I have a requirement to perform more than just the 7 channel 2-wire impedance measurements available on the ADuCM350. In order to achieve the required 20 channel measurement I have implemented a custom board based on the ADuCM chip with a 4 pole switch on each of the AFE pins. After sweeping the first 7 channels I switch to the next pole of the switch and sweep the next 7, and so on.
The issue I am seeing is that when the AFE is open the ADuCM350 is still reporting some high impedance values (100kOhm ~ 1M ohm +) at higher frequencies. I'm guessing there must be some sort of issue with the switches or layout. Can someone offer some suggestions as to how to check the source of this?
The datasheet of the switch used is attached for reference