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1. (WO2018162365) PHYSIOLOGICAL MEASUREMENT DEVICE WITH COMMON MODE INTERFERENCE SUPPRESSION
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CLAIMS

1. A method for minimizing common mode interference in a physiological measurement system (108, 210, 312) having input channels (106) and analog circuitry electrically coupled to electrodes (104) for measuring an electrophysiological signal, the method comprising:

receiving analog test signals (202) at the input channels;

generating response signals at the analog circuitry (204, 304) in response to receiving the analog test signals;

converting each response signal into digital data samples (208); storing, in a memory of the physiological measurement system, the digital data samples in association with each of the input channels;

analyzing the digital data samples for each of the input channels to determine a reference input channel;

determining a set of digital filter coefficients for each input channel other than the reference input channel; and

applying a filter (114, 308) to each input channel during operation of said physiological measurement system, wherein each filter operates according to a digital filter coefficient from the set of digital filter coefficients to minimize time-domain differences between the reference input channel and each input channel other than the reference input channel.

2. The method of claim 1, wherein the analog test signals include a square wave that is superimposed with a sine wave.

3. The method of claim 2, wherein converting each response signal into digital samples includes sampling at least one response signal at a rate that is greater than a frequency of the sine wave.

4. The method of claim 2, wherein the square wave has a frequency that is less than a bandwidth of the physiological measurement system.

5. The method of claim 1, wherein the set of digital filter coefficients are calculated according to a least squares error estimation.

6. The method of claim 1, wherein analyzing the digital data samples for each of the input channels to determine the reference input channel comprises:

identifying a response signal corresponding to a last zero crossing.

7. The method of claim 1, wherein analyzing the digital data samples for each of the input channels to determine the reference input channel comprises:

identifying a response signal corresponding to a slowest slew rate.

8. The method of claim 1, wherein the filter at each input channel is a finite impulse response filter.

9. The method of claim 8, wherein the set of digital filter coefficients comprises at least 2 coefficients.

10. The method of claim 1, wherein converting each response signal into digital data samples is performed using sequential data sampling with an analog to digital converter

(206, 306) and a multiplexer that is connected between the analog to digital converter and the analog circuitry.

11. The method of claim 10, wherein the sequential data sampling is performed at least at 32000 samples per second.

12. A physiological measurement device, comprising:

input channels comprising electrodes that are configured to receive physiological measurement signals;

analog circuitry (204, 304) connected to the input channels and configured to receive the physiological measurement signals and, in response, output response signals;

an analog to digital converter (206, 306) connected to the analog circuitry and configured to convert one or more response signals into digital samples; and

one or more filters (308) connected to the analog to digital converter and

configured to filter the digital samples, wherein each of the one or more filters operates according to a coefficient for minimizing time-domain differences between the response signals.

13. The physiological measurement device of claim 12, further comprising:

a signal processor (310) configured to provide a differential signal based on a difference between filtered digital samples of at least two different response signals.

14. The physiological measurement device of claim 12, wherein each of the one or more filters is assigned to an input channel of the input channels, and the coefficient for each filter is based on a calibration of the input channel.

15. The physiological measurement device of claim 12, wherein the one or more filters further operate to conform the digital samples to be more similar to a response signal corresponding to a predetermined input channel of the input channels.