Filter in transmitter

[abcyin]

Hi,

As the signal from the TX baseband is really large that the active blocks could not bare it, thus the signal should first be attenuated, and the filter after the DAC in the transmitter will also present some attenuation as I see, and the filter is active in most cases, but why not just use some passive RC networks to generate the attenuation? what's the difference between the active filter and the passive RC filter in case only attenuation is required?

Thanks in advance,
abcyin

 

[LvW]

what's the difference between the active filter and the passive RC filter in case only attenuation is required?

In this context, it is important HOW MUCH attenuation you require at a certain frequency. Active filters allow larger Q values if compared with passive RC.
If you like to use a passive filter - comparable with active circuits - you must use RLC topologies.

 

[abcyin]

Hi, LvW,

Thanks for your reply.

Actually, the attenuation is a range, like -20dB to -3dB, why it's so important as you said?