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EETE JULAUG 2012

The +5% tolerance of this usually a large part capacitor was an important of our design work. parameter when selecting it is well known that the process. The I3T50 pro- transistor param- cess is well controlled and eters vary widely we were able to work closely over temperature. Fig. 3: The patch antenna with on Semiconductor to thankfully in this transmits RF power to the lens. meet this requirement. application the pa- the actual coupling between the lens antenna and the patch tient’s eye maintains antenna can vary by a factor of 3 or more depending upon the the device at around relative orientation of the two coils. this wide variation in input 34ºC (temperature power meant that the circuit needed to operate reliably and of the surface of the safely over a large input power range. the low dropout of the eye). active rectifier helped minimize losses at low power levels, while this saved both a current shunt safety circuit avoided overvoltage within the in design time and device when high power levels were received. as power levels simulation time as were in the μW range there was no danger of any self-heating we were able to run related discomfort in the eye. simulations with the signals coming from the strain gauge are very small a much reduced Fig. 4: The portable data recorder such that the LSB of the aDC is at the microvolt level. Keeping corner set. anSem connects to the patch antenna through the switching noise of the rectifier away from the ADC was a will now manage the a thin flexible data cable and gathers the problem both at circuit level and at layout level. noise coupling complete aSiC life measurements transmitted by the lens. through the substrate had to be mitigated through clever use of cycle for Sensimed, the high voltage pockets available in the I3T50 process. including industrialization and supply chain for volume produc- in this application the die is mounted directly onto a trans- tion, leaving Sensimed to concentrate on serving their market. parent lens structure. Care had to be taken with light sensitivity for the medical market the most important thing is to translate of the circuitry. the back die had to be metal coated to prevent the customer’s requirements into a complete and physically light penetration. Meeting specifications over temperature is realizable specification. We provide innovative analog solutions to the most challenging applications in sensor and sensor interfaces, power management, and wireless. www.electronics-eetimes.com Electronic Engineering Times Europe July/August 2012 33


EETE JULAUG 2012
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