ADAPTIVE SAMPLING

• US 20110066053A1
• Filed: 09/14/2010
• Published: 03/17/2011
• Est. Priority Date: 09/14/2009
• Status: Active Grant

• Current Assignee: IMEC International
• Original Assignee: IMEC International
• Inventors: YAZICIOGLU, Refet Firat
• Granted Patent: US 8,755,868 B2
• Time in Patent Office: Days
• US Class Current: 600/509
• CPC Class Codes: A61B 2560/0209 adapted for power saving
• CPC Class Codes: A61B 5/30 Input circuits therefor
• CPC Class Codes: A61B 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• CPC Class Codes: A61B 5/366 Detecting abnormal QRS complex, e.g. widening
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/7232 involving compression of the physiological signal, e.g. to extend the signal recording period
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

A method and apparatus is disclosed for adaptively sampling an analogue signal to increase the sampling rate in the presence of high frequency content within the signal, for example, QRS complex of an ECG signal. In one aspect, a change in a derivative of the analogue signal is used to control a voltage-controlled oscillator to provide a clock signal for an analogue-to-digital converter. The change in the derivative is compared to an automatically controlled threshold value. The clock signal controls the sampling rate of the analogue-to-digital converter so that the sampling rate is increased from one level, where only P and T waves are present to another higher level when the QRS complex has been detected.

Claims

1. A method of adaptively sampling a high frequency component of an analogue signal, the method comprising:

a) determining a derivative of the analogue signal;

b) detecting a change in the derivative of the analogue signal;

c) sampling the analogue signal using a sampling frequency; and

d) controlling the sampling frequency of the analogue signal based at least in part on the change in the derivative of the analogue signal, the process of controlling the sampling frequency of the analogue signal comprises comparing the change in the derivative of the analogue signal with an automatically controlled threshold value.

2. The method according to claim 1, wherein the process d) further comprises generating the automatically controlled threshold value from an expected average activity value and an extracted average activity value.

3. The method according to claim 2, wherein the process d) further comprises comparing the extracted average activity value with the expected average activity value.

4. The method according to claim 2, further comprising deriving the extracted average activity value from the analogue signal.

5. The method according to claim 2, wherein the analogue signal comprises an electrocardiogram signal and the process d) further comprises deriving the expected average activity value from a beat frequency of the electrocardiogram signal.

6. The method according to claim 1, wherein the process c) comprises adjusting the sampling frequency to sample the analogue signal in accordance with the comparison between the derivative of the analogue signal and the threshold value.

7. The method according to claim 6, wherein the sampling frequency is increased to correspond with the high frequency component of the analogue signal.

8. The method according to claim 6, wherein the sampling frequency is decreased to correspond with other lower frequency components of the analogue signal.

9. The method according to claim 1, wherein the process c) is carried out using an analogue-to digital converter.

10. An apparatus for adaptively sampling a high frequency component of an analogue signal, the apparatus comprising:

a sampling device configured to sample the analogue signal at a sampling frequency; and

a control device configured to control the sampling device, the control device comprising an activity detection device configured to detect a derivative of the analogue signal and to use a change in the derivative of the analogue signal to alter the sampling frequency of the sampling device, the activity detector comprising a comparator that compares the derivative of the analogue signal with an automatically controlled threshold value.

11. The apparatus according to claim 10, wherein the automatically controlled threshold value is generated from an expected average activity value and an extracted average activity value.

12. The apparatus according to claim 10, wherein the comparator generates a difference between the extracted average activity value and the expected average activity value that is used to automatically control the threshold value.

13. The apparatus according to claim 12, wherein the threshold value is increased when the extracted average activity value is greater than the expected average activity value.

14. The apparatus according to claim 12, wherein the threshold value is decreased when the extracted average activity value is less than the expected average activity value.

15. The apparatus according to claim 10, wherein the activity detection device comprises a differentiator configured to generate the derivative of the analogue signal.

16. The apparatus according to claim 10, wherein the threshold value is derived from the derivative of the analogue signal.

17. The apparatus according to claim 10, wherein the sampling device comprises an analogue-to-digital converter configured to convert the analogue signal into a digital representation thereof in accordance with the sampling frequency.

18. An analogue signal processor comprising the apparatus according to claim 10.

19. The analogue signal processor according to claim 18 in the form of an application specific integrated circuit.

20. A device for adaptively sampling a high frequency component of an analogue signal, the device comprising:

means for determining a derivative of the analogue signal;

means for detecting a change in the derivative of the analogue signal;

means for sampling the analogue signal using a sampling frequency; and

means for controlling the sampling frequency of the analogue signal based at least in part on the change in the derivative of the analogue signal, the process of controlling the sampling frequency of the analogue signal comprises comparing the change in the derivative of the analogue signal with an automatically controlled threshold value.