A method of producing a diode drive current in an oximeter includes sensing
at least a part of a current passing through the diode and converting the
sensed current to a sensed voltage, inputting the sensed voltage to a
feedback amplifier for stabilizing the current passing through the diode,
and eliminating an offset voltage across inputs of the feedback amplifier.
A pulse oximeter includes a diode for emitting light flashes, a feedback
amplifier having inputs, a feedback capacitor, and an output, the feedback
amplifier stabilizing a current passing through the diode, a nulling
amplifier having inputs, a nulling capacitor, and an output, the nulling
amplifier charging and discharging the feedback capacitor until the inputs
of the feedback amplifier are at a same voltage. The operation may include
synchronizing an elimination of input offset voltages of the feedback and
nulling amplifiers with on or off state of diode current.
