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ecg amp circuit comparison

david sun77114
Expert 2140 points
Other Parts Discussed in Thread: INA333, INA326, ADS1294, ADS1298, OPA333

I'm searching for a ECG circuit, i found one at page 15 on ina333 data sheet, I also noticed that at page 28 of "geting the most out of your instrumentation amplifier design".slyt226, there is an example using ina326, could anyone tell me the major difference of these two design. where can I buy a evaluate board of these front end.

thank you

 

  • 0
    TI__Expert 7185 points

     The only major difference between these 2 designs is that the circuit in the INA333 data sheet is using the Wilson Central voltage (average voltage between the right arm, left arm, and left leg) for the RL drive instead of the common voltage between the right and left arm.  Typically the Wilson Central voltage is used to derive a reference potential for the chest leads (V1 - V6) and not used to drive the right leg.  The design in slyt226 is more common, but the RL potential can be derived by the summation of numerous electrode voltages if desired.  For more information read the following post:

    http://e2e.ti.com/support/amplifiers/precision_amplifiers/f/14/p/115885/420505.aspx#420505

    For a good monolithic ECG device, check out the ADS1298--there are EVMs available that will allow you to measure ECG potential with very few external components.

    Matt

     

     

     

     

  • 0 in reply to Matthew Hann
    Expert 2140 points

    Thank you very much for reply, I am working on a low cost app, AdS1298 seems too expensive, ADS1294 is close. the power consumption is my second concern.  and the package is too big. I like the design in the link 420505, could you please send me a copy of the tina project? I never used it before. I would like to use msp430 with 24bit ad. what is the sample rate on mp430.

    appreciate you help

  • 0 in reply to david sun77114
    TI__Expert 7185 points

    I have attached a more "convergence friendly" version of the ECG schematic that I posted in 420505.  The INA333 and the OPA333 are complex simulation models and oftentimes finding an operating point can require several simulation iterations.  I have removed the DC offset servo integrator and the gain stage to help with this.  You can add these back into the circuit, but in general with ECG I would recommend simulating only the relevant pieces of the circuit to avoid longer simulation times.

    Matt

    ECG_External.TSC
  • 0 in reply to Matthew Hann
    Prodigy 40 points

    thank you very much. I will show you result after I complete a prototype board. I checked "Email me replies to this post" don't understand why it is not work.

  • 0 in reply to Matthew Hann
    Expert 2140 points

    Hi Matt

    I changed V1 from 5v to 3v or 4v, and run an transient simulation, both of them got 'operating point not found' error. is this design work at 3v. i'm trying to lower the power consume by lower the voltage. any suggestions are appreciated.

    thanks

     

    david

     

  • 0 in reply to david sun77114
    TI__Expert 7185 points

    Yes, convergence is quite often a challenge when conditions change with these ECG circuits.  Often what I have to do is either add a large resistor to ground off of the output of each amplifier and/or an initial condition (i.e. VCC/2) to help things converge.  There is nothing inherently wrong with the circuit when you change the supply voltage from 5V to 3V, it is simply a convergence issue.  Also, it often helps to sequentially analyze pieces of the circuit (i.e. remove the pieces that are not important).

    I hope this helps.

    Matt

  • 0 in reply to Matthew Hann
    Expert 2140 points

    thank you very much, I have ordered samples from TI and purchased parts from digikey. going to build a prototype. do you have an estimation of the power consumption of the design. i hope it less than 3mA, is it possible. for just front end.

  • 0 in reply to david sun77114
    TI__Expert 7185 points

    David,

    For the AFE, I would estimate the following:

    *INA333 Gain stage = 50uA

    *OPA333 Feedback Integrator = 20uA

    *OPA333 Right Leg Drive buffer + amp = 40uA

    *OPA333 Gain Stage = 20uA

    In total about 130-150uA, and if you add another active filter stage using another 1 or 2 OPA333 devices you are still looking at only a total quiescent current of 200uA.

    -Matt

  • 0 in reply to Matthew Hann
    Prodigy 40 points

    thank you very much.

  • 0 in reply to Matthew Hann
    Prodigy 40 points

    Hi Matt,

    this is what I got from my first try. I didn't use exact value as in the schematic because I couldn't get some value like 600p cap. I think it is not bad, I am going to turn the filters.

    by the way do you know where I can bought a similar pre amp board. thanks.

     

    David

     

  • 0 in reply to david sun77940
    TI__Expert 7185 points

    Hi David,

    Unfortunately, we do not have an actual ECG board using this INA333 front end for purchase.

    Matt

  • 0 in reply to Matthew Hann
    Prodigy 40 points

    any other front end amp for ECG is good for me, except 1298.