a variable attenuator

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maxascent

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I require an attenuator that is capable of attenuating a signal from 0 to 250 MHz. The signal could be a dc voltage or some waveform. I have seen some digital attenuators that are used for RF and was wondering if these would work. Otherwise I would need to design my own so any thoughts on a circuit would be appreciated.

TIA

Jon
 

I have seen 3 FETs set up as a PI attenuator. Since they have a broad frequency response, they would work very well from low frequency up to 250 MHz.

The trick is that they need to be DC biased, so you put one DC gate voltage on the two shunt fets, and a different gate voltage on the series mounted FET. But the Vgs depends on what you source voltage is too. So I am not sure how you would get such a thing to work down to DC frequency.

The DC signal you are trying to input to the attenuator will vary the DC bias point of the fet you are trying to control
 

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