Impedance measuring instrument

• US 8,896,331 B2
• Filed: 02/01/2008
• Issued: 11/25/2014
• Est. Priority Date: 02/01/2008
• Status: Active Grant

• Current Assignee: Keithley Instruments, Inc.
• Original Assignee: Keithley Instruments, Inc.
• Inventors: Niemann, James A.
• Primary Examiner(s): Valone, Thomas F
• Application Number:
  US12/024,721
• Publication Number:
  US 20090195261A1
• Time in Patent Office: 2,489 Days
• Field of Search: None
• US Class Current: 324/713
• CPC Class Codes: G01R 27/02 Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant by measuring phase angle only G01R25/00
• CPC Class Codes: G01R 27/16 Measuring impedance of element or network through which a current is passing from another source, e.g. cable, power line

Abstract

A measurement instrument for measuring the impedance of a device under test (DUT) includes a first source of either a voltage or a current and a second source of either a voltage or a current, wherein the first source is connectable in a first feedback relationship with the DUT and the second source is connectable in a second feedback relationship with both the DUT and the first source. The first and second sources are operated respectively as a current source responsive to the current through the DUT and a voltage source responsive to the voltage across the DUT or operated respectively as a voltage source responsive to the voltage across the DUT and a current source responsive to the current through the DUT. The second feedback relationship has a narrower bandwidth than the first feedback relationship. The resulting voltage across the DUT and the current through the DUT establish the measured impedance of the DUT.

Claims

1. A measurement instrument for measuring the impedance of a device under test (DUT), said instrument comprising:

a first source of either a voltage or a current; and

a second source of either a voltage or a current, wherein the first source is connectable in a first feedback relationship with said DUT and said second source is connectable in a second feedback relationship with said DUT, said first feedback relationship being contained within said second feedback relationship, said first and second sources being operated respectively as a current source responsive to the current through the DUT and a voltage source responsive to the voltage across the DUT or operated respectively as a voltage source responsive to the voltage across the DUT and a current source responsive to the current through the DUT, said second feedback relationship having a narrower loop bandwidth than said first feedback relationship, the resulting voltage across the DUT and the current through the DUT establishing the measured impedance of the DUT.

2. A measurement instrument according to claim 1, wherein said DUT is a solar cell, said first source is a current source and said second source is a voltage source.

3. A measurement instrument according to claim 1, wherein said DUT is a motor, said first source is a voltage source and said second source is a current source.

4. A measurement instrument according to claim 1, wherein said second source provides a DC operating point for said DUT.