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ADS1293: Noise interference from AC power and BLDC motor

ray yang
Prodigy 160 points
Part Number: ADS1293


Hi,

We are experiencing ECG signal interference problems and provide the register settings and circuit diagrams.

Please give us suggestions, thank you.

Register mapping,

        { 0x01, 0x0A },    // 0, 0x01,0x00; ch1-Routing; 
        { 0x02, 0x1C },    // 1, 0x02,0x00; ch2-Routing; 
        { 0x03, 0x2E },    // 2, 0x03,0x00; ch3-Routing;  Positive:IN5 + Negative:IN6,<- A; 00-10 1-110
        { 0x04, 0x00 },    // 3, 0x04,0x00; pace-Routing;  Non-Pace Channel
        { 0x05, 0x00 },    // 4, 0x05,0x00; Batt.-Routing; Non-Battery Monitoring
        { 0x06, 0x08 },    // 5, 0x06,0x08; Lead-Off Detect Control;  DC lead-off detection;
        { 0x07, 0x00 },    // 6, 0x07,0x00; Lead-Off Detect Enable;  0/1:Dis/En-able Lead-Off Detect; 0x070B
        { 0x08, 0x00 },    // 7, 0x08,0x00; Lead-Off Detect Current;  25 * 0.008uA = 200nA; 0x0832
        { 0x09, 0x00 },    // 8, 0x09,0x00; AC Lead-Off Detect Control; Input signal freq.
        { 0x0A, 0x03 },    // 9, 0x0A,0x00; Common-Mode Detect Enable; Disable "Common-Mode Detect" using XX channel; 0x0A30;
        { 0x0B, 0x00 },    // A, 0x0B,0x00; Common-Mode Detect Control;  Low-bandwidth mode & Medium low cap-drive mode
        { 0x0C, 0x40 },    // B, 0x0C,0x00; Right-Leg Drive Control;
        { 0x0D, 0x00 },    // C, 0x0D,0x00; Wilson Reference Input one Selection; First buffer amplifier connected to input IN1
        { 0x0E, 0x00 },    // D, 0x0E,0x00; Wilson Reference Input two Selection; second buffer amplifier connected to input IN2
        { 0x0F, 0x00 },    // E, 0x0F,0x00; Wilson Reference Input three Selection; second buffer amplifier connected to input IN3
        { 0x10, 0x00 },    // F, 0x10,0x00; Wilson Reference Control;  Goldberger reference disabled & Wilson reference output internally connected to IN6
        { 0x11, 0x00 },    // 0, 0x11,0x00; Internal Reference Voltage Control; CM and RLD reference voltage is on &  Internal reference voltage is on
        { 0x12, 0x04 },    // 1, 0x12,0x00; Clock Source and Output Clock Control;  Start the clock & Clock to digital disabled & : Use external crystal on XTAL
        { 0x13, 0x07 },    // 2, 0x13,0x00; Analog Front End Frequency and Resolution; Clock frequency 102400 Hz & High-resolution mode
        { 0x14, 0x00 },    // 3, 0x14,0x00; Analog Front End Shutdown Control; Active sigma-delta modulator & instrumentation amplifier
        { 0x15, 0x07 },    // 4, 0x15,0x00; Analog Front End Fault Detection Control; Disable the instrumentation amplifier fault detection
        { 0x16, 0x00 },    // 5, 0x16,0x00; RESERVED;
        { 0x17, 0x01 },    // 6, 0x17,0x01; Analog Pace Channel Output Routing Control; Analog pace channel output disconnected & shut down
        { 0x1F, 0x03 }, // 7, 0x1F, Digital Output Drive Strength; Digital Output Drive Strength -- High drive mode
        { 0x21, 0x08 }, // 8, 0x21, R2 Decimation Rate; 8 (default)
        { 0x22, 0x10 }, // 9,0x22, R3 Decimation Rate for Channel 1; R1=16 => 128(25Hz)/64(50Hz)/32(100Hz)/16(200Hz)/8(400Hz)/6(533Hz)/4(800Hz)
        { 0x23, 0x10 }, // A,0x23, R3 Decimation Rate for Channel 2; 200Hz
        { 0x24, 0x10 }, // B,0x24, R3 Decimation Rate for Channel 3
        { 0x25, 0x00 }, // C, 0x25, R1 Decimation Rate; R1=4
        { 0x26, 0x00 }, // D, 0x26, ECG Filter Disable; ECG filter enabled
        { 0x27, 0x08 }, // E, 0x27, Data Ready Pin Source; DRDYB pin not asserted
        { 0x28, 0x40 }, // F, 0x28, SYNCB In/Out Pin Control; Disable the SYNCB pin
        { 0x29, 0x00 }, // 0, 0x29, Optional Mask Control for DRDYB Output
        { 0x2A, 0x00 }, // 1, 0x2A, Mask Error on ALARMB Pin
        { 0x2E, 0x33 }, // 2, 0x2E, Digital Filter for Analog Alarm Signals
        { 0x2F, 0x00 }  // 3, 0x2F, Configure Channel for Loop Read Back Mode; Disable data read back

Ray Yang

  • 0
    TI__Mastermind 19815 points

    Hi,

    May I ask what does it mean by ECG signal interference problems?

    How does signal look like?

    Can you do FFT and/or frequency analysis to see what might be the frequency of the interference? 

    What might be the signal source used?

    Is RLD electrode used? 

    What's U7 MAX30034 over there? Why is there RLD_OUT from there?

    and

    Do you happen to have an ADS1293 evaluation kit/board(EVM)?

    ---------------------------------------------

    and,

    let's take a step back, before trying to acquire ECG signal, have you been able to read the

    1. Figure 82. REVID: Revision ID

    2. Internal test signal described in 8.3.3 Test Mode and 8.6.2 Input Channel Selection Registers for 1 and all channels -

    TST1 Test signal selector

    01: Connect channel one to positive test signal

    10: Connect channel one to negative test signal

    11: Connect channel one to zero test signal

    Thanks

  • 0 in reply to ChienChun Yang
    Prodigy 160 points

    Hi ChienChun,

    The message replies are as follows,
    1. Figure 82. REVID: Revision ID  , ID = 0x40
    2. Do you happen to have an ADS1293 evaluation kit/board(EVM)? No, it's our design.
    3. What might be the signal source used?   ECG simulator

    I'll check with the EE engineer and get back to you on the rest of the questions, thank you.

    Ray Yang

  • 0 in reply to ray yang
    Prodigy 160 points

    Hi ChienChun,

    Updated the news,

    1)  Figure 82. REVID: Revision ID  ,    ID = 0x40
    2)  Do you happen to have an ADS1293 evaluation kit/board(EVM)?     No, it's our design.
    3)  What might be the signal source used?   ECG simulator

    4) Can you do FFT and/or frequency analysis to see what might be the frequency of the interference?

    We can't measure it, but when we connect Earth Ground, the signal is not interfered. The problem is that we are a Portable Device and can't connect

    5)    Is RLD electrode used?     No, No electrode, only RLD on PCB.

    6)  What's U7 MAX30034 over there? Why is there RLD_OUT from there?   Defibrillation / Surge / ESD Protector
    7)  Internal test signal described in 8.3.3 Test Mode and 8.6.2 Input Channel Selection Registers for 1 and all channels -

    TST1 Test signal selector

         01: Connect channel one to positive test signal

         10: Connect channel one to negative test signal

         11: Connect channel one to zero test signal

    Is this to teach us that the ECG provides a self-test signal?

    8)  How does signal look like?

    Ray Yang

  • 0 in reply to ray yang
    TI__Mastermind 19815 points

    Hi,

    The internal test signals are simple fundamental DC signal test to ensure the ADS can read some internal DC signal correctly and investigate the intrinsic noises of the device.  It may not be necessary for now as they can already read&show the ECG signal from ECG simulator.

    ----------------------------------------------------------------------------------------------------------------------------

    Thanks for the plot.

    So, it seems the noises might be from or related AC power lines.

    To confirm, they could do internal short test or external short test to record some baseline noise and then do FFT, frequency analysis, so that they could know/confirm whether the interference is 50/60 Hz or not.

    How is the product powered? by Battery or AC adapter to DC?

    Do they have have low noise LDO and/or isolator in their design?

    What do they mean by AC adapter or without AC adapter? Does such AC adapter connect to the PC or to their ECG instrument product?

    Please try and use&connect RLD electrode to ECG simulator as it's known that using RLD electrode help improve SNR, CMRR and reduce noises.

    Thanks 

  • 0 in reply to ChienChun Yang
    Prodigy 160 points

    Hi ChienChun,

    1) How is the product powered? by Battery or AC adapter to DC?

     Portable device, lithium battery powered, it can also be charged via external AC adapter.

    2)  Do they have have low noise LDO and/or isolator in their design?

    This item needs to be confirmed with the EE Engineer.

    3) What do they mean by AC adapter or without AC adapter?

    without AC adapter: lithium battery powered

    AC adapter: AC to DC and charge lithium batteries

    4) AC adapter connect to the PC ? No

    5) or to their ECG instrument product?  No, the ECG emulator is powered by a lithium-ion battery.

    Thank You.

  • 0 in reply to ray yang
    TI__Mastermind 19815 points

    Hi,

    So, apparently, the noises come from the AC adapter, which they will need to consider changing or improving or use better/improve power management modules design to clean up/reduce the noises.

    And, please try to use RLD electrode to see whether that could help.

    Thanks

  • 0 in reply to ChienChun Yang
    Prodigy 160 points

    Hi ChienChun,

    Updated the news,

    1) How is the product powered? by Battery or AC adapter to DC?
    BAT 16V or DC19V from Adapter -> switching DC2DC 5V-> isolated DC2DC(5Vto5V)-> LDO 4V3 and 3V3

    2) Do they have have low noise LDO and/or isolator in their design?
    isolated DC2DC and TI digital  isolator ISO7221CDR
    isolated DC2DC (5V to 5V)
    LDO 3V3 and 4V3
    Low output noise voltage
    VNO = 38 μVrms (typ.) at 2.5 V-output, IOUT = 10 mA, 10 Hz ≤ f ≤ 100 kHz

    3) We would also like to try Fully-Differential Amplifiers to amplify the ECG signal, would TI recommend it?

    Thanks

    Ray Yang

  • 0 in reply to ray yang
    TI__Mastermind 19815 points

    Hi,

    Thanks for letting me know.

    Regarding to 3) We would also like to try Fully-Differential Amplifiers to amplify the ECG signal, would TI recommend it?

    I am from data converter ADC department, and the amplifier inside the ADS is actually an instrumentation amplifier(i.e. a kind of differential amplifier).

    If you need fully differential amplifier you may need to open a ticket under 

    https://www.ti.com/amplifier-circuit/instrumentation/overview.html

    https://www.ti.com/amplifier-circuit/instrumentation/products.html

    Amplifiers forum.

    to see what other TI amplifier experts suggest.

    Other resources you may look into are 

    https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/893304/faq-designing-with-general-purpose-op-amps

    https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/818894/faq-how-do-instrumentation-amplifiers-inas-fit-into-my-design

    Thanks

  • 0 in reply to ChienChun Yang
    TI__Mastermind 19815 points

    Hi,

    Since I haven't heard back from you,

    I am closing the ticket.

    Thanks