Vector ammeter having digital signal processing unit

• US 4,935,692 A
• Filed: 11/30/1988
• Issued: 06/19/1990
• Est. Priority Date: 11/30/1987
• Status: Expired due to Term

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Wakasugi, Tomio
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): Harvey, Jack B.
• Application Number:
  US07/278,134
• Time in Patent Office: 566 Days
• Field of Search: 324/62, 324/64, 324/57 R, 324/123 R, 324/123 C, 324/99 D, 324/99 R
• US Class Current: 324/607
• 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

Abstract

An improved type of vector impedance measuring instrument is disclosed. The vector impedance is a vector current relative to (or normalized to) a pertinent voltage. A transducer for converting the impedance to corresponding current and voltage includes a digital signal processing unit. The vector value of the current is derived from parameter values set in the digital signal processing unit. This configuration eliminates a conventional vector ratio detector, which conventionally followed the transducer, saves cost, reduces size, and achieves high performance. Also, algorithms implemented in the digital signal processing unit are easily modified for a variety of transfer functins phase compensation, and corrections.

Claims

1. A vector ammeter comprising:

a source for producing an AC reference signal;

means for coupling the AC reference signal to a device being measured to produce an AC measurement signal;

an amplifier having an input to which the AC measurement signal is applied;

an analog-to-digital converter having an input connected to an output of the amplifier;

digital signal processing means having an input connected to an output of the analog-to-digital converter, the digital signal processing means for decomposing the AC measurement signal into two quadrature components corresponding to the real and imaginary parts of the AC measurement signal;

at least one digital-to-analog converter having an input connected to an output of the digital signal processing means;

the amplifier, the analog-to-digital converter, the digital signal processing means, and the digital-to-analog converter being connected in cascade to constitute a forward amplification portion; and

a feedback circuit inserted between an output of the forward amplification portion and the input of the amplifier;

the real and imaginary parts of the AC measurement signal reduced by the digital signal processing means comprising data for determining one of a ratio of the AC measurement signal to the AC reference signal and a vector voltage across the device being measured.

2. The vector ammeter of claim 1 wherein the digital signal processing means comprises:

a pair of digital phase-sensitive detectors having respective inputs connected to the output of the analog-to-digital converter;

means for applying a digital cosine wave to another input of one of the digital phase-sensitive detectors;

means for applying a digital sine wave to another input of the other digital phase-sensitive detector;

the respective phase-sensitive detectors for calculating the product of the respective cosine and sine waves and the output from the analog-to-digital converter;

a pair of accumulators having respective inputs connected to respective outputs of the digital phase-sensitive detectors, the accumulators for digitally integrating signals at the respective outputs of the digital phase-sensitive detectors; and

a pair of gain adjusters having respective inputs connected to respective outputs of the accumulataors, the gain adjusters for setting a selectable gain.

3. The vector ammeter of claim 2 wherein there is a pair of digital-to-analog converters and respective outputs of the gain adjusters of the digital signal processing means are connected to respective inputs of the digital-to-analog converters.

4. The vector ammeter of claim 3 wherein the digital-to-analog converters are quadrant multiplication type digital-to-analog converters and wherein the digital-to-analog converters receive the AC reference signal for energizing the device being measured and a signal shifted in phase by 90 degrees with respect to the AC reference signal, respectively.

5. The vector ammeter of claim 4, further comprising a 90-degree phase shifter connected between the source of the AC reference signal and one of the digital-to-analog converters for producing the signal shifted in phase by 90 degrees with respect to the AC reference signal.

6. The vector ammeter of claim 3, further comprising a timing generator for producing a timing signal in synchronism with the AC reference signal.

7. The vector ammeter of claim 2 wherein the digital signal processing means further comprises:

a pair of demodulating digital modulators having respective inputs connected to respective outputs of the gain adjusters; and

a digital adder having respective inputs connected to respective outputs of the demodulating digital modulators;

an output of the adder being connected to the digital-toanalog converter, the digital-to-analog converter for converting the signal produced by the adder into an AC signal proportional to a reference DC signal.

8. The vector ammeter of claim 7, further comprising a timing generator for producing a timing signal in synchronism with the AC reference signal.

9. A vector ammeter comprising:

a forward amplifier chain which cascades;

(a) amplifier means to which is input an AC current;

(b) analog-to-digital converter means;

(c) digital signal processing means;

(d) digital-to-analog converter means; and

(e) feedback circuit means connected between an output of the digital-to-analog converter means and the input of the amplifier; and

characterized in that the digital signal processing means orthogonally decomposes the AC input current into real and imaginary components;

the real and imaginary components of the AC input current comprising data for determining one of a ratio of the AC input current to an AC reference current and a voltage across a device being measured through which the AC input current flows.

10. The vector ammeter of claim 9 wherein the digital signal processing means comprises:

a pair of digital phase-sensitive detectors having respective inputs connected to an output of the analog-to-digital converter;

means for applying a digital cosine wave to another input of one of the digital phase-sensitive detectors;

means for applying a digital sine wave to another input of the other digital phase-sensitive detector;

the respective phase-sensitive detectors for calculating the product of the respective cosine and sine waves and the output from the analog-to-digital converter;

a pair of accumulators having respective inputs connected to respective outputs of the digital phase-sensitive detectors, the accumulators for digitally integrating signals at the respective outputs of the digital phase-sensitive detectors; and

a pair of gain adjusters havino respective inputs connected to respective outputs of the accumulators, the gain adjusters for seeking a selectable gain.

11. The vector ammeter of claim 10 wherein the digital-to-analog converter means comprises a pair of digital-to-analog coverters and respective outputs of the gain adjusters of the digital signal processing means are connected to respective inputs of the digital-to-analog converters.

12. The vector ammeter of claim 11 wherein the digital-to-analog converters are quadrant multiplication type digital-to-analog converters and wherein the digital-to-analog converters receive the AC reference current for energizing the device being measured and a signal shifted in phase by 90 degrees with respect to the AC reference current, respectively.

13. The vector ammeter of claim 12, further comprising a 90 degree phase shifter connected between a source of the AC reference current and one of the digital-to-analog converters for producing the signal shifted in phase by 90 degrees with respect to the AC reference current.

14. The vector ammeter of claim 11, further comprising a timing generator for producing a timing signal in synchronism with the AC reference current.

15. The vector ammeter of claim 10 wherein the digital signal processing means further comprises:

a pair of demodulating digital modulators having respective inputs connected to respective outputs of the gain adjusters; and

a digital adder having respective inputs connected to respective outputs of the demodulating digital modulators;

an output of the adder being connected to the digital-to-analog converter means, the digital-to-analog converter means for converting the signal produced by the adder into an AC signal proportional to a reference DC signal.

16. The vector ammeter of claim 15, further comprising a timing generator for producing a timing signal in synchronism with the AC reference current.