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ADS1292RECG-FE: LEAD 1 Derivation with ADS1292-FE Eval Board and Channel usage?

Frank Roberts
Intellectual 355 points
Part Number: ADS1292RECG-FE
Other Parts Discussed in Thread: ADS1292, ADS1292R

Hello,

  I am a bit confused as to how the ADS1292R-FE Eval board produces a LEAD 1 ECG waveform based on the configuration in the schematic.  Possibly part of this misunderstanding is simply a lacking of understanding of how LEAD generation is actually performed. 

The schematic shows the following electrodes going into Channel2 with a 51Kohm & 47pF Cap RC filter in between the Electrode and the ADC input.

ELA =>  IN2P

ERA => IN2N

LEAD 1 = RA-LA

So the assumption is that simply by reading Ch2 we should get what is referred to as LEAD 1, correct?

Secondarily on CH1 of the ADC ELA and ERA are fed into IN1P and IN1N respectively though the signals fed into CH1 have what appear to be a Bias circuit as there is are 2 10M Resistor 1 attached to AVDD and the other attached to GND. 

1) What is CH1 actually used for is it part of the Respiration Calculation?  Is the purpose of the 10M Resistors on the Eval board to provide a Bias?  If so why wouldn't the RLD be used? 

2) Then the CH1 electrode signals for ELA/ERA are connected to IN3P and IN3N respectively.  So my assumption is somehow CH1 is used in conjunction with CH3 ADC Data to provide a valid respiration output. 

I have read through both the ADS1292 datasheet, the ADS1292R-FE User Manual way too many times and it seems like there is just some significant gaps in explanation as to how the ADS1292R and ADS1292R-FE Eval boards work and the signal/outputs that should be used to come up with the various ECG related data.

Regards,

Frank

  • 0
    TI__Mastermind 38745 points

    Hello Frank,

    You are correct. The leads can be generated by simply measuring the voltage between two electrodes so when channel 2 measures LA-RA, the output is Lead I.

    1. It is not as much of a calculation as it is an excitation circuit. I think after you read this app note and then re-read the section on respiration measurement in the datasheet, you will have a better understanding of how that works. Essentially those passive components are ac coupling because the signal that channel 1 is measuring is an amplitude modulated ac carrier square wave. You don't want to use RL as the bias if you are using it in its loop functionality because then it will contain some inverted common-mode signal on it rather than ac ground.
    2. IN3P and IN3N are also the RESP_MODP and RESP_MODN pins and in this application they are serving the function of the excitation source. You will understand their function better after reading that app note.

    Regards,

    Brian Pisani