Active autoranging current sensing circuit
AssigneeKeithley Instruments, LLC
InventorsWayne C. Goeke, Martin J. Rice
Life of this patent
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Abstract
A range-changing circuit for a measurement device having a desirable range includes an array of graduated impedances. And amplifier supplies an electrical voltage to at least one of the impedances of the array. A voltage sensing and limiting switch is provided in a feedback path of the amplifier. The switch limits said electrical voltage supplied to said at least one of the impedances in response to a sensed voltage that is sensed by the switch. An electrical voltage in the desirable range is developed across a different one of the impedances of the array based on an operation of the switch.
Claims13
A range-changing circuit for a measurement device having a desirable range, said range-changing circuit comprising:
- an array of graduated impedances;
- a first amplifier, wherein the first amplifier supplies an electrical voltage to at least one of the impedances of the array;
- a voltage sensing and limiting switch in a feedback path of the first amplifier;
- and
- a second amplifier,
- the switch being operable to limit said electrical voltage supplied to said at least one of the impedances in response to a sensed voltage that is sensed by the switch and to develop an electrical voltage in the desirable range across a different one of the impedances of the array based on an operation of the switch, and
- wherein the second amplifier, based on said operation of the switch, supplies electrical current to said different one of the impedances when the electrical voltage in the desirable range is developed across said different one of the impedances.
A measurement system for performing measurements on a device under test, the system comprising:
- a source-measure unit for selectively supplying a voltage signal to the device under test in a first operating mode and a current signal to the device under test in a second operating mode;
- and
- an automatically range-changing current-to-voltage converter circuit having a desirable voltage range, said converter circuit including:
- an array of graduated impedances;
- a first amplifier, wherein the first amplifier supplies an electrical voltage to at least one of the impedances of the array;
- and
- a voltage sensing and limiting switch in a feedback path of the first amplifier;
- and
- a second amplifier,
- the switch being operable to limit said electrical voltage supplied to said at least one of the impedances in response to a sensed voltage that is sensed by the switch and to develop an electrical voltage in the desirable voltage range across a different one of the impedances of the array based on an operation of the switch, and
- wherein the second amplifier, based on said operation of the switch, supplies electrical current to said different one of the impedances when the electrical voltage in the desirable voltage range is developed across said different one of the impedances.
A range-changing circuit for a feedback-type current measurement device having a desirable range, comprising:
- an array of impedance elements in serial relationship, the impedance value of said impedance elements progressively ranging from an upstream high value to a downstream low value;
- and
- a voltage-sensing driver for each of an upstream and a downstream impedance element in said array, wherein the voltage-sensing driver for the upstream impedance element drives current through the upstream impedance element and any downstream impedance elements unless a voltage limit is sensed by the voltage sensing driver for the upstream impedance element and when the voltage limit is sensed, the voltage-sensing driver for the downstream impedance element switches from an off mode and drives current through the downstream impedance element and any additional downstream impedances, the circuit thereby providing said desirable range.
Dependencies are inferred from the claim text.