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We have 8 AD7147 on operating on a single 2-layer PCB which. Devices operate properly as long as only one AD7147 is exciting the electrodes. From the posts available at the ENGINEER zone I suspect the problem lies in the interference caused by the unsynchronized excitation signals. As our board space is quite limited, we can only have about 4 mm wide GND stripes between the AC shields. Would a 4-layer PCB with a bottom ground covering all the shields (moving the 2 layers currently used for routing and shielding the electrode signals to the two topmost PCB layers) sufficiently isolate the AD7147s. Alternatively, is there perhaps a way to synchronize the excitation signals?
I suspect that the excitation signals from each AD7147 are interfering with each other. Because they are not synchronized, if the sensors are close to each other, then the excitations will interfere, and cause noise in the sensor measurements.
There are two options - if this is possible, you can modify your sensor design to keep the sensors controlled by each AD7147 apart, to reduce the interference. However, I guess this will not be possible if you are tight for space.