Attenuator (electronics)

An attenuator or attenuator, Eng. attenuator, is an element which is connected in the signal path, to reduce the signal amplitude or its level. A voltage divider is an attenuator.

Depending on the type of signal distinction is electrical and optical attenuators. Attenuators feature in a wide frequency range with a constant damping. Must be distinguished from frequency-dependent elements, such as high-pass, low-pass or band-pass.

The slowdown is often specified in decibels ( dB); 20 dB corresponds to an attenuation of the voltage to 1/ 10; which corresponds to a weakening of the power to 1 /100.

Optical Attenuators

Optical transmission systems are designed so that they can transmit signals over long fiber links. The transmit power of the laser diode in the transmitter must therefore be correspondingly high, so that in spite of line loss on the receiver side, a sufficient signal level is obtained. In practice, however, there is a situation where two transmission devices that are not far apart from each other are optically connected to each other. In such cases an attenuator is incorporated in the transmission path between transmitter and receiver, so that the high transmission power is not overloaded, the receiving diode. So the attenuator to increase damping and thereby simulating a longer fiber link. Optical Attenuator with fiber connection can also be used for measurement purposes.

Optical attenuator are also required for the laser beams, for example for beam diagnosis system in which an intense laser beam is attenuated, so that the beam profile can be detected by a CCD camera.

Optical attenuators or attenuator usually use absorption filter, but can also be based on reflection.

Electrical attenuator

While simple voltage dividers are used for voltage adjustment as in audio technology, attention must be paid to the impedance matching with electric attenuators for high frequencies - so it must be the input impedance and the output impedance equal to the characteristic impedance of the lines to be. Also for measuring amplifier high input impedance attenuator are often used, their input and output impedance are equal ( and equal to the amplifier ); this attenuator can be combined with each other or replaced by a bridge, without the input impedance of the circuit changes (example: input attenuator of oscilloscopes ). Combinations of switchable attenuators for accurate attenuation are also called step attenuator, or attenuator.

Attenuators with the same input and output impedance can (PI pad german) or T circuit (german T pad) be constructed in a π - circuit; the π - circuit is more frequently used. If the resistors on the input and output sides are not the same, takes place simultaneously with the attenuation of an impedance matching instead.

Attenuators for high input impedance of the resistors are still small capacitors connected in parallel in order to achieve a frequency independent attenuation in spite of the unavoidable stray capacitances.

Spatial devices in waveguides for the ( variable ) absorption of a part of the high frequency energy are also called attenuators ( ferrites, cable coverings ... ).

Calculation

For a given impedance and attenuation factor between input voltage and output voltage (or damping ratio in dB)

To calculate the resistance of a symmetric π - attenuator from

For the T-junction, the resistance arising from