A Signal-Processing Bridge-Sensor Interface

If you have used bridge sensors for, say, pressure or strain measurements, you understand the difficulties of setting up these sensors so they deliver useful information. Most of these sensors are sensitive to temperature and produce non-linear outputs. Instrumentation amplifiers or differential amplifiers to create a high-level signal for an analog-to-digital converter. Then, of course, the raw ADC values require some processing to linearize the values and account for offsets and temperature. Now, imagine that all those steps can exist in one integrated circuit.

ZMD, based in Dresden, Germany, has developed such an IC aimed at manufacturers of sensors, but also applicable to add-on signal-conditioning in resistive bridge-sensor circuits. The ZSSC3017 provides a set of inputs for the bridge itself, an internal temperature reference, programmable preamplifiers, a 16-bit analog-to-digital converter (ADC) and an 18-bit digital signal processor.The IC’s programmable-gain differential amplifier operates on signals within the range of 12.5 to 160mV/V

The built-in DSP block makes this IC particularly interesting because it provides hard-wired algorithms that will correct for 10 offsets, gains, temperature coefficients, and second-order nonlinearities. During a calibration–explained in the ZSSC3017 data sheet–the IC reads correction coefficients provided by an external controller, and saves these values in flash memory. The data sheet also explains the math used by the DSP block to perform internal compensations.

This memory also stores configuration bits that determine the data-output mode, data-update frequency, amplifier gains, input-signal polarity, chopper-amplifier operations, and so on. Because the IC saves information in flash memory, people can make changes in the field. The chip uses an I2C-like interface to communicate with a host controller. According to ZMD, “The interface is mainly based on the I2C-standard but [is] not absolutely I2C- standard compliant.”

The ZSSC3017 is available as die for wafer bonding or in a TSSOP14 package. Packaged-part prices: 1.13 Euro or $US 1.59 in 10K quantities. ZMD has sample packaged devices and die available now. For more information, visit: www.zmdi.com/products/sensor-signal-conditioner/zssc3017/. The ZSSC3017 looks like a useful and inexpensive interface IC for resistive bridge sensors. –Jon Titus