Designing a unviversal data logger using analog switches and PSOC5LP

Why can't I just use shunt and zener+current limiter resistor .
Many of Arduino user have used this easy technique. Psoc can take input till 5.5 and delsigma has +- 6volt adc . A 200 ohm resistor keeps voltage below 4.5v. and a zener will do it's job

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You are correct, just R and Vz would suffice. However the diff amp approach
allows one to handle a larger CM range that just ground.

Note what DelSig takes +/- 6V ? Thats not the case for PSOC, it is also
bounded by Analog Supply Rail limits. If you config it to use w/o input
buffer it will CM 100 mV outside its rails. Thats the limit. So 100 mV above
Vdda, and 100 mV below Vssa are limits. Note thats with A/D still returning
correct values. The general analog pin limit is of course VSSA, VSSD.

Regards, Dana.