Attenuator

An attenuator , or reducer is a component to the one that is switched into the signal path signal in its amplitude or its level to decrease. A voltage divider is also an attenuator.

Depending on the type of signal, a distinction is made between electrical and optical attenuators. Attenuators have constant attenuation over a wide frequency range. This must be distinguished from frequency-dependent elements such as high-pass , low-pass or band-pass .

The attenuation is usually given in decibels (dB) . A 20 dB reduction in voltage corresponds to a tenth of the value in front of the attenuator. This means that the transmitted power is reduced to 1/100.

Optical attenuators

Optical transmission systems are designed in such a way that they can transmit signals over long fiber optic links. The transmission power of the laser diode in the transmitter must therefore be correspondingly high so that a sufficient signal level is achieved despite the line attenuation on the receiver side . In practice, however, there is the situation that two transmission devices that are not far apart are optically connected to each other. In such cases, an attenuator is built into the transmission path between the transmitter and receiver so that the high transmission power does not override the receiving diode. The attenuator increases the attenuation and thus simulates a longer fiber optic link. Optical attenuators with a fiber optic connection are also used for measurement purposes.

Electric attenuator

π-circuit (top) and T-circuit (bottom)

While about in audio technology simple voltage divider for voltage adjustment to be used must be in electrical attenuators for high frequencies the impedance matching be taken - so it must have the input impedance and the output impedance equal to the characteristic impedance be the lines. Attenuators whose input and output impedance are the same (and the same as that of the measuring amplifier) are also often used for measuring amplifiers with high input impedance; these attenuators can be combined with each other or replaced by a bridge without changing the input impedance of the circuit (example: input attenuator of oscilloscopes ). Switchable combinations of attenuators for precise attenuation are also called step attenuator or attenuator referred.

Attenuators with the same input and output impedance can be constructed in a π circuit (PI pad) or T circuit (T pad); the π circuit is used more often. If the resistances on the input and output sides are not equal, an impedance matching takes place at the same time as the attenuation.

A special case of the T circuit is the (horizontal) H circuit. The horizontally lying resistors R1 are divided (typically 50:50) and duplicated in the lower branch. The output voltage is thus with a 50:50 split symmetrically between the input voltage. This is similarly possible with the π circuit.

When attenuating high input impedance, small capacitors are connected in parallel to the resistors in order to achieve frequency-independent attenuation despite the unavoidable stray capacitances.

Spatial arrangements in waveguides for (variable) absorption of part of the high-frequency energy are also referred to as attenuators ( ferrites , line coatings ...).

Calculations

With a given impedance and an attenuation factor between input voltage and output voltage (or attenuation level in dB) ${\ displaystyle Z}$ ${\ displaystyle 1 / a}$ ${\ displaystyle U_ {1}}$ ${\ displaystyle U_ {2}}$ ${\ displaystyle \ Delta L}$