Precision silicon humidity/temperature sensors

December 05, 2013 // By Graham Prophet
Silicon Labs' Si701x/2x “Sensor on a Chip” family simplifies relative humidity sensing for consumer, industrial and automotive designs

Silicon Labs has introduced a family of relative humidity (RH) and temperature sensors that simplify RH sensing designs with power efficiency. Si701x/2x sensors combine a standard CMOS mixed-signal IC with a proven technique of measuring humidity using a polymer dielectric film. The new family enables accurate RH sensing for home automation, HVAC, refrigeration, healthcare, remote monitoring, automotive and industrial equipment. When combined with Silicon Labs’ “energy-friendly” microcontrollers and wireless ICs, the Si701x/2x family enables measuring, controlling and reporting environmental conditions for a wide range of connected devices linked to the Internet of Things.

The Si701x/2x sensor family provides a superior alternative to legacy RH sensing approaches, which use discrete resistive or capacitive RH sensing elements along with analogue circuits for temperature compensation and signal conditioning. These discrete solutions typically require a large bill of materials and PCB area and suffer from lower reliability and risk of contamination. In contrast to discrete approaches, the Si701x/2x monolithic ICs cut cost and complexity, being fully calibrated and SMT compatible. The integrated CMOS design provides the highest long-term reliability, and an optional filter cover provides added protection against contamination. The factory-installed cover – a Teflon membrane sealed at the top of the IC – protects the sensor not only during PCB assembly but also throughout the device’s entire lifetime, shielding the sensing element from dust, dirt and cleaning agents during operation.

With a 3.3 V power supply voltage and 8-bit resolution, the Si701x/2x sensors consume 1.9 µW average on-chip power when taking one sample per second, which is up to six times lower power than competing RH sensors. The sensors maintain ±3% RH maximum accuracy over a wider range of humidity (from 0 to 80% RH) than competing RH/temperature sensors. The sensors also maintain ±0.4 °C maximum temperature accuracy over a wider temperature range (from -10 to +85 °C) than competing devices. The Si701x/2x family has the lowest long-term RH drift at <0.25% RH