Here’s another post contributed to Planet Analog:
Andrew Kelly, IC/Systems Architect, Cactus Semiconductor
In a previous post, The Enabling Chip Technologies Behind Miniature Implantable Medical Devices, we discussed miniaturization technologies necessary for enabling miniature implantable medical devices (MIMDs) that are gaining fast and widespread market acceptance and use. These devices have truly ushered in a new era of treatment capabilities. The proper combination of these technologies can produce compelling design opportunities.
Enabling chip technologies include chip-scale packaging (CSP), solid-state batteries (SSBs), micro-electromechanical systems (MEMS), and application-specific integrated circuits (ASICs). By taking full advantage of these technologies, new MIMD designs can enjoy significant power and size reduction benefits. They can be well-suited to fitting specific requirements of medical applications.
Medical design opportunity considerations
Military applications can have significant temperature ranges from -55° to 125° Celsius. Industrial applications can range from -40° to 85° Celsius, while commercial applications can range from 0° to 70° Celsius. However, medical applications require far more specific temperature ranges. Pre-implant temperature ranges are from 10° to 50° Celsius, and post-implant temperature ranges can be from just 35° to 40° Celsius. The significantly more narrow temperature range in medical implantable applications can greatly reduce circuit design complexity, leading to both system power and size reductions.
In addition, designers must consider the specific frequency requirements of MIMDs. For example, the bandwidth for EEG/ECG is expected to be ~200Hz. Meanwhile, blood pressure monitors typically operate at ~100Hz. And, accelerometers operate around 1 kHz, as do stimulation therapy devices. Most off-the-shelf commercial components are designed to operate at much higher frequencies and thus consume more power. Designing specifically for the lower-frequency operation of most implantable medical devices can result in significant power savings.
Other MIMD specifications include moderate precision requirements. For example, the DAC amplitude of a stimulator needs to run at ~8 bits, while the resolution of an ECG/EEG ADC requires ~12 to 16 bits. Pressure sensor ADC resolutions are often ~10 bits, and the ADC resolution of accelerometers is commonly ~8 bits. The moderate precision requirements, coupled with the lower frequency or sampling rates mentioned in the preceding paragraph, allow for smaller and lower-power data converter designs.
Proper implementation of non-volatile memory (NVM) is also important. It’s often included in most microcontroller units (MCUs), and, by definition, non-volatile memory retains the memory content when power is removed. Therefore, the MCU’s non-volatile memory can be used to calibrate analog circuits. An inline calibration step during production can help reduce analog performance requirements, simplifying design and reducing power. Read the rest at Planet Analog.
