and frequency out.
For example, in an analog sound recording, the frequency of a pure tone striking a microphone creates a corresponding variation in the current passing through it. An increase in the volume of the sound causes the fluctuation of current to increase while keeping the same rhythm.
The primary disadvantage of analog signalling is that any system has noise in it -- that is, random variations. As the signal is copied and re-copied, or transmitted over long distances, these random variations become dominant. Electrically these losses are lessened by shielding, good connections and several cable types such as coax and twisted pair.
The effects of noise make signal loss and distortion impossible to recover, since amplifying the signal to recover attenuated parts of the signal amplifies the noise as well.
See digital for a discussion of digital vs. analog.
Sources: Some of an earlier version of this article was originally taken from Federal Standard 1037C in support of MIL-STD-188.
See also:
The above article is adapted from from Wikipedia All Wikipedia article text is available under the terms of the GNU Free Documentation License
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