AN871| Application Note
Maxim/Dallas > App Notes > AUTOMOTIVE
SENSOR SIGNAL CONDITIONERS
Keywords: piezoresistive, pressure sensors, micromachine pressure sensors, pressure control systems, monocrystalline, silicon transducer, temperature, pizoresistive
Dec 07, 2001
APPLICATION NOTE 871
Demystifying Piezoresistive Pressure Sensors
Monocrystalline silicon pressure sensors have come into wide use in recent years. Though manufactured with semiconductor technology, they also operate on the resistive principle. The resistance change in a monocrystalline semiconductor (a piezoelectric effect) is substantially higher than that in standard strain gauges, whose resistance changes with geometrical changes in the structure. Conductivity in a doped semiconductor is influenced by a change (compression or stretching of the crystal grid) that can be produced by an extremely small mechanical deformation. Using a signal conditioning integrated circuit to temperature compensate and amplify the signal offers superior performance over discrete circuits. Semiconductor components that use new signal processing techniques for piezoresistive pressure sensors have enabled precise, automatic, and low-cost electronic compensation of the standard error parameters. The resulting simplification and convenience have opened a wide field of new applications, includin
g the use of bridge sensors for properties other than pressure. Because most control systems operate with electrical signals, pressure or force must be converted to current or voltage before further processing or analysis. Capacitive and resistive signal transducers are commonly used for this purpose. Capacitive sensors detect pressure as a capacitance associated with the distance between two (or more) diaphragms, which changes in response to a change in pressure. To provide useful output, this capacitance change is usually expressed as attenuation of an AC signal or as a frequency shift in a resonant circuit.
In resistive sensors, pressure changes the resistance by mechanically deforming the sensor, enabling the resistors in a bridge circuit, for example, to detect pressure as a proportional differential voltage across the bridge. Conventional resistive pressure measurement devices include film resistors, strain gauges, metal alloys, and polycrystalline semiconductors. Monocrystalline silicon pressure sensors have come into wide use in recent years. Though manufactured with semiconductor technology, they also operate on the resistive principle. The resistance change in a monocrystalline semiconductor (a piezoelectric effect) is substantially higher than that in standard strain gauges, whose resistance changes with geometrical changes in the structure. Conductivity in a doped semiconductor is influenced by a change (compression or stretching of the crystal grid) that can be produced by an extremely small mechanical deformation. As a result, the sensitivity of monocrystalline sensors is higher than that of most oth
er types. Specific advantages are:
q q
High sensitivity, >10mV/V Good linearity at constant temperature
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