The sensor with a “ratiometric output” means that the sensor’s electrical output signal will change in proportion to the change in a supply voltage. Ratiometric sensors are the unamplified sensors without the built-in power-supply regulation.
Ratiometric Architecture of Safran Colibrys Accelerometers
SAFRAN Colibrys capacitive MEMS accelerometers’ electronic design is ratiometric – it utilizes the internal voltage reference (Vmid), which is derived directly from the power supply line (Vdd). This design choice provides users with the two main advantages:
- a very low dependency from the variation of the electronic alimentation (power supply input voltage) due to the fact that the input voltage is continuously measured and scaled in the hardware;
- the stability of measurements due to the fact that the ratio of power supply versus variation of power supply (mV/V) stays constant whatever the excitation voltage is applied.
Integration and Digitilization of Ratiometric Sensors
Safran Colibrys datasheets contain the chapter “Recommended Circuit”, which gives the full list of recommendations for the optimal integration of ratiometric accelerometers. Power supply management section points out that the low-noise, high-stability and low-thermal drift power supply is indispensable for correct bias, scale factor, noise and thermal accelerometer performances.
In order to preserve accelerometers’ ratiometric proprietaries during the digitalization process, ratiometric ADC is recommended. Ratiometric ADC has a very low dependency from power supply variations, which are often caused by system’s temperature change, turn-on-turn-off and coupling with adjacent systems – climate control, ventilation, heating. As ratiometric ADC will deliver output measurements automatically adjusted to the variation of power supply (in V/V units), the amount of scaling required to return the appropriate units will be reduced and signal treatment time will be shortened.