US-12625171-B2 - Current sensing circuit

US12625171B2US 12625171 B2US12625171 B2US 12625171B2US-12625171-B2

Abstract

In accordance with an embodiment, a method of measuring a load current flowing through a current measurement resistor coupled between a source node and a load node includes: measuring a first voltage across a replica resistor when a first end of the replica resistor is coupled to the source node and a second end of the replica resistor is coupled to a reference current source; measuring a second voltage across the replica resistor when the second end of the replica resistor is coupled to the source node and the first end of the replica resistor is coupled to the reference current source; measure a third voltage across the current sensing resistor; and calculating a corrected current measurement of the load current based on the measured first voltage, the measured second voltage and the measured third voltage.

Inventors

Paolo Angelini

Assignees

STMICROELECTRONICS S.R.I.

Dates

Publication Date: 20260512
Application Date: 20231024
Priority Date: 20210428

Claims (20)

1 . A current sensing circuit comprising: a current sensing resistor coupled between a source node and a load node; a replica resistor having a same temperature behavior as the current sensing resistor; a voltage measurement circuit coupled to the current sensing resistor and the replica resistor, the voltage measurement circuit configured to: measure a first voltage across the replica resistor in response to a first end of the replica resistor being coupled to the source node and a second end of the replica resistor being coupled to a reference current source, measure a second voltage across the replica resistor in response to the second end of the replica resistor being coupled to the source node and the first end of the replica resistor being coupled to the reference current source, and measure a third voltage across the current sensing resistor; and a correction circuit coupled to the voltage measurement circuit and configured to produce a corrected current measurement value indicative of a current flowing through the current sensing resistor based on the measured first voltage, the measured second voltage, and the measured third voltage.
2 . The current sensing circuit of claim 1 , wherein the voltage measurement circuit comprises: a first plurality of switches coupled between the replica resistor and the voltage measurement circuit; a second plurality of switches coupled between the current sensing resistor and the voltage measurement circuit; a first switch coupled between the source node and the first end of the replica resistor; a second switch coupled between the source node and the second end of the replica resistor; a third switch coupled between the first end of the replica resistor and the reference current source; and a fourth switch coupled between the second end of the replica resistor and the reference current source.
3 . The current sensing circuit of claim 2 , further comprises a controller configured to: close the first plurality of switches, the first switch and the fourth switch when the voltage measurement circuit measures the first voltage; close the first plurality of switches, the second switch and the third switch when the voltage measurement circuit measures the second voltage; and close the second plurality of switches when the voltage measurement circuit measures the third voltage.
4 . The current sensing circuit of claim 1 , wherein: the voltage measurement circuit comprises an analog to digital converter; and the correction circuit comprises a digital calibration circuit coupled to an output of the analog to digital converter.
5 . The current sensing circuit of claim 4 , wherein the digital calibration circuit is configured to: calculate an average of the measured first voltage and the measured second voltage; and calculate the corrected current measurement value based on a difference between the measured third voltage and the calculated average.
6 . The current sensing circuit of claim 1 , wherein the replica resistor and the current sensing resistor arranged in the current sensing circuit are co-located to have the same temperature behavior as each other.
7 . The current sensing circuit of claim 1 , wherein the replica resistor and the current sensing resistor exhibit the same thermal drift, mechanical stress, and aging.
8 . A device, comprising: an electrical load; and a current sensing circuit, comprising: a current sensing resistor coupled between a source node and a node of the electrical load, a replica resistor having a same temperature behavior as the current sensing resistor, a voltage measurement circuit coupled to the current sensing resistor and the replica resistor, the voltage measurement circuit configured to: measure a first voltage across the replica resistor in response to a first end of the replica resistor being coupled to the source node and a second end of the replica resistor being coupled to a reference current source; measure a second voltage across the replica resistor in response to the second end of the replica resistor being coupled to the source node and the first end of the replica resistor being coupled to the reference current source; and measure a third voltage across the current sensing resistor, and a correction circuit coupled to the voltage measurement circuit and configured to produce a corrected current measurement value indicative of a current flowing through the current sensing resistor based on the measured first voltage, the measured second voltage, and the measured third voltage.
9 . The device of claim 8 , wherein the voltage measurement circuit comprises: a first plurality of switches coupled between the replica resistor and the voltage measurement circuit; a second plurality of switches coupled between the current sensing resistor and the voltage measurement circuit; a first switch coupled between the source node and the first end of the replica resistor; a second switch coupled between the source node and the second end of the replica resistor; a third switch coupled between the first end of the replica resistor and the reference current source; and a fourth switch coupled between the second end of the replica resistor and the reference current source.
10 . The device of claim 9 , wherein the current sensing circuit further comprises a controller configured to: close the first plurality of switches, the first switch and the fourth switch when the voltage measurement circuit measures the first voltage; close the first plurality of switches, the second switch and the third switch when the voltage measurement circuit measures the second voltage; and close the second plurality of switches when the voltage measurement circuit measures the third voltage.
11 . The device of claim 8 , wherein: the voltage measurement circuit comprises an analog to digital converter; and the correction circuit comprises a digital calibration circuit coupled to an output of the analog to digital converter.
12 . The device of claim 11 , wherein the digital calibration circuit is configured to: calculate an average of the measured first voltage and the measured second voltage; and calculate the corrected current measurement value based on a difference between the measured third voltage and the calculated average.
13 . The device of claim 8 , wherein the replica resistor and the current sensing resistor arranged in the current sensing circuit are co-located to have the same temperature behavior as each other.
14 . The device of claim 8 , wherein the replica resistor and the current sensing resistor exhibit the same thermal drift, mechanical stress, and aging.
15 . A method, comprising: measuring, by a voltage measurement circuit, a first voltage across a replica resistor in response to a first end of the replica resistor being coupled to a source node and a second end of the replica resistor being coupled to a reference current source, a current sensing resistor being coupled between the source node and a load node, a replica resistor having a same temperature behavior as the current sensing resistor, the voltage measurement circuit being coupled to the current sensing resistor and the replica resistor; measuring, by the voltage measurement circuit, a second voltage across the replica resistor in response to the second end of the replica resistor being coupled to the source node and the first end of the replica resistor being coupled to the reference current source; and measuring, by the voltage measurement circuit, a third voltage across the current sensing resistor; and producing, by a correction circuit coupled to the voltage measurement circuit, a corrected current measurement value indicative of a current flowing through the current sensing resistor based on the measured first voltage, the measured second voltage, and the measured third voltage.
16 . The method of claim 15 , wherein the voltage measurement circuit comprises: a first plurality of switches coupled between the replica resistor and the voltage measurement circuit; a second plurality of switches coupled between the current sensing resistor and the voltage measurement circuit; a first switch coupled between the source node and the first end of the replica resistor; a second switch coupled between the source node and the second end of the replica resistor; a third switch coupled between the first end of the replica resistor and the reference current source; and a fourth switch coupled between the second end of the replica resistor and the reference current source.
17 . The method of claim 16 , further comprising: closing the first plurality of switches, the first switch and the fourth switch when the voltage measurement circuit measures the first voltage; closing the first plurality of switches, the second switch and the third switch when the voltage measurement circuit measures the second voltage; and closing the second plurality of switches when the voltage measurement circuit measures the third voltage.
18 . The method of claim 15 , wherein: the voltage measurement circuit comprises an analog to digital converter; and the correction circuit comprises a digital calibration circuit coupled to an output of the analog to digital converter.
19 . The method of claim 18 , further comprising: calculating, by the digital calibration circuit, an average of the measured first voltage and the measured second voltage; and calculating, by the digital calibration circuit, the corrected current measurement value based on a difference between the measured third voltage and the calculated average.
20 . The method of claim 15 , wherein the replica resistor and the current sensing resistor arranged in the current sensing circuit are co-located to have the same temperature behavior as each other, and wherein the replica resistor and the current sensing resistor exhibit the same thermal drift, mechanical stress, and aging.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a divisional of U.S. application Ser. No. 17/655,891, filed on Mar. 22, 2022, which claims the benefit of Italian Patent Application No. 102021000010766, filed on Apr. 28, 2021, which applications are hereby incorporated herein by their reference. TECHNICAL FIELD Embodiments are directed to current sensing circuits. BACKGROUND Accurate estimation of absorbed power is a desirable feature in RX/TX (receiver/transmitter) wireless charger devices. Such estimation is facilitated by integrated circuits that provide an accurate current sensing feature. Various conventional solutions proposed to that effect include a (high-side) shunt resistor (briefly, “shunt”) followed by an analog front end (amplifier, filter), an analog-to-digital converter (ADC), and digital back-end processing. Shunt accuracy and stability have direct consequences on measurement accuracy. Conventional solutions to address these issues can be ascribed to two different approaches. A first approach involves using external “discrete” shunt resistors, which can be accurate and stable. Drawbacks possibly associated with such an approach include cost, package complexity and difficulty in calibrating the chip alone. Another approach involves using integrated shunt resistors and applying temperature calibration. An issue related to such other approach lies in that temperature calibration involves accurate temperature sensing and may not be able to compensate drifts, which may occur after in-factory calibration. Accuracy over the expected lifetime of the circuit and the associated device is correspondingly reduced. SUMMARY One or more embodiments may relate to a corresponding device. A wireless charging device may be exemplary of such a device. One or more embodiments may be related to a corresponding method. One or more embodiments facilitate achieving a high overall accuracy over the whole lifetime of a high-side current sensor based on an integrated shunt resistor with a run-time self-calibration capability. or more embodiments involve features that can be added to basic current sensor architecture, namely: an accurate current reference, based on a switched/capacitor approach, for instance, a scaled replica of the shunt resistor which can comprise a set of resistance elements like the elements used for the shunt resistor, with the shunt resistor and the replica forming an interdigitated structure, and a set of (high-voltage, HV) switches configured to switch the inputs of an amplifier stage between coupling to the output pins of the shunt resistor and coupling to the output pins of the shunt replica, and a digital signal processing circuit block which can be used to apply runtime calibration coefficients to a digital output from the measurement function. In one or more embodiments, a replica shunt can be provided that is adequately matched with the shunt resistor (e.g., by being co-located, that is arranged at the same location, possibly with mutually interdigitated structures) and the same analog front-end circuitry (amplifier, advantageously followed by an analog-to-digital converter) can be used during a self-test phase and a current measurement phase. This facilitates relying on the assumption that the offset and sensitivity drifts of the self-test chain are the same as the offset and the sensitivity drifts of the measurement chain. Accordingly, the output of the current sensor can be calibrated at runtime using information acquired during a self-test phase. In one or more embodiments, shunt and analog front-end inaccuracies can be tracked and compensated continuously. Advantageously, in one or more embodiments, a self-test reference current that is stable (over the circuit lifetime) can be provided using a switched-capacitor reference generator capable of producing a current that is dependent on a bandgap voltage, a clock frequency, and a capacitance. It is noted that such elements may be (much) more stable than shunt resistors and are currently available in production. One or more embodiments may offer advantageous features such as an accurate current reference, based on the switched-capacitor approach; a scaled replica of the shunt resistor is provided which includes a set of resistance elements equal to the elements used for the shunt resistor with interdigitated architecture; a set of (high-voltage, HV) switches can be used to periodically switch the input of the amplifier from the shunt output pins to the shunt replica output pins; a digital signal processing block can be used to apply runtime calibration coefficients to the measurement digital output; and a temperature sensor and a temperature compensation circuitry (as commonly used in conventional solutions) can be dispensed with. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments will now be described, by way of example only, with references to the annexed figures, wherein: FIG. 1 is a block diagram of a conventional cu