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Theory of operation

The LIS3LV02DL is a high performance, low-power, LGA packaged, digital output 3-axis linear accelerometer. The complete device includes a sensing element and an IC interface able to take the information from the sensing element and to provide a signal to the external world through an I2C/SPI serial interface.

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.

The complete measurement chain is composed by a low-noise capacitive amplifier which converts into an analog voltage the capacitive unbalancing of the MEMS sensor and by three ΣΔ analog-to-digital converters, one for each axis, that translate the produced signal into a digital bit stream. The ΣΔ converters are tightly coupled with dedicated reconstruction filters which remove the high frequency components of the quantization noise and provide low rate and high resolution digital words. The charge amplifier and the ΣΔ converters are operated respectively at 61.5 kHz and 20.5 kHz. The data rate at the output of the reconstruction depends on the user selected Decimation Factor (DF) and spans from 40 Hz to 2560 Hz.

The acceleration data may be accessed through an I2C/SPI interface thus making the device particularly suitable for direct interfacing with a microcontroller.

The LIS3LV02DL features a Data-Ready signal (RDY) which indicates when a new set of measured acceleration data is available thus simplifying data synchronization in digital system employing the device itself. The LIS3LV02DL may also be configured to generate an inertial Wake-Up, Direction Detection or Free-Fall interrupt signal accordingly to a programmed acceleration event along the enabled axes.

The IC interface is factory calibrated for sensitivity (So) and Zero-g level (Off).

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.

Performance order

Date: 2015-12-18; view: 157

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