Control of spectral agressors in a physiological signal monitoring device

Patent metadata

Field	Value
Publication number	US-9521979-B2
Application number	US-201313862238-A
Country	US
Kind code	B2
Filing date	Apr 12, 2013
Priority date	Mar 15, 2013
Publication date	Dec 20, 2016
Grant date	Dec 20, 2016

Abstract

This disclosure describes techniques for controlling spectral aggressors in a sensing device that uses a chopper amplifier to amplify an input signal prior to sampling the signal. In some examples, the techniques for controlling spectral aggressors may include generating a chopper-stabilized amplified version of an input signal based on a chopper frequency, sampling the chopper-stabilized amplified version of the input signal at a sampling rate to generate a sampled signal, and analyzing a target frequency band of the sampled signal. The chopper frequency and the sampling rate may cause spectral interference that is generated due to the chopper frequency to occur in the sampled signal at one or more frequencies that are outside of the target frequency band of the sampled signal. The techniques for controlling spectral aggressors may reduce the noise caused by the chopper frequency in the resulting sampled signal, thereby improving the quality of the signal.

First claim

The invention claimed is:

1. A signal monitoring device comprising:
a chopper amplifier configured to receive an input signal and generate a chopper-stabilized amplified version of the input signal based on a chopper frequency;
an analog-to-digital converter configured to sample the chopper-stabilized amplified version of the input signal at a sampling rate to generate a sampled signal; and
a processor configured to analyze a target frequency band of the sampled signal,
wherein the chopper frequency and the sampling rate cause spectral interference that is generated by the chopper frequency to occur in the sampled signal at one or more frequencies that are outside of the target frequency band of the sampled signal, and
wherein the chopper frequency is equal to one of:
an odd multiple of one half of the sampling rate, or
an odd multiple of one half of the sampling rate plus or minus a difference between one half of the sampling rate and a target spectral aggressor frequency that is outside of the target frequency band of the sampled signal.

2. The device of claim 1 , wherein the chopper frequency is greater than a 1/f corner frequency of an amplifier included in the chopper amplifier.

3. The device of claim 1 , wherein the chopper frequency is configured to satisfy the following equation:
F master =n*F S +F S /2
where F master is the chopper frequency, F S is the sampling rate, and n is a non-negative integer.

4. The device of claim 3 , wherein n is selected based on at least one of a noise characteristic of an amplifier included in the chopper amplifier, a flicker noise characteristic of the amplifier included in the chopper amplifier, and a 1/f corner frequency of the flicker noise characteristic of the amplifier included in the chopper amplifier.

5. The device of claim 3 , wherein n is selected such that the chopper frequency is greater than a 1/f corner frequency of an amplifier included in the chopper amplifier.

6. The device of claim 1 , wherein the chopper frequency is configured to satisfy the following equations:

δ
=

F
S

2

-

F
target

F
master

=

n
*

F
S

+

F
S

2

±
δ

where F master is the chopper frequency, F target is a target spectral aggressor frequency, F S is the sampling rate, and n is a non-negative integer.

7. The device of claim 6 , wherein n is selected based on at least one of a noise characteristic of an amplifier included in the chopper amplifier, a flicker noise characteristic of the amplifier included in the chopper amplifier, and a 1/f corner frequency of the flicker noise characteristic of the amplifier included in the chopper amplifier.

8. The device of claim 6 , wherein n is selected such that the chopper frequency is greater than a 1/f corner frequency of an amplifier included in the chopper amplifier.

9. The device of claim 1 , wherein the input signal is a brain signal and the target frequency band is one of an alpha, beta, gamma or fast ripple frequency band of the brain signal.

10. The device of claim 9 , wherein the brain signal comprises at least one of an electroencephalogram (EEG) signal, an electrocorticogram (ECoG) signal, a local field potential (LFP) signal, or a single cell action potential signal.

11. The device of claim 1 , wherein the processor is further configured to determine a power level of the target frequency band in the sampled signal.

12. The device of claim 1 , wherein the processor is further configured to determine a power fluctuation of the target frequency band in the sampled signal.

13. The device of claim 1 , wherein the chopper amplifier is further configured to:
modulate an amplitude of the input signal based on the chopper frequency to produce a modulated signal;
amplify an amplitude of the modulated signal to produce an amplified signal;
demodulate the amplified signal to produce a demodulated signal; and
generate the chopper-stabilized amplified version of the input signal based on the demodulated signal.

14. The device of claim 13 , wherein the chopper amplifier is further configured to low-pass filter the demodulated signal to generate the chopper-stabilized amplified version of the input signal.

15. The device of claim 1 , wherein the chopper amplifier, the analog-to-digital converter, and the processor are included in an implantable medical device.

16. A method for monitoring a signal comprising:
generating a chopper-stabilized amplified version of an input signal based on a chopper frequency;
sampling the chopper-stabilized amplified version of the input signal at a sampling rate to generate a sampled signal; and
analyzing information contained in a target frequency band of the sampled signal,
wherein the chopper frequency and the sampling rate cause spectral interference that is generated due to the chopper frequency to occur in the sampled signal at a frequency that is outside of the target frequency band of the sampled signal, and
wherein the chopper frequency is equal to one of:
an odd multiple of one half of the sampling rate, or
an odd multiple of one half of the sampling rate plus or minus a difference between one half of the sampling rate and a target spectral aggressor frequency that is outside of the target frequency band of the sampled signal.

17. The method of claim 16 , wherein the chopper frequency is greater than a 1/f corner frequency of an amplifier included in the chopper amplifier.

18. The method of claim 16 , wherein the chopper frequency is configured to satisfy the following equation:
F master =n*F S +F S /2
where F master is the chopper frequency, F S is the sampling rate, and n is a non-negative integer.

19. The method of claim 18 , wherein n is selected based on at least one of a noise characteristic of an amplifier included in the chopper amplifier, a flicker noise characteristic of the amplifier included in the chopper amplifier, and a 1/f corner frequency of the flicker noise characteristic of the amplifier included in the chopper amplifier.

20. The method of claim 18 , wherein n is selected such that the chopper frequency is greater than a 1/f corner frequency of an amplifier included in the chopper amplifier.

21. The method of claim 16 , wherein the chopper frequency is configured to satisfy the following equations:

δ
=

F
S

2

Assignees

• Medtronic Inc

Inventors

• Stanslaski Scott R
• Carlson David L
• Cong Peng
• Denison Timothy J
• Linde David E
• Jensen Randy M

Classifications

• A61B5/31

  for electroencephalography [EEG] · CPC title

• A61B5/374

  Detecting the frequency distribution of signals, e.g. detecting delta, theta, alpha, beta or gamma waves · CPC title

• A61B5/7225 Primary

  Details of analogue processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation (input circuits for detecting, measuring, or recording bioelectric or biomagnetic signals A61B5/30; specific diagnostic methods using bioelectric or biomagnetic signals A61B5/316) · CPC title

• A61B5/7217

  of noise originating from a therapeutic or surgical apparatus, e.g. from a pacemaker · CPC title

• A61B5/04004

  Human Necessities · mapped topic