Hi,
Please correct me if I am wrong.
In the datasheet, the Right Leg Drive amplifier input is dervied from the ECG signals after the differential PGA. By doing so, most of the common mode noise (mainly supply noise) would have been removed by the differential PGA since differential amp will also removed common mode noise. So the input to the RLD amplifier, which is the output of the differential PGA, will have very little common mode noise. Using the output of the PGA to drive the RLD will means that the gain of the RLD needs to be very high to have a meaningful common mode noise cancellation.
For our previous design, we usually derived the RLD amp inputs from the inverted WCT. The WCT is derived directly from the ECG leads so the common mode noise will be quite large and more representative of the actual common mode noise in the environment.
Based on the above, it seems that the RLD amp is not a good candidate for common mode noise cancellation. Can you advise any advantage of using the on chip RLD amplifier instead of using the WCT with external inverter opamp ?
