ADS1293: Noise interference from AC power and BLDC motor

ray yang

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.

        { 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

over 2 years ago

0 ChienChun Yang over 2 years ago

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 ray yang over 2 years ago in reply to ChienChun Yang

Prodigy 150 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 ray yang over 2 years ago in reply to ray yang

Prodigy 150 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 ChienChun Yang over 2 years ago 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 ray yang over 2 years ago in reply to ChienChun Yang

Prodigy 150 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 ChienChun Yang over 2 years ago 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 ray yang over 2 years ago in reply to ChienChun Yang

Prodigy 150 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 ChienChun Yang over 2 years ago 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