DIVISION APPROXIMATION FOR IMPLANTABLE MEDICAL DEVICES

• US 20090198304A1
• Filed: 03/11/2009
• Published: 08/06/2009
• Est. Priority Date: 10/29/2004
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Drew, Touby A.
• Granted Patent: US 7,848,796 B2
• Time in Patent Office: Days
• US Class Current: 607/45
• CPC Class Codes: G06F 7/4833 Logarithmic number system
• CPC Class Codes: G06F 7/535 Dividing only

Abstract

Methods and devices for performing division approximation in implantable and wearable self-powered medical devices. The present invention provides rapid methods for performing an approximation of division on fixed point numbers, where the methods are easily implemented in small, low power consumption devices as may be found in implantable medical devices. One example of use is in rapidly determining the approximate ratio between foreground and background activity in seizure detection algorithms. Some methods approximate the ratio of Numerator (N) to Denominator (D) by raising 2 to the power of the difference in the number of zeros to the left of the Most Significant Set Bit (MSSB) of D vs. N. Some methods may also pad bits to the right of the approximate ratio MSSB using bits from the right of the N MSSB, and/or pre-process the smaller of D or N by rounding the value upward. Methods may be implemented in firmware and/or in discrete logic.

Claims

1. A method for detecting a seizure in an implantable or wearable medical device (IMD), the method comprising:

executing an algorithm having a plurality of ratio determinations of foreground seizure energies divided by background seizure energies, in which the algorithm uses a ratio estimation in place of fixed point division to determine a majority of the ratios,

wherein the ratio estimation includes estimating a Numerator (N) divided by a Denominator (D), the estimating including obtaining a result as a function of 2 raised to the power of the difference between the most significant set bit position (MSSB) of the D and the MSSB of the N; and

generating an indication of a detected seizure at least in part as a function of the ratio determinations with the self-powered IMD or the self-powered wearable medical device.

2. The method of claim 1, in which the ratio estimation includes estimating the Numerator.

3. The method of claim 1, in which the ratio estimating includes estimating the Denominator.

4. The method of claim 1, in which the ratio estimating includes estimating the Numerator and the Denominator.

5. The method of claim 1, in which the ratio result of claim 1 has a MSSB, further comprising setting a bit just to the right of the ratio MSSB to equal the value of a bit just to the right of the N MSSB.

6. The method of claim 1, in which the ratio result of claim 1 has a MSSB, further comprising setting a number of M bits to the right of the ratio MSSB to have the value as the same number of M bits just to the right of the N MSSB.

7. The method of claim 6, in which M has a value of at least 1.

8. The method of claim 6, in which M is equal to all bits to the right of the MSSB of the ratio result of claim 6.

9. The method of claim 1, in which the smaller of the N or the D is first processed by rounding up the smaller of the N or the D, and the rounded up number is used in the method of claim 1.

10. The method of claim 6, in which the smaller of the N or the D is first processed by rounding up the smaller of the N or the D, and the rounded up number is used in the method of claim 1.

11. A computer readable medium having computer executable instructions for executing the method of claim 1.