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Original question:

ADS1298: Detection of Hardware Pace

ADS1298: Detection of Pacemaker circuits with ADS1298

Ahmed Sabry
Prodigy 150 points
Part Number: ADS1298
Other Parts Discussed in Thread: ADS1261, ADS7042

Dear All, 

Regarding the output of the pacemaker from the two pins of the AFE ADS1298, TESTP_PACE_OUT1 and TEST_PACE_OUT2.

We are currently working on a detection circuit of pacemaker based on the paper written by Brian Pisani with name TI Precision Designs: Verified Design Software Pacemaker Detection Reference Design.

But instead of using the SAR ADC ADS7042, we are using the ADS1261 with its software to acquire the data to make an algorithm to detect the pacemaker signal from it.

The ECG + PACE signal is obtained from a Whaleteq simulator of model SECG 4.0 to make sure that the detection of pacemaker pulses is done based on IEC standards IEC 60601-2-25, IEC 60601-2-27, IEC 60601-2-47, and its specifications are available on this page: https://www.whaleteq.com/en/Products/Detail/18/SECG%204.0#tag=proOverview.

Here is the schematics for the connection of the input stages of the ECG leads to the AFE, taking in your consideration that the PGA of the AFE is set to 6.

According to the datasheet, to acquire the pacemaker pulses, only one channel must be selected at a time, so we select channel 2 to acquire the pacemaker pulse from the TESTP_PACE_OUT.

The problem appears with the pulses with small values or duration, and here is the spectrum for the samples after performing the filters (Analog and digital) on it.

2mv - 2ms

2mv - 500us

2mV - 100us

As you can see here, the pulse of the pacemaker signal is so small, the 2ms and 500us duration can be detected, but the smallest one (with 100us duration) can not be detected due to its small duration and amplitude. 

Also, the signals taken from the other pin (TESTN_PACE_OUT) contains higher noise than the even ones.

Is there any way to reduce this noise, or to detect these small pulses.

Also another question, according to IEC 60601-2-25/27/47, it's required to detect the pace on every single channel, including the chest leads also, in this case how we can configure the PACE Register?, as you can see, the chest leads are connected to the WCT on there negative differential side.

Looking forward to your reply.

  • 0
    TI__Guru 64186 points

    Hello Ahmed,

    Thank you for your post.

    May I ask you what drove your decision to choose the ADS1261? Depending on the filter type that you use, this device may not have the adequate signal bandwidth to detect the higher frequency components in pacemaker pulses.

    I'm not sure what would cause a difference in the noise on TESTP_PACE_OUT1 and TESTN_PACE_OUT2. Are you selecting the same ECG lead on both PACE amplifiers for comparison? The PACE amplifier inputs are selected via the PACE register (15h).

    Best regards,

  • 0 in reply to Ryan Andrews
    Prodigy 150 points

    We have been choose the ADS1261 because its higher sampling rate and it has 24-bit high precision ADC, it is needed on our design for the pace detection algorithms and other required functions, and now we are in the phase of the studying the behavior of the pacemaker signals received from the two pins of the AFE, we are trying to plot the received signals using matlab and add any required filters on it, other than these available on the hardware, and we have no problem to analyse the signals starting from 700mV to 2mV, the problem only occurred with the signal containing pacemaker pulse with amplitude 2mV and 100us, as shown on the pictures attached on the main post of this topic.

    we are now selecting the ECG lead I, which is can be derived from LA and RA, from channel 2 of the AFE as stated on our schematics, also attached on the main post of this topic, and the selection is done through the PACE register as stated on the AFE Datasheet.

    Do you suggest any further information to overcome this problem??

    and please regarding the pacemaker pulse to be derived from the chest leads (V1 to V6) how can i select them through the PACE register, as stated on schematics, the negative input of every channel is connected to the WCT.

    For example, if i want to capture the pacemaker signal from V1, as stated on the schematics V1 is connected to IN8P, and the negative side is connected to the WCT, which value is to be added in the pace odd channels PACEO[1:0]?

    And again we are asking about that because it is needed to be performed according to IEC 60601-2-25/27/47 standards.

    Looking forward to your reply.

    Thanks and best regards.

  • 0 in reply to Ahmed Sabry
    TI__Guru 64186 points

    Hello Ahmed,

    Just to clarify, the max data rate for the ADS1261 is only 8 kSPS faster than the ADS1298. More importantly, the maximum -3-dB bandwidth for the ADS1261 is only 8.167 kHz (see Table 6 of the data sheet). The maximum -3-dB bandwidth in the ADS1298 is 8.384 kHz, (slightly higher, but nearly the same). I think you'll need much higher bandwidth to see the pacemaker pulse with 2 mV amplitude and 100 us pulse width. We have a reference design using a SAR ADC that you may be interested in:

    http://www.ti.com/lit/ug/tidub75/tidub75.pdf

    The PACEE and PACEO registers always connect the differential PGA output to the PACE amplifiers - there is no way to connect only one of the electrodes to the PACE amplifiers. Please correct me if I'm wrong, but I believe the IEC criteria for pace detection refers to monitoring for pace on all leads, not individual electrodes. Therefore, I believe monitoring Lead V1 = V1 - WCT would be acceptable. Again, let me know if that's not the case.

    Best regards,