Electronic device with reduced process extension band gap

Abstract

There is provided an electronic device comprising a terminal configured to receive a bandgap voltage reference generated by incorporating a first base-emitter voltage, the first base-emitter voltage being subjected to a process variation, the electronic device comprising a first transistor configured to receive a bandgap voltage reference generated by incorporating a second base-emitter voltage, the first transistor being subjected to a process variation, and a second transistor configured to receive a bandgap voltage reference generated by incorporating a second base-emitter voltage. And a first transistor having a base configured to be exposed to the bandgap voltage reference, the first transistor biased by a constant collector current corresponding to the first base-emitter voltage and configured to provide a shift voltage VE based on reducing the bandgap voltage reference by a second base-emitter voltage, the second base-emitter voltage is subjected to the process variation, and the electronic device includes a second transistor having the same type as the first transistor, the second transistor including an emitter configured to be exposed to the shift voltage, and a second transistor having the same type as the first transistor, the second transistor including an emitter configured to be exposed to the shift voltage. And the second transistor is biased by a constant base current and is configured to provide a recovered bandgap voltage based on increasing the shift voltage by a third base-emitter voltage.

Description

Technical Field

[0001] The present application relates to electronic devices, and more particularly to electronic devices having a bandgap voltage reference. Background Art

[0002] Transistors, particularly bipolar junction transistors (BJTs), are fundamental components in electronic devices and integrated circuits, enabling amplification, switching, and signal processing. However, despite their importance, the performance and characteristics of transistors can be affected by inherent variations that occur during the manufacturing process, known as process variations.

[0003] Process variations in transistors are primarily due to variations in the fabrication process, including lithography steps, doping steps, and diffusion steps. These variations can cause deviations in key transistor parameters such as current gain (β), base-emitter voltage (VBE), and cutoff frequency. As a result, process variations can cause inconsistent transistor performance, which in turn affects device functionality, reliability, and yield.

[0004] There are many sources of process variation in transistors. Variations in doping levels and implant depths during fabrication can directly affect the electrical characteristics of the transistor. In addition, variations in lithography and etching processes can affect the size and alignment of transistor structures, resulting in variations in channel width, length, and contact area.

[0005] Process variations in transistors pose a significant challenge to circuit designers and manufacturers as they can hinder the achievement of desired performance and complicate the design optimization process. Addressing and reducing process variations is critical to ensuring consistent and reliable transistor characteristics between different devices and manufacturing batches.

[0006] The process variation of the base-emitter voltage VBE is inversely proportional to the process variation of the current gain β, because both are mainly affected by the variation of the base Gummel number, which is a parameter related to the BJT manufacturing process.

[0007] In other words, the VBE and β of a BJT are affected by process variations, which are inherent variations that occur during the manufacturing process. Therefore, process variations in VBE and β exhibit an inverse relationship: VBE∝1 / β. In other words, if VBE increases due to process variations, β is likely to decrease, and vice versa.

[0008] VBE also varies directly with collector current IC, and IC = β*IB. In a BJT, there is a direct relationship between the base-emitter voltage VBE and the collector current IC. The collector current IC depends on the product of the current gain β and the base current IB. Therefore, an increase in IC will increase VBE, and vice versa. Summary of the invention

[0009] In a bipolar junction transistor (BJT), the base-emitter voltage VBE is affected by various factors, including process variations and collector current IC. Typically, the base-emitter voltage VBE varies directly with the collector current IC, meaning that an increase in collector current IC increases the base-emitter voltage VBE. Process variations cause VBE and β to vary accordingly. The relationship is inverse, and the degree to which the two variations are coupled depends on the process and the specific bipolar transistor within the process.

[0010] By maintaining a constant base current IB instead of a constant collector current IC, the process variation of VBE is partially offset by the β variation. When the base current IB is kept constant, a process corner with a high base-emitter voltage VBE or a low base-emitter voltage VBE will have a low collector current IC or a high collector current IC, respectively, which reduces VBE and, therefore, reduces the overall VBE variation across the process.

[0011] This method of controlling VBE via constant IB is generally useful, but may be particularly useful in certain applications where a precise and consistent voltage reference or bias is required.

[0012] By minimizing the effects of process variations on VBE, it is easier to achieve the desired performance and stability in circuits utilizing BJTs.

[0013] Therefore, in a first aspect of the present disclosure, an electronic device according to claim 1 is provided, the electronic device comprising: a terminal configured to receive a bandgap voltage reference VBG generated by incorporating a first base-emitter voltage VBE1, the first base-emitter voltage VBE1 being subject to process variations; a first transistor comprising a base configured to be exposed to the bandgap voltage reference VBG, wherein the first transistor is biased by a constant collector current IC corresponding to the first base-emitter voltage VBE1 and is configured to provide a shift voltage VE based on reducing the bandgap voltage reference VBG by a second base-emitter voltage VBE2, the second base-emitter voltage VBE2 being subject to the process variations; and a second transistor of the same type as the first transistor, the second transistor comprising an emitter configured to be exposed to the shift voltage VE, wherein the second transistor is biased by a constant base current IB and is configured to provide a restored bandgap voltage VBG2 based on increasing the shift voltage VE by a third base-emitter voltage VBE3.

[0014] VBE process variations can be improved by running the base-emitter voltage VBE at a constant base current IB rather than the collector current IC, and this results in a simpler and less process-sensitive approach. In other words, by controlling IB rather than IC, the variation in VBE can be reduced or made more consistent between different transistors or manufacturing processes.

[0015] In other words, it can be determined that operating the BJT at a constant base current significantly improves the VBE variation over the bipolar process corner. Therefore, in various embodiments of electronic devices according to the present disclosure, an existing bandgap reference (with or without curvature correction) can be employed, and a VBE that is less sensitive to the process can be used to replace the high process variability VBE. This can be achieved in a simple and process-independent manner by subtracting the old VBE and adding the new VBE.

[0016] In other words, an existing bandgap voltage reference VBG can be used and can be stepped down to a constant IC bias VBE and then stepped up again to a constant IB bias VBE. This helps avoid the offset (current or voltage) associated with the summing amplifier relative to the PTAT reference.

[0017] The third base-emitter voltage VBE3 does not introduce process variations back into the signal because its effective process variations are compensated by operating the second transistor at a constant base current IB. In other words, the third base-emitter voltage VBE3 can be considered "clean" from the process variations because it is not related to a fixed current but to a beta-proportional collector current (e.g., a PTAT current). Note also that in some embodiments, the bandgap voltage reference VBG may be curvature corrected, while in other embodiments, it may not be curvature corrected.

[0018] In some embodiments, the third base-emitter voltage VBE3 is based on a PTAT current that is proportional to absolute temperature.

[0019] In some embodiments, the electronic device includes a branch connected to the emitter of the first transistor and to the emitter of the second transistor such that the branch is configured to carry a total emitter current IE. Note that the total emitter current is equal to β*IB+ICORE.

[0020] In some embodiments, the electronic device includes a current mirror arranged to mirror a total emitter current IE; wherein the current mirror includes: a first branch configured to carry a proportional base current β*IB and a core current ICORE; and a second branch configured to carry the total emitter current IE.

[0021] In some embodiments according to the first alternative, the first branch comprises:

[0022] a current mirror arranged to mirror a proportional base current β*IB supplied to the collector of the second transistor;

[0023] a transistor comprising a base configured to be exposed to a constant base current IB; wherein the transistor is configured to provide a proportional base current β*IB in a first branch; and

[0024] A terminal is arranged to supply a core current ICORE into the first branch to be added to the proportional base current β*IB.

[0025] In some embodiments according to the second alternative, the first branch comprises:

[0026] a current mirror arranged to mirror a core current ICORE supplied to a collector of the first transistor; and

[0027] A transistor is arranged in parallel with the current mirror of the first branch; wherein the transistor includes a base configured to be exposed to a constant base current IB; and wherein the transistor is configured to provide a proportional base current β*IB into the first branch for addition to the mirror core current ICORE.

[0028] In some embodiments, the first base-emitter voltage VBE1 is subject to process variations due to being generated by a bandgap core transistor, and wherein the first transistor and the second transistor are of the same type as the core transistor.

[0029] The embodiments described herein are provided for illustrative purposes and should not be construed as limiting the scope of the present disclosure. It should be understood that the present disclosure encompasses other embodiments and variations within the scope of the appended claims. The present disclosure is not limited to the specific configurations, arrangements, and features described herein. The present disclosure has a wide range of applicability and should not be limited to the specific examples provided. The disclosed embodiments are merely exemplary, and those skilled in the art will appreciate that various modifications and alternative designs may be made without departing from the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In the following description, several exemplary embodiments will be described in more detail with reference to the accompanying drawings to aid understanding, in which:

[0031] Figure 1 A first embodiment of an electronic device according to the present disclosure is schematically shown.

[0032] Figure 2A second embodiment of the electronic device according to the present disclosure is schematically shown.

[0033] Figure 3 An example of a core circuit related to the present disclosure is schematically shown. DETAILED DESCRIPTION

[0034] Figure 1 A first embodiment 100 of an electronic device according to the present disclosure is schematically shown.

[0035] The electronic device 100 includes: a terminal 103 configured to receive a bandgap voltage reference VBG generated by incorporating a first base-emitter voltage VBE1, the first base-emitter voltage VBE1 being subject to process variations; a first transistor 101 including a base configured to be exposed to the bandgap voltage reference VBG, wherein the first transistor is biased by a constant collector current IC corresponding to the first base-emitter voltage VBE1 and is configured to provide a shift voltage VE based on reducing the bandgap voltage reference VBG by a second base-emitter voltage VBE2, the second base-emitter voltage VBE2 being subject to the process variations; and a second transistor 102 of the same type as the first transistor, including an emitter configured to be exposed to the shift voltage VE, wherein the second transistor is biased by a constant base current IB and is configured to provide a restored bandgap voltage VBG2 based on increasing the shift voltage VE by a third base-emitter voltage VBE3.

[0036] The third base-emitter voltage VBE3 does not introduce process variations back into the signal, since its effective process variations are compensated by operating the second transistor at a constant base current IB.

[0037] The base current of the bipolar differential pair is injected into the VBG node. Depending on the bandgap topology, this node may be low impedance or already compensated for the existing bandgap base current.

[0038] Furthermore, the electronic device 100 may include a branch 104 connected to the emitter of the first transistor 101 and to the emitter of the second transistor 102, such that the branch 104 is configured to carry a total emitter current IE. As shown, this total emitter current IE may be equal to β*IB+ICORE.

[0039] Furthermore, the electronic device 100 may include a current mirror 105 arranged to mirror the total emitter current IE. The current mirror 105 may include: a first branch 107 configured to carry a proportional base current β*IB and a core current ICORE (which may be equal to a constant collector current IC); and a second branch 106 configured to carry the total emitter current IE.

[0040] The current mirror 105 may further include a transistor 108 and a transistor 109 .

[0041] Furthermore, the first branch 107 may include a current mirror 110 arranged to mirror a core current ICORE supplied to the collector of the first transistor 101. The current mirror 110 may include a transistor 111 and a transistor 112.

[0042] The first branch 107 may further include a transistor 115 arranged in parallel with the current mirror 110 of the first branch 107. The transistor 115 may include a base configured to be exposed to a constant base current IB; and the transistor 115 may be configured to provide a proportional base current β*IB into the first branch 107 to be added to the mirror core current ICORE.

[0043] As another option, the old PTAT voltage can be tapped and an adder used to add the PTAT to the "constant base current" VBE. However, this approach requires more transistors and has a greater potential for mismatches and other non-idealities.

[0044] Figure 2 A second embodiment 200 of an electronic device according to the present disclosure is schematically shown. Here, as in the above-mentioned first embodiment, the electronic device 200 includes: a terminal 103, which is configured to receive a bandgap voltage reference VBG generated by incorporating a first base-emitter voltage VBE1, the first base-emitter voltage VBE1 being subject to process variations; a first transistor 101, which includes a base configured to be exposed to the bandgap voltage reference VBG, wherein the first transistor is biased by a constant collector current IC corresponding to the first base-emitter voltage VBE1 and is configured to provide a shift voltage VE based on reducing the bandgap voltage reference VBG by a second base-emitter voltage VBE2, the second base-emitter voltage VBE2 being subject to the process variations; and a second transistor 102 of the same type as the first transistor, which includes an emitter configured to be exposed to the shift voltage VE, wherein the second transistor is biased by a constant base current IB and is configured to provide a restored bandgap voltage VBG2 based on increasing the shift voltage VE by a third base-emitter voltage VBE3.

[0045] Furthermore, the electronic device 200 may include a branch 104 connected to the emitter of the first transistor 101 and to the emitter of the second transistor 102, such that the branch 104 is configured to carry a total emitter current IE. As shown, this total emitter current IE may be equal to β*IB+ICORE.

[0046] Furthermore, the electronic device 200 may include a current mirror 105 arranged to mirror the total emitter current IE. The current mirror 105 may include: a first branch 107 configured to carry a proportional base current β*IB and a core current ICORE (which may be equal to a constant collector current IC); and a second branch 106 configured to carry the total emitter current IE.

[0047] The current mirror 105 may further include a transistor 108 and a transistor 109 .

[0048] In addition, the first branch 107 may include: a current mirror 201, which is arranged to mirror the proportional base current β*IB supplied to the collector of the second transistor 102; a transistor 204, which includes a base configured to be exposed to a constant base current IB; wherein the transistor is configured to provide a proportional base current β*IB in the first branch; and a terminal 205, which is arranged to supply a core current ICORE to the first branch 107 so as to be added to the proportional base current β*IB.

[0049] Note that in other words, transistor 204 is therefore arranged to produce a proportional base current, ie β*IB. This current flows in two places: out of the base to form part of the tail current, and through the current mirror to force the second transistor 102 to conduct the same current (once the loop is closed).

[0050] The second embodiment 200 reduces the risk of mismatch (randomly and systematically). Errors in the tail current are less likely to corrupt the current in the second transistor 102. The current through the second transistor 102 will likely be very low at cold beta and low beta to avoid dropping current at hot beta and high beta.

[0051] In fact, the second embodiment 200 allows a more reasonable current level to be selected to achieve a given performance.

[0052] The topology of the embodiments described in this disclosure also facilitates providing a low impedance bandgap reference.

[0053] Figure 3 The core circuitry arranged to supply the described bandgap voltage reference and various other currents (including IB and β*IB) is shown schematically.

[0054] Note that other embodiments according to the present disclosure may be designed as PNP as well as NPN. The MOSFETs shown in the exemplary first and second embodiments described above are mainly used as reflectors, so the circuit may also be considered independent of the MOSFET type or rated voltage, and the circuit may therefore be designed without a MOSFET and using only a BJT.

[0055] Unless the context clearly dictates otherwise, the singular forms "a", "an" and "the" as used in this application and the claims include the plural forms. The systems, devices and methods described herein should not be construed as limiting in any way. On the contrary, the present disclosure is directed to all novel and non-obvious features and aspects of the various disclosed embodiments, individually and in various combinations and sub-combinations with each other. The disclosed systems, methods and devices are not limited to any particular aspect or feature or combination thereof, nor do the disclosed systems, methods and devices require the presence of any one or more specific advantages or problem solving. Any theory of operation is for ease of explanation, but the disclosed systems, methods and devices are not limited to such theory of operation.

[0056] Although the operations of some of the disclosed methods are described in a particular sequential order for ease of presentation, it should be understood that this description encompasses rearrangement unless the specific language described below requires a specific ordering. For example, the operations described in sequence may be rearranged or performed simultaneously in some cases. In addition, for simplicity, the accompanying drawings may not show the various ways in which the disclosed systems, methods, and devices can be used in combination with other systems, methods, and devices. In addition, the specification sometimes uses terms like "obtain" and "output" to describe the disclosed methods. These terms are high-level abstractions of the actual operations performed. The actual operations corresponding to these terms will vary depending on the specific implementation and will be easily recognized by those skilled in the art.

[0057] It should be understood that, in order to simplify and clarify the description, reference numbers in different figures may have been repeated, where appropriate, to indicate corresponding or similar elements. In addition, many specific details are set forth in order to provide a thorough understanding of the examples described herein. However, it will be appreciated by those skilled in the art that the examples described herein may be practiced without these specific details. In other cases, methods, procedures, and components have not been described in detail to avoid confusion regarding the related features described. The drawings are not necessarily drawn to scale, and the proportions of certain components may be exaggerated to better illustrate details and features. This description should not be considered to limit the scope of the examples described herein.

[0058] Reference Number List

[0059] 100 First Embodiment

[0060] 101 The First Transistor

[0061] 102 Second transistor

[0062] 103 terminal

[0063] 104 Branch Road

[0064] 105 Current Mirror

[0065] 106 Second Branch Road

[0066] 107 First Branch Road

[0067] 108 Transistors

[0068] 109 Transistor

[0069] 110 Current Mirror

[0070] 111 Transistor

[0071] 112 Transistors

[0072] 113 Transistor

[0073] 114 Transistors

[0074] 115 Transistor

[0075] 200 Second Embodiment

[0076] 201 Current Mirror

[0077] 202 Transistor

[0078] 203 Transistor

[0079] 204 Transistor

[0080] 205 terminal

[0081] 206 Transistors

[0082] 300 core circuits

Claims

1. An electronic device, comprising: a terminal configured to receive a bandgap voltage reference (VBG) generated by incorporating a first base-emitter voltage (VBE1), wherein VBE1 is subject to process variations; a first transistor including a base configured to be exposed to the VBG, wherein the first transistor is biased by a constant collector current (IC) corresponding to the VBE1, and the first transistor is configured to provide a shift voltage (VE) based on reducing the VBG by a second base-emitter voltage (VBE2), and wherein the VBE2 is subject to the process variation; and a second transistor of the same type as the first transistor, the second transistor comprising an emitter configured to be exposed to the VE, wherein the second transistor is biased by a constant base current (IB), and the second transistor is configured to provide a restored bandgap voltage (VBG2) based on increasing the VE by a third base-emitter voltage (VBE3). 2 . The electronic device of claim 1 , wherein the VBE3 is based on a proportional to absolute temperature (PTAT) current.

3. The electronic device of claim 1, further comprising a branch connected to the emitter of the first transistor and to the emitter of the second transistor such that the branch is configured to carry a total emitter current (IE).

4. The electronic device of claim 2, further comprising a branch connected to the emitter of the first transistor and to the emitter of the second transistor such that the branch is configured to carry a total emitter current (IE).

5. The electronic device of claim 3 , further comprising a current mirror arranged to mirror the IE, wherein the current mirror comprises: a first branch configured to carry a proportional base current (β*IB) and a core current (ICORE); as well as A second branch, where the second branch is configured to carry the IE.

6. The electronic device according to claim 5, wherein the first branch comprises: a current mirror arranged to mirror the β*IB supplied to the collector of the second transistor; a transistor including a base configured to be exposed to the IB, wherein the transistor is configured to provide the β*IB in the first branch; as well as A terminal is arranged to supply the ICORE into the first branch for addition to the β*IB.

7. The electronic device according to claim 5, wherein the first branch comprises: a current mirror arranged to mirror the ICORE supplied to the collector of the first transistor; as well as A transistor is arranged in parallel with the current mirror of the first branch, wherein the transistor includes a base configured to be exposed to the IB, and wherein the transistor is configured to provide the β*IB into the first branch for addition with the ICORE.

8. The electronic device of claim 1, wherein the VBE1 is subject to process variations due to being produced by a bandgap core transistor, and wherein the first transistor and the second transistor are of the same type as the core transistor.

9. The electronic device of claim 2, wherein the VBE1 is subject to process variations due to being produced by a bandgap core transistor, and wherein the first transistor and the second transistor are of the same type as the core transistor.

10. The electronic device of claim 3, wherein the VBE1 is subject to process variations due to being produced by a bandgap core transistor, and wherein the first transistor and the second transistor are of the same type as the core transistor.

11. The electronic device of claim 4, wherein the VBE1 is subject to process variations due to being produced by a bandgap core transistor, and wherein the first transistor and the second transistor are of the same type as the core transistor.

12. The electronic device of claim 5, wherein the VBE1 is subject to process variations due to being produced by a bandgap core transistor, and wherein the first transistor and the second transistor are of the same type as the core transistor.

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