Patent ID: 6054867
Filing Date: 2000-04-25
Classification: G01R

Abstract:
A method for stabilizing a feedback loop in impedance measuring equipment, said impedance measuring equipment having means for applying a measurement voltage to a first measurement terminal of a device under test (DUT), a feedback loop for receiving a current that flows out a second terminal of said DUT, means for measuring transmission characteristics of said feedback loop, and a variable phase shifter for adjusting a phase shift within said feedback loop, wherein a current flowing through said DUT is measured while holding said second measurement terminal at an electrical potential close to ground, comprising the steps of:a) measuring transmission characteristics of said feedback loop for at least three impedance standards connected across said first and second measurement terminals, said impedance standards having impedance values spanning a range of DUT impedances;b) calculating a phase shift amount based on measurement results for said three impedance standards obtained in step a); andc) applying said phase shift amount to said variable phase shifter so as to modify the phase shift amount in said feedback loop, said phase shift amount applied to said feedback loop so as to maintain stability of said feedback loop over an entire said range of DUT impedances.