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ADAS1000-4 distortion of respiration signal when using ext. power supply adapter

Category: Hardware
Product Number: ADAS1000-4

Hello,

We are using the ADAS1000-4 chip in our new medical device which is used among other things to detect Apnea (stopping of breathing). The device has in-built battery which can be charged by an external power supply adapter. The patient side of the device is isolated by a distance of 8 mm from the rest the circuitry. The respiration signal is filtered by a digital low-pass filter with Fc = 2Hz.

During the field tests, we came across some issues concerning mostly with the respiration.

One channel ECG and the Respiration are acquired using 3 electrodes RA, LA and LL. To acquire  respiration, we are using only a pair of RA and LA.

The one channel ECG can be set to RA-LA, LL - RA and LL - LA. Depending on which pair of electrodes is selected for ECG, the remaining one will be used as RLD.

In case we set ECG and Respiration to RA - LA with RLD driving the LL electrode everything is working correctly.

When the device is powered by the external power supply adapter,we observed signal distortion in the respiration measurement channel. During this measurement we set ECG to LL - RA and the Respiration to RA - LA with RLD driving the LA electrode. The same happens when we set ECG to LL- LA with RA – LA for Respiration with RLD driving the RA electrodes.


Our ADS1000-4 configuration for the case ECG= LL - RA:

RESPCTL = 0x0034F7

CMREFCTL = 0x60301A

 

The pictures below shows the behaviour.

Figure 1 Respiration Signal (RA – LL)l) in case the device is NOT connected to the ext. power supply

Figure 2: Apnoe Signal (RA – LL) in case the device is NOT connected to the ext. power supply

Figure 3: Respiration Signal (RA – LL) in case the device is connected to the ext. power supply

Figure 4: Apnoe Signal (RA – LL) in case the device is  connected to the ext. power supply

Has anyone an idea why this happen and how we can overcome this?

Parents
  • Hi,

    Is it possible for you to run an FFT analysis in the data to know the frequency of the noise? Based on the noise frequency, you might need to develop filter using external components 

    regards,

    Mark

  • Hi Mark,

    Thank you for the info. I will try to do an FFT Analysis to find the frequency of the noise (I assume it is 50 Hz but i'm not sure). But my question is why ADAS1000-4 behave like this, when I change the lead configuration? With Lead I everything seems to work well. The effect appear when one electrode from the selected pair is used as RLD. When the selected pair has no driving RLD the effect does not occur (or it's not so visible).

    An additional question: In the register CMREFCTL Register we have the possibility to select the electrode for reference drive. If RLD_OUT is NOT selected (RLDSEL = 0000) than how the ext. feedback components will close the loop?

    Regards,

    Alex

Reply
  • Hi Mark,

    Thank you for the info. I will try to do an FFT Analysis to find the frequency of the noise (I assume it is 50 Hz but i'm not sure). But my question is why ADAS1000-4 behave like this, when I change the lead configuration? With Lead I everything seems to work well. The effect appear when one electrode from the selected pair is used as RLD. When the selected pair has no driving RLD the effect does not occur (or it's not so visible).

    An additional question: In the register CMREFCTL Register we have the possibility to select the electrode for reference drive. If RLD_OUT is NOT selected (RLDSEL = 0000) than how the ext. feedback components will close the loop?

    Regards,

    Alex

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