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ADS1293EVM: Negative cycle clipping in ADS1293 EVM

Ajay Rathor
Prodigy 70 points
Part Number: ADS1293EVM
Other Parts Discussed in Thread: ADS1293

Hi,

We are using ADS1293-EVM evolution board. We have removed R25,R26 and R28 registers to disconnect msp430 SPI And Conneced with our MCU SPI,
For Signal Input giving input with 3.5mm Audio Jack custom cable we have verified on CRO Signal is Proper.

We have use 3-Lead ECG configuration according to ADS1293 Datasheet and giving 200 Hz sine-wave and able to receive sine-wave output on ECG-Channel-1 and getting 6400 samples per second 

Below Register config we have used for ECG.

writeRegister(0x00,0x00);
writeRegister(0x01,0x11);           //Connect channel 1’s INP to IN2 and INN to IN1.
writeRegister(0x02,0x019);        //Connect channel 2’s INP to IN3 and INN to IN1.
writeRegister(0x03,0x00);
writeRegister(0x07,0x0F);
writeRegister(0x08,0xFF);
writeRegister(0x09,0x00);
writeRegister(0x0A,0x07);
writeRegister(0x0B,0x00);
writeRegister(0x0C,0x04);
writeRegister(0x12,0x04);
writeRegister(0x13,0x18);
writeRegister(0x14,0x00);
writeRegister(0x17,0x05);
writeRegister(0x21,0x01);
writeRegister(0x22,0x01);
writeRegister(0x23,0x01);
writeRegister(0x25,0x07);
writeRegister(0x26,0x00);
writeRegister(0x27,0x08);
writeRegister(0x29,0x00);
writeRegister(0x2E,0x33);
writeRegister(0x2F,0x30);
writeRegister(0x50,0x00);
writeRegister(0x00,0x01);

Reading This Registers for ECG data:- readRegister(0x37);  readRegister(0x38);  readRegister(0x39);

But When we use Pace Channel for getting 10,000 samples per second,  negative Cycle clipped from signal.

We have configured this registers for Pace configuration:-

writeRegister(0x00,0x00);
writeRegister(0x01,0x11);              //Connect channel 1’s INP to IN2 and INN to IN1.

writeRegister(0x02,0x019);            //Connect channel 2’s INP to IN3 and INN to IN1.
writeRegister(0x03,0x00);
writeRegister(0x04,0x11);              //FLEX_PACE_CN set to IN1(-) , IN2(+)
writeRegister(0x07,0x0F);
writeRegister(0x08,0xFF);
writeRegister(0x09,0x00);
writeRegister(0x0A,0x07);
writeRegister(0x0B,0x00);
writeRegister(0x0C,0x04);
writeRegister(0x12,0x04);
writeRegister(0x14,0x00);
writeRegister(0x17,0x02);
writeRegister(0x21,0x02);             //R2 decimation rate set to 5
writeRegister(0x22,0x01);             //R3 decimation rate foe channnel 1 set to 4
writeRegister(0x23,0x01);             //R3 decimation rate foe channnel 2 set to 4
writeRegister(0x25,0x07);             //Standard pace data rate set to 2 for all channel(default)
writeRegister(0x26,0x00);
writeRegister(0x27,0x01);
writeRegister(0x29,0x00);
writeRegister(0x2E,0x33);
writeRegister(0x2F,0x03);
writeRegister(0x50,0x00);
writeRegister(0x00,0x01);

Reading This Registers:- readRegister(0x31); readRegister(0x32);

After using this configuration our Negative signal is clipped This is what we get:-


Can you please guide me through why ECG signal is achieved according to given input But Negative signal clipped while using PACE channel?

  • 0
    TI__Guru 66176 points

    Hello Ajay,

    Do you still need help with this issue?

    What are the amplitude and common-mode voltages of your input sine wave? Can you provide the raw data for a few periods of samples using the ECG data and PACE data registers?

    Regards,

    Ryan

  • 0 in reply to Ryan Andrews
    Prodigy 70 points

    Hi Ryan,

    Thank you for your response. We are providing a 500Hz sine wave signal via a 3.5mm audio jack and a +/- 200mV signal at the input. The attached zip file has an xlsx file with a plot of the graph that we created by converting the raw data as well as a raw data file for the ECG channel is also attached and Input Observed From CRO.

    500hz.zip
    However, when we use the same setup for the pace channel (+/- 200mV signal at input and 500Hz Sine wave signal from 3.5mm Audio Jack), we get negative cycle clipping when we try to obtain 10,000 samples per second. Is it possible to achieve a complete sine wave using the pace channel?

  • 0 in reply to Ajay Rathor
    TI__Guru 66176 points

    Thanks, Ajay. Even the data from the zip file looks a bit distorted when compared to the sine wave measured on the scope. This voltage is applied to IN2 and routed internally to INP, correct? What is the voltage applied to IN1 (used as INN)? For linear operation, the inputs to the instrumentation amplifier stage must follow the input common-mode voltage range below:

    Can you check the status of the OUTP_HIGH/LOW and OUTN_HIGH/LOW error bits? 

    Regards,

    Ryan

  • 0 in reply to Ryan Andrews
    Prodigy 70 points

    Hi Ryan,

    Every parameter has been examined. The data sheet is used to set it. We are able to read a complete sine wave at 800 Hz and 6400 sps after changing a few register configurations for a single channel. However, when we switch to the PACE channel, our negative signal is clipped. The register configurations for the ECG channel are shown below. Could you please advise us on what changes to make in order to obtain the correct output at 10,000 sps in the PACE channel?

    void setup_ECG_data() {
    writeRegister(0x00,0x00); //stop data conversion
    writeRegister(0x01,0x0A); //Connect channel 1’s INP to IN1 and INN to IN2.
    writeRegister(0x03,0x00);
    writeRegister(0x04,0x00);
    writeRegister(0x05,0x00);
    writeRegister(0x06,0x00);
    writeRegister(0x07,0x0F); //lead off detect enable for IN1,IN2,IN3 and IN4
    writeRegister(0x08,0xFF); //setting lead off detect current
    writeRegister(0x09,0x00); //clock driver factor k = 1(default)
    writeRegister(0x0A,0x07); //common mode detect enable register
    writeRegister(0x0B,0x00); //common mode detect control(default) (Low Bandwidth and Low cap drive mode)
    writeRegister(0x0C,0x04); //RLD control Register
    writeRegister(0x0D,0x00);
    writeRegister(0x0E,0x00);
    writeRegister(0x0F,0x00);
    writeRegister(0x10,0x00);
    writeRegister(0x11,0x00);
    writeRegister(0x12,0x04); //clock source and output clock source
    writeRegister(0x13,0x08); //AFE Increase sampling freq
    writeRegister(0x14,0x00); //AFE shoutdown(All Active default)
    writeRegister(0x15,0x00);
    writeRegister(0x16,0x00);
    writeRegister(0x17,0x05); //analog pace channel output routing control
    writeRegister(0x18,0x00);
    writeRegister(0x19,0x00);
    writeRegister(0x1A,0x00);
    writeRegister(0x1B,0x00);
    writeRegister(0x1C,0x00);
    writeRegister(0x1D,0x00);
    writeRegister(0x21,0x01); //R2 decimation rate set to 4
    writeRegister(0x22,0x01); //R3 decimation rate foe channnel 1 set to 4
    writeRegister(0x23,0x02); //R3 decimation rate foe channnel 2 set to 4
    writeRegister(0x24,0x02);
    writeRegister(0x25,0x01); //Double pace data rate set to 2 for all channel(default)
    writeRegister(0x26,0x00); //ECG filter enabled for channel 1,2 and 3 (default)
    writeRegister(0x27,0x08); //driven by channel 1 ECG
    writeRegister(0x28,0x00);
    writeRegister(0x29,0x00); //optional masking for drdyd output(default)
    writeRegister(0x2A,0x00);
    writeRegister(0x2B,0x00);
    writeRegister(0x2C,0x00);
    writeRegister(0x2D,0x00);
    writeRegister(0x2E,0x33);
    writeRegister(0x2F,0x30);
    writeRegister(0x30,0x00);
    writeRegister(0x31,0x00);
    writeRegister(0x32,0x00);
    writeRegister(0x33,0x00);
    writeRegister(0x34,0x00);
    writeRegister(0x35,0x00);
    writeRegister(0x36,0x00);
    writeRegister(0x37,0x00);
    writeRegister(0x38,0x00);
    writeRegister(0x39,0x00);
    writeRegister(0x3A,0x00);
    writeRegister(0x3B,0x00);
    writeRegister(0x3C,0x00);
    writeRegister(0x3D,0x00);
    writeRegister(0x3E,0x00);
    writeRegister(0x3F,0x00);
    writeRegister(0x40,0xFF);
    writeRegister(0x50,0x00);
    writeRegister(0x60,0x00);
    writeRegister(0x62,0x00);
    writeRegister(0x00,0x01); //start data convesion
    }

  • 0 in reply to Ajay Rathor
    TI__Guru 66176 points

    Hello Ajay,

    I have a setup running in the lab with your device configuration. I can see that the input waveform is violating the input common-mode range of the INA in the ADS1293. Shifting the common-mode voltage to 200 mV allows the INA output to swing within the linear range.

    I'm still looking into the possible discrepancy between your ECG and PACE register configuration. Meanwhile, can you retest with the proper input common-mode voltages applied to INP and INM?

    Regards,

    Ryan