Pulse-based impedance measurement instrument

• US 5,633,801 A
• Filed: 10/11/1995
• Issued: 05/27/1997
• Est. Priority Date: 10/11/1995
• Status: Expired due to Fees

• Current Assignee: Fluke Corporation (Fortive Corp.)
• Original Assignee: Fluke Corporation (Fortive Corp.)
• Inventors: Bottman, Jeffrey S.
• Primary Examiner(s): Ramirez, Ellis B.
• Assistant Examiner(s): DAM, TUAN QUANG
• Application Number:
  US08/540,927
• Time in Patent Office: 594 Days
• Field of Search: 364/481-482, 364/484, 364/486, 364/571.01, 364/571.02, 364/571.04, 324/512, 324/519-522, 324/525, 324/527, 324/600, 324/601, 324/612, 324/615-617, 324/638-639, 324/641, 324/649, 324/650, 324/654, 324/658
• US Class Current: 702/65
• 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 31/11 using pulse reflection methods
• CPC Class Codes: H04L 43/50 Testing arrangements

Abstract

In accordance with the present invention, a pulse-based impedance measurement instrument is provided. A pulse generator repetitively generates a stimulus pulse to a device under test (DUT). A digitizer circuit, consisting of a sample-and-hold circuit, an analog to digital converter, and acquisition memory, repetitively samples the response voltage across the DUT to create a time record of the voltage as a function of time during a pulse response measurement. Each time record is operated on by a Fast Fourier Transform (FFT) which converts the voltage versus time information into voltage versus frequency information in a manner well known in the art. By measuring a set of calibration resistors with known resistance values to generate a set of complex calibration constants, the impedance measurement instrument provides measurements of complex impedance and return loss versus frequency of a DUT.

Claims

1. A pulse-based impedance measurement instrument, comprising:

(a) an instrument connector for coupling to a device under test;

(b) a pulse generator coupled to said instrument connector for generating stimulus pulses to said device under test;

(c) a digital sampling circuit coupled to said instrument connector for receiving and sampling a response signal from said device under test to provide digital measurement values;

(d) an acquisition memory coupled to said sampling circuit for receiving and storing said digital measurement values to form a time record of said response signal;

(e) a microprocessor coupled to said acquisition memory to receive said time record, wherein said microprocessor;

performs a fast Fourier transform on said time record to obtain a frequency domain representation, and

calculates a set of complex impedance values of said device under test using said frequency domain representation and a set of calibration constants derived from measurements of a set of calibration resistors; and

(f) a display coupled to said microprocessor to visually display said set of complex impedance values.

2. A pulse-based impedance measurement instrument according to claim 1 wherein:

said stimulus signal is repetitively generated, and

said time record is acquired by repetitive digital sampling of said response signal.

3. A pulse-based impedance measurement instrument according to claim 1 wherein:

said microprocessor calculates a set of return loss values from said set of complex impedance values; and

said display visually displays said set of return loss values.

4. A pulse-based impedance measurement instrument, comprising:

(a) an instrument connector for coupling to a device under test;

(b) a pulse generator coupled to said instrument connector for repetitively generating stimulus pulses across said device under test;

(c) a digital sampling circuit coupled to said instrument connector for repetitively sampling a response signal from said device under test at selected time delays from said stimulus pulse and providing digital measurement values;

(d) an acquisition memory coupled to said digital sampling circuit for receiving said digital measurement values, said acquisition memory storing said digital measurement values in memory locations corresponding to said selected time delays to build a time record of said response signal;

(e) a microprocessor coupled to said acquisition memory to receive said time record, wherein said microprocessor;

performs a fast Fourier transform on said time record to obtain a frequency domain representation, and

calculates a set of complex impedance values of said device under test using said frequency domain representation and a set of calibration constants derived from measurements of a set of calibration resistors; and

(f) a display coupled to said microprocessor to visually display said set of complex impedance values.

5. A pulse-based impedance measurement instrument according to claim 4 wherein:

said microprocessor calculates a set of return loss values from said set of complex impedance values; and

said display visually displays said set of return loss values.

6. A pulse-based method of measuring complex impedance, comprising:

(a) measuring a plurality of calibration resistors to obtain calibration time records;

(b) calculating a fast Fourier transform of each of said calibration time records to produce a plurality of calibration frequency domain representations;

(c) calculating a set of calibration constants from said calibration frequency domain representations;

(d) measuring a device under test to produce a time record;

(e) calculating a fast Fourier transform of said time record to produce a frequency domain representation;

(f) calculating a set of complex impedance values from said frequency domain representation and said set of calibration constants; and

(g) visually displaying said set of complex impedance values.

7. A pulse-based method of measuring complex impedance according to claim 6 further comprising:

(a) repetitively generating a stimulus pulse to said device under test; and

(b) repetitively sampling a response signal from said device under test to obtain said time record.

8. A pulse-based method of measuring complex impedance according to claim 6 further comprising:

calculating a set of return loss values from said set of complex impedance values; and

visually displaying said set of return loss values.