• State Resolved
  • Replies 2 replies
  • Subscribers 46 subscribers
  • Views 112 views
  • Users 0 members are here
Support feedback
Options
Options
Related

ADS1298: V1~V2 and V3~V6 are reverse of phase in a 12ch ECG with ADS1298

Kiyoung Lee
Prodigy 10 points
Part Number: ADS1298
Other Parts Discussed in Thread: ADS1294

Tool/software:

Dear Sir,

A 12ch ECG was configured using the ADS1298 as shown in the schematic below.
I connected RA to INxN, the negative port of ADS1298, and LA, LL, V1 ~ V6 to INxP to get the ECG waveform, which shows V1,V2 in the same phase and V3 ~ V6 in inverted phases.

I thought that all Vx channels should be in the same phase.

In addition, for reference, I set the WCT1 register(address 18h) to 0x00 (which shows V1,V2 in the same phase and V3 ~ V6 in inverted phases),

but when I set the WCT1 to 0x10, i.e. AVR_CH4 to 1, V2 is inverted and becomes the same phase as V3~V6.

Also, the Chip Label is ADS1298, but when I read the ID control register(address 00h), I get a value of 128, which gives me Device ID = 000 (4ch ADS1294).

This is also strange.

Any advice on this would be appreciated.

Thank you.

  

  • 0
    TI__Guru 66286 points

    Hello Kiyoung, 

    Thank you for your post. 

    The ID register should read back as 0x92 or 0xD2. Bit 4 should be fixed to 1b for all device variants. Can you check that the power-on reset procedure is followed correctly? The easiest way to check is to keep power supplies on and to pulse the /RESET pin low and high again. Then, send the SDATAC opcode, followed by RREG for 0x00. 

    Even without the correct Device ID, all 8 channels seem to be operating as expected. The polarity of the chest leads is completely dependent on the patient or simulator output. As you are not using the WCT amplifiers (all are powered down), it does not make sense to set address 18h to 0x10. Please leave as default 0x00.

    Regards,

    Ryan

  • 0 in reply to Ryan Andrews
    Prodigy 10 points

    Hello Ryan,

    I read that a wakeup time of 9msec is required (according to the ADS1298 datasheet) after setting /PWDN to high.
    In practice, I used 8msec~, which solved the problem.
    Now the Device ID of ADS1298 is 0x92 and it reads correctly.
    Also, the ADS1298 resets normally, so V3~V6 behaves the same as V1~V2 polarity as expected.

    I really appreciate your kind response,
    Thank you very much.