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ADS1298: Detection of Hardware Pace

Fabio Soriano
Intellectual 2345 points
Part Number: ADS1298

Hi Team,

I received the following request, can you help me?

#########################################################

I want to ask some questions regarding the AFE ADS1298.

Regarding the detection of Hardware Pace, i tried the approach stated on the design created by Tony Calabria.

http://www.ti.com/lit/ug/slau511/slau511.pdf

http://www.ti.com/tool/tipd111 

I used the same design, taking in consideration the modification stated on the design document to remove unwanted noise and frequencies.

Still have problems in the detection of the hardware pace with small amplitudes (Smaller than 4mV with pulses of 100 uS).

We use ECG simulators to produce pace signals, and these equipment are CE certified based on standards IEC 60601-2-25, IEC 60601-2-27, IEC 60601-2-47.

The pace signal produced from the AFE is so small, i know that the Gain is 0.4, but also after setting the gain to 12, the same problem still exists.

 Is there any other way to detect the Hardware pace than this analog method?

And also i have another question, Regarding the chip ADS1298R, i only find the 64-LFBGA package, is the 64-TQFP will be available again?

#########################################################

Regards,

Fabio

  • 0
    TI__Guru 57336 points

    Hi Fabio,

    Thanks for posting your customer's questions.

    The ADS1298R will only be made available in the BGA package. There is not a TQFP version availalbe for the 'R' devices.

    What is the magnitude of the pacemaker pulse measured at the input of the channel for the customer's test? Gain of 12 might be saturating the PGA output.

    Also, what are the analog supply voltages? Is the customer biasing the input signals near mid-supply? This is necessary in order to ensure the input signals are within the common-mode range of the PGA.

    Ask the customer to apply a sine wave at the input (i.e. 10 Hz, 100 mVpp) and set the PGA gain to 6 V/V (default). Remember to use a mid-supply common-mode voltage (i.e. connect INxN to mid-supply, and apply the sine wave to INxP with mid-supply offset). The PACE output will be the differential output of the PGA (about 600 mVpp) times 0.4 V/V = 150 mVpp. Disconnect all circuitry from the PACE output.

    One other important note: the bandwidth of the PGA decreases with gain. Refer to Table 5 in the data sheet for PGA Gain vs. Small-Signal Bandwidth.

    Best regards,

  • 0 in reply to Ryan Andrews
    Prodigy 150 points

    Hi Ryan,

    It's Ahmed Sabry from Pulse for integrated solutions, 

    Gain of the PGA is 6, the default one.

    The analog supply voltage are 5V with respect to the ground, no bi-polar voltages.

    The reference of the input signals is done internally using CONFIG resisters, which is 2.5V.

    We are trying to detect the Pacemaker small amplitudes (2mv with 2ms and 2mv with 0.1ms).

    Would you please specify more details about the test stated on your comment, and what do you mean by disconnection all circuitry?, currently i'm using the external circuit stated in the document issued by Tony Calabria, about the detection of Hardware Pace using Slope Detection, should i remove this circuit??

  • 0 in reply to Ahmed Sabry
    TI__Guru 57336 points
    Hi Ahmed,

    By disconnecting circuitry from the TEST_PACE_OUT pins, I was hoping to remove any load from the pin and to verify that the gain of the signal chain was correct inside the ADS1298. The reference voltage should not matter since the raw analog signal is coming directly from the PGA output.

    The bandwidth of the PGA is limited further with increase in gain - that may be one reason to explain why the amplitude of the PACE amplifier output is smaller than expected.

    Can you share more details about the test setup and results so far? How do the output signals compare to the simulation results shown in the TI Design document? There is also the raw simulation file located at the bottom of the TI Design web page:
    http://www.ti.com/tool/TIPD111

    Can you also provide the register settings used for the ADS1298?

    Regards,