Impairment of common mode rejection by mismatched electrode impedances

Quantitative analysis

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

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 ratio (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.

Original languageEnglish (US)
Pages (from-to)296-302
Number of pages7
JournalAmerican Journal of EEG Technology
Volume35
Issue number4
StatePublished - 1995

Fingerprint

Electric Impedance
Electrodes
Intraoperative Monitoring
Evoked Potentials
Needles
Noise
Electroencephalography
Metals

Keywords

  • Amplifiers
  • artifacts
  • common mode rejection ratio
  • electrodes
  • impedance
  • intraoperative neurophysiologic monitoring

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

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title = "Impairment of common mode rejection by mismatched electrode impedances: Quantitative analysis",
abstract = "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 ratio (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.",
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TY - JOUR

T1 - Impairment of common mode rejection by mismatched electrode impedances

T2 - Quantitative analysis

AU - Legatt, Alan D.

PY - 1995

Y1 - 1995

N2 - 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 ratio (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.

AB - 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 ratio (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.

KW - Amplifiers

KW - artifacts

KW - common mode rejection ratio

KW - electrodes

KW - impedance

KW - intraoperative neurophysiologic monitoring

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