I need to design a universal analog input module .I have referred to CN-0209.But I could not understand the purpose of ADG442 used in the circuit.Can I get help?
For quick reference, here is a link to the circuit note: http://www.analog.com/cn0209
In CN0209, the purpose of ADG442 is to allow for high precision thermocouple measurements.
One other thing to mention is that in thermocouple mode there is a 2.25V bias voltage generated for the thermcouple by the AD8617 in the circuit,
Another universal input reference circuit that may interest you is CN0325: www.analog.com/cn0325. This is a single channel universal input solution, and allows for a fully configurable input with 4 terminal blocks (like CN0209), or a lower cost option using 6 terminal blocks.