EKG ECG Amplifier with Right Leg Drive Explained

An Electrocardiogram or ECG Amplifier with Right Leg Drive is explained in this video which is the 209th example in my Analog Circuit Playlist. The first stage of a differential instrumentation amplifier is designed to provide a programmable gain using a number of 1% precision resistors and a 10k Ohm potentiometer that can adjust the differential gain between 6x to 201x for the desired ECG or EKG signal. The third op amp is designed to operate as a low pass inverting amplifier driving the right leg of the patient with 3dc cut off frequency of bandwidth of 125 Hz to amplify the unwanted common mode interference (for example 60 Hz main power interference). The feedback amplifier has a voltage gain of -20x in this design resulting in overall gain of 1/21 or basically an attenuation of 21x for the unwanted common interference.