DC decoupled current measurement

Patent metadata

Field	Value
Publication number	US-9594097-B2
Application number	US-201414305562-A
Country	US
Kind code	B2
Filing date	Jun 16, 2014
Priority date	Jun 14, 2011
Publication date	Mar 14, 2017
Grant date	Mar 14, 2017

Abstract

A circuit arrangement for measuring a load current provided to a load via a first load terminal of a load transistor is disclosed. In accordance with one example of the invention, the circuit arrangement includes a sense transistor coupled to the load transistor to provide a sense current representing the load current at a first load terminal of the sense transistor. The first load terminals of the load and the sense transistors are at respective floating electric potentials. A floating sense circuit coupled between the load terminals of sense transistor and load transistor, at least in one mode of operation the sense circuit receives the sense current and provides a floating signal representing the sense current. A non-floating measurement circuit is coupled to the sense circuit via a DC decoupling capacitor for transferring the floating signal representing the sense current to the non-floating measurement circuit. The measurement circuit is configured to provide an output signal representing the floating signal and thus the sense current.

First claim

What is claimed is:

1. A circuit arrangement for measuring a load current provided to a load via a first load terminal of a load transistor, the circuit arrangement comprising:
a sense transistor operatively coupled to the load transistor to provide a sense current representing the load current at a first load terminal of the sense transistor, wherein the first load terminals of the load and the sense transistors are at respective floating electric potentials;
a floating sense circuit operatively coupled between the load terminals of the sense transistor and the load transistor, wherein at least in one mode of operation the sense circuit receives the sense current and provides a floating signal representing the sense current;
a DC decoupling capacitor; and
a non-floating measurement circuit operatively coupled to the sense circuit via the DC decoupling capacitor for transferring the floating signal representing the sense current to the non-floating measurement circuit,
wherein the measurement circuit is configured to provide an output signal representing the floating signal and thus the sense current.

2. The circuit arrangement of claim 1 , wherein the floating sense circuit and the non-floating measurement circuit are configured to transfer the floating signal by switching the DC decoupling capacitor.

3. The circuit arrangement of claim 1 , wherein the floating sense circuit includes a shunt resistor conducting the sense current and switching circuitry configured to connect one terminal of the DC decoupling capacitor either to a first or to a second terminal of the shunt resistor using semiconductor switches.

4. The circuit arrangement of claim 3 , wherein the measurement circuit is configured to apply a defined voltage to the DC decoupling capacitor while coupled to the first terminal of the shunt resistor and to observe a voltage swing at a low side terminal of the DC decoupling capacitor when switching the DC decoupling capacitor from the first terminal of the shunt resistor to the second terminal of the shunt resistor.

5. The circuit arrangement of claim 4 , wherein the measurement circuit includes an analog-to-digital converter configured to convert the voltage swing into a digital output word.

6. The circuit arrangement of claim 1 , further comprising:
a digital register providing a first digital word,
a current output digital-to-analog converter coupled to the sense transistor and configured to set the sense current to a current value representing the first digital word, and
a comparator that is sequentially capacitively coupled to the load terminals of the load transistor and the sense transistor and is configured to compare the potentials at the load terminals,
wherein, in a second mode of operation, a digital register value is iteratively varied until either a matching of the potentials at the load terminals is detected or a maximum number of iterations has been reached.

7. The circuit arrangement of claim 6 , further comprising a coupling capacitor which is connectable, via a controllable switch, between a comparator input and either the load terminal of the sense transistor or the load terminal of the load transistor.

8. The circuit arrangement of claim 6 , wherein the digital register is a successive approximation register.

9. The circuit arrangement of claim 6 , wherein the digital register is varied dependent on a comparator output which is indicative of whether the potentials of the load terminals match or of which potential is higher.

10. The circuit arrangement of claim 9 , wherein the digital register value is increased to increase the digital-to-analog-converter output current when the potential at the load terminal of the sense transistor is higher than of the load transistor, and vice versa.

11. The circuit arrangement of claim 6 , wherein the mode of operation is switched dependent on the potential of the load terminal of the load transistor or the sense transistor.

12. The circuit arrangement of claim 1 , wherein the mode of operation is switched dependent on the potential of the load terminal of the load transistor or the sense transistor.

13. The circuit arrangement of claim 1 , wherein the sense current and the load current are DC currents.

14. A method of measuring a current of a sense transistor coupled to a load transistor, the method comprising:
coupling a first terminal of a coupling capacitor to a first terminal of a shunt resistor coupled between load terminals of the load transistor and the sense transistor during a first time period;
coupling the first terminal of the coupling capacitor to a second terminal of the shunt resistor during a second time period;
measuring a voltage difference between a voltage of a second terminal of the coupling capacitor during the first time period and a voltage of the second terminal of the coupling capacitor during the second time period; and
generating a measurement signal based on the measured voltage difference.

15. The method of claim 14 , wherein generating the measurement signal comprises:
applying an output of a current output digital-to analog converter to the load terminal; and
updating a successive approximation register based on the measured voltage difference.

16. The method of claim 14 , further comprising coupling the load terminal of the sense transistor to a reference node via a first resistor when a voltage difference between the load terminal of the load transistor and the reference node is greater than a threshold voltage.

17. The method of claim 14 , wherein a DC sense current passes through the shunt resistor coupled between load terminals of the load transistor and the sense transistor, respectively, thus causing different potentials at the first and the second terminals of the shunt resistor.

18. A circuit comprising:
a sensing circuit configured to be coupled to an output terminal of a load transistor via a first input terminal, and a load terminal of a sense transistor via a second input terminal, wherein the sensing circuit comprises a switching network configured to selectively couple the first input terminal and a second input terminal to an output node of the sensing circuit; and
a measurement circuit having an input capacitively coupled to an output of the sensing circuit, wherein the measurement circuit is configured to provide an output value indicative of current of the sense transistor.

19. The circuit of claim 18 , further comprising:
a resistor coupled between the first input terminal and the second input terminal; and
a first switch coupled between the resistor and the output node of the sensing circuit, wherein the first switch is configured to be closed when a voltage of the first input terminal is below a threshold voltage.

20. The circuit of claim 19 , wherein:
the switching network is configured to couple a first terminal of the resistor to the measurement circuit via a coupling capacitor during a first time period, and then couple a second terminal of the resistor to the measurement circuit via the coupling capacitor during a second time period; and
the measurement circuit is configured to measure a voltage difference at a terminal of the coupling capacitor between the first time period and the second time period, and generate the output value indicative of current of the sense transistor based on the measured voltage difference.

21. The circuit of claim 18 , further comprising:
a current generator having an current output coupled to the second input terminal;
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Assignees

• Infineon Technologies Ag

Inventors

• Bogner Peter
• Petruzzi Luca

Classifications

• G01R1/20

  Modifications of basic electric elements for use in electric measuring instruments; Structural combinations of such elements with such instruments · CPC title

• G01R19/0092 Primary

  Measuring current only · CPC title

• H01L2221/00

  Electricity · mapped topic

• G01R1/00

  Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00 (constructional details particular to {electromechanical} arrangements for measuring the electric consumption G01R11/02) · CPC title

• H02M1/00

  Details of apparatus for conversion · CPC title