IMPEDANCE MEASURING CIRCUIT

• US 20130214800A1
• Filed: 01/29/2013
• Published: 08/22/2013
• Est. Priority Date: 10/02/2009
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Inventors: Beck, Riley D., Layton, Kent D., Tyler, Matthew A., Grange, Scott R.
• Granted Patent: US 9,329,216 B2
• Time in Patent Office: Days
• US Class Current: 324/691
• CPC Class Codes: G01R 15/18 using inductive devices, e.g. transformers
• 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
• CPC Class Codes: G01R 27/18 Measuring resistance to earth , i.e. line to ground
• CPC Class Codes: H02H 1/0092 concerning the data processing means, e.g. expert systems, neural networks
• CPC Class Codes: H02H 1/04 Arrangements for preventing response to transient abnormal conditions, e.g. to lightning or to short duration over voltage or oscillations; Damping the influence of dc component by short circuits in ac networks
• CPC Class Codes: H02H 3/33 using summation current transformers H02H3/347 takes precedence

Abstract

A method and circuit for determining a circuit element parameter in a ground fault circuit interrupter circuit. An electrical signal provided to a first node is used to generate another electrical signal at a second node. The electrical signal at the second node is multiplexed with a modulation signal to generate a modulated signal that is then filtered and converted into a digital representation of a portion of the circuit element parameter. The electrical signal at the second node is multiplexed with the modulation signal after it has been phase shifted to produce a modulated signal that is filter and converted into a digital representation of another portion of the circuit element parameter. In another aspect, a slope based solenoid self-test method is used for self-testing in a GFCI circuit. Alternatively, a method for determining a wiring fault is provided using a digital filter.

Claims

1. A single wound single current transformer impedance measurement circuit for determining a circuit element parameter, comprising:

a transconductance amplifier having first and second input terminals and first and second output terminals;

a first detector having first and second input terminals and an output terminal, the first input terminal coupled to the first output terminal of the transconductance amplifier and the second input terminal coupled for receiving a first electrical signal; and

a second detector having first and second input terminals and an output terminal, the first input terminal coupled to the second output terminal of the transconductance amplifier.

2. The single wound single current transformer impedance measurement circuit of claim 1, wherein the first detector detects a real part of an impedance and the second detector detects an imaginary part of the impedance.

3. The single wound single current impedance measurement circuit of claim 1, wherein

the first detector comprises a first modulator having first and second terminals that serve as the first and second input terminals of the first detector and an output terminal;

a first low pass filter coupled to the output terminal of the first modulator, and wherein

the second detector comprises a second modulator having first and second terminals that serve as the first and second input terminals of the first detector and an output terminal; and

a second low pass filter coupled to the output terminal of the first modulator.

4. A circuit parameter measurement circuit, comprising:

a transconductance amplifier having first and second inputs and first and second outputs; and

a first detector having a first input and an output, the first input of the first detector coupled to the first output of the of the transconductance amplifier.

5. The circuit parameter measurement circuit of claim 4, further including a ground to neutral detector having an input and an output, the input coupled to the output of the first detector.

6. The circuit parameter measurement circuit of claim 5, further including a digital filter coupled to the output of the ground to neutral detector.

7. The circuit parameter measurement circuit of claim 6, further including a second detector coupled between the transconductance amplifier and the digital filter.

8. The circuit parameter measurement circuit of claim 4, wherein the detector is an impedance detector.

9. The circuit parameter measurement circuit of claim 8, further including a third detector coupled between the transconductance amplifier and the digital filter.

10. The circuit parameter measurement circuit of claim 9, further including

a switch having first, second, and third terminals and a control terminal, the first terminal coupled to the first input of the transcondutance amplifier and the second terminal coupled for receiving a bias voltage;

and

a stimulus waveform generator coupled to the third terminal of the switch and the control terminal coupled to the digital control circuit.

11. The circuit element parameter network of claim 4, further comprising:

a first converter having an input and a first output, the first input of the first detector coupled to the first output of the first converter; and

a second detector having a plurality of inputs and an output, a first input of the second detector coupled to the first output of the first converter and the second input of the second detector coupled for receiving the first signal.

12. The circuit element parameter network of claim 11, wherein the first detector comprises:

a first modulator having first and second inputs and an output; and

a first low pass filter having an input and an output, the input of the first low pass filter coupled to the output of the first modulator and the output of the first low pass filter serving as the output of the first detector, and the second detector comprises;

a second modulator having first and second inputs and an output;

a phase shifting element having an input and an output, the input serving as the first input of the second detector; and

a second low pass filter having an input and an output, the input of the second low pass filter coupled to the output of the second modulator and the output of the second low pass filter serving as the output of the second detector.

13. The circuit element parameter network of claim 11, wherein the first converter includes a second output and the first detector comprises:

a first switch having a control terminal and first and second terminals, the first terminal coupled to the first output of the first converter;

an inverter having an input coupled for receiving the first electrical signal and an output coupled to the control terminal of the first switch;

a second switch having a control terminal and first and second terminals, the first terminal coupled to the second output of the first converter, the second terminal coupled to the second terminal of the first switch, and the control electrode of the second switch coupled for receiving the first signal;

a first low pass filter having an input commonly connected to the second terminals of the first and second switches and an output, and wherein the second detector comprises;

a phase shifting element having an input and an output, the input coupled to the control terminal of the second switch;

a third switch having a control terminal and first and second terminals, the control terminal of the third switch coupled to the output of the phase shifting element and the first terminal of the third switch coupled to the second output of the converter;

a fourth switch having a control terminal and first and second terminals, the first terminal of the fourth switch coupled to the first terminal of the converter, the second terminal coupled to the second terminal of the third switch;

a second inverter having an input and an output, the input of the second inverter coupled to the control terminal of the third switch and the output of the second inverter coupled to the control terminal of the fourth switch; and

a second low pass filter having an input commonly connected to the second terminals of the third and fourth switches and an output.

14. The circuit element parameter network of claim 4, further including a first converter coupled between the first output of the transconductance amplifier and the first input of the detector.

15. The circuit element parameter network of claim 14, further including a band pass filter coupled between the first converter and the first output of the transconductance amplifier.

16. The circuit element parameter network of claim 14, wherein the first converter is one of a current to voltage converter, an analog to digital converter, or a voltage/current replicator and inverter.

17. The circuit element parameter network of claim 14, wherein the first converter comprises a second output, and further including a second detector having a plurality of inputs and an output, a first input of the second detector coupled to the second output of the first converter and the second input of the second detector coupled for receiving the first signal.

18. The circuit element parameter network of claim 14, wherein the first converter further includes a second output and the first detector further includes a third input coupled to the second output of the first converter, the circuit element parameter network further comprising:

a second converter having an input and first and second outputs, the input of the second converter coupled to the second output of the transconductance amplifier; and

a second detector having a plurality of inputs and an output, a first input of the second detector coupled to the first output of the second converter, a second input of the second detector coupled for receiving the first signal, and the third input of the second detector coupled to the second output of the second converter.

19. The circuit element parameter network of claim 18, wherein the first detector comprises:

a first switch having a control terminal and first and second terminals, the first terminal coupled to the first output of the first converter;

an inverter having an input coupled for receiving the first electrical signal and an output coupled to the control terminal of the first switch;

a second switch having a control terminal and first and second terminals, the first terminal coupled to the second output of the first converter, the second terminal coupled to the second terminal of the first switch, and the control electrode of the second switch coupled for receiving the first signal; and

a first low pass filter having an input commonly connected to the second terminals of the first and second switches and an output, and wherein the second impedance comprises;

a phase shifting element having an input and an output, the input coupled to the control terminal of the second switch;

a third switch having a control terminal and first and second terminals, the control terminal of the third switch coupled to the output of the phase shifting element;

a fourth switch having a control terminal and first and second terminals, the first terminal of the fourth switch coupled to the first terminal of the second converter, the second terminal coupled to the second terminal of the third switch;

a second inverter having an input and an output, the input of the second inverter coupled to the control terminal of the fourth switch and the output of the second inverter coupled to the control terminal of the fourth switch; and

a second low pass filter having an input commonly connected to the second terminals of the third and fourth switches and an output.

20. A circuit element parameter network, comprising:

a transconductance amplifier having first, second, and third inputs and first and second outputs, the first output coupled to a first node;

a first switch having a control terminal and first and second terminals, the first terminal of the first switch coupled to the second output of the transconductance amplifier;

a second switch having a control terminal and first and second terminals, the first terminal of the second switch coupled to the third output of the transconductance amplifier, the second terminal of the second switch coupled to the second terminal of the first switch, and the control terminal of the second switch coupled for receiving a first signal;

an inverter having an input and an output, the input coupled to the control terminal of the second switch and the output coupled to the control terminal of the first switch; and

a first operational amplifier having first and second inputs and an output, the output coupled to a second node and to the second input of the first operational amplifier.

21. The circuit element parameter network of claim 20, wherein the second terminals of the first and second switches coupled to a third node, and further including:

a resistor coupled between the second and third nodes; and

a capacitor coupled between the second and third nodes.

22. The circuit element parameter network of claim 21, further including a single wound single current transformer circuit having first and second terminals, the first terminal coupled to the first node and the second terminal coupled to the second node.

23. The circuit element parameter network of claim 22, further including:

a single wound single current transformer circuit having first and second terminals, the first terminal coupled to the first node and the second terminal coupled to the second node;

a second operational amplifier having first and second inputs and an output, the output coupled to a fourth node;

a third switch having a control terminal and first and second terminals, the first terminal coupled to the first input of the second operational amplifier, the second terminal coupled to the first terminal of the single wound single current transformer;

a first resistor coupled between the first node and the second terminal of the single wound single current transformer; and

a first capacitor coupled between the first and second terminals of the single wound single current transformer circuit.