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High Frequency High Common Mode Rejection Passive Differential Measurement Probe

IP.com Disclosure Number: IPCOM000085055D
Original Publication Date: 1976-Feb-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Simonic, RB: AUTHOR [+2]

Abstract

This probe provides the capability of measuring node voltage where common mode (CM) noise is much higher than the differential signal (DM) to be measured. Since the probe utilizes passive components, it can be applied to the measurement of high-level transient circuit noise that could damage active circuits.

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High Frequency High Common Mode Rejection Passive Differential Measurement Probe

This probe provides the capability of measuring node voltage where common mode (CM) noise is much higher than the differential signal (DM) to be measured. Since the probe utilizes passive components, it can be applied to the measurement of high-level transient circuit noise that could damage active circuits.

In the drawing, the CM noise is represented by generator 1 and generator 2 is the source of the difference voltage o be measured between nodes 3a and 3b by probe 4. A balanced current transformer 5 produces a signal that is conveyed to the hybrid junction 13 via externally shielded cable 7.

The probe load presented to nodes 3a and 3b is represented by the critically balanced, capacitor oupled resistor at 6. This resistor is fixed in value within a narrow range to maximize the probe response linearity, i.e., to minimize the reactive loading effect of distributed stray shunt capacitance and wiring distributed series inductance.

The source impedance at generator 2 may be determined by making two voltage measurements utilizing two resistor's values at 6. A probe loading correction factor is applied, if required, to obtain the true voltage V(DM).

A radio-frequency bonding strap 8 connects shield 10 to the reference ground plane 9, in order to minimize the voltage coupling effect through unavoidable stray capacitance among probe elements 10, 4, 5 and the signal output line 7. Hybrid ju...