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Sensor Conditioning Options

One of the big challenges of MEMS sensor development is the fact that the raw sensor signals need to be conditioned before being read and acted on. This is done in the “ASIC” that ordinarily accompanies the sensor, typically on a separate die and co-packaged with the sensor (unless done on the same chip in a CMOS-friendly MEMS process). A well-known sensor design challenge is the fact that the ASIC has to be designed alongside the sensor, but that, until tools become more accurate, the actual sensor output isn’t known until the sensor has been built (and perhaps after a couple of design spins); that makes it very hard to co-design the ASIC and build it in parallel with the sensor.

Sensors are inherently analog devices, so it takes an analog front end to condition those signals – or at least convert them to digital for further digital processing. If you have a plain sensor with analog outputs and no encapsulated ASIC, then you have to build your own analog conditioning circuit.

Two companies are providing programmable conditioning circuits to avoid both the serial ASIC design issue and the need to build a discrete analog conditioning circuit. They allow a system designer to adjust the tuning of the conditioning network on the target board. This obviously has benefits over doing the manual circuit by hand, and it also means that any effect that the mounting or location of the sensor might have on the sensor output can be factored into the conditioning. Of course, as compared to a sensor with a co-packaged ASIC, it’s an additional chip and work.

Both Si-Ware and Renesas have such chips, Renesas’ recently announced. Si-Ware announced early last summer an actual development platform, the SWS61111, that features their own ASIC chip, the SWS1110. There’s also an FPGA on the board; the system allows a designer to determine the optimal conditioning configuration and then burn it into the ASIC, which has e-fuses for storing a one-time-programmable (OTP) setting.

Meanwhile, Renesas has announced its Smart Analog configurable conditioning circuit. It comes with its own graphic tool to enable tuning without requiring that you be an analog expert. There are two versions: one that it is intended to be paired with a microcontroller, and one that has the microcontroller co-packaged with the Smart Analog part. In both cases, the Smart Analog settings are stored in the microcontroller’s NVM.

You can find more in the earlier Si-Ware release or the more recent Renesas release.

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