CURRENT SENSE AMPLIFIER FOR VOLTAGE CONVERTER

• US 20070188219A1
• Filed: 01/11/2007
• Published: 08/16/2007
• Est. Priority Date: 01/18/2006
• Status: Active Grant

• Current Assignee: Infineon Technologies Americas Corp. (Infineon Technologies AG)
• Original Assignee: International Rectifier Corporation (Infineon Technologies AG)
• Inventors: Segarra, Daniel
• Granted Patent: US 7,489,186 B2
• Time in Patent Office: Days
• US Class Current: 330/2
• CPC Class Codes: G01R 19/32 Compensating for temperature change

Abstract

A current sense amplifier for a voltage converter wherein the voltage converter has at least one channel providing an output current through an output inductor, the current sense amplifier monitoring the current in the at least one channel through the output inductor, the current sense amplifier comprising a plurality of variable gain amplifiers, there being at least one more variable gain amplifier than channels in the voltage converter, whereby at least one variable gain amplifier is in a calibration mode for a preset period of time during which the variable gain amplifier is compensated for an offset error and the gain of the variable gain amplifier is calibrated to compensate for temperature of the output inductor, while during said preset period of time any remaining variable gain amplifiers are connected to monitor the channel current in each output inductor.

Claims

1. A current sense amplifier for a voltage converter wherein the voltage converter has at least one channel providing an output current through an output inductor, the current sense amplifier monitoring the current in the at least one channel through the output inductor, the current sense amplifier comprising:

a plurality of variable gain amplifiers, there being at least one more variable gain amplifier than channels in the voltage converter, whereby at least one variable gain amplifier is in a calibration mode for a preset period of time during which the variable gain amplifier is compensated for an offset error and the gain of the variable gain amplifier is calibrated to compensate for temperature of the output inductor, while during said preset period of time any remaining variable gain amplifiers are connected to monitor the channel current in each output inductor.

2. The current sense amplifier of claim 1, wherein the voltage converter comprises a multiphase converter having a plurality of channels each contributing to a total output current, and each channel having an output inductor, the current sense amplifier monitoring the current in each channel through each respective inductor.

3. The current sense amplifier of claim 2, further comprising

an input multiplexer having a plurality of inputs coupled to monitoring circuits monitoring the currents in each of said output inductors and at least one additional input comprising a calibration input for the variable gain amplifier being calibrated,

the input multiplexer having outputs coupled to inputs of each of the variable gain amplifiers;

an output multiplexer having inputs coupled to the outputs of the variable gain amplifiers and outputs coupled to provide control functions for the multiphase converter and at least one calibration function for the variable gain amplifiers; and

a controller for operating the input and output multiplexers to connect the input multiplexer inputs to the variable gain amplifiers and to connect the outputs of the variable gain amplifiers to the output multiplexer outputs in a preset sequence so that each of the variable gain amplifiers are calibrated at preset intervals.

4. The current sense amplifier of claim 3, further wherein the least recently calibrated variable gain amplifier is always the next variable gain amplifier to be calibrated.

5. The current sense amplifier of claim 3, wherein the gain of each variable gain amplifier is adjusted during calibration so that an output of the variable gain amplifier is maintained constant despite temperature variations of said output inductors.

6. The current sense amplifier of claim 5, further comprising a thermal monitoring circuit for monitoring the temperature of at least one of said output inductors, said thermal monitoring circuit providing a signal related to the inductor temperature.

7. The current sense amplifier of claim 6, further comprising a gain adjusting circuit for adjusting the gain of said variable gain amplifier in response to change in the temperature of said output inductor, said gain adjusting circuit comprising a switching circuit for switching an input of said variable gain amplifier at a preset time to receive an input of said thermal monitoring circuit and a feedback circuit connected to said variable gain amplifier to change the gain of said variable gain amplifier to maintain an output of said variable gain amplifier constant in response to said input of said thermal monitoring circuit.

8. The current sense amplifier of claim 3, further wherein said calibration function comprises an offset adjustment of said variable gain amplifier.

9. The current sense amplifier of claim 8, wherein said variable gain amplifier comprises an amplifier providing a differential output signal, and wherein, to compensate for an offset error of said differential output signal, an offset determining circuit is provided to trim the variable gain amplifier to compensate for the offset error.

10. The current sense amplifier of claim 9, wherein the offset determining circuit comprises a comparator circuit coupled to an output of the output multiplexer comprising the calibration function, and

further wherein said variable gain amplifier has a differential input pair, and further comprising a circuit for shorting said differential input pair at a preset time during which said variable gain amplifier is in the calibration mode, and whereby said comparator circuit is provided with an output of said variable gain amplifier when the differential input pair of said variable gain amplifier is shorted for determining the amount of offset error present in said variable gain amplifier;

and further comprising a feedback circuit coupling an output of said comparator to a trimming input of said variable gain amplifier to trim said variable gain amplifier for said offset error.

11. The current sense amplifier of claim 10, wherein said feedback circuit comprises a digital successive approximation register and a digital to analog converter providing an analog output to trim the variable gain amplifier for the offset error.

12. The current sense amplifier of claim 2, wherein the current sense amplifier comprises a plurality of inductor current sense circuits, one for each output inductor, and wherein each current sense circuit comprises an RC filter disposed across the output inductor such that the current monitored is proportional to the voltage across an inherent DC resistance of the output inductor.

13. The current sense amplifier of claim 6, wherein the thermal monitoring circuit include a thermistor and a resistor reference.

14. The current sense amplifier of claim 3, wherein the output mulitplexer couples the variable gain amplifiers to the multiphase converter circuit so as to control the voltage positioning of an output voltage of the converter with respect to output current;

current balance between channels of the multiphase converter; and

an overcurrent limit for the multiphase converter.

15. The current sense amplifier of claim 3, further comprising a plurality of current splitters coupling the outputs of the variable gain amplifiers to said inputs of said output multiplexer.

16. The current sense amplifier of claim 3, wherein each variable gain amplifier comprises a differential input amplifier transistor pair wherein a first current proportional to a voltage difference between inputs to the input transistor pair is developed across a resistor coupling the input transistor pair and further comprising:

respective further transistors each coupled in series with the transistors of the input pair and wherein current equal to the sum and difference of a reference current and said first current is developed in respective ones of the further transistors coupled in series with the input transistor pair;

further comprising a gain stage for developing currents equal to a gain factor multiplied by said sum and difference currents and for developing an output current proportional to said gain factor multiplied by said first current; and

further comprising a gain adjustment stage for adjusting the gain factor based on an external input.

17. The current sense amplifier of claim 16, further comprising an offset calibration circuit having an output, and wherein the output of said offset calibration circuit is provided across said resistor to adjust the current flowing in said resistor to compensate for an offset error of said variable gain amplifier.

18. The current sense amplifier of claim 16, wherein the external input is a temperature dependent signal.

19. A variable gain amplifier comprising:

a differential input amplifier comprising a pair of transistors each having an input across which an input voltage is provided, the transistors being coupled such that each transistor is provided in series with a respective current source providing a reference current and whereby a current is developed across a resistor element coupling the transistors that is proportional to the voltage between the inputs;

further comprising further transistors each coupled in series with a transistor of the transistor pair, and wherein the further transistors are arranged such that a current is developed in each further transistor due to the voltage provided across the inputs that is substantially equal to, in one further transistor, a sum of the reference current and the current in the resistor element, and in the other further transistor, a difference between the reference current and the current in the resistor element;

further comprising a gain stage for developing currents equal to a gain factor multiplied by said sum and difference currents and for developing an output signal proportional to said gain factor multiplied by said current through said resistor element;

further comprising an interface for selectively providing a signal proportional to a variable across said inputs of said differential amplifier to drive said output signal to an output value; and

a gain setting circuit responsive to said output value that produces a gain setting signal to adjust the gain of said variable gain amplifier.

20. The variable gain amplifier of claim 19, wherein the variable is a temperature dependent signal produced by a temperature sensing element.

21. The variable gain amplifier of claim 19, further comprising:

an electronically variable resistor coupled in series with each further transistor, and wherein the resistance of each electronically variable resistor is adjustable such that the current in the further transistors is respectively equal to said sum and difference currents.

22. The variable gain amplifier of claim 21, further wherein said further transistors have control inputs connected to a fixed voltage source.

23. The variable gain amplifier of claim 21, further wherein said gain stage comprises two gain stage transistors wherein said sum and difference currents multiplied by the gain factor are developed, said two gain stages transistors being coupled respectively in series with further electronically variable resistors, said two gain stage transistors having control inputs coupled to a variable gain control voltage source that sets the gain factor and that is responsive to said gain setting signal.

24. The variable gain amplifier of claim 23, wherein said gain stage transistors are coupled to a current mirror circuit to convert said sum and difference current signals multiplied by the gain factor to a single ended current signal referred to a common reference.

25. The variable gain amplifier of claim 24, wherein the single ended current signal is coupled to a further amplifier circuit to provide said output signal.

26. The variable gain amplifier of claim 23, wherein each of said electronically variable resistors comprise MOSFETs operated in the triode mode and each of said transistors comprise MOSFETs.

27. The variable gain amplifier of claim 19, further comprising an offset adjusting circuit comprising a circuit providing a trimming current through said resistor element such that the current through the resistor element is set to zero when said inputs are shorted.

28. The variable gain amplifier of claim 19, further comprising a sample and hold circuit for sampling a voltage developed by said gain setting signal across a resistor thereby to set said gain factor.

29. The variable gain amplifier of claim 26, wherein said electronically variable resistors each comprise two devices, a static MOSFET device and a variable resistance MOSFET device.

30. A thermal calibration circuit for adjusting the gain of a variable gain amplifier, the thermal calibration circuit comprising:

an interface for receiving a signal that varies with temperature and for providing a signal related to the variation of the temperature;

a variable gain amplifier having an input and an output;

the signal related to the variation of the temperature being selectively coupled to said input;

a circuit at the output of said variable gain amplifier for developing a first current proportional to a difference between a current developed at the output of said variable gain amplifier and a reference current; and

said first circuit driving a further circuit to produce a gain control signal for adjusting the gain of the variable gain amplifier.

31. The thermal calibration circuit of claim 30, wherein the interface receives a temperature dependent signal from a thermistor having a reference voltage applied across the thermistor generated across a precision resistor element and develops said signal related to the variation of the temperature comprising a current signal, said current signal developing a voltage signal across an input resistor selectively coupled to said input by a switching circuit.

32. The thermal calibration circuit of claim 31, wherein the thermistor generates a signal related to the temperature of an output inductor of a voltage converter.

33. The thermal calibration circuit of claim 31, wherein said variable gain amplifier has differential inputs and outputs, and wherein the differential outputs are coupled to a reference current source and a current mirror circuit for developing said first difference current;

and further wherein said further circuit comprises a pair of transistors that generates said gain control signal by comparing said first difference current to a reference current developed by a fixed bias voltage.

34. The thermal calibration circuit of claim 33, further wherein said further circuit includes a current limiting circuit for setting a limit on said gain control signal.

35. The thermal calibration circuit of claim 33, wherein said variable gain amplifier includes a circuit for developing a gain control voltage from said gain control signal and a sample and hold circuit for selectively sampling said gain control voltage to set the gain of said variable gain amplifier.