Medical cable authentication apparatuses and methods are disclosed. Some embodiments herein provide a medical cable assembly for use in a patient monitoring system including authentication circuit. The authentication circuit can provide a signal indicative of whether the medical cable assembly is compatible, or desirable for use with a particular patient monitor and/or sensor. The authentication circuit can include a substantially constant current source that drives a capacitor, wherein a voltage signal provided by a patient monitor drives the current source, and the voltage across the capacitor is used to generate an authentication output signal.
