Voltage Proportioning
Methods of powering a sensor using the same voltage source that acts as the reference for the analog to digital converter eliminate errors from supply fluctuations. Ratiometric excitation ensures that the sensor output and the converter scale move in unison. If the source voltage drops by one percent, the measured signal and the digital full-scale both drop by the same amount.
The resulting digital count remains unchanged.
Circuit Efficiency
Efficiency is improved because this configuration removes the need for high-precision, low-drift voltage regulators within the measurement chain. While non-ratiometric systems require absolute stability, ratiometric excitation allows for the use of simpler power supplies. Most bridge-based sensors, such as those used for pressure or weight, benefit from this architecture.
The accuracy of the final reading depends on the ratio rather than the absolute value of the excitation.
Signal Conditioning
Differential amplifiers must be designed to handle common-mode voltages that scale with the supply. Using ratiometric excitation requires careful layout to ensure that noise on the supply line is filtered equally for the sensor and the converter. Any imbalance in the filtering will introduce a measurement error.
Designers often place the converter and the sensor on the same local power rail to maintain tracking.
Application Limit
Application of this technique is limited for sensors that produce an absolute output voltage independent of the excitation level.
