Differential amplifiers are used in many laboratories to record bioelectrical activity of various parts of the auditory system. Calibration of the amplifier gain factor should be a frequent, routine procedure to insure against unsuspected errors in measurement. Especially where the biological signal is very small, as in recording the alternating current cochlear potential, such errors may loom relatively large.
Calibration of the gain of a differential amplifier cannot be done until the differential balance is properly adjusted. The first step, therefore, is to obtain proper differential balance, and this is done by optimizing common mode rejection (CMR). In order to facilitate routine checks of both CMR and gain factor, we here present a simple procedure which utilizes equipment standard in most auditory laboratories. The equipment consists of: (1) oscillator, (2) precision dB attenuator, and (3) oscilloscope or precision voltmeter.
Adjusting Common Mode Rejection
Differential amplifiers optimize the signal-to-noise ratio by
Meikle MB, Copeland AB. Calibration of Differential Amplifiers Used in Biological Recording. Arch Otolaryngol. 1973;98(1):66–67. doi:10.1001/archotol.1973.00780020070019
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