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ADG507A multiplexer ground

Thread Summary

The user inquired about operating the ADG507A Multiplexer with isolated power supply common and inputs from the digital ground and IC ground to prevent noise injection into the analog input. The final answer confirms that the GND of the ADG507A must be connected to the ground of the power supply and digital logic, as both are referenced to GND within the device.
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Hi,

I'm working with the ADG507A Multiplexer. I currently have it set according to the schematic:

The output goes to an AD595 Thermocouple Amplifier, and the input connects to a grounded thermocouple. The AD595 requires a connection to ground from the thermocouple, which forces the 1Mohm resistor from the thermocouple to the power supply common.

We have had some concern that the digital ground could inject noise through the analog input to anything on the other end. So we are considering isolating the power supply common and the inputs from the digital ground and the IC ground, like the following schematic:

Can the ADG507A operate in this configuration? Or does it require a reference to the power supply common?

Thanks,

Benjamin Russon