Hewlett-Packard Company

Heinz Sommer

Stefan Traub

Joachim Vester

A receiver or preamplifier for differential signals, in particular electrocardiogram signals, includes n electrodes to provide at least one signal at an acceptable common mode rejection ratio, even if the subject to which the electrodes are applied has a different ground potential than the assigned monitor. This is achieved by two current sources which are controlled by a sum signal representing a sum of the electrode signals, said current sources injecting a corresponding current into the electrodes.

Receiver for differential signals with means for adjusting a floating

An adapter cable is used for connecting a pulsoximetry sensor unit to a medical measuring device. The pulsoximetry sensor unit comprises, among other components, two antiparallel-connected, light-emitting diodes, which are activated alternatingly by a pulse current source of the medical measuring device. Between said pulsoximetry sensor unit and said medical measuring device, a plurality of grounding lines extend within the adapter cable. In the case of a short circuit between one of the two supply lines of the antiparallel-connected, light-emitting elements and one of the grounding lines, the fault current is caused to flow in the grounding lines to a first node in accordance with the present invention, said first node being adapted to be connected to a reference potential of the medical measuring device via a first resistor. The voltage drop across said first resistor will cause firing of a thyristor structure, if a limit value is exceeded, provided that the instantaneous control phase of the pulse current source of the medical measuring device can cause an activation of a predetermined element of the two light-emitting elements. The triggered thyristor circuit will cause an activation of a switch, which will establish a shunt to the light-emitting elements.

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Boeblingen, Germany

Heinz Sommer