Rejection Performance
A performance specification for ratiometric sensors that measures how well the device maintains its proportional output scaling despite fluctuations or noise on the excitation voltage line determines the sensor’s immunity to power supply instability. High ratiometric supply rejection prevents supply voltage variations from translating into false measurement changes. This characteristic is critical when sensors and analog-to-digital converters share the same power supply, but the supply experiences transient drops due to other system loads.
Proportional Scaling
Ratiometric sensors are designed so that their output voltage is directly proportional to both the measured physical quantity and the supply voltage. Achieving high ratiometric supply rejection requires that any change in the supply voltage produces an identical, proportional shift in the sensor’s internal biasing and amplification stages. If the internal circuitry does not track the supply voltage perfectly, a scaling error is introduced.
This tracking accuracy is especially important in automotive applications where the five-volt supply can fluctuate.
Noise Suppression
High-frequency noise on the supply line must be filtered or rejected to prevent it from corrupting the sensor output signal. The ratiometric supply rejection of a sensor typically degrades as the noise frequency increases because the internal compensation circuitry has limited bandwidth. Engineers must use external decoupling capacitors and low-noise regulators to support the sensor in high-frequency environments.
Calibration Verification
Testing the ratiometric performance involves systematically varying the supply voltage and measuring the output deviation under a constant physical input. During this verification process, the ratiometric supply rejection is calculated by comparing the actual output ratio to the ideal ratio across the entire supply voltage range.
