Attenuators are two-port electronic devices, consisting of a series of resistors that reduce the strength of a radio or audio signal. Attenuators are considered passive circuits as they work without the need for a power supply. They are available as either fixed attenuators with a fixed attenuation level or as a continuously changing attenuator.
Signals are typically sent from one device or location to another, and they may come in the form of voltage signals, current signals, and data signals. Depending on the distance that the signal travels, the strength of the signal varies. Increased distance results in a weaker signal, and this gradual loss is called attenuation and is measured in decibels.
While attenuation may pose a challenge for the long-distance transfer of signals, it can be quite useful in other instances. Attenuators have the ability to reduce the power of signals without disturbing their waveform. They are often found in signal generator circuits, and help reduce the strength of high-level signals before applying them to antenna circuits.
Within attenuators, resistors are arranged as a voltage divider network. However, the design of an attenuator is dependent upon the line of geometry connecting wires between devices. Moreover, attenuators are either balanced or unbalanced, depending on the line. For example, attenuators used alongside coaxial lines are unbalanced in nature while attenuators used with twisted-pair lines are balanced.
An attenuator circuit can be either linear or reciprocal and unidirectional or bidirectional based on the application at hand. Additionally, the circuit can be constructed symmetrically wherein there is not a difference between the input and output port. If this is the case, the left post is typically considered as input while the right port is considered as an output.
Attenuators may also be found as built-in circuits in signal generators and as stand-alone circuits. If they are used as stand-alone circuits, they are positioned in series between a signal source and a load circuit on the signal path. In this case, the attenuator must match the source impedance and load impedance.
There are many different types of attenuators, most of which will be covered in the next section. It is important to note that attenuators are generally available as either fixed attenuators or adjustable attenuators. The former are called “attenuator pads,” and are used for values ranging from 0dB to 100dB.
Attenuators are usually found in RF and optical applications. While RF attenuators are used in electronic circuits, optical attenuators find use in fiber optics. An RF-based design comes in a few types including fixed type, step type, and programmable type attenuators.
The resistor network within these attenuators is locked at a predetermined attenuation value. The values are positioned along the signal path to attenuate the power of the transmitted signal. They can be unidirectional or bidirectional, and they are available as either surface mount, waveguide, or coaxial types. In a chip-based design, varying materials are deposited on the thermally conductive substrate to develop the resistance. The resistance value is determined by the dimensions of the chips and the materials used to manufacture the chip itself.
Similar to fixed attenuators, step attenuators consist of a push-button that allows operators to manually adjust attenuation values. This type can be used in either chip, waveguide, or coaxial designs.
Also called a “digital step attenuator,” programmable attenuators are controlled by a computer-driven external control signal. They are controlled by TTL logic circuits with a step size range of 2 to 32. If the voltage applied to the attenuator is less than 1V, the logic level will be 0. For voltages that are 3V or higher, the logic level is 1. These logic levels are utilized to control the single-pole and double-throw switches that are connected to several attenuators on the signal path.
Before concluding this blog, we want to cover optical attenuators. The major difference between RF attenuators and optical attenuators lies in the fact that the latter attenuate light waves rather than electrical signals. Optical attenuators absorb or dissipate light according to the attenuation values all while not affecting the waveform. Similar to RF attenuators, optical attenuators are also available as fixed, variable, and programmable types.
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