I'm finding I don't understand how to properly configure the settings for the anti-alias filter in the ICM-42688. It is weird that the 42688 allows the anti-alias filters to be bypassed completely for the gyro and accel. You would think an AA filter is required to satisfy the Nyquist criteria for an analog to digital conversion. In section 5 of the data sheet, figure 8 shows the signal path. Is the ICM 42688 working at 32 kHz all the way up to the input of the UI Filter Block? After being processed by the UI Filter Block, is the signal then downsampled to the ODR selected? Or is the signal working at the output data rate selected starting when it is input into the anti-alias filter? The "Decimation Filter (32kHz)" block is also not explained in the datasheet. What is the purpose of that block in the signal path?
The reason for this confusion is I need an ODR of 100 Hz for the gyro. Naturally the anti-alias filter would then be set to below 50 Hz, or 42 Hz as that is what the 42688 allows. When this is done, the gyro rotation data has spurs when testing with a rate table. These spurs do not occur with other sensors tested simultaneously with the 42688. As the anti-alias 3dB bandwidth is increased, or I bypass the AA completely, the spur issue goes away. If the input sample rate into the AA filter is indeed much higher than the ODR selected, I can live with a high AA bandwidth.