USE OF EMBEDDED PROGRAMMABLE NON-VOLATILE MEMORY IN IMPLANTABLE MEDICAL DEVICES
Publication Date: 2005-Mar-03
The IP.com Prior Art Database
The use of Programmable Non-Volatile Memory (PNVM) in implantable medical devices provides a way to overcome certain limitations of ROM and RAM. The use of PNVM expands concepts of what is possible with implantable medical devices. The quantity of memory allocated for data storage may be significantly increased without significantly impacting energy consumption, greatly increasing the ability to record events while a patient is physically and/or temporally removed from a clinic. Such recorded data could pertain to physiological events, device performance, and the interplay between the two.
IN IMPLANTABLE MEDICAL DEVICES
Implantable medical devices, such as pacemakers and defibrillators, generally are controlled by integrated circuit (IC) microprocessors, which require memory for code and/or data storage.
Various types of microprocessor memory exist. In a simplified architecture of a typical medical device, code (program instruction) is stored in Read-Only Memory (ROM), and data is stored in Random Access Memory (RAM). Both types of memory have notable drawbacks.
ROM, once created, is permanent and cannot be changed. The code stored in ROM at the time of manufacture cannot be updated with improvements.
RAM, on the other hand, can be re-written, but requires a constant power supply to persist. Ideally, RAM circuits require an operating voltage to maintain their integrity, but draw no current when in a non-changing state. In reality, RAM suffers from static leakage current that results in constant power dissipation. Hence, in a medical device, the energy source (battery) must continually supply power to RAM to retain its contents. The leakage current and power draw increase as the amount of RAM is increased. Further, if the power supply voltage is reduced a sufficient magnitude and duration, the contents of RAM may be lost. A significant power demand elsewhere in the device could cause such a reduction if the demand is not otherwise compensated for in the electrical design. For example, delivery of defibrillation pulses puts significantly higher power demands on an implantable defibrillator than required on average.
The use of Programmable Non-Volatile Memory (PNVM) in implantable medical devices provides a way to overcome the aforementioned limitations of ROM and RAM. A common type of PNVM is "flash" memory, as commonly used (circa 2004), for example, as a storage medium for digital cameras and in highly-portable "thumb drives" for computer data.
"Programmable" refers to the ability to re-write PNVM (unlike ROM). One implication of re-writability with respect to code storage is that the PNVM can be fabricated on the same integrated circuit (IC) as other components, such as the microprocessor, saving space and possibly enabling device size reductions. While ROM containing code may be fabricated on the same IC as the microprocessor, the cost of modifying the IC every time...