Impairment of common mode rejection by mismatched electrode impedances: Quantitative analysis
Impairment of common mode rejection by mismatched electrode impedances: Quantitative analysis
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DOI：
10.1080/00029238.1995.11080527
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发表时间：
1995-12-01
期刊：
影响因子：
--
通讯作者：
Legatt, AD
中科院分区：
文献类型：
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作者：
Legatt, AD
即使电极阻抗较低，输入电极阻抗不匹配也会导致EEG和诱发电位记录出现噪声。本文对这一现象进行了定量分析，并举例说明：在每个放大器输入端，记录电极阻抗和放大器输入阻抗形成一个分压器。当输入电极阻抗不相等时，在患者身体两个位置上同等存在的共模信号在放大器的两个（反相和同相）输入端以不同幅度出现。因此，共模信号的一部分被放大，就好像它是差分信号一样。放大器的有效共模抑制比（CMRR）降低到一个值，该值可以用数学方法表示为放大器的理想CMRR、输入阻抗和两个输入电极之间的阻抗差的函数。当环境电噪声水平通常很高时，平衡的输入电极阻抗在术中监测中尤为重要。不同类型的记录电极之间的记录（例如，在针和金属杯表面电极之间）可能产生阻抗失配，从而产生噪声记录。
Mismatched input electrode impedances can lead to noisy EEG and evoked potential recordings even if the electrode impedances are low. This paper presents a quantitative analysis of the phenomenon and illustrative examples.At each amplifier input, the recording electrode impedance and the amplifier's input impedance form a voltage divider. When input electrode impedances are unequal, a common mode signal that is present equally at the two locations on the patient's body appears at different magnitudes at the two (inverting and noninverting) inputs of the amplifier,. thus, part of the common mode signal is amplified as if it were a differential signal. The effective common mode rejection Patio (CMRR) of the amplifier is reduced to a value that can be expressed mathematically as a function of the amplifier's ideal CMRR, its input impedance, and the impedance difference between the two input electrodes.Balanced input electrode impedances are particularly important during intraoperative monitoring, when ambient electrical noise levels are typically high. Recordings between different types of recording electrodes (e.g., between needle and metal cup surface electrodes) are likely to produce impedance mismatches, and thus noisy recordings.