Attenuator (electronics)
From Wikipedia, the free encyclopedia
An attenuator is an electronic device that reduces the amplitude or power of a signal without appreciably distorting its waveform.
An attenuator is effectively the opposite of an amplifier, though the two work by different methods. While an amplifier provides gain, an attenuator provides loss, or gain less than 1.
Attenuators are usually passive devices made from simple voltage divider networks. Switching between different resistances forms adjustable stepped attenuators and continuously adjustable ones using potentiometers. For higher frequencies precisely matched impedances or complex LC circuits are used.
Fixed attenuators in circuits are used to lower voltage, dissipate power, impedance matching and tuning circuits. In measuring signals attenuator pads or adaptors are used to lower the amplitude of the signal a known amount to enable measuments, or to protect the measuring device from signal levels that might damage it. Attenuators are also used to 'match' impedances by lowering apparent SWR. Power attennuators are used as loads for dissipating power while allowing the small output to be used for measument or other purposes.
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[edit] Attenuator characteristics
Key specifications for attenuators are: [1]
- Attenuation expressed in decibels of relative power. As a rule of thumb 3dB pad halves power, 6dB quarters, 10dB is tenth, 20dB is 100th, 30dB one in one thousend and so on. For voltage you double the dBs so for example 6dB is half in voltage.
- Frequency bandwidth, for example DC-18GHz
- Power dissipation depends on mass and surface area of resistance material as well as possible additional cooling fins.
- SWR is the standing wave ratio for input and output ports
- Accuracy
- Repeatability
[edit] RF attenuators
Radio frequency attenuators are typically coaxial in structure with precision connectors as ports and coaxial, microstrip or thin-film internal structure. Above SHF special waveguide structure is required.
Important characteristics are accuracy, low SWR, flat frequency-response and repeatability. The size and shape of the attenuator depends on its ability to dissipate power. RF attenuators are used as loads for tuning and matching transmitters, matching different stages in transmitters and receivers and as known attenuations and protective dissipations of power in measuring RF signals.
[edit] Audio attenuators
A line-level attenuator in the preamp or a power attenuator after the power amplifier uses electrical resistance to reduce the amplitude of the signal that reaches the speaker, reducing the volume of the output. A line-level attenuator has lower power handling, such as a 1/2-watt potentiometer. A power attenuator has higher power handling, such as 10 or 50 watts.
In audio electronics, attenuators are used as a dummy load by sending all of the power to the resistor and none to the speaker, in order to silence or reduce the output volume of an audio amplifier (for example, a guitar amplifier). Silencing an amplifier is useful for biasing the positive and negative signal crossover, for running bench tests such as measuring the amplifier's maximum output wattage, and for adding line-level effects between a guitar amplifier and a guitar speaker.
