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ADS1292R: ADS1292R Resp

HECTOR
Intellectual 536 points
Part Number: ADS1292R

Tool/software:

Hello everyone 

We use ADS1292R in bipolar mode ; +/-2.5V . i saw ithe evalution kit for respiration part there is an high pass filter at the inputs with  pull up  resistor to +V and pull down resistor to -V   as Vbias . since in my case i use bipolar power can i use only one resistor to ground (0v) ? 

i saw that its better to use a high pass filter greater that 60Hz to reject  Ac noise ; but how higher i can do ? for example can i use 1khz high filter ? 

Regards 

Hector

  • 0
    TI__Guru 64036 points

    Hi Hector,

    Nice to hear from you. 

    A pull-down resistor to GND may also work fine since this is near mid-supply. However, it may be better to use a pull-up resistor connected to RLDOUT and enable the internal RLDREF voltage. This way, the RLD amplifier will act as a mid-supply buffer and you might see less noise coupling from the ground plane. You will need to connect RLDOUT to RLDINV to complete the feedback path as well. An RC network of 1M||1.5nF would limit the bandwidth to 106 Hz and reduce the noise contributed by the amplifier itself.

    I would not suggest to decrease the filter capacitor lower than 470pF. We have observed significantly reduced respiration signal swing for capacitors below this value and a R-divider of 10M||10M (or 5M to mid-supply).

    Regards,

    Ryan

  • 0 in reply to Ryan Andrews
    Intellectual 536 points

    Hi Ryan ; 

    Thank you . 

    i have attached the shematic ; please could you check  it?  for RLDout do you mean i need only to set it for mid supply only ?  or mid supply +  feedback from channel 1 respiration input to  decrease  the common mode noise ? 

    Also I use channel 2 for single ended input +/-2,5V?    i connect channel 2N to GnD  ; should we add a resistor  and filter ?  or direct GND  would be ok ? 

    Regards 

    Sami

    ADS_1292r_texas.pdf

  • 0 in reply to HECTOR
    Intellectual 536 points

    Hello ; 

    Any update here ? 

    Regards 

    Hector

  • 0 in reply to HECTOR
    TI__Guru 64036 points

    Hi Sami,

    The common-mode sensing could be used as well. As this is just a register configuration, I suggest evaluating the performance as just a mid-supply buffer before adding the common-mode sensing.

    For single-ended inputs, it's ok to connect IN2N to ground. What is channel 2 measuring in your application? Currently your schematic does not show anything connected to CH2.

    Regards,

    Ryan

  • 0 in reply to Ryan Andrews
    Intellectual 536 points

    Hello Ryan ; 

    Sorry for the delay . 

    I use 1M ohm pull up to RLDout to 2.2nF ( RLDout will me set to mid supply , so it will be virtual ground since we use bipolar power plus sensing the inputs to cancel noise using 1M//1.5nF)  ; so now the cuttoff freq is 72HZ ; is ıt ok ? 

    for single-end we use an output from other circuit where data can be between +/-2V  . so we will set the gain 1 and vref to 4v . and IN2N conencted to ground .