• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Subscribers 46 subscribers
  • Views 1088 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

ADS1298 Right Leg Drive (RLD) problem

ADS1298: ADS1298 Right Leg Drive Not Working

Gurjant Sidhu
Prodigy 40 points
Part Number: ADS1298

 Hi Everyone,

I am having trouble getting the RLD to work on my ADS1298 board.  For a certain application I want to see how the ECG signal improves with the RLD being disabled vs enabled. When RLD is disabled I am applying 1.5V common mode bias to the body using the RLDOUT pin with the RLDIN and RLDOUT disconnected (JP1 pin open).  When RLD is enabled I am connecting the RLDOUT to the body and the RLDIN  and RLDOUT is connected (JP1 pin closed) and RLD_SENS is enabled on channel 1. I have two electrodes connected CH-1 during the test and another electrode connected to RLDOUT which bias's the body. 

The problem I am having is I don't see an improvement in the common mode rejection with the RLD being disabled vs enabled, the FFT looks the same in both cases. I am mostly interested in rejecting 60hz noise.

One of the TI forums suggested swapping the default 392Kohm||0.01uF (BW 40 hz)  resistor and capacitor RLD loop (between RLDOUT AND RLDINV)  on the board with something that has a higher bandwidth.  I removed R8 and C20 and soldered female headers to RLDOUT and RLDINV so that I could place a different combination of resistor and capacitors, you can see it in the picture of the board I attached.  I tried using 2.2 Mohm || 1nF  (BW of 72 hz) and 1 Mohm || 1nf  (BW of159 hz) , but with no success since the FFT looked the same with the RLD enabled or disabled.        

The settings I am using are attached below. Thanks in advance for any help! :) 

 

RLD Enabled Settings:

Register Settings:

         

ADS1298 PIN CONFIGURATIONS:

JP20-AVSS---CONNECTED TO GROUND 

JP2--AVDD- 3V    

JP1-CLOSED (RLD input to mux and RLD output connected)

JP17-RLDOUT pin connected to body 

CH1- +/- ECG leads connected to body

Board Picture:

RLD Disabled and 1.5V common mode bias applied to body Settings:

Register Settings

     

 ADS1298 PIN CONFIGURATIONS:

JP20-AVSS---CONNECTED TO GROUND 

JP2--AVDD- 3V    

JP1-OPEN (RLD input to mux and RLD output not connected)

JP17-RLDOUT pin connected to body ( Bias body with 1.5V) 

CH1- +/- ECG leads connected to body 

Board Picture:

  • 0
    TI__Mastermind 49041 points
    Hello Gurjant,

    Thanks for your post and welcome to the forum!

    Sorry for the delay in response. I will review your settings and get back to you shortly!
  • 0
    TI__Mastermind 49041 points
    Hi Gurjant,

    For your RLD enabled test, I see that you have CH1 powered down in the register settings. Without the channel powered on, there is no input to the RLD derivation circuit. Please provide power to CH1.
  • 0 in reply to Alexander Smith
    Prodigy 40 points
    I accidentally uploaded the wrong register settings. I updated the post to include the register setting I was using.
  • 0 in reply to Gurjant Sidhu
    TI__Mastermind 49041 points
    Hello Gurjant,

    What happens if you remove the 1.5V common mode bias voltage from the non RLD enabled test?

    Since the purpose of the RLD is to introduce a bias voltage to the patient, the only thing that is changing between tests is the magnitude of the bias voltage. Either way, this bias will be canceled due to the differential measurement. I believe a more accurate test would be to measure without any bias vs bias generated by RLD.
  • 0 in reply to Alexander Smith
    Prodigy 40 points

    When I remove the 1.5V common mode bias voltage from the non RLD enabled test the signal becomes significantly more noisier. 

    The picture below is the result of the RLD being enabled and RLD bias being applied to the test subject.  The signal is less noisy. 

    For my test however I need to compare, the 1.5V bias being applied vs bias generated by RLD. Since I am trying to see the advantage of adding RLD to the reference electrode. 

  • 0 in reply to Gurjant Sidhu
    TI__Mastermind 49041 points
    Hi Gurjant,

    As I said in my previous post, I don't think you will see much of an improvement the way your test is currently set up. Since RLD is a derivation of the channels being fed to it, using at least the LL, LA, and RA leads would yield a more accurate result.

    What is your test signal source? Using a simulator and a patient may yield different results.