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心电信号是取自人体的生物电差模信号,它通常伴随有较大的噪声背景电压。混杂进心电信号的噪声电压主要是50赫芝市电干扰电压,它来源于心电图测量现场周围的市电供电线路和各种耗电仪器设备。一个未经接地的人体可能感应有几伏以至十几伏的50赫芝电压。即使将人体右腿接地,50赫芝干扰电流在流经有限的接地电阻时,仍然会使人体具有一定的50赫芝干扰电压。对心电放大器而言,这种干扰电压是共模信号电压。因此,为了在放大心电信号的同时也能有效地抑制50赫芝共模干扰电压,必须力求提高心电放大器的共模抑制比CMRR。
ECG signal is taken from the body’s bioelectric differential mode signal, which is usually accompanied by a larger noise background voltage. The noise voltage mixed into the ECG is mainly the 50 Hz interference voltage, which is derived from the mains supply lines and various power-consuming equipment around the ECG measurement site. An ungrounded human body may sense a 50 Hertz voltage of a few volts or even ten volts. Even with the human right leg grounded, a 50 Hertz interference current still causes the human body to have a certain 50 Hz interference voltage when flowing through a limited ground resistance. For ECG amplifiers, this interference voltage is the common mode signal voltage. Therefore, in order to amplify the ECG signal while effectively suppressing the 50 Hz common mode interference voltage, we must strive to improve the CMRR of the cardiac amplifier.