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[LSM6DS3] Very High Noise Issue

Question asked by yang.max on Aug 26, 2016
Latest reply on Sep 1, 2016 by Petr S

I am currently trying to do some initial noise analysis of LSM6DS3 using STEVAL-MKI160V1 adapter board and STEVAL-MKI109V2 mother board. The software that I am using for obtaining data is Unico GUI. The problem is that gyroscopes and accelerometers noise levels are higher than I expected by more than 2 orders of magnitude. Here is how I did:

I first changed a couple of registers for low noise operation; CTRL1_XL was set to 10(hex), CTRL2_G was set to 10 (hex) for the lowest bandwidth of the low pass filters.High-performance bit was set to 0 for the high performance operation for both gyro and acc. This gives me very high noise outputs (see fig.1 & fig.2Y-axis unit is deg/h and mgfor gyros and accs, respectively). To plot these graphs, I saved LSB data into a file using Unico GUI save function and multiplied those LSB numbers by 8.75*1000/3600 for the gyros (full-scale range was 245dps), and by 0.061/1000 for the accs (full scale range was2g).

I thought these results were very suspicious, so I checked on the register values directly from the registers OUT_H_XL and OUT_H_G, and they did not seem to be changing this much, but only by around 10-20 LSBs. So I looked into FIFO data in Unico GUI and saved those LSB values from FIFO, and the results are shown in fig 3 (only gyros are plotted for this one). They are much less noisy, and the noise level seems to be within the region, although the Z-axis shows a bit strange behavior. 

Here is my question. Am I doing something wrong that I see very noisy outputs when I read data from those sensors using Unico GUI? Why are they so noisy, and why do they give me much less noisier results when I read them from FIFO? I am new to STmicro inertial sensors, and I hope anyone could help me with this. Thanks in advance!