Low frequency impedance measurement with source measure units

• US 9,829,520 B2
• Filed: 08/22/2011
• Issued: 11/28/2017
• Est. Priority Date: 08/22/2011
• Status: Active Grant

• Current Assignee: Keithley Instruments, Inc.
• Original Assignee: Keithley Instruments, Inc.
• Inventors: Sobolewski, Gregory
• Primary Examiner(s): NATALINI, JEFF WILLIAM
• Application Number:
  US13/214,693
• Publication Number:
  US 20140145729A1
• Time in Patent Office: 2,290 Days
• Field of Search: 324713
• 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 27/025 Measuring very high resistances, e.g. isolation resistances, i.e. megohm-meters

Abstract

A method for measuring the impedance of a DUT having a capacitance of less than 1 pF includes applying a voltage or current signal to the DUT, the voltage or current signal including an AC component having a non-zero frequency of less than 1 kHz; monitoring a current or voltage signal, respectively, through the DUT in response to the voltage or current signal; digitizing the voltage signal and the current signal synchronously; and calculating the impedance from the digitized voltage and current signals.

Claims

1. A method for measuring the impedance of a DUT having a capacitance of less than 1 pF, said method comprising:

applying a voltage signal produced by a first source measure unit to said DUT, said voltage signal including an AC component having a non-zero frequency of less than 1 kHz;

monitoring with a second source measure unit a current signal through said DUT in response to said voltage signal;

digitizing said voltage signal and said current signal synchronously; and

calculating said impedance from said digitized voltage and current signals, wherein said second source measure unit adds a DC bias voltage to said voltage signal and the difference of the voltage signal and the DC bias voltage is applied through a second source measure unit sensing impedance resulting in said current signal being forced through said DUT by said source measure units.