Switchable attenuators

Updated July 9. 2005

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Switchable attenuators offer mechanically or electrically controllable attenuation states. There are two broad categories of switchable attenuators, switched network attenuators, and switched element attenuators.

An index of this page:

Switched-network attenuators

Switched-element attenuators

Digital attenuators (stepped attenuators)

Switched-network attenuators

Switched-network attenuators are versatile, once you've built one you can easily change the attenuation value. That is why this approach is most often used by hybrid vendors. PIN diode switches are used to create two (or perhaps more) paths.

Rule of thumb: for a switched attenuator (or gain) network, if the combined switch isolation is 20 dB greater than the desired attenuation change, the leakage through the isolated high-gain path will pull the gain of the low-gain path no more than +/- 1 dB. Example: you want a 20 dB switched attenuator. If the two SPDT switches each provide 20 dB isolation (half of 20 dB + 20 dB), then you can expect 19 to 21 dB attenuation range.

Switched-element attenuators

This type of attenuator is more clever than the previous one, here we start with a network such as a pi pad, and create resistive elements that can have two or more values. Using FETs as the switching mechanism, this scheme is often implemented in MMIC format, The network can be a pi or tee pad, or even a reflection attenuator.

Digital attenuators (stepped attenuators)

Digital attenuators are not really digital anything. They are used to provide more than one step in attenuation. Perhaps they should be called stepped attenuators.

There are many, many ways to create a digital

Bit size

LSB

attenuation range

power handling