I'm surprised it is doing anything. 

--  You need at least 5V across the part to wake it up

--  It is not RR input;  you need to stay at least 1.5V away from either rail.

Try an ADA4084-2 or an ADA4528-2

For the LMC662,, you could also look at:

ADA4691…

Hi,

    That was a very helpful piece of information.Thanks.

1. If I select voltage signals for both channel1 and channel2 ,the voltage will pass through the ADG1414 and then to AD8676.But in this case ,won't the voltages overlap?
2. I want to modify…

Elias,

  What does TRRS mean??

  What is your highest signal frequency?

  Depending on whether you need to go to DC or not and can AC couple, you could use op amps

that have millivolts of offset, rather than <100 uV which drives up the price.

  Also…

Hi Ching.

First of all, the initial requeriments of my project:

     - 8 universal analog inputs (RTD, TC, 4-20, Voltage). 3 header pins.

     - Each channel can be configurated independently for RTD, TC ... measurement mode. Another choice if this option…