Is decimation filter after or befor down sampling?

[Mogogo]

My input is one serial bit stream from modulator with sampling rate Fs = 4MHz.
I want to have a resolution of N = 12 bit.

Do i get the correct output if i first downsample and then filter my signal?

 

[tiger_shark]

In multi-rate systems, you first filter your signal to make sure the decimation does not affect any distotion to the data and then decimate. However, I have a feeling that your case is in different domain, something like a sigma/delta or st.

TS