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An Analog circuit (or analogue circuit) is an electrical network designed to process signals that are continuously variable. Such signals are called analog signals. They differ from digital signals in that any fluctuation in the signal will change the value it represents. In digital circuits, quantisation means that a range of signal levels can represent the same value.

Origin of term

The word "analog" implies a direct analogy between the variations in the signal and variations in the phenomena that produce that signal. That is to say, the signal is analogous to the natural phenomena, unlike digital signals.

Analog signals

Analog signals are signals that have two characteristics. 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 Centigrade. 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.

In the analog circuit each voltage represents a unique temperature. In the digital circuit, different voltage levels can represent the same information(the same temperature), which is known as quantization.

In the example above, voltage was used to represent the information of interest, though any electrical property may have been used. Commonly voltage, current, frequency, and phase are used.

The basic building block of analog circuits is the operational amplifier, which is itself an analog circuit. It can perform a large number of functions useful in analog electronics, including addition, subtraction, multiplication, division, integration, differentiation and signal comparisons.

Analog and Digital Electronics

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

The first electronic devices invented and mass produced were analog. However, as time progressed digital circuits have become predominant in electronics. It is important to note that analog 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 analog or digital circuits.

The main diferences between analog and digital electronics are listed below:

Noise: Because the way information is encoded in analog 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 lot of factors afect 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 analog electronics, because of the way information is represented and how noise affects digital and analog signals.

Speed: This is where analog electronics really outshines digital electronics. Analog ciruits are several times faster than their digital counterparts. Depending on the operation, analog circuits can be several hundreds or hundreds of thousands of times faster digital circuits. This is because information in digital circuits is represented by bits, while in analog 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 analog electronics could easily be represented by a voltage, and transmiting that voltage takes the same time to transmit one bit, so the analog 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. One again, analog circuits have much more bandwith than digital, and can process/transmit more information in the same time.

Design Dificulty: Digital systems are much easier and smaller to design than comparable analog circuits. This is one of the main reasons why digital systems are more common than analog. An analog 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 analog, digital is cheaper to manufacture.

Future of Analog Electronics

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

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

Analog circuit functions

• Analog multipliers
• electronic amplifiers
• electronic filters
• electronic oscillators
• Phase-locked loops
• electronic mixers
• Power conversion
• Electronic power supply
• impedance matchers
• operational amplifiers
• comparators
• Voltage regulators

See also

• Analog signal
• Digital circuit

References

1. 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.

• Electronic circuits
• Electronic engineering