LIS2L02AL_06 STMICROELECTRONICS [STMicroelectronics], LIS2L02AL_06 Datasheet - Page 9

• Manufacturer Part Number: LIS2L02AL_06
• Description: MEMS INERTIAL SENSOR:2-axis - +/-2g ultracompact linear accelerometer
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

LIS2L02AL
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3.1
3.2
3.3
Functionality
The LIS2L02AL is a high performance, low-power, analog output 2-axis linear
accelerometer packaged in a LGA package. The complete device includes a sensing
element and an IC interface able to take the information from the sensing element and to
provide an analog signal to the external world.
Sensing element
A proprietary process is used to create a surface micro-machined accelerometer. The
technology allows to carry out suspended silicon structures which are attached to the
substrate in a few points called anchors and are free to move in the direction of the sensed
acceleration. To be compatible with the traditional packaging techniques a cap is placed on
top of the sensing element to avoid blocking the moving parts during the moulding phase of
the plastic encapsulation.
When an acceleration is applied to the sensor the proof mass displaces from its nominal
position, causing an imbalance in the capacitive half-bridge. This imbalance is measured
using charge integration in response to a voltage pulse applied to the sense capacitor.
At steady state the nominal value of the capacitors are few pF and when an acceleration is
applied the maximum variation of the capacitive load is up to 100fF.
IC Interface
In order to increase robustness and immunity against external disturbances the complete
signal processing chain uses a fully differential structure. The final stage converts the
differential signal into a single-ended one to be compatible with the external world.
The signals of the sensing element are multiplexed and fed into a low-noise capacitive
charge amplifier that implements a Correlated Double Sampling system (CDS) at its output
to cancel the offset and the 1/f noise. The output signal is de-multiplexed and transferred to
two different S&Hs, one for each channel and made available to the outside.
The low noise input amplifier operates at 200 kHz while the two S&Hs operate at a sampling
frequency of 66 kHz. This allows a large oversampling ratio, which leads to in-band noise
reduction and to an accurate output waveform.
All the analog parameters (Zero-g level, sensitivity and self-test) are ratiometric to the
supply voltage. Increasing or decreasing the supply voltage, the sensitivity and the offset will
increase or decrease almost linearly. The self test voltage change varies cubically with the
supply voltage.
Factory calibration
The IC interface is factory calibrated for sensitivity (So) and Zero-g level (Voff).
The trimming values are stored inside the device by a non volatile structure. Any time the
device is turned on, the trimming parameters are downloaded into the registers to be
employed during the normal operation. This allows the user to employ the device without
further calibration.
Functionality
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