AC impedance measuring device

• US 8,878,549 B2
• Filed: 03/15/2011
• Issued: 11/04/2014
• Est. Priority Date: 03/16/2010
• Status: Active Grant

• Current Assignee: Yokogawa Electric Corporation
• Original Assignee: Yokogawa Electric Corporation
• Inventors: Nakanishi, Hirofumi, Okada, Shuhei
• Primary Examiner(s): Baldridge, Benjamin M
• Application Number:
  US13/048,029
• Publication Number:
  US 20110227587A1
• Time in Patent Office: 1,330 Days
• Field of Search: 324/649
• US Class Current: 324/649
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables

Abstract

An AC impedance measuring device includes: a signal generator configured to provide a first signal on which a period signal is superimposed to a DUT; a Fourier transform unit configured to perform Fourier transform on current data and voltage data output from the DUT using a transformation window while sequentially shifting a start time of the transformation window, thereby obtaining a plurality of Fourier transform data strings of the voltage data and the current data; a difference sequence calculator configured to sequentially calculate a first difference sequence of the Fourier transform data strings of the voltage data and a second difference sequence of the Fourier transform data strings of the current data; and an impedance calculator configured to calculate an impedance of the DUT based on a ratio of the first difference sequence and the second difference sequence.

Claims

1. An AC impedance measuring device, comprising:

a signal generator that provides a first signal on which a period signal is superimposed to a DUT (device under test);

a Fourier transform unit that performs Fourier transform on current data and voltage data output from the DUT using a transformation window having a time width that is an integral multiple of a period of the first signal, while sequentially shifting a start time of the transformation window, thereby obtaining a plurality of Fourier transform data strings of the voltage data and the current data, wherein at least one of the current data and the voltage data includes a transient response;

a difference sequence calculator that sequentially calculates a first difference sequence of the Fourier transform data strings of the voltage data and a second difference of the Fourier transform data strings of the current data; and

and impedance calculator that calculates an impedance of the DUT based on a ratio of the first difference sequence and the second difference sequence.

2. The device of claim 1,

wherein the Fourier transform unit sequentially shifts the start time of the transformation window in a range of one-sixth to five-sixths of the period of the first signal.

3. The device of claim 1,

wherein the period signal includes a plurality of frequency components, and the impedance calculator calculates the impedance of the DUT for each of the frequency components.

4. The device of claim 2,

wherein the period signal includes a plurality of frequency components, and

the impedance calculator calculates the impedance of the DUT for each of the frequency components.

5. The device of claim 1, further comprising:

a sampling unit that converts the current data and the voltage data output from the DUT into a digital signal based on a sample clock.

6. The device of claim 1, further comprising:

a current data storage unit; and

a voltage data storage unit.

7. The device of claim 1, further comprising:

a display unit that displays the impedance of the DUT.

8. The AC impedance measuring device of claim 1, wherein the difference sequence calculation process of the Fourier transform data strings of the voltage data is obtained by shifting the transformation window and calculating the difference sequences from the Fourier transform data strings repeatedly until the Fourier transform data strings are united into one calculation.

9. The AC impedance measuring device of claim 1, wherein the arithmetic unit sets an operation start time (Step S1), sets the time width of the transformation window (Step S2), acquires the current data and the voltage data as the Fourier transform data used for an operation (Step S3), performs Fourier transform on the acquired current data and voltage data (Step S4), stores a Fourier transform result, creates a Fourier transform data string (Step S5), and repeatedly performs steps S1 to S5 a predetermined number of times while changing the operation start time each time.