Hi,
what do you expect?
Someone to do your job?
We gave all necessary informations and links to informations. But it seems you didn´t read it.
We asked questions about your requirements, but you didn´t answer them.
You give statements that can´t be fulfilled: "error free". There is nothing that can be considered error free. You may minimize them. How? --> read through the given links
Klaus
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I often see zener diodes to protect ADCs inputs from high voltage.
I doubt this is a good solution.
* they cause unlinearity. This means errors (mainly DC) and distortion (mainly AC).
* the zener current is noisy
* there is no positive overvotage protection when ADC is powered OFF
I did some measurements on diode current vs diode voltage.
Here the results.
* I only had a BZX85C5V1 by hand, but I think it is comparable.
* For error calculations I used 6700 Ohms which equals the source resistance of the OP´s circuit
You see
* at 2.7V about 1% error
* at 3.6V about 10% error
Therefore I recommend to use
* a signal diode to GND (for negative input voltages)
* a signal diode to VCC (for positive vervoltages)
* capacitors at VCC to GND (big enough to handle ESD energy)
* for high energy or low value capacitors I additionally recommend an overvoltage protection at VCC
Improvements:
* use schottky diodes for lower voltage drop
* use "low leakage current" diodes for even less error
* use an additional series resistor (maybe 100 Ohms) between diodes and ADC input ... to limit input current.
Klaus