Freescale Semiconductor is a leading company in the field of electronic sensors, offering a wide and complete family of acceleration, pressure, and proximity sensors. With over 25 years of experience in the sensors design and manufacturing, with more than 750 million MEMS-based sensors delivered, Freescale Semiconductor meets the customers’ demand for sensor solutions

1. Published on Your Electronics Open Source (http://dev.emcelettronica.com)
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Inside Freescale Sensor Products
By slovati
Created Mar 26 2009 - 07:08
Freescale Semiconductor is a leading company in the field of electronic sensors, offering a wide and
complete family of acceleration, pressure, and proximity sensors. With over 25 years of experience in
the sensors design and manufacturing, with more than 750 million MEMS-based sensors delivered,
Freescale Semiconductor meets the customers? demand for sensor solutions.
Acceleration sensors
[1]
The acceleration sensors offered by Freescale Semiconductor are all MEMS (Micro Mechanical Electrical
Systems) based and are suitable for the measurement of change in forces associated to tilt, fall, motion,
vibration, shock, and positioning. The devices are able to measure accelerations from 1.5g up to 200g, and
can have single, dual, or triple axis sensing capability (X, XY, XYZ, or Z axis of sensitivity).
Accelerometers are composed of two units located on the same chip (as shown in the following picture):
g-cell (the acceleration transducer): it is a micromachined capacitive sensing unit composed of
many beams connected to a central mass which can freely move between them. The acceleration
applied to the sensor moves the g-cell modifying its capacitance. The g-cell is hermetically sealed
on the wafer layer, thus making a robust and reliable sensor. The g-cell is designed so that its
resonant frequency is much higher than the cut-off frequency of the internal low-pass filter: in this
way, the resonant frequency does not affect the accelerometer response.
control IC (a CMOS ASIC): its function is to measure the g-cell capacitance variations and
compute the corresponding acceleration value. Other tasks performed by this chip are: signal
amplification, signal conditioning, low pass filtering (a 4-pole switched capacitor filter with a Bessel
implementation), and temperature compensation. The output signal produced by the control IC is
ratiometric and proportional to the acceleration.
These sensors are very fast, with low power consumption and low supply voltage. They can be divided into
analog and digital sensors. Analog sensors are normally interfaced with analog to digital converters (ADC),

2. often integrated on many microcontrollers. For this purpose, their output has a 2.5V offset so that positive
and negative acceleration can be measured. The output DC offset can also be modified according to the
customers? need. Digital sensors are available with an I2C or SPI interface.
Acceleration sensors have also a self-test function which verifies the electrical and mechanical integrity of
the sensor; this feature can be activated either prior or after the device installation and it is suitable for
critical applications such as airbag systems. Freescale accelerometers provide also a status pin which
signals a fault condition such as: supply voltage below the low voltage detection threshold (LVD), clock
oscillator failure, and internal EPROM parity error. The fault latch can be reset by issuing a self-test
procedure: nevertheless, it will be asserted again when at least one of the above conditions is met.
Typical applications of acceleration sensors are as follows:
automotive field: airbags, crash detectors, fuel shut-off valve (occurs when a crash condition is
detected), braking systems, tire pressure monitoring system (TPMS), stability control systems
industrial and consumer field: gaming, HDD protection, GPS dead reckoning, MP3 players, image
stabilization, navigation systems, e-compass, motion sensing
healthcare and fitness field: pedometers, rehabilitation equipments, sports medicine and
diagnostics systems
Pressure sensors
[2]
Freescale Semiconductor?s provides a wide range of pressure sensors; all the devices are MEMS-based,
with a silicon micromachined and electromechanical structure. The sensors family provides devices able to
measure pressure up to 150 psi (1000 KPa) including both positive and negative pressure, with
temperature compensation, calibration, and signal conditioning features.
They can be grouped into three main categories:
differential: pressure is applied to both the opposite sides of the wafer sensing element (P1 and
P2 in the following picture), and the difference in pressure between the two points is measured by
the sensor
gauge: on the upper side of the sensor is applied the pressure (P1 in the following picture),
whereas the bottom side is left at the ambient atmospheric pressure
absolute: pressure is applied to the upper side of the sensor, whereas the bottom side is vacuum-
sealed inside the reference chamber of the die during manufacturing, with a zero-pressure
reference value (see next picture)

3. Typical applications of pressure sensors are as follows:
automotive and avionics field: air speed indicator, air flow measurement, altimeter, ejection seat
control, oil pressure sensor, fuel level indicator, suspension system, tire pressure monitoring system
industrial and consumer field: barometers, flow rate indicator, balancing, robotics, air and water
filtering systems
healthcare and fitness field: blood pressure, heart monitor, kidney dialysis, blood gas and serum
analysis
Proximity sensors
[3]
Proximity sensors are used in applications where non-contact sensing of objects is requested. They are
especially intended for small or simple interfaces where just few controls (or ?touchbuttons?) are involved.
Freescale Semiconductor has recently announced a new series of proximity capacitive touch sensor
controllers with an I2C interface: the MPR031 and MPR032. MPR03X are designed to operate either with
two electrodes (touch panels) and IRQ enabled, or three electrodes and IRQ disabled. Average supply
voltage is very low (about 8 ?A) thus allowing a very long life even for small batteries. These devices have
very compact dimensions: 2 x 2 x 0.65 mm in dual flat no lead (DFN) 8-pin package and they require only
an external 75 K? resistor (with a 1% tolerance). Typical applications for the MPR03X devices are: mobile
phones, multimedia players, Bluetooth headsets, remote control, PC peripherals, lighting controls, watch
and alarm clock, table lamps, dimmers, and electronic products. The I2C interface allows communication
with a host controller at a maximum data rate of 400 kbps, whereas the I2C addresses are fixed and set to
0x4A (MPR031) and 0x4B (MPR032).
Using both MPR03X in the same circuit allows to achieve 4-6 electrodes, depending whether the IRQ pin is
used or not. When it is used, the IRQ pin signals to host controller a change in the electrode status (it can
be either a touch or release action); the host controller can then acquire the electrode status by reading the
associated register on the device. MPR03X have a built-in calibration feature which continually adjust the
baseline capacitance of each electrode; the host controller has only to set the delta thresholds related to
the touch and release events.
Read the Italian version: La famiglia di sensori Freescale [4]
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[5]
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Hardware pressure proximity sensor
Trademarks
Source URL: http://dev.emcelettronica.com/inside-freescale-sensor-products
Links:
[1] http://www.freescale.com/webapp/sps/site/overview.jsp?nodeId=0112691118&tid=rspf
[2] http://www.freescale.com/webapp/sps/site/overview.jsp?nodeId=0112699036&tid=rspf
[3] http://www.freescale.com/webapp/sps/site/taxonomy.jsp?nodeId=0112698268&tid=rspf
[4] http://it.emcelettronica.com/la-famiglia-di-sensori-freescale
[5] http://it.emcelettronica.com/contact/freescale