STMicroelectronics recently introduced a new infrared sensor that uses thermal MOSFETs (TMOS) instead of lenses and passive infrared pixels. ST claims the space savings of TMOS technology can help designers improve performance and save board space in densely integrated designs.
ST's newest IR sensors use a completely different sensing mechanism that does not require an IR lens.
Modern infrared detectors have been around since the 1960s and have become popular among hobbyists for their simple implementation as motion sensors. While traditional PIR techniques require motion to detect a target, TMOS-based sensors can accomplish presence detection even when the target is stationary.
In this article you will learn about ST's new TMOS IR sensor STHS34PF80 and how it can be applied.
Ultrasensitive temperature dependence
At the heart of the STHS34PF80 are several TMOS transistors for IR detection. Each transistor (built on the SOI process) operates in the subthreshold region, making the drain-source current dependent on temperature. Therefore, any change in the amount of infrared radiation (produced by any warm object) absorbed by the gate of the transistor can very reliably determine the presence or movement of a target.
Subthreshold conduction generates a lower but temperature-dependent current to isolate the sensor from temperature and infrared radiation.
The subthreshold operation of the TMOS transistors results in low drain-source currents (compared to other regions of operation), saving overall power consumption and improving sensitivity. A typical PIR sensor requires a Fresnel lens to focus enough infrared radiation and produce a measurable response. The STHS34PF80 can operate without a lens, which proves its sensitivity.
ST builds TMOS devices together with digital and analog circuits to realize small, high-performance infrared detectors with motion and presence detection.
In addition to the infrared detection hardware, the digital readout circuitry is built using ST's SOI CMOS technology, enabling an extremely small overall package size. This dense integration combined with lensless operation makes this sensor an invaluable tool for further sensor size reduction.
A New Vision for Smart Devices
ST has identified a variety of applications that could benefit from the new sensor, such as security alarms, occupancy monitoring, and smart lighting and appliances.
The sensor's lensless field of view enables a variety of applications in a small package size.
The sensor has an 80-degree field of view (FOV) range of up to 4 m without a lens. An optical bandpass filter on the input ensures that ambient light conditions do not affect detection capabilities.
The input transmittance highlights the sensor's ability to operate independently of visible light, providing designers with enhanced sensing capabilities.
If designers require greater range or field of view, they can integrate custom or commercial Fresnel lenses to improve performance. ST is already producing the sensor with a compatible evaluation board that designers can use to test the sensor's performance in specific application scenarios.
For more information, please visit perceptive-ic.com.
