Apparatus for accurately measuring impedance and method used therein

• US 6,581,016 B1
• Filed: 07/27/1999
• Issued: 06/17/2003
• Est. Priority Date: 07/30/1998
• Status: Expired due to Fees

• Current Assignee: Renesas Electronics Corporation
• Original Assignee: NEC Electronics Corporation (Renesas Electronics Corporation)
• Inventors: Yukawa, Akira
• Primary Examiner(s): Hoff, Marc S.
• Assistant Examiner(s): Barbee, Manuel L.
• Application Number:
  US09/362,011
• Time in Patent Office: 1,421 Days
• Field of Search: 702/57, 702/58, 702/64-66, 702/69, 702/108-112, 702/116, 702/117, 702/118, 702/120, 702/124, 702/126, 702/127, 702/183, 702/185, 702/189, 702/191, 702/195, 324/600, 324/605, 324/76.12, 324/76.52, 324/76.77, 324/76.78
• 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 27/16 Measuring impedance of element or network through which a current is passing from another source, e.g. cable, power line

Abstract

An apparatus for measuring an impedance produces an alternating current from digital codes representative of a sine wave, and converts an ac voltage due to an alternating current flowing into an object to a digital signal; a multiplier successively multiplies the binary values of the digital signal by the binary values of the digital codes representing the sine wave and a cosine wave, an accumulator successively adds the products, and a microcomputer calculates the impedance of the object on the basis of the sums of products, thereby improving the accuracy of the calculating result.

Claims

1. An apparatus for measuring an impedance of an object, comprising:

a port connected to said object;

a periodic signal generator connected to said port, and supplying a first analog signal periodically varied and produced from a first digital signal through said port to said object for generating a second analog signal varied due to said impedance;

a digital signal generator producing a second digital signal from said second analog signal; and

a data processor connected to said periodic signal generator and said digital signal generator, and supplied with said first digital signal and said second digital signal for determining said impedance through multiplication between said first digital signal and said second digital signal.

2. The apparatus as set forth in claim 1, in which said first digital signal represents a series of discrete values on a first periodic wave and another series of discrete values on a second periodic wave different in phase by 90 degrees from said first periodic wave.

3. The apparatus as set forth in claim 2, in which said first periodic wave and said second periodic wave are a sine wave and a cosine wave, respectively.

4. The apparatus as set forth in claim 2, in which said periodic signal generator includes

a memory for storing digital codes representative of a part of said series of discrete values,

a controller repeatedly connected to said memory and reading out said part of said series of discrete values in different orders in a time sharing fashion for producing said first digital signal, and

a digital-to-analog converter connected between said memory and said port for producing an alternating current serving as said first analog signal.

5. The apparatus as set forth in claim 4, in which said part of said series of discrete value is on a quarter of said first periodic wave, and said controller reads out said part of said series of discrete value from one end toward the other end from said other end of said one end, from said one end toward said other end after an inversion of a polarity of said discrete values and from said other end to said one end under said inversion of said polarity.

6. The apparatus as set forth in claim 2, in which said periodic signal generator includes

a memory storing digital codes representative of a part of said series of discrete values,

a controller connected to said memory and repeatedly reading out said part of said series of discrete values in different orders in a time sharing fashion for producing said first digital signal,

a digital-to-analog converter connected between said memory for converting said first digital signal to an analog signal,

a voltage follower connected between said digital-to-analog converter and said port for producing an alternating current voltage serving as said first analog signal from said analog signal.

7. The apparatus as set forth in claim 6, in which said part of said series of discrete value is on a quarter of said first periodic wave, and said controller reads out said part of said series of discrete value from one end toward the other end, from said other end of said one end, from said one end toward said other end after an inversion of a polarity of said discrete values and from said other end to said one end under said inversion of said polarity.

8. The apparatus as set forth in claim 1, in which said digital signal generator includes an analog-to-digital converter connected between said port and said data processor.

9. The apparatus as set forth in claim 8, in which said digital signal generator further includes

a noise source for generating a noise signal representative of an irregular noise, and

a mixer having a first input node connected to said port, a second input node connected to said noise source and an output node connected to said analog-to-digital converter for mixing said second analog signal with said noise signal.

10. The apparatus as set forth in claim 8, in which said port has an output node and an input node connected to said periodic signal generator for supplying an alternating current voltage serving as said first analog signal to said object, and said digital signal generator further includes a resistive element connected between said output node of said object and a constant voltage source for generating a voltage signal varied between both ends thereof, an amplifier having input nodes connected to said both ends, respectively for increasing the magnitude of said voltage signal and an output node connected to said analog-to-digital converter.

11. The apparatus as set forth in claim 1, in which said first digital signal represents a series of discrete values on a first periodic wave and another series of discrete values on a second periodic wave different in phase by 90 degrees from said first periodic wave, and said second digital signal represents a first series of binary values related to a real part of said impedance and a second series of binary values related to an imaginary part of said impedance.

12. The apparatus as set forth claim 11, in which said data processor includes

a multiplier connected to said periodic signal generator and said digital signal generator for multiplying the first series of binary values and said second series of binary values by said series of discrete values and said another series of discrete values for producing first products and second products,

an accumulator connected to said multiplier and accumulating said first products and said second products for producing a first sum of products and a second sum of products,

a first data storage for storing said first sum of products and said second sum of products, and

a computer connected to said register for determining said impedance on the basis of said first sum of products and said second sum of products.

13. The apparatus as set forth in claim 12, in which said computer brings said first sum of products and said second sum of products to a first square and a second square, respectively, calculates the sum of said first square and said second square, and finds a square root of said sum for determining said impedance.

14. The apparatus as set forth in claim 12, in which said data processor further includes a second data storage for separately storing said series of discrete values and said another series of discrete values.

15. The apparatus as set forth in claim 12, in which said accumulator repeats the accumulation over predetermined periods for eliminating noise components from said first sum of products and said second sum of products.

16. The apparatus as set forth in claim 12, in which said series of discrete values has plural sub-series of discrete values on said first periodic wave at different frequencies, respectively, and said another series of discrete values has plural sub-series of discrete values on said second periodic wave at different frequencies.

17. The apparatus as set forth in claim 16, in which said computer determines plural values of said impedance at said different frequencies.

18. A method for measuring an impedance of an object, comprising the steps of:

a) generating a first analog signal from a first digital signal;

b) supplying said first analog signal to said object for producing a second analog signal varied due to said impedance;

c) converting said second analog signal to a second digital signal; and

d) determining said impedance through a multiplication between said first digital signal and said second digital signal.

19. The method as set forth in claim 18, in which said step b) includes the sub-steps of

b-1) supplying said first analog signal to said object for producing a preliminary analog signal varied due to said impedance, and

b-2) mixing a noise signal representative of an irregular noise with said preliminary analog signal for producing said second analog signal.

20. The method as set forth in claim 19, in which said series of discrete values and said another series of discrete values are on plural periodic waves different in frequency and other periodic waves different in phase from said plural periodic waves at 90 degrees, respectively, and said impedance has different values respectively corresponding to the different frequencies.

21. The method as set forth in claim 18, in which said first digital signal represents a series of discrete values on a first periodic wave and another series of discrete values on a second periodic wave, and said second digital signal represents a first series of binary values related to a real part of said impedance and a second series of binary values related to an imaginary part of said impedance, and

said step d) includes the sub-steps of

d-1) multiplying said first series of binary values and said second series of binary values by said series of discrete values and said another series of discrete values for producing first products and second products,

d-2) accumulating said first products and said second products so as to obtain a first sum of products and a second sum of products,

d-3) bringing said first sum of products and said second sum of products to a square and a second square,

d-4) calculating a sum of said first square and said second square, and

d-5) finding a square root of said sum representative of an absolute value proportional to said impedance.