Sensor Frontends

Since the founding of Fraunhofer IMS, we have been working on miniaturized sensor technology. The sensor thereby converts the parameter to be measured (temperature, pressure, photons, thermal radiation, etc.) into an electrical signal. However, the signal is often of low amplitude and also susceptible to interference if it has to be transmitted over longer distances. To exploit the maximum performance of the sensor, signal conditioning is therefore required as close to the sensor as possible. The electronic circuits used for this purpose are usually analog in this first stage and are generally referred to as the sensor frontend. For transmission to a higher-level system, the analog signals are then usually converted to digital form.

 

Analog sensor front-end circuits can be of various types. In the simplest case, the sensor signal is amplified to a higher amplitude in order to be less susceptible to interference. However, other functions can also be associated with it, such as programmable amplification to allow calibration of the sensor with electronics, or adjustable offset compensation to make best use of its measurement range. The settings used for this are made digitally, transmitted via a suitable interface (e.g. SPI or RS485) and permanently stored in EEPROM memories. A sensor with electronics thus form a calibrated system; nevertheless, the set values can also be reprogrammed via the digital interface. The concept of Industry 4.0-compliant access to sensor nodes is thus effectively supported.

 

Sensor frontend electronics, however, include many other components besides amplifiers. For example, some sensors provide the measurement signal not as a voltage, but as a change in capacitance, and first require a converter to transfer the capacitance value into a voltage before the signal can be amplified. Similarly, the sensor may supply a current, which must be converted accordingly into a voltage for further signal processing.

 

Sensor frontend circuits can make a major contribution to improving signal quality by performing filtering functions. In addition to suppressing unwanted frequency ranges, so-called chopper amplifiers are mainly used here, which are capable of reducing the 1/f noise that occurs in integrated circuits. For high-precision applications, so called autozero amplifiers can be used, which are able to eliminate their own offset voltage.