Medical Reliability A Medical Matter

Robert Tong looks at how new technology is filling a growing need for reliable, low-power implant devices.

Medical device technology has recently advanced rapidly, enabling better and less intrusive patient care. Semiconductor designs are ever-shrinking and combine analogue circuits and digital signal processing in a single device, helping designers bring new generations of reliable, low-power, implant devices to market.

The availability of numerous analogue and digital IP building blocks will help to reduce development time and costs, and simplify the implementation of technology in medical applications.

As well as combining analogue and digital signal processing in close proximity on a ASIC, medical implant devices are integrating ultra-low-power medical implant communication service (MICS) radios. This is taking the performance and usefulness of implanted devices to another level; the data collected and processed by the implant can be transmitted wirelessly, so that medical professionals can monitor patients and make clinical decisions without causing any discomfort. The low power radios also mean that the implanted devices can be reprogrammed remotely.

The low data rate (between 10kbits/s and 20kbits/s) and short-range requirements of medical applications make relatively small demands on power. However, as any extension to the effective life of an implanted device is a benefit, semiconductor companies have taken steps to reduce the radio's power consumption. AMI Semiconductor, for example, uses a feature called 'sniff mode,' whereby the radio is normally in powered-down mode, waking periodically to poll the appropriate radio frequency for the presence of an inquiring RF signal. The acquisition poll frequency can be preset to suit the needs of a specific application.

The continuing market desire for smaller form factors, lower power consumption and greater functionality is keeping the pressure on medical semiconductor designers to innovate. Making the challenge harder is the prerequisite of reliability combined with the often conflicting demand for low cost.

The variety of medical applications for semiconductors is increasing as more biomedical equipment classes take advantage of what single-chip, small-form-factor, mixed-signal electronics has to offer. For example, being able to combine analogue and digital signals in close proximity alongside wireless comms has enabled the development of new implantable cardiac rhythm management (CRM) products such as neurostimulators, drug pumps, and glucose and pressure sensors.

Outside the body, similar technology has facilitated the design and manufacture of a new generation of digital hearing aids that offer far superior performance to their analogue predecessors. They are housed in packages so small that they can be fitted discreetly into the ear canal. In more recent developments, devices are being developed that allow hearing-aid users to communicate via mobile phone and other Bluetooth compatible devices. All single-chip ASIC/ASSP solutions for implantable medical applications are required to consume as little power as possible to extend battery life and lengthen the time between replacement procedures. In many applications there is an additional challenge — while achieving the lowest possible power consumption, the ASIC/ASSP must also be capable of delivering high voltage signals.

Historically, the conflicting requirements of low power and high-voltage have meant that two separate chips had to be developed. Application size constraints have proved the key driver in forcing the two chips together, requiring new manufacturing processes to be developed that allow low power and high voltage to coexist in a single device.

Special isolation schemes such as the deep trench barrier process used by AMIS physically separate low-power circuits from high-power voltages. The deep trench barrier is added to a modified version of a CMOS semiconductor manufacturing process that is commonly used in medical electronics.

Continuing developments in semiconductor design will no doubt provide innovative solutions to alleviate a widening range of medical conditions.

TAGS: Medical
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