Hewlett-packard Corporation

Hewlett-packard Company

Stefan Traub

Frank Rochlitzer

Heinz Sommer

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

In a four element modified bridge circuit for measurement purposes at least one impedance element is variable according to a magnitude to be measured. Via a first operational amplifier a DC supply voltage is connected across two bridge nodes facing each other, and at the other two nodes facing each other an output signal is delivered corresponding to the magnitude to be measured. By means of a second operational amplifier one of the output nodes is virtually drawn to ground so that the signal at the second output bridge node is referenced to ground. Thus, the signal at the second output node corresponds to the desired measured magnitude without a superimposed power supply voltage and may be amplified by a third standard operational amplifier without the need of a differential amplifier circuit.

Modified bridge circuit for measurement purposes

A linear regulated D.C. power supply includes two control elements for regulating two separate unregulated D.C. voltage sources. An enabling means is used to enable the one of the two control elements which is operating at the lower instantaneous power dissipation level and to supply the regulated output of that selected control element to a load.

Regulated power supply

A circuit for converting a triangular waveform into a sinusoidal waveform using the non-linear transfer characteristic of a first transistor differential amplifier. Second and third differential amplifiers are parallel-connected to said first differential amplifier with the slopes of their transfer characteristics in opposite sense thereto and having their operating points shifted on their transfer characteristics in opposite directions with regard to each other and symmetrically to the operation point of said first differential amplifier so that the resulting overall transfer characteristic of said first, second and third differential amplifiers has zero slope at the extremal amplitudes of said triangular waveform.

Sine-shaping circuit

An input circuit for electronic instruments, particularly measuring instruments, has an input for an input signal with a DC and an AC component and has an output for connection to the electronic instrument. A direct current or direct voltage source is provided, and a compensating circuit compensates the DC component of the input signal in such a way that the AC component is isolated and presented at the output. The compensating circuit is basically an impedance network consisting of three resistors connected in a .pi.-style with the two outer resistors being connected to direct voltage or direct current sources which are jointly variable in such a way that they cancel each other at the input and the DC component of the input signal can be compensated at the output.

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Boblingen, Germany

Stefan Traub