matin-kh
Member level 3
Hi,
I have a question regarding the below circuit.
The circuit below is for measuring ECG and at the same time it wants to measure the mismatched impedance of the electrodes connected to the body by adding a common mode signal "Vadd" in the positive input of the DRL opamp OPDRL. In the related paper it says:
"The measurement circuit operates as follows: Any voltage appearing at the positive input of the DRL opamp OPDRL forces the DRL loop to react in such a way that the differential input voltage of the DRL opamp is again zero. For a sinusoidal signal this is true as long as the frequency remains within the bandwidth of the DRL loop. As a result, the sinusoidal voltage Vadd appears as a common mode voltage to the input of the differential amplifier. This additional common mode voltage is rejected by the CMRR of the instrumentation amplifier. Except for the part which is converted to a differential signal by the electrode-skin impedance mismatch (potential divider effect) and amplified by the differential mode gain of each instrumentation amplifier."
I cannot understand the red sentences. What is the bandwith of the DRL loop? and why the signal frequency sould remain with this bandwith?
Thanks
I have a question regarding the below circuit.
The circuit below is for measuring ECG and at the same time it wants to measure the mismatched impedance of the electrodes connected to the body by adding a common mode signal "Vadd" in the positive input of the DRL opamp OPDRL. In the related paper it says:
"The measurement circuit operates as follows: Any voltage appearing at the positive input of the DRL opamp OPDRL forces the DRL loop to react in such a way that the differential input voltage of the DRL opamp is again zero. For a sinusoidal signal this is true as long as the frequency remains within the bandwidth of the DRL loop. As a result, the sinusoidal voltage Vadd appears as a common mode voltage to the input of the differential amplifier. This additional common mode voltage is rejected by the CMRR of the instrumentation amplifier. Except for the part which is converted to a differential signal by the electrode-skin impedance mismatch (potential divider effect) and amplified by the differential mode gain of each instrumentation amplifier."
I cannot understand the red sentences. What is the bandwith of the DRL loop? and why the signal frequency sould remain with this bandwith?
Thanks