I am working on Data Acquisition of Low voltage signal which is in the amplitude range of 0.1uV to 1uV and frequency range of 1Hz to 5kHz. I need help to choose filter ics for this application. I am looking for 50/60Hz Notch filter IC , and filter ICs which operate below 10kHz frequency.

Please help me in this regard.

Thanks,

Thejesh

Hi Thejesh,

If you design an amplifier in front of a data acquisition system for such low input levels, you should consider designing the circuit completely differential, if possible. This will have the advantage that ideally only the signal of interest is amplified, as it appears as a differential signal at the amplifier's inputs, but the unwanted noise, which is induced into both lines of the input equally as a common mode signal, will be rejected by the full common mode rejection of the differential amplifier. Thus, if your input signal source allows for differential connection, this will surely help suppressing line frequency noise. Remember - any circuit is a loop - there is always a current path from the source and there is always a current path back to it. In circuit layout, always keep in mind to keep the areas enclosed by the current from and back to any source as small as possible (-> minimize their mutual inductance). A smaller mutual inductance will yield in a smaller noise voltage induced by a magnetic (noise) field. It should be taken care of that both legs of a differential input are treated as symmetric as possible, regarding layout, but also from the component values perspective. Even the tolerances of the components in both legs may otherwise lead to the effect that common mode noise, which would ideally be completely suppressed by the common mode rejection of a differential input, will be translated into a differential signal by different values in both legs and then appear as noise superimposed to the input signal. As an additional help in suppressing noise at line voltage frequencies, most of the Sigma Delta ADCs designed for such low frequency applications feature an integrated digital filter that suppresses noise at line frequencies of 50/60Hz.

Regards,

Thomas