Analogue electronics

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Analogue electronics are those electronic systems with a continuously variable signal; they differ from digital electronics. The term "analogue" originally described the relationship between a signal and a voltage or current that represented the signal.

1 Description
2 Analogue signals
3 Inherent noise
4 Analogue vs. digital electronics
5 Future of analogue electronics
6 See also
7 References

[edit] Description

Analogue is usually thought of in an electrical context, but mechanical, pneumatic, hydraulic, and other systems may also use analogue signals.

The word "analogue" implies an analogy between cause and effect, voltage in and voltage out, current in and current out, sound in and sound out. Analogue circuits do not involve quantisation of information into digital format. Whatever the original quantity, whether sound, light, pressure, temperature, or an exceeded limit, the source signal information being handled by the circuit remains continuous from end to end.

[edit] Analogue signals

Main article: Analog signal

An analogue signal uses some property of the medium to convey the signal's information. For example, an aneroid barometer uses angular position as the signal to convey pressure information. Electrically, the property most commonly used is voltage followed closely by frequency, current, and charge.

Any information may be conveyed by an analogue 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.

They can take any value from a given range, and each unique signal value represents different information. Simply put, any change in the signal is meaningful, and each level of the signal represents a different and unique level of the phenomenon that it represents. For example, suppose the signal is being used to represent temperature, with one Volt representing one degree Celsius. In such a system 10 Volts would represent 10 degrees, and 10.1 Volts would represent 10.1 degrees. A similar digital circuit may only represent temperature to the nearest degree, so that 10.0 Volts and 10.1 Volts would both represent exactly 10 degrees.<ref>In practical digital circuits, multiple signals are used to represent a single value, typically using binary encoding. In such a circuit, 10 degrees would more likely be represented (for example) as a set of 4 signals of 1V, 0V, 1V and 0V.</ref>

In an analogue 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 analogue.

[edit] Inherent noise

The primary disadvantage of analogue 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.

Another method of conveying an analogue signal is to use modulation. In this, some base signal (e.g., a sinusoidal carrier wave) has one of its properties altered: amplitude modulation (AM) involves altering the amplitude of a sinusoidal voltage waveform by the source information, frequency modulation (FM) changes the frequency. Other techniques, such as changing the phase of the base signal do also work.

[edit] Analogue vs. digital electronics

Since the information is encoded very differently in analogue and digital electronics, the way they process a signal is consequently very different. However, most operations that can be performed with an analogue signal can also be performed with a digital signal but in a different way.

The first electronic devices invented and mass produced were analogue. However, as time passed, digital circuits have become predominant in electronics. It is important to note that analogue and digital devices are the same, the only difference is the way they represent and process information. The same basic components can be used for analogue or digital circuits.

The main differences between analogue and digital electronics are listed below:

Noise: Because the way information is encoded in analogue circuits, they are much more susceptible to noise than digital circuits, since a small change in the signal can represent a significant change in the information present in the signal and can cause the information present to be lost, corrupted or otherwise made useless. In digital electronics, because the information is quantized, as long as the signal stays inside a range of values, it represents the same information. This is one of the main reasons that digital electronic circuits are predominant. In fact, digital circuits use this principle to regenerate the signal at each logic gate, lessening or removing noise.

Precision: A number of factors affect how precise a signal is, mainly the noise present in the original signal and the noise added by processing. See Signal to Noise Ratio. In digital electronics it is much easier to have high precision signals than in analogue electronics, because of the way information is represented and how noise affects digital and analogue signals.

Speed: Analogue circuits are several times faster than their digital counterparts. Depending on the operation, analogue circuits can be several hundreds or hundreds of thousands of times faster than digital circuits. This is because information in digital circuits is represented by bits, while in analogue electronics it is represented by a property of the signal itself. For example, transmitting a value digitally may require sending 64 bits in succession. The same signal in analogue electronics could easily be represented by a voltage, and transmitting that voltage takes the same time to transmit one bit, so the analogue signal in this case is at least 64 times faster than digital.

Bandwidth: Simply put, bandwidth is the amount of information a given circuit can cope with. Again, analogue circuits have much more bandwidth than digital, and can process/transmit more information in the same time.

Design Difficulty: Digital systems are much easier and smaller to design than comparable analogue circuits. This is one of the main reasons why digital systems are more common than analogue. An analogue circuit must be designed by hand, and the process is much less automated than for digital systems. Also, because the smaller the integrated circuit (chip) the cheaper it is, and digital systems are much smaller than analogue, digital is cheaper to manufacture.

[edit] Future of analogue electronics

The field of analogue electronics nowadays deals with high speed, high performance devices that need the unique advantages provided by analogue circuits. Also, digital circuits are an abstraction of analogue circuits, but remain analogue circuits. As technology progresses and transistors get smaller and smaller, it becomes more and more important when designing digital circuits to account for effects usually present only in analogue circuits, requiring expertise in analogue circuits.

The range of applications of analogue circuits will probably continue to reduce, being replaced by digital circuits because of their smaller size, cheaper cost and easier design. Analogue circuits will never cease to exist, but will continue to exist as a speciality field for high performance circuits, or as a high performance part of a digital chip, as integrated circuits with analogue and digital circuits in the same substrate become more popular.