Which of these two designs is better?

Hello All,

Can someone suggest me which of the following two designs is better and why?

I have 4 signals in the following configuration for each-

I/Pi -> NI-Bufferi -> LPFi -> I-Gaini -> O/Pi where i=1to4

Now if I want to add them together (summing) is it better to sum them after their LPFs or is it better to sum them before and then pass through an LPF?

Lets say I select CH1 as master, so if I decide to sum all 4, is the below configuration better?

I/Pi -> NI_Bufferi -> I-Summing1 -> LPF1 -> I-Gain1 -> O/P1

or

I/Pi -> NI-Bufferi -> LPFi -> I-Summing1 -> O/P1

NI = Non-Inverting, I = Inverting.

Any ideas/suggestions are greatly appreciated.

thanks.

If the four LPF are all identical, then you can add the buffered signals before using a single LPF and final gain stage.

If the LPF have different characteristics, then you need to apply the filtering to each signal prior to summation.

Thanks for your reply. All four LPFs are identical, so from what you suggested, scenario (1) works better.

Now, coming to choosing op-amps, which one to choose between LM6181(current feedback) vs AD811 (voltage feedback video op-amp)? The input signal will be a PMT input and the output will be fed into a framegrabber.

Any suggestions on that?

thanks