Freescale Semiconductor, Inc.
Acceleration Sensor FAQ’s
We have discovered that many of our customers have
similar questions about certain aspects of our accelerome-
ter’s technology and operation. Here are the most frequently
asked questions and answers that have been explained in
relatively non–technical terms.
Q. What is ratiometricity?
A. Ratiometricity simply means that the output offset
voltage and sensitivity scales linearly with applied supply
voltage. That is, as you increase supply voltage the
sensitivity and offset increase linearly; as supply voltage
decreases, offset and sensitivity decrease linearly. This
is a key feature when interfacing to a microcontroller or
an A/D converter. Ratiometricity allows for system level
cancellation of supply induced errors in the analog to
digital conversion process. Refer to the Special Features
section under the Principle of Operation for more
information.
Q. What is the g–cell?
A. The g–cell is the acceleration transducer within the
accelerometer device. It is hermetically sealed at the
wafer level to ensure a contaminant free environment,
resulting in superior reliability performance.
Q. What does the output typically interface with?
A. The accelerometer device is designed to interface with an
analog to digital converter available on most microcontrol-
lers. The output has a 2.5 V DC offset, therefore positive
and negative acceleration is measurable. For unique
customer applications, the output voltage can be scaled
and shifted to meet requirements using external circuitry.
Q. Is the accelerometer device sensitive to electro
static discharge (ESD)?
A. Yes. The accelerometer should be handled like other
CMOS technology devices.
Q. What is the resonant frequency of the g–cell?
Q. Can the g–cell part “latch’’?
A. The resonant frequency of the g–cell is much higher than
the cut–off frequency of the internal filter. Therefore, the
resonant frequency of the g–cell does not play a role in
the accelerometer response.
A. No, overrange stops have been designed into the g–cell to
prevent latching. (Latching is when the middle plate of
the g–cell sticks to the top or bottom plate.)
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Motorola Sensor Device Data
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