Bidirectional current sensor for power field effect transistor

Abstract

A bi-directional current sensing circuit allows sensing a supply current flowing through a power field effect transistor regardless of the direction of the supply current. The bidirectional current sense circuit outputs a current sense signal representative of a supply current to a current sense output node. The bidirectional current sensing circuit includes a power field effect transistor and two current sensing circuits. One of the current sensing circuits senses the supply current when the supply current flows in the positive direction. Another current sensing circuit senses the supply current when the supply current flows in the negative direction.

Description

BACKGROUND OF THE INVENTION

[0001] Electronic circuits typically include transistors that act as electronic switches for regulating or controlling the current in a portion of the circuit. One type of transistor is a field effect transistor in which a voltage is applied to a gate terminal to turn the transistor on and off. A semiconductor channel region is provided between a drain terminal and a source terminal. When the transistor is on, current flows through the semiconductor channel region between the drain terminal and the source terminal. When the transistor is off, little or no current flows through the semiconductor channel region between the drain terminal and the source terminal. The gate terminal is disposed over the semiconductor channel region between the source terminal and the drain terminal. The voltage on the gate terminal creates an electric field that affects whether the semiconductor channel region conducts current, hence the term "field effect transistor".

[0002] Silicon has traditionally been used to fabricate transistors. However, semiconductor materials with a wider bandgap can be used to fabricate transistors that conduct higher power and operate at a higher efficiency than silicon transistors. Silicon carbide (SiC), aluminum nitride (AlN), zinc oxide (ZnO), and gallium nitride (GaN) are all examples of wide bandgap semiconductor materials that can be used in power electronic devices. One way to use such wide bandgap semiconductor materials is to form two different semiconductor materials to form a heterojunction therebetween.

[0003] The two semiconductor materials can have sufficiently different bandgaps such that when brought together, the bandgap of the junction drops just below the Fermi level within the channel layer. This means that electrons can flow freely within this region. This region is thin in depth and forms a plane parallel to the upper surface of the channel region. Therefore, this region is referred to as the "2DEG" region to emphasize its planar form. Additionally, due to the high mobility of electrons in this region, this region is also referred to as the 2DEG "electron sea". Thus, the 2DEG region is highly conductive. The 2DEG region can form the channel region of a power semiconductor to allow high current with relatively low resistance to pass through. A field effect transistor using such a 2DEG is referred to as a "high electron mobility transistor" (or HEMT).

[0004] Some HEMTs can be used for amplification and switching purposes in high power circuits and can sometimes be referred to as "power transistors". Power transistors can typically operate at currents greater than 1 ampere to several hundred amperes. Additionally, power transistors can transfer powers greater than 1 watt to several hundred watts or even more. However, it may be beneficial to measure the current flowing through a power transistor.

[0005] The subject matter claimed herein is not limited to embodiments that solve any disadvantages or operate only in environments such as those described above. Instead, this background is provided only to illustrate an example technical field in which some embodiments described herein may be practiced. SUMMARY OF THE INVENTION

[0006] The embodiments described herein relate to a bidirectional current sensing circuit that allows sensing of the supply current through a power field effect transistor regardless of the direction of flow of the supply current. The bidirectional current sensing circuit outputs a current sensing signal representative of the supply current to a current sensing output node. For clarity, when the supply current flows from the drain node of the power transistor to the source node, the current is defined as flowing in the "positive direction". On the other hand, when the supply current flows from the source node of the power transistor to the drain node, the current is defined as flowing in the "negative direction".

[0007] The bidirectional current sensing circuit includes a power field effect transistor and two current sensing circuits. When the supply current flows in the positive direction, one of the current sensing circuits senses the supply current, and this current sensing circuit is sometimes referred to herein as the "positive" current sensing circuit. On the other hand, when the supply current flows in the negative direction, the other current sensing circuit is used to sense the supply current, and this current sensing circuit is sometimes referred to herein as the "negative" current sensing circuit.

[0008] Each of the positive current sensing circuit and the negative current sensing circuit includes a sensing transistor, an operational amplifier, a variable current source, and a mirror current source. Each of the sensing transistors in the sensing transistors can be a scaled-down version of the power transistor. For clarity, the elements of the positive current sensing circuit will be referred to as "first" elements, while the elements of the negative current sensing circuit will be referred to as "second" elements. The exact connections between the elements of the bidirectional current sensing circuit will be described in more detail in the detailed description section. However, a brief description of the function of the bidirectional current sensing circuit will now be described.

[0009] When the supply current flows in the positive direction, the first operational amplifier causes the first variable current source to output a first sensing current to the drain node of the first sensing transistor. When the supply current flows in the positive direction, the first sensing current is proportional to the supply current. The first mirror current source mirrors the first sensing current and outputs a first mirror current to the current sensing output node. Accordingly, when the supply current flows in the positive direction, the first mirror current can be used to generate a current sensing signal (representative of the supply current) at the current sensing output node.

[0010] On the other hand, when the supply current flows in the negative direction, the second operational amplifier causes the second variable current source to output a second sensing current to the source node of the second sensing transistor. When the supply current flows in the negative direction, the second sensing current is proportional to the supply current. The second mirror current source mirrors the second sensing current and draws a second mirror current from the current sensing output node. Accordingly, when the supply current flows in the negative direction, the second mirror current can be used to generate a current sensing signal (representative of the supply current) at the current sensing output node.

[0011] Accordingly, regardless of the direction in which the supply current flows through the power MOSFET, the bidirectional current sensing circuit allows sensing of the supply current flowing through the power MOSFET.

[0012] Additional features and advantages will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the teachings herein. The features and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims. The features of the invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] To describe the manner in which the advantages and features of the circuits, systems, and methods described herein can be obtained, a more particular description of the embodiments briefly described herein will be presented by reference to the specific embodiments thereof shown in the drawings. It is to be understood that these drawings depict only typical embodiments of the circuits, systems, and methods described herein and are thus not to be considered limiting of their scope, and certain circuits, systems, and methods will be described and explained with additional specificity and detail by use of the drawings, in which:

[0014] Figure 1 illustrates a bidirectional current sensing circuit in which the principles described herein may be practiced and is merely one example of a bidirectional current sensing circuit consistent with the principles described herein;

[0015] Figure 2 illustrates a bidirectional current sensing circuit that is Figure 1 an example of a bidirectional current sensing circuit, but more particularly illustrates examples of a positive current sensing circuit and a negative current sensing circuit; and

[0016] Figure 3 illustrates a bidirectional current sensing circuit that is Figure 2 an example of a bidirectional current sensing circuit, but having several additional components. DETAILED DESCRIPTION

[0017] The embodiments described herein relate to a bidirectional current sensing circuit that allows sensing of the supply current through a power MOSFET regardless of the direction of flow of the supply current. The bidirectional current sensing circuit outputs a current sensing signal representative of the supply current to a current sensing output node. For clarity, when the supply current flows from the drain node of the power transistor to the source node, the current is defined as flowing in the "positive direction". On the other hand, when the supply current flows from the source node of the power transistor to the drain node, the current is defined as flowing in the "negative direction".

[0018] The bidirectional current sensing circuit includes a power field effect transistor and two current sensing circuits. When the supply current flows in the positive direction, one of the current sensing circuits in the current sensing circuit is used to sense the supply current, and thus this current sensing circuit is sometimes referred to as the "positive" current sensing circuit in this article. On the other hand, when the supply current flows in the negative direction, another current sensing circuit is used to sense the supply current, and thus this current sensing circuit is sometimes referred to as the "negative" current sensing circuit in this article.

[0019] Each of the positive current sensing circuit and the negative current sensing circuit includes a sensing transistor, an operational amplifier, a variable current source, and a mirror current source. Each sensing transistor in the sensing transistors can be a miniaturized form of the power transistor.

[0020] Figure 1 The bidirectional current sensing circuit 100 that can practice the principles described herein is illustrated, and is only one example of a bidirectional current sensing circuit consistent with the principles described herein. Regardless of the direction in which the supply current flows, the bidirectional current sensing circuit 100 allows the supply current passing through the power field effect transistor 110 to be sensed. The bidirectional current sensing circuit 100 outputs a current sensing signal representing the supply current to the current sensing output node 101. By way of example only, the power field effect transistor 110 can be a gallium nitride (GaN) field effect transistor.

[0021] The power field effect transistor 110 has a gate node 111 that controls whether current flows between the drain node 112 and the source node 113 of the power field effect transistor. The load 120 can be connected to the drain node 112 of the power field effect transistor 110, and can supply the supply current passing through the power field effect transistor 110 bidirectionally. For clarity, when the supply current flows from the drain node 112 of the power field effect transistor 110 to the source node 113, the supply current is defined as flowing in the "positive direction". On the other hand, when the supply current flows from the source node 113 of the power field effect transistor 110 to the drain node 112, the supply current is defined as flowing in the "negative direction". For brevity, the power field effect transistor 110 is sometimes referred to as the "power transistor 110" in this article.

[0022] The bidirectional current sensing circuit 100 further includes two current sensing circuits 130 and 140. The current sensing circuit 130 is used to sense the supply current when the supply current flows in the positive direction, and thus this current sensing circuit is sometimes referred to as the "positive" current sensing circuit 130 in this article. On the other hand, the current sensing circuit 140 is used to sense the supply current when the supply current flows in the negative direction, and thus this current sensing circuit is sometimes referred to as the "negative" current sensing circuit 140. For illustrative purposes only, the positive current sensing circuit 130 and the negative current sensing circuit 140 are inFigure 1 is shown connected to the drain node 112 of the power transistor 110. However, reference will be made to Figure 2 more specifically illustrate the exact connections between the power transistor 110, the positive current sensing circuit 130, and the negative current sensing circuit 140.

[0023] When the power supply current flows through the power transistor 110 in the positive direction, the positive current sensing circuit 130 outputs a current signal 131 to the current sensing output node 101 (as shown by the dashed arrow labeled "131"). The current signal 131 represents the power supply current when the power supply current is positive. Therefore, when the power supply current is positive, the current signal 131 can be used to generate a current sensing signal (representing the power supply current) at the current sensing output node 101.

[0024] On the other hand, when the power supply current flows through the power transistor 110 in the negative direction, the negative current sensing circuit 140 outputs a current signal 141 to the current sensing output node 101 (as shown by the dashed arrow labeled "141"). The current signal 141 represents the power supply current when the power supply current is negative. Therefore, when the power supply current is negative, the current signal 141 can be used to generate a current sensing signal (representing the power supply current) at the current sensing output node 101.

[0025] Accordingly, regardless of the direction in which the power supply current flows through the power transistor 110, the bidirectional current sensing circuit 100 generates a current sensing signal representing the power supply current flowing through the power transistor 110 at the current sensing output node 101.

[0026] Figure 2 Illustrated is a bidirectional current sensing circuit 200, which is an Figure 1 example of the bidirectional current sensing circuit 100 of Figure 2 but more specifically shows examples of the positive current sensing circuit 130 and the negative current sensing circuit 140. For simplicity, in Figure 1 the same element numbers as in Figure 1 are used to illustrate the power field effect transistor 110 and the load 120. In addition, the bidirectional current sensing circuit 200 includes a positive current sensing circuit 230 and a negative current sensing circuit 240, which are

[0027] The positive current sensing circuit 230 includes a sensing field effect transistor 231, an operational amplifier 232, a variable current source 233, and a mirror current source 234. For clarity, in Figure 2The elements of the positive current sensing circuit 230 are represented by a dashed box. For simplicity, the sense field effect transistor 231 is sometimes referred to herein simply as the "sense transistor 231". The sense transistor 231 can be a miniaturized version of the power transistor 110. That is, the sense transistor 231 can be the same as the power transistor 110 except that the sense transistor 231 has, for example, a channel width that is 500 times smaller than the channel width of the power transistor 110. Additionally, the sense transistor 231 can be formed on the same epitaxial stack as the power transistor 110. In this case, the on-resistance of the sense transistor 231 will be 500 times larger than the on-resistance of the power transistor 110.

[0028] The sense transistor 231 has a gate node 231G that controls whether current flows between its drain node 231D and its source node 231S. Although not explicitly shown in Figure 2 the sense transistor 231's gate node 231G is connected to the gate node 111 of the power transistor 110. Additionally, the source node 231S of the sense transistor 231 and the source node 113 of the power transistor 110 are each connected to a reference voltage source 250 (e.g., providing ground).

[0029] The operational amplifier 232 has an input node 232a connected to the drain node 112 of the power transistor 110 and has an input node 232b connected to the drain node 231D of the sense transistor 231. The variable current source 233 supplies a variable amount of current to the drain node 231D of the sense transistor 231. The variable amount of current supplied by the variable current source 233 depends on the output signal at the output node 232c of the operational amplifier 232 and is proportional to the supply current when the supply current is positive. This is because when the supply current is positive, the operational amplifier 232 and the variable current source 233 work together to make the voltage at the drain node 231D of the sense transistor 231 approximately the same as the voltage at the drain node 112 of the power transistor 110, as will be explained later. The variable current source 233 interacts with the mirror current source 234 (e.g., via a current mirror represented by a dashed arrow) such that the mirror current source 234 mirrors the variable amount of current supplied by the variable current source 233. Thus, the mirror current source 234 supplies a mirror current to the current sensing output node. This mirror current is approximately equal to (or at least proportional to) the varying current from the variable current source 233.

[0030] The negative current sensing circuit 240 also includes a sense field effect transistor 241, an operational amplifier 242, a variable current source 243, and a mirror current source 244. For clarity, in Figure 2The elements of the negative current sensing circuit 240 are represented by the dashed box in the figure. For simplicity, the sense field effect transistor 241 is sometimes referred to as the "sense transistor 241" in this text. The sense transistor 241 can also be a miniaturized version of the power transistor 110. That is, the sense transistor 241 can be the same as the power transistor 110, except that the sense transistor 241 has, for example, a channel width that is 500 times smaller than the channel width of the power transistor 110. In addition, the sense transistor 241 can be formed on the same epitaxial stack as the power transistor 110. In this case, the on-resistance of the sense transistor 241 will be 500 times larger than the on-resistance of the power transistor 110.

[0031] The sense transistor 241 has a gate node 241G that controls whether current flows between its drain node 241D and its source node 241S. Although not explicitly shown in the figure, the gate node 241G of the sense transistor 241 is also connected to the gate node 111 of the power transistor 110. In addition, the drain node 241D of the sense transistor 241 is connected to the drain node 112 of the power transistor 110. Figure 2 The operational amplifier 242 has an input node 242a connected to the reference voltage source 250 and an input node 242b connected to the source node 241S of the sense transistor 241. The variable current source 243 supplies a variable amount of current to the source node 241S of the sense transistor 241. The variable amount of current supplied by the variable current source 243 depends on the output signal at the output node 242c of the operational amplifier 242 and is proportional to the supply current when the supply current is negative. This is because when the supply current is negative, the operational amplifier 242 and the variable current source 243 work together to make the voltage at the source node 241S of the sense transistor 241 approximately equal to the voltage provided by the reference voltage source (e.g., ground), as will be explained later. The variable current source 243 interacts with the mirror current source 244 (e.g., via a current mirror represented by the dashed arrow) such that the mirror current source 244 mirrors the variable amount of current supplied by the variable current source 243. Therefore, the mirror current source 244 draws a mirror current from the current sensing output node 101. This mirror current is approximately equal to (or at least proportional to) the varying current from the variable current source 243.

[0032] The operational amplifier 242 has an input node 242a connected to the reference voltage source 250 and an input node 242b connected to the source node 241S of the sense transistor 241. The variable current source 243 supplies a variable amount of current to the source node 241S of the sense transistor 241. The variable amount of current supplied by the variable current source 243 depends on the output signal at the output node 242c of the operational amplifier 242 and is proportional to the supply current when the supply current is negative. This is because when the supply current is negative, the operational amplifier 242 and the variable current source 243 work together to make the voltage at the source node 241S of the sense transistor 241 approximately equal to the voltage provided by the reference voltage source (e.g., ground), as will be explained later. The variable current source 243 interacts with the mirror current source 244 (e.g., via a current mirror represented by the dashed arrow) such that the mirror current source 244 mirrors the variable amount of current supplied by the variable current source 243. Therefore, the mirror current source 244 draws a mirror current from the current sensing output node 101. This mirror current is approximately equal to (or at least proportional to) the varying current from the variable current source 243.

[0033] In operation, it is assumed that a gate voltage (e.g., positive 6 volts) is applied to the connected gate nodes of each of the power transistor 110 and the sense transistors 231 and 241. Additionally, it is assumed that the supply current flowing through the power transistor 110 is positive (i.e., the current flows from the drain node 112 to the source node 113). In this case, due to the on-resistance of the power transistor 110, a positive voltage (e.g., single-digit volts) is induced at the drain node 112 of the power transistor 110 compared to the reference voltage source 250 (which will be considered as ground in further discussion). In this situation, the operational amplifier 232 and the variable current source 233 together act as a feedback circuit that makes the voltage at the drain node 231D of the sense transistor 231 approximately equal to the voltage at the drain node 112 of the power transistor 110.

[0034] For example, if the drain voltage at the drain node 231D of the sense transistor 231 is slightly higher than the drain voltage at the drain node 111 of the power transistor 110, the output signal from the operational amplifier 232 will cause the variable current source 233 to reduce the amount of current it supplies to the drain node 231D of the sense transistor 231. Since the on-resistance of the sense transistor 231 is relatively constant, this adjustment will reduce the drain voltage at the drain node 231D of the sense transistor 231. On the other hand, if the drain voltage at the drain node 231D of the sense transistor 231 is slightly lower than the drain voltage at the drain node 112 of the power transistor 110, then the output signal from the operational amplifier 232 will cause the variable current source 233 to increase the amount of current it supplies to the drain node 231D of the sense transistor 231, thereby increasing the drain voltage at the drain node 231D of the sense transistor 231 as well. Thus, the feedback loop provided by the operational amplifier 232 and the variable current source 233 stabilizes the drain voltage at the drain node 231D of the sense transistor 231 to be approximately at the drain voltage of the power transistor 110.

[0035] Accordingly, when the supply current is positive, each of the power transistor 110 and the sense transistor 231 operates under substantially the same conditions. That is, each of the power transistor 110 and the sense transistor 231 has the same voltages applied to its respective gate node (e.g., positive 6 volts), drain node (e.g., a single-digit volt), and source node (e.g., ground). Additionally, recall that the sense transistor 231 is a scaled-down replica of the power transistor 110, e.g., having 500 times the on-resistance of the power transistor 110. Thus, when the supply current is positive, the current flowing through the sense transistor 231 is proportional to the supply current flowing through the power transistor 110. More specifically, the current flowing through the sense transistor 231 provided by the variable current source 233 is equal to the supply current multiplied by the ratio of the on-resistance of the power transistor 110 to the on-resistance of the sense transistor 231. In other words, if the channel width of the sense transistor 231 is 500 times smaller than the channel width of the power transistor 110, the sense current through the sense transistor 231 will be proportional to the current through the power transistor 110 (and 500 times smaller than the current flowing through the power transistor 110).

[0036] The mirror current source 234 mirrors the current provided by the variable current source 233. Thus, the mirror current source 234 provides (approximately equal to) a mirrored current of the current provided by the variable current source 233 to the current sense output node 101. Then, this mirrored current (which is a positive current signal) itself can be the current sense signal at the current sense output node 101, or can be used to generate a current sense signal at the current sense output node 101, as will be further explained below with reference to Figure 3 Further explanation.

[0037] For example, in the case where the sense transistor 231 has a channel width 500 times smaller than the channel width of the power transistor 110, the current flowing through the sense transistor 231 will be approximately 500 times smaller than the supply current. In the case where the mirror current source 234 provides a mirrored current equal to the current provided by the variable current source 233, the mirrored current will also be approximately 500 times smaller than the supply current. Thus, if the mirrored current is the current sense signal at the current sense output node 101, this current sense signal will also be 500 times smaller than the supply current.

[0038] However, the principles described herein are not limited to the ratio between the current flowing through the sense transistor 231 and the supply current, not limited to the mirror current source 234 accurately mirroring the current provided by the variable current source 233, and not limited to the target ratio between the current sense signal at the current sense output node 101 and the supply current. For example, assume the goal is to have a current sense signal at the current sense output node 101 that is 500 times smaller than the supply current. This can also be achieved, for example, by using a sense transistor 231 having a channel width that is 1000 times smaller than the channel width of the power transistor 110, and then by using a mirror current source 234 that provides a mirror current twice that provided by the variable current source 233. As another alternative example, this can be achieved by using a sense transistor 231 having a channel width that is 5000 times smaller than the channel width of the power transistor 110, and then by using a mirror current source 234 that provides a mirror current ten times that provided by the variable current source 233.

[0039] In any case, when the supply current is positive, the positive current sensing circuit 230 is used to generate a current sense signal representing the supply current at the current sense output node 101.

[0040] Now assume that the supply current flowing through the power transistor 110 is negative (e.g., the current flows from the source node 113 to the drain node 112). In this case, due to the on-resistance of the power transistor 110, a negative voltage (e.g., a single-digit negative volt) is induced at the drain node 112 of the power transistor 110. When the voltage at the drain node 112 is negative, the positive current sensing circuit 230 becomes inoperative. This is because, in order to induce a negative voltage at the drain node 231D of the sense transistor 231, the variable current source 233 must provide a negative current to the drain node 231D of the sense transistor 231. However, the variable current source 233 can only provide a minimum of zero amperes of current and thus cannot provide a negative current. Therefore, in this case, the variable current source 233 does not provide current, and thus no current is provided to the current sense output node 101 via the mirror current source 234.

[0041] However, when the supply current is negative and thus the voltage at the drain node 241D of the sense transistor 241 is negative, current is allowed to flow from the source node 241S to the drain node 241D of the sense transistor 241. Therefore, in this case, the operational amplifier 242 and the variable current source 243 together function as a feedback circuit that makes the voltage at the source node 241S approximately equal to the reference voltage (e.g., ground) provided by the reference voltage source 250.

[0042] For example, if the source voltage at the source node 241S of the sense transistor 241 is slightly higher than the reference voltage at the reference voltage source 250 (e.g., ground), then the output signal from the operational amplifier 242 will cause the variable current source 243 to reduce the amount of current it supplies to the source node 241S of the sense transistor 241, thereby also reducing the source voltage on the source node 241S of the sense transistor 241. On the other hand, if the source voltage at the source node 241S of the sense transistor 241 is slightly lower than the reference voltage provided by the reference voltage source 250, then the output signal from the operational amplifier 242 will cause the variable current source 233 to increase the amount of current it supplies to the source node 241S of the sense transistor 241, thereby also increasing the source voltage on the source node 241S of the sense transistor 241. Thus, the feedback loop provided by the operational amplifier 242 and the variable current source 243 stabilizes the source voltage at the source node 241S of the sense transistor 241 to be approximately at the reference voltage provided by the reference voltage source 250.

[0043] Accordingly, when the supply current is negative, each of the power transistor 110 and the sense transistor 241 operates under the same conditions. That is, each of the power transistor 110 and the sense transistor 241 has the same voltages applied to its respective gate node (e.g., positive 6 volts), drain node (e.g., a single-digit volt), and source node (e.g., ground). Additionally, recall that the sense transistor 241 is also a miniaturized replica of the power transistor 110, e.g., having 500 times the on-resistance of the power transistor 110. Thus, when the supply current is negative, the current flowing through the sense transistor 241 is proportional to the supply current flowing through the power transistor 110. More specifically, the current flowing through the sense transistor 241 provided by the variable current source 243 is equal to the supply current multiplied by the ratio of the on-resistance of the power transistor 110 to the on-resistance of the sense transistor 241. In other words, if the channel width of the sense transistor 241 is 500 times smaller than the channel width of the power transistor 110, then the sense current through the sense transistor 241 will be proportional to the current through the power transistor 110 (and 500 times smaller than the current flowing through the power transistor 110).

[0044] The mirror current source 244 mirrors the current provided by the variable current source 243. Thus, the mirror current source 244 draws a mirror current from the current sense output node 101, where this mirror current is approximately equal to the current provided by the variable current source 243. Then, this mirror current (which is a negative current signal) itself can be the current sense signal on the current sense output node 101, or it can be used to generate a current sense signal on the current sense output node, as will be explained later with reference to Figure 3 explained.

[0045] For example, in a case where the sense transistor 241 has a channel width that is 500 times smaller than the channel width of the power transistor 110, the current flowing through the sense transistor 241 will be approximately 500 times smaller than the supply current. In a case where the mirror current source 244 draws a mirror current equal to the current provided by the variable current source 243, the mirror current will also be approximately 500 times smaller than the supply current. Thus, if the mirror current is the current sense signal on the current sense output node 101, this current sense signal will also be 500 times smaller than the supply current.

[0046] However, similar to the positive current sense circuit 230, the operating principle of the negative current sense circuit 240 is not limited to the ratio between the current flowing through the sense transistor 241 and the supply current, is not limited to the mirror current source 244 precisely mirroring the current provided by the variable current source 243, and is not limited to the target ratio between the current sense signal on the current sense output node 101 and the supply current. However, in one embodiment, the target ratio can be the same regardless of whether the supply current flowing through the power transistor 110 is positive or negative. In any case, when the supply current is negative, the negative current sense circuit 240 is used to generate (at the current sense output node 101) a current sense signal representing the supply current.

[0047] Recall that when the supply current flowing through the power transistor 110 is negative, the positive current sense circuit 230 does not function to supply current to the current sense output node 101. On the other hand, when the supply current flowing through the power transistor 110 is positive, the negative current sense circuit 240 does not draw current from the current sense output node 101. This is because the variable current source 243 cannot supply a negative current to the source node 241S of the sense transistor 241. Thus, when the supply current is positive, the variable current source 243 does not supply current, and thus no current is drawn from the current sense output node 101 via the mirror current source 244.

[0048] Accordingly, regardless of the direction in which the supply current flows through the power transistor 110, the bidirectional current sense circuit 200 allows a current sense signal representing the supply current to be generated at the current sense output node 101.

[0049] In some embodiments, the current sense signal at the current sense output node 101 can be a voltage signal instead of a current signal. Figure 3 The bidirectional current sense circuit 300 is illustrated, which is an example of the bidirectional current sense circuit 200 for Figure 2 but with a current sense resistor 310 added. The current sense resistor 310 is used to convert the mirror current provided by the mirror current source 234 and the mirror current source 244 into a voltage signal at the current sense output node 101.

[0050] That is, when the supply current is positive, the mirror current source 234 provides a mirror current proportional to the supply current to the current sense output node 101. This mirror current passes through the current sense resistor 310 and induces a positive voltage signal representing the supply current at the current sense output node 101. On the other hand, when the supply current is negative, the mirror current source 244 draws a mirror current proportional to the supply current from the current sense output node 101. This mirror current passes through the current sense resistor 310 and can induce a negative voltage signal representing the supply current at the current sense output node 101.

[0051] However, in order to facilitate the reading of the voltage signal (i.e., the current sense signal) at the current sense output node 101 by a device connectable to the current sense output node, the bidirectional current sense circuit 300 further includes a voltage offset voltage source 320. The voltage offset voltage source 320 offsets all voltage signals at the current sense output node 101 upward to be positive. For example, the voltage offset voltage source 320 can provide +5 volts. Thus, if the supply current is zero, the voltage signal at the current sense output node 101 will be at approximately +5 volts. If the supply current is positive, the voltage signal at the current sense output node 101 can range, for example, from approximately +5 volts to +9 volts. On the other hand, if the supply current is negative, the voltage signal at the current sense output node 101 can range, for example, from +1 volt to approximately +5 volts. However, the principles described herein are not limited to the voltage provided by the voltage offset voltage source 320, not limited to the current sense signal at the current sense output node 101, particularly the voltage signal or current signal, and not limited to the range of any voltage signal or current signal at the current sense output node 101.

[0052] In addition, Figure 3 the bidirectional current sense circuit 300 includes a negative current sense circuit 340, which is Figure 2 an example of the negative current sense circuit 240, but the negative current sense circuit 340 includes additional components that can assist in correct current mirroring. For simplicity, the same element numbers are used in Figure 3 the negative current sense circuit 340 to label the same elements of Figure 2 the negative current sense circuit 240.

[0053] The negative current sense circuit 340 further includes an intermediate mirror current source 345 and a diode 346. By way of example only, the diode 346 can be a diode-connected transistor. When the supply current is negative, the variable current source 243 outputs a variable amount of current, as described previously with reference to Figure 2 above. However, in Figure 3Among them, the intermediate mirror current source 345 mirrors the current provided by the variable current source 243 and outputs an intermediate mirror current (which is approximately equal to the current from the variable current source 243) through the diode 346. Then the mirror current source 244 mirrors the current flowing through the diode 346. In this way, the mirror current source 244 draws a mirror current from the current sensing output node 101, where the mirror current is approximately equal to the current provided by the variable current source 243.

[0054] Accordingly, regardless of the direction of the supply current, the bidirectional circuit according to the principles described herein is capable of generating a current sensing signal (which can be a voltage signal or a current signal) representing the supply current at the current sensing output node 101. The bidirectional current sensing circuit 300 is also capable of manipulating the current sensing signal so that it can be more easily read by a device connected to the current sensing output node 101.

[0055] Text support part

[0056] Clause 1. A bidirectional current sensing circuit configured to output a current sensing signal at a current sensing output node, the current sensing signal indicating a supply current flowing through a power field effect transistor, the bidirectional current sensing circuit comprising: the power field effect transistor having a source node connected to a reference voltage source; a first sensing field effect transistor having a gate node connected to the gate node of the power field effect transistor and a source node also connected to the reference voltage source; a first operational amplifier having a first input node connected to the drain node of the power field effect transistor and a second input node connected to the drain node of the first sensing field effect transistor; a first variable current source configured to provide a variable amount of current to the drain node of the first sensing field effect transistor in response to a signal at the output node of the first operational amplifier; a first mirror current source configured to mirror the current provided by the first variable current source and output a first mirror current to the current sensing output node; a second sensing field effect transistor having a gate node connected to the gate node of the power field effect transistor and a drain node connected to the drain node of the power field effect transistor; a second operational amplifier having a first input node connected to the reference voltage source and a second input node connected to the source node of the second sensing field effect transistor; a second variable current source configured to provide a variable amount of current to the source node of the second sensing field effect transistor in response to a signal at the output node of the second operational amplifier; and a second mirror current source configured to mirror the current provided by the second variable current source and draw a second mirror current from the current sensing output node.

[0057] Clause 2. The bidirectional current sensing circuit according to Clause 1, the bidirectional current sensing circuit further comprising a current sensing resistor coupled between the reference voltage source and the current sensing output node.

[0058] Clause 3. The bidirectional current sensing circuit according to Clause 2, the bidirectional current sensing circuit further comprising a voltage offset voltage source having a negative terminal connected to the reference voltage source and a positive terminal connected to the current sensing resistor such that the current sensing resistor and the voltage offset voltage source are connected in series between the reference voltage source and the current sensing output node.

[0059] Clause 4. The bidirectional current sensing circuit according to Clause 1, the bidirectional current sensing circuit further comprising: an intermediate mirror current source configured to mirror the current provided by the second variable current source and configured to output an intermediate mirror current; and a diode connected between the intermediate mirror current source and the reference voltage source, the diode being forward biased from the intermediate mirror current source to the reference voltage source such that the intermediate mirror current is provided to the anode of the diode, the second mirror current source being configured to mirror the current provided by the second variable current source by mirroring the intermediate mirror current flowing through the diode.

[0060] Clause 5. The bidirectional current sensing circuit according to Clause 4, the diode being a diode-connected field effect transistor.

[0061] Clause 6. The bidirectional current sensing circuit according to Clause 5, the power field effect transistor, the first sensing field effect transistor, the second sensing field effect transistor, and the diode-connected field effect transistor each being a gallium nitride (GaN) transistor.

[0062] Clause 7. The bidirectional current sensing circuit according to Clause 1, each of the power field effect transistor, the first sensing field effect transistor, and the second sensing field effect transistor being a gallium nitride transistor.

[0063] Clause 8. The bidirectional current sensing circuit according to Clause 1, each of the power field effect transistor, the first sensing field effect transistor, and the second sensing field effect transistor being at least partially formed on multiple portions of the same epitaxial stack.

[0064] Clause 9. The bidirectional current sensing circuit according to Clause 1, the reference voltage source providing ground.

[0065] Clause 10. The bidirectional current sensing circuit according to Clause 1, the bidirectional current sensing circuit further comprising a load connected to the drain node of the power field effect transistor, the load being configured to bidirectionally provide the supply current passing through the power field effect transistor.

[0066] Clause 11. The bidirectional current sensing circuit according to Clause 10, wherein when the load supplies the power supply current from the drain node of the power field effect transistor to the source node of the power field effect transistor, the current sensing signal on the current sensing output node is at least partially generated by the first mirror current, and when the load supplies the current from the source node of the power field effect transistor to the drain node of the power field effect transistor, the current sensing signal on the current sensing output node is at least partially generated by the second mirror current. Invention 2: Slide 12

[0067] Although the subject matter has been described in language specific to structural features and / or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the features or acts described above, or to the order of the acts described above. On the contrary, the described features and acts are disclosed as example forms of implementing the claims.

[0068] The present disclosure may be implemented in other specific forms without departing from its essential features. The described embodiments are to be considered illustrative in all respects and not restrictive. All changes that come within the meaning and range of equivalency of the claims are embraced within their scope.

[0069] When an element is introduced in the appended claims, the articles "a", "an", "the", and "said" are intended to mean that there is one or more of the elements. The terms "comprising", "including", and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

Claims

1. A bidirectional current sensing circuit configured to output a current sensing signal at a current sensing output node, the current sensing signal indicating a supply current flowing through a power field effect transistor, the bidirectional current sensing circuit comprising: The power field effect transistor having a source node connected to a reference voltage source; A first sensing field effect transistor having a gate node connected to the gate node of the power field effect transistor and a source node also connected to the reference voltage source; A first operational amplifier having a first input node connected to the drain node of the power field effect transistor and a second input node connected to the drain node of the first sensing field effect transistor; A first variable current source configured to provide a variable amount of current to the drain node of the first sensing field effect transistor in response to a signal at the output node of the first operational amplifier; A first mirror current source configured to mirror the current provided by the first variable current source and output a first mirror current to the current sensing output node; A second sensing field effect transistor having a gate node connected to the gate node of the power field effect transistor and a drain node connected to the drain node of the power field effect transistor; A second operational amplifier having a first input node connected to the reference voltage source and a second input node connected to the source node of the second sensing field effect transistor; A second variable current source configured to provide a variable amount of current to the source node of the second sensing field effect transistor in response to a signal at the output node of the second operational amplifier; And A second mirror current source configured to mirror the current provided by the second variable current source and draw a second mirror current from the current sensing output node.

2. The bidirectional current sensing circuit according to claim 1, further comprising a current sensing resistor coupled between the reference voltage source and the current sensing output node.

3. The bidirectional current sensing circuit according to claim 2, further comprising a voltage offset voltage source having a negative terminal connected to the reference voltage source and a positive terminal connected to the current sensing resistor such that the current sensing resistor and the voltage offset voltage source are connected in series between the reference voltage source and the current sensing output node.

4. The bidirectional current sensing circuit according to claim 1, further comprising: An intermediate mirror current source configured to mirror the current provided by the second variable current source and configured to output an intermediate mirror current; And A diode, the diode being connected between the intermediate mirror current source and the reference voltage source, the diode being forward biased from the intermediate mirror current source towards the reference voltage source such that the intermediate mirror current is provided to the anode of the diode. The second mirror current source is configured to mirror the current provided by the second variable current source by mirroring the intermediate mirror current flowing through the diode.

5. The bidirectional current sensing circuit according to claim 4, wherein the diode is a diode-connected field effect transistor.

6. The bidirectional current sensing circuit according to claim 5, wherein each of the power field effect transistor, the first sensing field effect transistor, the second sensing field effect transistor, and the diode-connected field effect transistor is a gallium nitride (GaN) transistor.

7. The bidirectional current sensing circuit according to claim 1, wherein each of the power field effect transistor, the first sensing field effect transistor, and the second sensing field effect transistor is a gallium nitride transistor.

8. The bidirectional current sensing circuit according to claim 1, wherein each of the power field effect transistor, the first sensing field effect transistor, and the second sensing field effect transistor is at least partially formed on multiple portions of the same epitaxial stack.

9. The bidirectional current sensing circuit according to claim 1, wherein the reference voltage source provides a ground.

10. The bidirectional current sensing circuit according to claim 1, the bidirectional current sensing circuit further comprising a load connected to the drain node of the power field effect transistor, the load being configured to bidirectionally provide the supply current through the power field effect transistor.

11. The bidirectional current sensing circuit according to claim 10, wherein when the load provides the supply current from the drain node of the power field effect transistor to the source node of the power field effect transistor, the current sensing signal at the current sensing output node is at least partially generated by the first mirror current, and when the load provides the current from the source node of the power field effect transistor to the drain node of the power field effect transistor, the current sensing signal at the current sensing output node is at least partially generated by the second mirror current.

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