Division approximation for implantable medical devices

• US 7,848,796 B2
• Filed: 03/11/2009
• Issued: 12/07/2010
• Est. Priority Date: 10/29/2004
• Status: Expired due to Fees

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Drew, Touby Austin
• Primary Examiner(s): EVANISKO, GEORGE ROBERT
• Application Number:
  US12/401,896
• Publication Number:
  US 20090198304A1
• Time in Patent Office: 636 Days
• Field of Search: 607/1, 607/2, 607/45, 600/544, 600/545
• US Class Current: 600/544
• 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:

generating a plurality of ratio determinations of foreground seizure energies divided by background seizure energies;

generating a majority of the plurality of ratio determinations using a ratio estimation comprising estimating a Numerator (N) divided by a Denominator (D) to generate a ratio result, the estimating including raising 2 raised to the power of a difference between a most significant set bit position (MSSB) of the D and a MSSB of the N; and

generating an indication of a seizure with the IMD or the wearable medical device based at least in part on the plurality of ratio determinations.

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

3. The method of claim 2, in which the ratio estimation includes estimating the Denominator.

4. The method of claim 1, in which the ratio estimation 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 result MSSB to equal a 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 M bits just to the right of the ratio result MSSB to have values of 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 6, further comprising rounding up the smaller of the N or the D.

10. The method of claim 1, further comprising rounding up the smaller of the N or the D.

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