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ADS1292: Inverted waveform of ADS1292

Part Number: ADS1292

Hi,

I'm testing eeg using ads1292.

I got a problem when using RLDIN.

I made a circuit to use four electrodes.

- Ch1 : IN1P

- Ch2 : IN2P

- Reference : RLDIN 

- Ground : RLDOUT


The problem is waveform direction of ch1 and ch2 data.

If i use dry type electrode, ch2 waveforn is  reversed by ch1 waveform.

(If i use 3M electrode, ch1 waveform and ch2 waveform become same.)

Why does the direction of the two channels change in this case?

This is my register setting.

0x00, //ID
0x01, //CONFIG1 : 250SPS
0xF0, //CONFIG2 : enable Lead-off comparator, enable reference buffer, reference 4V
0x10, //LOFF
0x62, //Channel1
0x62, //Channel2
0x35, //RLD_SENS
0x0F, //LOFF_SENS
0x40, //LOFF_STAT
0x02, //RESP1
0x03, //RESP2
0x03 //GPIO

And, this is my schematic.

ads1292 part.pdf

  • Hi Youngjun,

    It sounds like there is a difference in the internal connection of the electrode. I recommend checking whatever literature is supplied with the electrodes you purchased to verify this. Please let us know if you have additional questions on the ADS1292! 

  • hi, alexander smith.

    Then,  is there no problem with my register setting and schematic?

    regards,

    youngjun.

  • Hi Youngjun,

    It looks like you are trying to implement an EEG type of application, correct? In your schematic, you have electrodes connected to IN1P and IN2P, and IN1N and IN2N have the option of 0 ohms to GND. Your reference electrode can be connect to the INxN inputs in two ways:

    1. External connection, routed to each INxN pin directly. 
    2. Internal connection, using the RLDIN pin.

    Currently you are using MUXn[3:0] = 0010, which will measure your reference electrode again mid-supply. The INxP electrode will be disconnected from PGA:

    To measure IN1P and IN2P against the reference electrode with internal connection, use MUXn[3:0] = 0111:

    The CMRR of the system will be better if you route the reference electrode directly to IN1N and IN2N externally.

    Best regards,