I'm working on an application that could perform impedance spectroscopy, chronoamperometry, and cyclic voltammetry with 3-electrode configuration on 4 samples simultaneously.
The goal is to keep the samples independently biased during chronoamperometry measurements, and also minimize the time to take impedance spectra on all four samples. To realize that, I plan to employ 4x AD5941 hooked on the same SPI bus, but with independent Chip Select channels and RE/WE/CE. Basically, that would be the circuit below, repeated 4 times:
DVDD and AVDD are 3.3 V supplies, AD_RST is a common reset pin for all four chips, and GPIO0 is being provisioned to serve as an interrupt later on.
I plan to keep the external component count to a minimum. The resistance of the samples I intend to measure ranges from 10k to 100M ohms.
I have some questions:
1. Could all four chips share the same 16 MHz crystal?
2. Is it necessary to have an external RCAL? If so, should I choose a value closer to the samples I intend to measure?
3. Is it necessary to have RTIAs connected to AIN0-AIN3 like in the EVAL-AD5940ELCZ?
4. Are the values of the remaining components reasonably correct? I just have one shot to get the hardware correct, will figure out the firmware later. I'm using mostly the EVAL-AD5940ELCZ as the starting point.
5. Am I doing something obviously wrong? Please let me know, I am very new to designing circuits.
Any comment is greatly appreciated!