Current sensing circuit with electrostatic discharge protection

Abstract

A circuit allows for accurate power transistor current sensing and electrostatic discharge protection. The circuit includes a power field effect transistor and a sense field effect transistor. The sense transistor current is proportional to (but far less than) the power transistor current. Thus, the power transistor current can be measured by instead measuring the sense transistor current. The gate nodes of the transistors are connected together, and the drain nodes of the transistors are connected together. However, the source nodes of the transistors are not directly connected to each other, instead connected together via a protection resistor. When the circuit is exposed to an electrostatic discharge at the source of the sense transistor, charge that would otherwise damage the sense transistor flows in and instead is shared between the two transistors via the protection resistor.

Description

Background Art

[0001] Electronic circuits typically include transistors, which act as electronic switches that regulate or control the flow of current in parts 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 or off. A semiconductor channel region is disposed between the drain terminal and the source terminal. When the transistor is on, current flows through the semiconductor channel region between the source terminal and the drain terminal. When the transistor is closed, little or no current flows through the semiconductor channel region between the source terminal and the drain terminal. The gate terminal is disposed above the semiconductor channel region between the source terminal and the drain terminal. The voltage on the gate terminal generates a field that affects whether the semiconductor channel region conducts current, hence the name "field effect transistor."

[0002] However, there are other types of transistors. In each transistor, when the transistor is turned "on" by applying a sufficient voltage to the control node, current flows through the channel from the input node to the output node. For example, in a field effect transistor, the control node will be the gate terminal, the input node will be one of the source terminal or the drain terminal, and the output node will be the other of the source terminal or the drain terminal.

[0003] Typical transistors are used for amplification and switching purposes in electronic circuits. On the other hand, power transistors are used to carry larger currents, have higher voltage ratings, and can be used more typically in power supplies, battery charging, etc. Power transistors can typically operate with currents greater than 1 ampere up to one thousand amperes or even greater. Power transistors can carry power greater than 1 watt up to hundreds of watts or even greater. However, measuring the current through a power transistor can still be beneficial.

[0004] The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is provided merely to illustrate one example technology area in which some embodiments described herein may be practiced. Summary of the invention

[0005] This Summary is provided to introduce in a simplified form selected concepts that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0006] Embodiments described herein relate to a circuit that allows accurate power transistor current sensing and electrostatic discharge protection. The circuit includes a power field effect transistor (also referred to as a "power transistor") and a sensing field effect transistor (also referred to as a "sensing transistor"). The current through the sensing transistor is proportional to (but much less than) the current through the power transistor. Therefore, the current through the power transistor can be measured by measuring the current through the sensing transistor instead.

[0007] The power transistor has a gate node that controls whether current flows between the drain node and the source node of the power transistor. Similarly, the sensing transistor has a gate node that controls whether current flows between the drain node and the source node of the sensing transistor. The gate nodes of the power transistor and the sensing transistor are connected together. In addition, the drain nodes of the power transistor and the sensing transistor are also connected together. However, the source nodes of the power transistor and the sensing transistor are not directly connected to each other, but are connected together via a protection resistor, as will be explained later.

[0008] While the sense transistor allows accurate sensing of the current through the power transistor, the small sense transistor may be more susceptible to damage from electrostatic discharge, particularly at the source node of the sense transistor. For example, electrostatic discharge may occur during the manufacturing process when a person, machine, test probe, or other object that may carry an electrical charge touches the circuit.

[0009] To protect the sense transistor from electrostatic discharge, the circuit includes a protection resistor placed between the source node of the sense transistor and the source node of the power transistor. Thus, when the circuit is exposed to electrostatic discharge at the source node of the sense transistor, the large influx of charge that would otherwise damage the small sense transistor is instead shared between the sense transistor and the power transistor via the protection resistor.

[0010] Additional features and advantages will be set forth in the following description, and some features and advantages will be apparent from the description or may be learned by practicing the teachings herein. The features and advantages of the present invention may be realized and obtained by the instruments and combinations particularly pointed out in the appended claims. The features of the present invention will become more fully apparent from the following description and the appended claims or may be learned by practicing the present invention as set forth below. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order 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 specific embodiments thereof illustrated in the accompanying drawings. It should be understood that these figures depict only typical embodiments of the circuits, systems, and methods described herein, and therefore should not be considered limiting of the scope thereof. Certain circuits, systems, and methods will be described and explained in greater detail and detail through the use of the accompanying drawings, in which:

[0012] Figure 1 A circuit is shown in which the principles described herein can be practiced and is only one example of a circuit consistent with the principles described herein; and

[0013] Figure 2 A top view of a circuit in the form of an epitaxial stack deposited on a common semiconductor substrate is shown. Figure 1 Circuit example. DETAILED DESCRIPTION

[0014] Embodiments described herein relate to a circuit that allows accurate power transistor current sensing and electrostatic discharge protection. The circuit includes a power field effect transistor (also referred to as a "power transistor") and a sensing field effect transistor (also referred to as a "sensing transistor"). The current through the sensing transistor is proportional to (but much less than) the current through the power transistor. Therefore, the current through the power transistor can be measured by measuring the current through the sensing transistor instead.

[0015] The power transistor has a gate node that controls whether current flows between the drain node and the source node of the power transistor. Similarly, the sensing transistor has a gate node that controls whether current flows between the drain node and the source node of the sensing transistor. The gate nodes of the power transistor and the sensing transistor are connected together. In addition, the drain nodes of the power transistor and the sensing transistor are also connected together. However, the source nodes of the power transistor and the sensing transistor are not directly connected to each other, but are connected together via a protection resistor, as will be explained later.

[0016] While the sense transistor allows accurate sensing of the current through the power transistor, the small sense transistor may be more susceptible to damage from electrostatic discharge, particularly at the source node of the sense transistor. For example, electrostatic discharge may occur during the manufacturing process when a person, machine, test probe, or other object that may carry an electrical charge touches the circuit.

[0017] To protect the sense transistor from electrostatic discharge, the circuit includes a protection resistor placed between the source node of the sense transistor and the source node of the power transistor. Thus, when the circuit is exposed to electrostatic discharge at the source node of the sense transistor, the large influx of charge that would otherwise damage the small sense transistor is instead shared between the sense transistor and the power transistor via the protection resistor.

[0018] Figure 1 A circuit 100 is shown in which the principles described herein may be practiced and is only one example of a circuit consistent with the principles described herein. Circuit 100 is structurally designed to allow accurate power transistor current sensing and electrostatic discharge protection. Circuit 100 includes a power field effect transistor 110, a sensing field effect transistor 120, and a protection resistor 130. However, for simplicity, power field effect transistor 110 may be referred to as "power transistor 110", and sensing field effect transistor 120 may be referred to as "sensing transistor 120". The principles described herein are not limited to the types of power transistors and sensing transistors. However, in a very specific example, each of power transistor 110 and sensing transistor 120 may be a gallium nitride field effect transistor.

[0019] When the power transistor 110 and the sense transistor 120 are turned on, current passes through the power transistor 110 and the sense transistor 120. For example, the sense transistor 120 may be a miniaturized replica of the power transistor 110. For example, the ratio of the gate width of the power transistor 110 to the gate width of the sense transistor 120 may be 100 or more, or even one thousand or more, or even several thousand. Thus, the on-resistance of the sense transistor 120 is greater than the on-resistance of the power transistor 110 by a factor of the ratio of the gate width of the power transistor 110 to the gate width of the sense transistor 120. Thus, the current through the sense transistor 120 is proportional to (but much less than) the current through the power transistor 110. Thus, the large current through the power transistor 110 may be determined by measuring the current through the sense transistor 120 instead, and adjusted by the ratio between the gate width of the power transistor 110 and the gate width of the sense transistor 120.

[0020] The power transistor 110 includes a gate node 111 that controls whether current flows between a drain node 112 and a source node 113 of the power transistor 110. Likewise, the sense transistor 120 includes a gate node 121 that controls whether current flows between a drain node 122 and a source node 123 of the sense transistor 120. As an example, when a high voltage (e.g., positive 6 volts) is applied to the gate nodes 111 and 121, the corresponding transistors 110 and 120 are turned on, and when a low voltage (e.g., zero volts) is applied to the gate nodes 111 and 121, the corresponding transistors 110 and 120 are closed.

[0021] The gate node 111 of the power transistor 110 and the gate node 121 of the sense transistor 120 are connected together. In addition, the drain node 112 of the power transistor 110 and the drain node 122 of the sense transistor 120 are connected together. However, the source node 113 of the power transistor 110 and the source node 123 of the sense transistor 120 are not directly connected together. Instead, the protection resistor 130 is connected between the source node 113 of the power transistor 110 and the source node 123 of the sense transistor 120.

[0022] In this particular example, gate nodes 111 and 121 are connected to an external gate terminal 141, to which a gate voltage can be applied to control the on / off state of transistors 110 and 120. In addition, drain nodes 112 and 122 are connected to an external drain terminal 142, to which a drain voltage can be applied. For example, in the case of transmitting a large amount of power, at least when transistors 110 and 120 are closed, the drain voltage may be quite high, even on the order of hundreds of volts. Similarly, source node 113 of power transistor 110 is connected to an external power source terminal 143 (e.g., ground). Finally, source node 123 of sense transistor 120 is connected to an external sense source terminal 144, which will carry a signal (e.g., a current signal or a voltage signal) from which the current through power transistor 110 can be determined.

[0023] Although the sense transistor 120 allows accurate sensing of the current through the power transistor 110, the sense transistor 120 alone is susceptible to damage by electrostatic discharge (referred to herein as “ESD”) that may be inadvertently applied to the external sense source terminal 144. As an example, in Figure 1 , it is assumed that the circuit 100 does not include the protection resistor 130. If an ESD occurs at the external sense source terminal 144, all the charge inflow from the ESD will be sent to the very small gate-source capacitance of the sense transistor 120. In fact, this charge may be too much for the sense transistor 120 and may cause severe damage to the sense transistor 120.

[0024] To overcome this weakness of the sense transistor 120, the circuit 100 includes a protection resistor 130 connected between the source node 123 of the sense transistor 120 and the source node 113 of the power transistor 110. Therefore, the charge inflow due to ESD at the external sense source terminal 144 is instead shared between the sense transistor 120 and the power transistor 110. The resistance value of the protection resistor 130 can be selected so that ESD protection of the source node 123 of the sense transistor 120 is achieved, but accurate current sensing is still maintained. That is, if the resistance value of the protection resistor 130 is too large, the current sensing will be highly accurate, but the ESD protection will be reduced because there is not enough charge inflow from the ESD to flow to the source node 113 of the power transistor 110. On the other hand, if the resistance value of the protection resistor 130 is too small, the ESD protection will be increased, but the current sensing accuracy will be reduced because the currents through the transistors 110 and 120 will lose proportionality.

[0025] Therefore, the resistance value of the protection resistor 130 can be selected so as to achieve sufficient ESD protection while maintaining sufficiently accurate current sensing. As an example, the product of the resistance value of the protection resistor 130 and the gate width of the sensing transistor 120 can be greater than 10 ohm mm (ohm mm). For example, if the gate width of the sensing transistor 120 is 0.1 mm, and the resistance value of the protection resistor 130 is 100 ohms or greater, this may be the case. As another example, the product of the resistance value of the protection resistor 130 and the gate width of the sensing transistor 120 may be greater than 50 ohm mm. For example, if the gate width of the sensing transistor 120 is 0.1 mm, and the resistance value of the protection resistor 130 is 500 ohms or greater, this may be the case.

[0026] In another non-limiting example, the resistance of the protection resistor 130 may be greater than the on-resistance of the sensing transistor 120. Furthermore, the resistance of the protection resistor 130 may be greater than two times, or even five times, the on-resistance of the sensing transistor 120. In any case, the principles described herein are not limited to a particular gate width of any of the sensing transistor 120 and the power transistor 110, are not limited to the on-resistance of the sensing transistor 120 and the power transistor 110, and are not limited to a particular resistance value of the protection resistor 130.

[0027] As previously expressed, to achieve accurate current sensing, sense transistor 120 may be a miniaturized replica of power transistor 110. This may be the case, for example, if power transistor 110 and sense transistor 120 are fabricated on the same semiconductor substrate using portions of the same epitaxial stack epitaxially deposited on the semiconductor substrate.

[0028] Figure 2 A top view of a circuit 200 in the form of an epitaxial stack deposited on a common semiconductor substrate is shown. The top view is viewed downward in the opposite direction of the epitaxial growth direction of the epitaxial stack. For example, Figure 2 A coordinate system 201 is shown where the y-axis is vertical in the plane of the page, the x-axis is horizontal in the plane of the page, and the z-axis is perpendicular to the plane of the page. Epitaxial growth is in the positive z-direction, and the top view is viewed in the negative z-direction. The plane of the page is the xy plane. The semiconductor substrate on which the epitaxial stack is grown is parallel to the xy plane.

[0029] The circuit 200 may be Figure 1 1. Circuit 200 includes various active regions 210, which are ubiquitous except within window 210A where resistor 230 is located. Circuit also includes contact portions 220D, 220G, 220S, and 220SS (shown in solid line form and collectively referred to as "contact portions 220" hereinafter). Each of contact portions 220 is elongated in the y-direction, which is parallel to the y-axis and also parallel to the semiconductor substrate.

[0030] As an example, these active regions 210 may be connected to the Figure 1 The active region 210 may be connected to the gate node, drain node, and source node of the power transistor 110 and the sense transistor 120 via various drain contact portions 220D. Figure 1 The connected drain nodes 112 and 122 and may be connected to the Figure 1 However, active region 210 may be connected to source node 113 of power transistor 110 via various power source contact portions 220S, and to source node 123 of sense transistor 120 via sense source contact portions 220SS. The centermost power source contact portion 220S and sense source contact portion 220SS may be collinear with each other.

[0031] Figure 1 The resistor 130 can also be Figure 2In the embodiment of the present invention, the resistive portion 230 is epitaxially represented, for example, in the form of a resistive portion 230, which is also collinear with both the centermost power source contact portion 220S and the sensing source contact portion 220SS. The resistive portion 230 can be epitaxially formed between the collinear power source contact portion 220S and the sensing source contact portion 220SS, so that the power source contact portion 220S and the sensing source contact portion 220SS are electrically connected with a certain amount of resistance therebetween. In one embodiment, the resistive portion 230 can be made of the same conductive material as the power source contact portion 220S and the sensing source contact portion 220SS, and have the same width as them.

[0032] However, in another embodiment, the resistor portion 230 may be made of a different conductive material than any of the power source contact portion 220S and the sense source contact portion 220SS, and have a different width (i.e., cross-sectional thickness in the x-direction) than any of them. In fact, the resistance value of the resistor portion 230 may be selected by selecting a specific conductive material for the resistor portion 230 and by selecting a specific width (in the x-direction) for the resistor portion 230. For example, the resistance of the resistor portion 230 may be increased by selecting a conductive material with a larger inherent resistance and / or by selecting a thinner conductive width for the resistor portion 230. On the other hand, the resistance of the resistor portion 230 may be reduced by selecting a conductive material with a smaller inherent resistance and / or by selecting a wider conductive width for the resistor portion 230.

[0033] Additionally, the resistance of the resistive portion 230 may be increased or decreased by increasing or decreasing, respectively, the distance in the y-direction between the sensing source contact portion 220SS and the collinear power source contact portion 210S, and thus, respectively, increasing or decreasing the length (in the y-direction) of the resistive portion 230. This may be accomplished, in part, by adjusting the distance in the y-direction of the window 210A in the active region 210. In any case, the principles described herein are not limited to a particular conductive material for the resistive portion 230, a conductive width of the resistive portion 230, a length of the resistive portion 230, and a particular distance between the sensing source contact portion 220SS and the collinear power source contact portion 220S.

[0034] Thus, a circuit has been described that allows: 1) accurate current sensing of large currents through a power transistor via the use of a sense transistor; and 2) electrostatic discharge protection of the sense transistor via a protection resistor connected between the source node of the sense transistor and the source node of the power transistor.

[0035] Literal support part

[0036] Item 1. A circuit comprising: a power field effect transistor having a gate node, the gate node controlling whether current flows from the drain node of the power field effect transistor to the source node of the power field effect transistor; a sensing field effect transistor having a gate node, the gate node controlling whether current flows from the drain node of the sensing field effect transistor to the source node of the sensing field effect transistor, the gate node of the sensing field effect transistor being connected to the gate node of the power field effect transistor, the drain node of the sensing field effect transistor being connected to the drain node of the power field effect transistor; and a resistor connected between the source node of the sensing field effect transistor and the source node of the power field effect transistor.

[0037] Clause 2. The circuit of clause 1, wherein the resistor has a resistance of at least 500 ohms.

[0038] Clause 3. The circuit of clause 1, wherein the resistor has a resistance of at least 100 ohms.

[0039] Item 4. The circuit of Item 1, wherein the resistance of the resistor is greater than an on-resistance of the sense field effect transistor.

[0040] Clause 5. The circuit of clause 1, wherein the resistance of the resistor is greater than twice the on-resistance of the sense field effect transistor.

[0041] Clause 6. The circuit of Clause 1, wherein the resistance of the resistor is greater than five times the on-resistance of the sense field effect transistor.

[0042] Item 7. The circuit of Item 1, wherein a product of a resistance of the resistor and a gate width of the sense field effect transistor is greater than 50 ohm·mm.

[0043] Item 8. The circuit of Item 1, wherein a product of a resistance of the resistor and a gate width of the sense field effect transistor is greater than 10 ohm·mm.

[0044] Clause 9. The circuit of Clause 1, wherein the power field effect transistor and the sense field effect transistor are fabricated on a semiconductor substrate using portions of a same epitaxial stack epitaxially deposited on the semiconductor substrate.

[0045] Item 10. According to the circuit described in Item 9, the power field effect transistor includes a source contact portion, which is elongated in a specific direction parallel to the semiconductor substrate and connected to the source node of the power field effect transistor; and the sensing field effect transistor includes a source contact portion, which is elongated in a specific direction and connected to the source node of the sensing field effect transistor, and the source contact portion of the sensing field effect transistor is collinear with the source contact portion of the power field effect transistor; wherein the resistor is a conductor that extends in a specific direction in line with the source contact portion of the power field effect transistor and the source contact portion of the sensing field effect transistor, thereby electrically coupling the source contact portion of the power field effect transistor and the source contact portion of the sensing field effect transistor with a resistance.

[0046] Clause 11. The circuit of clause 1, wherein each of the power field effect transistor and the sense field effect transistor is a gallium nitride field effect transistor.

[0047] Item 12. The circuit of Item 1, wherein the gate width of the power field effect transistor is at least 100 times greater than the gate width of the sense field effect transistor.

[0048] Although the subject matter has been described in language specific to structural features and / or methodological acts, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the described features or acts described above, or the order of acts described above. Rather, the described features and acts are disclosed as example forms of implementing embodiments.

[0049] Without departing from its essential characteristics, the present disclosure may be embodied in other specific forms. The described embodiments are to be considered in all respects as illustrative rather than restrictive. All changes within the equivalent meaning and scope of the claims are to be included within their scope.

[0050] When introducing elements in the appended claims, the articles "a," "an," "the," and "said" mean that there are 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 circuit comprising: a power field effect transistor having a gate node, the gate node controlling whether current flows from a drain node of the power field effect transistor to a source node of the power field effect transistor; a sense field effect transistor having a gate node, the gate node controlling whether current flows from a drain node of the sense field effect transistor to a source node of the sense field effect transistor, the gate node of the sense field effect transistor being connected to the gate node of the power field effect transistor, the drain node of the sense field effect transistor being connected to the drain node of the power field effect transistor; as well as A resistor is connected between the source node of the sense field effect transistor and the source node of the power field effect transistor.

2. The circuit of claim 1, the resistor having a resistance of at least 500 ohms.

3. The circuit of claim 1, the resistor having a resistance of at least 100 ohms.

4. The circuit according to claim 1, wherein: The resistance of the resistor is greater than the on-resistance of the sensing field effect transistor.

5. The circuit according to claim 1, wherein: The resistance of the resistor is greater than twice the on-resistance of the sensing field effect transistor.

6. The circuit according to claim 1, wherein: The resistance of the resistor is greater than five times the on-resistance of the sensing field effect transistor. 7 . The circuit of claim 1 , wherein a product of a resistance of the resistor and a gate width of the sensing field effect transistor is greater than 50 ohm·mm. 8 . The circuit of claim 1 , wherein a product of a resistance of the resistor and a gate width of the sensing field effect transistor is greater than 10 ohm·mm.

9. The circuit according to claim 1, wherein: The power field effect transistor and the sense field effect transistor are fabricated on a semiconductor substrate using portions of the same epitaxial stack epitaxially deposited on the semiconductor substrate.

10. The circuit according to claim 9, The power field effect transistor includes a source contact portion, the source contact portion being elongated in a specific direction parallel to the semiconductor substrate and connected to the source node of the power field effect transistor; and The sensing field effect transistor comprises a source contact portion, the source contact portion is elongated in the specific direction and connected to the source node of the sensing field effect transistor, the source contact portion of the sensing field effect transistor is collinear with the source contact portion of the power field effect transistor; in, The resistor is a conductor that extends colinearly with the source contact portion of the power field effect transistor and the source contact portion of the sensing field effect transistor in the specific direction, thereby electrically coupling the source contact portion of the power field effect transistor and the source contact portion of the sensing field effect transistor with resistance.

11. The circuit according to claim 1, wherein: Each of the power field effect transistor and the sensing field effect transistor is a gallium nitride field effect transistor.

12. The circuit of claim 1, the gate width of the power field effect transistor being at least 100 times greater than the gate width of the sense field effect transistor.

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