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I am thinking about using a voltage divider to scale down the signal by 2/3 (-1.76 dB) as the following circuit diagram:

schematic

simulate this circuit – Schematic created using CircuitLab

When I googled with a keyword attenuator, I got a list of attenuators such as:

http://www.jyebao.com.tw/img/FAT8.gif

With my poor knowwledge, they seem to be very similar. Is there a difference between a voltage divider and an attenuator?

Does an attenuator show a good performance when a signal has a high bandwidth? And a voltage divider is poor at manipulating a high speed signal?

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  • \$\begingroup\$ What is the input and output impedance your circuits are expecting? The circuit above has very high impedance - good for an electric guitar, not so good for a 50 Ohm radio transmitter. An attenuator for RF is generally made with three resistors, so you can keep both input and output impedance the same. \$\endgroup\$ – tomnexus Jul 21 '15 at 21:20
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The attenuators that your picture show are designed for the use with certain coaxial cables. These cables have a special wave-impedance (e.g. 50 ohm) which describes the relation of the H- and E-field of the electromagnetic wave that propagates in the dielectric of the cable. If your attenuator has an input impedance that differs from the wave-impedance, part of the energy of the wave will be reflected back to the signal source. That's why you have to use those special attenuators for high-frequency signals on a coaxial cable.

So yes, your suggestions are basically correct. In case of high-frequency signals a simple voltage divider with arbitrary resistors will not do the job quite well. In case of DC there is no difference.

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  • \$\begingroup\$ But most importantly, an attenuator has a matched impedance on input and output. DC aside, this is the difference. An attenuator requires 3 resistors, not just two. \$\endgroup\$ – tomnexus Jul 21 '15 at 21:17
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Basically, a voltage divider is the fundamental building block of an attenuator. For lower frequencies not much more is needed, but the higher you go in frequency, the more important it gets that throughout the whole device you stay to the intended transmission line impedance as much as possible. This involves better physical design, but can also involve filter components to counter the effect of parasitics.

Also often you have multiple voltage dividers ([un]balanced pi, T etc. configurations) to improve characteristics and for certain devices things like protection zeners (since often attenuators are used to protect precious equipment from high input voltages) or capacitive coupling.

You can then get very fancy and add other stuff to create voltage controlled attenuators and whatnot.

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