Why capacitor needed at output of attenuator

[ah.vinod]

Hi all,

Why is a capcitor needed at output of Pi Resistive attenuator if the input to attenuator is pure AC signal with Zero DC content. The attenuator is designed to work from 40MHz to 1GHz.

Regards
Vinod

 

[FvM]

It's not generally needed. But there may be other requirements in your application. (e.g. 40 MHz high-pass)

Industry standard attenuators are generally DC capable, without capacitors.

 

[ah.vinod]

Hi,

My circuit has an LNA followed by Attenuator and a tuner IC. the LNa output has DC blocking caps. so is it needed to add one more DC blocking cap just after attenuator. the input to LNA is 40MHz to 1GHz without any other frequency components

 

[FvM]

Are you sure, that no DC blocking is required at the tuner input? The datasheet should clarify.

 

[ah.vinod]

The Tuner needs a DC blocking cap but as there is no DC component in the signal which is coming to tuner, is dc block cap still needed

 

[FvM]

Depends on the tuner circuit. "needs a DC blocking cap" isn't a clear statement.

If the open input pin has zero DC bias, you don't need a capacitor.