Analog circuit

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It has been suggested that this article be merged with Analog electronics. (Discuss)

Analog circuit (or analogue circuit) refers to electronics systems with analog signals with any continuously variable signal. It differs from digital electronics in that small fluctuations in the signal are meaningful in that they are continuously variable rather than digitally quantised.

Origin of term

The word "analog" implies an analogy between cause and effect, voltage in and voltage out, current in and current out, sound in and sound out. An analog circuit is therefore an electric circuit that operates on analog signals.

Explanation

Analog electronics is sometimes confused with other sub-divisions of the general field of Electronics which include Power electronics and Digital electronics.

Analogs

The word "analog" implies an analogy between cause and effect, voltage in and voltage out, current in and current out, sound in and sound out. For example, in an analog sound recording, the variation in pressure of a sound striking a microphone creates a corresponding variation in the current passing through it or voltage across it. An increase in the volume or amplitude of the sound causes the fluctuation of the current or voltage to increase proportionally while keeping the same waveform or shape and electrical analog. Clocks with hands are often called analog displays; those that display digits are usually called digital displays. 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 sub division of a second.

In the field of Power Electronics analogs can be the Energy Storing variables such as the current in an Inductor or the Voltage across the terminals of a Capacitor.

Information and analog signals

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. 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 frequency, 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 do also work.

Analog circuits do not involve quantisation of information into digital format. The source signal information being measured over the circuit, whether sound, light, pressure, temperature, or an exceeded limit, remains continuous from end to end. See digital for a discussion of digital vs. analog.

Analog operations

While operating on an analog signal, an analog circuit changes the signal in some manner or manners. It may be designed to amplify, attenuate, provide isolation, distort, or modify the signal in some other way. It can be used to convert the signal into some other format such as a digital signal. Analog circuits also modify signals in unintended ways such as adding noise or distortion.

Analog Electronics is frequently confused with other sub-divisions of the general field of Electronics which include Power electronics and Digital electronics. Or in the field of Power Electronics can be the Energy Storing variables such as the current in an Inductor or the Voltage across the terminals of a Capacitor. 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 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 frequency, current, and charge.

For example, in an analog sound recording, the variation in pressure of a sound striking a microphone creates a corresponding variation in the current passing through it or voltage across it. An increase in the volume or amplitude of the sound causes the fluctuation of the current or voltage to increase proportionally while keeping the same waveform or shape and electrical analog.

Noise

Main article: Electronic noise

The effects of random noise can make signal loss and distortion impossible to recover, since amplifying the signal to recover attenuated parts of the signal often generates more noise and amplifies the noise as well.

Clocks with hands are often called analog displays; those that display digits are usually called digital displays. 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 sub division of a second.

Passive versus active

Passive analog circuits consume no external electrical power while active analog circuits use an electrical power source to achieve the designer's goals. An example of a passive analog circuit is a passive filter that limits the amplitude at some frequencies vs. others. A similar example of an active analog circuit is an active filter. It does a similar job only it uses an amplifier to accomplish a similar task.

Advantages of a passive analog circuit are it requires no power source, gives off less heat, and may produce less noise. Advantages of an active analog circuit is it can load the signal less, amplify as well as attenuate the signal and by using capacitors in combination with amplifiers it can simulate an inductor. Simulation of inductions has the advantage of reducing weight and cost.

Analog integrated circuit

Main article: Analog chip

Active or passive analog electronic circuits can be fabricated directly onto semiconductor substrates, such as silicon. Such circuits are called analog integrated circuits. They may occur as sub-systems of other digital systems (e.g., an analog comparator in a microcontroller.) Analog integrated circuit design is a highly specialized area.

Disadvantages of analog systems

The primary disadvantage of analog signalling is that any system has noise, that is random disturbances or variations in it. As the signal is copied and re-copied, or transmitted over long distances, these random variations become dominant and lead to signal degradation. Electrically these losses are lessened by shielding, good connections, and several cable types such as coax and twisted pair and using low noise amplifiers. The effects of random noise can make signal loss and distortion impossible to recover, since amplifying the signal to recover attenuated parts of the signal often generates more noise and amplifies the noise as well.

Sources: Some of an earlier version of this article was originally taken from Federal Standard 1037C in support of MIL-STD-188.

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