Electronic probe for measuring high impedance tri-state...

Electricity: measuring and testing – Testing potential in specific environment – Voltage probe

Reexamination Certificate

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Details

C324S149000, C324S754090

Reexamination Certificate

active

06175228

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to test and measurement instruments and more particularly to a probe having low impedance at high frequencies and high impedance at low frequencies.
BACKGROUND OF THE INVENTION
A typical measurement device designed to analyze tri-state logic systems which includes a low impedance probe (i.e., the probe is low impedance at all frequencies) will cause a floating data bus to be “tri-stated” when the probe is attached to the bus. That is, high speed, low impedance (~50 ohm) bus structures may tri-state to high impedances when a drive stops driving the bus. The low impedance probe may pull down the line depending on the value of the pull up resistors.
SUMMARY OF THE INVENTION
The present invention provides an improved probe for probing high speed, low impedance bus structures, for example. The probe comprises an AC termination portion and an RCR filter. In a first embodiment, the AC termination portion comprises a resistor and capacitor in series. The time constant formed by the AC termination portion is sufficiently larger than the time it takes a signal to travel through the cable of the probe. In a second embodiment, the resistor and capacitor are joined in series by an inductor in order to control the peak response of the probe.
The RCR filter comprises two resistors in series disposed between the AC termination resistor and ground. A capacitor is connected in parallel to the first resistor in order to achieve a flat pulse response from DC through to high frequencies.


REFERENCES:
patent: 4743839 (1988-05-01), Rush
patent: 5107201 (1992-04-01), Ogle
patent: 5172051 (1992-12-01), Zamborelli

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