# Noise problem using zener protection on precision analog inputs? [closed]

I have a circuit input that I need to measure down into the nanovolts, so it gets fed to a 24 bit ADC via some buffer amps. However, in order to protect the circuits from overload I am thinking of putting zener clamps across the unconditioned signal input lines. What, if any, noise problems might this cause?

Signals are low frequency (<1kHz) and voltages up to 15V

## closed as too broad by Andy aka, PeterJ, Daniel Grillo, Fizz, jippieNov 1 '15 at 10:26

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• Presumably it's an AC voltage you wish to measure? Why not show the proposed circuit? – Andy aka Oct 26 '15 at 9:40
• @Andyaka First, it is part of a complex analog PID loop and second because of confidentiality issues. It is an attempt to put some basic ESD on the inputs to the board. However, we do use more than 20 bits of resolution so any noise contribution from the (supposedly) non conducting zeners will show up – Dirk Bruere Oct 26 '15 at 10:03
• @DirkBruere You could at least show an equivalent schematic; things like input impedance may have an impact on the answer. – Nick Johnson Oct 26 '15 at 10:04
• Input impedance is around 10K, with two zeners being used back to back across the inputs. – Dirk Bruere Oct 26 '15 at 10:21
• I'm voting to close this question as off-topic because proper details can't be supplied about the circuit. Those details that can be provided make the question too broad to answer IMHO. – Andy aka Oct 26 '15 at 11:09