DocID026444 Rev 1

5/13

AN4508

Terminology

13

zero-g accuracy of ±20 mg means that the zero-g output varies typically in the range of

±20 mg around the expected ideal value.



TCOff - Zero-g level change vs. temperature: This parameter defines how much the

zero-g level is affected by temperature variations.



An - Acceleration noise density: This parameter defines the standard resolution the

user can obtain from the accelerometer (once the desired BW is selected).

1

 resolution =

. The higher BW leads to lower resolution.



NL - Non linearity: This parameter defines the maximum error between the outputs and

the best-fit straight line. For example, at ±2.0 g full-scale range, the non-linearity of

0.5% of FS means the largest error is 0.5% * 4000 mg = 2 mg, which corresponds to

0.1°. When the application requires measurements around the 0 g condition (as with tilt

measurement), the non-linearity effect is negligible and can be ignored.



CrossAx - Cross-axis sensitivity: The cross-axis effect arises due to natural

misalignment of die positioning on the package substrate. Even if negligible in most

applications, for very accurate tilt measurement the cross-axis sensitivity effect can be

easily compensated for by following the procedure in Section 2: Calibrating the

accelerometer. Moreover, when the device is placed on the final application board, the

accelerometer calibration compensates both the device cross-axis sensitivity, and the

misalignment between the accelerometer sensing axes and the board axes.

1.2

Definitions

Assume that the accelerometer is installed in a handheld device, such as a cell phone, a

PDA or simply on a PCB board as shown in Figure 1.

Figure 1. Accelerometer inside a handheld device

same direction as the device body axes.

Pitch and roll angles are referenced to the local horizontal plane, which is perpendicular to

the Earth's gravity.



Pitch (

that the pitch angle resolution is 0.1°, then it goes from 0° to +179.9° when rotating





BW Hz



