Signal Chain Adaptation for Piezoresistive and Capacitive Sensors
Adapting piezoresistive and capacitive sensors requires matching source impedance, suppressing parasitics, and isolating conversion noise floors.
Ratiometric Conversion
Analog Processing
Analog measurement methods express the sensor output as a percentage of the reference voltage rather than as an absolute potential. This ratiometric conversion is a standard technique in systems where the same power supply excites both the transducer and the analog-to-digital converter. If the supply voltage drifts up or down, the sensor output and the converter reference move in unison.
The resulting digital value remains unchanged, effectively canceling out the noise from the power source.
Error Cancellation
Precision of the measurement is improved because the system is insensitive to the absolute accuracy of the excitation voltage. In a bridge circuit, ratiometric conversion ensures that the measured strain or pressure is a function of the resistance change alone. This removes the need for high-stability voltage regulators in the instrument design.
Dynamic Range
Resolution of the digitized signal is maximized by matching the full-scale output of the sensor to the reference range of the converter. Because ratiometric conversion links these two points, the system always uses the maximum number of available digital bits regardless of supply fluctuations. This alignment prevents the loss of signal detail that would occur if the reference voltage moved independently of the sensor excitation.
Supply Sensitivity
Components that do not follow this proportional behavior introduce non-linearities into the data stream. While ratiometric conversion handles DC drift well, it cannot compensate for high-frequency noise that reaches the converter and the sensor at different times. Proper decoupling of the power lines is still required to maintain a high signal-to-noise ratio.
The benefit of this architecture is most apparent in automotive and industrial environments where battery voltages vary widely.