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Motorola Sensor Device Data
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DESIGN EXAMPLE COMPARISON SUMMARY
The preceding examples show how sources of variation can
affect the overall system resolution. The MPX2010 has
on–chip temperature compensation and calibration circuitry to
reduce device–to–device variations and temperature effects.
Consequently, when designing the fixed–value amplifier
circuitry, the resolution possible with the MPX2010 is almost
four times greater than the same amplifier circuit using an
MPX10. In both examples, both systems’ performance
(Resolution) are optimized to be the best possible, given the
distribution of the sensor device parameters and the other
component variations.
As stated previously if the methodology’s calculations show
that the sensor’s signal will always be within the dynamic
range of the amplifier (and high and low reference voltages of
the A/D), a software calibration may then be implemented to
nullify any room temperature device–to–device and
component variations.
It should be noted, however, that this methodology does not
consider how to obtain the best performance from a single
sensor system. Rather, the focus of the methodology is to
obtain the best possible system performance while
considering the distribution of device parameters that result
from manufacturing and other sources of variation. By
considering the sources of variation, the system may then be
mass–produced without individually calibrating the sensor
system hardware. Obviously, if each sensor system is
hand–calibrated, the performance will be better. However, the
hand–calibration also requires additional cost and time when
producing the sensor system.
CONCLUSION
To guarantee a specified performance when designing a
fixed–value circuit for sensor systems, all significant sources
of variation must be considered. By considering the sources
of variation (device–to–device variations, temperature effects,
and component tolerances), the system may be designed so
that the specified performance (resolution) is achieved while
still keeping the sensor’s amplified dynamic range within the
A/D window (or saturation levels of the amplifier). The
specified performance may be achieved in all cases by
applying the methodology described herein. By first calculat-
ing the Minimum Required Span to achieve the required
resolution in all scenarios and then determining if the
remaining dynamic range or headroom is large enough to
accommodate the sources of variation, the methodology
determines if the resolution requirement is feasible. If the
sources of variation are too large, the resolution requirement
may not be attainable. In such a case, the resolution
requirement should be relaxed, or the sources of variation
must be decreased. Finally, once the system is successfully
designed to ensure that the sensor signal will always be within
the dynamic range of the amplifier (and high and low reference
voltages of the A/D), a software calibration may be implement-
ed to nullify any room temperature device–to–device and
component variations.
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Freescale Semiconductor, Inc.
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