ARTIFICIAL TRANSMISSION LINE USING T-COIL SECTIONS

Abstract

An electrical circuit can be formed at least in part using lumped or discrete circuit elements to provide an artificial transmission line structure that can mimic the electrical properties of a corresponding actual transmission line structure. Such an artificial transmission line structure can generally consume less area than an actual transmission line structure lac0ure can be formed using two or more unit cells such as by cascading such cells as shown and described herein. The present inventors have recognized, among other things, that a unit cell of an artificial transmission line structure can include a t-coil section comprising magnetically-coupled inductors. Such an artificial transmission line structure can be used for applications such as phase shifting or to provide a delay line having a substantially constant group delay, among other applications.

Claims

1. An electronic circuit defining an artificial transmission line structure comprising at least two unit cells, wherein a respective unit cell amongst the at least two unit cells comprises: a first t-coil section defined by a first inductor mutually magnetically coupled and conductively coupled in series with a second inductor, and a first shunt capacitor coupled to a node between the first inductor and the second inductor; and a third inductor conductively coupled with the second inductor; wherein the third inductor is arranged to suppress or inhibit mutual magnetic coupling with the first inductor and the second inductor.

2. The electronic circuit of claim 1, wherein the third inductor is conductively coupled in series with the first shunt capacitor.

3. The electronic circuit of claim 2, comprising a second capacitor connected to bypass the first and second inductors, the second capacitor connected between an input node of the first t-coil section and an output node of the first t-coil section.

4. The electronic circuit of claim 1, wherein values of the first, second, and third inductors are specified to provide a substantially linear phase response in a specified range of frequencies.

5. The electronic circuit of claim 1, wherein a coupling coefficient corresponding to mutual magnetic coupling between the first inductor and the second inductor is established at an intermediate value between zero and one to provide a substantially linear phase response.

6. The electronic circuit of claim 5, wherein the intermediate value is between about 0.5 and about 0.7.

7. The electronic circuit of claim 1, wherein the first and second inductors have the same self-inductance value.

8. The electronic circuit of claim 1, wherein the third inductor is coupled in series with the second inductor.

9. The electronic circuit of claim 8, comprising a second t-coil section defined by the third inductor and a fourth inductor, the second t-coil section comprising a second shunt capacitor coupled to a node between third inductor and the fourth inductor.

10. The electronic circuit of claim 9, wherein the third inductor and the fourth inductor are arranged to suppress or inhibit mutual magnetic coupling between each other.

11. The electronic circuit of claim 8, comprising a second shunt capacitor coupled to a node between the second inductor and the third inductor.

12. The electronic circuit of claim 1, wherein the first and second inductors are defined by a symmetrical differential inductor.

13. The electronic circuit of claim 1, wherein the first and second inductors have the same self inductance value.

14. The electronic circuit of claim 1, comprising a phase shifter circuit including at least two selectable electrical paths coupling an input port to an output port, wherein one of the at least two selectable electrical paths comprises the artificial transmission line structure.

15. An electronic circuit defining an integrated phase shifter circuit, the electronic circuit comprising: a first electrical path to provide a first specified phase shift, the first electrical path comprising an artificial transmission line structure comprising at least two unit cells, wherein a respective unit cell amongst the at least two unit cells comprises: a first t-coil section defined by a first inductor mutually magnetically coupled and conductively coupled in series with a second inductor, and a first shunt capacitor coupled to a node between the first inductor and the second inductor; and a third inductor conductively coupled with the second inductor; wherein the third inductor is arranged to suppress or inhibit mutual magnetic coupling with the first inductor and the second inductor; and a second electrical path to provide a second specified phase shift different than the first specified phase shift; at least a first switch to selectively couple an input signal through the first electrical path or the second electrical path in response to a control signal.

16. The electronic circuit of claim 15, wherein values of the first, second, and third inductors are specified to provide a substantially linear phase response in a specified range of frequencies.

17. The electronic circuit of claim 15, wherein a coupling coefficient corresponding to mutual magnetic coupling between the first inductor and the second inductor is established at an intermediate value between about 0.5 and about 0.7.

18. A method for controlling a delay value for an electrical signal using a phase shifter circuit, the method comprising: receiving a control signal and, in response, selectively coupling the electrical signal through one of a first electrical path to provide a first specified phase shift or a second electrical path to provide a second specified phase shift different than the first specified phase shift; wherein the first electrical path comprises an artificial transmission line structure comprising at least two unit cells, wherein a respective unit cell amongst the at least two unit cells comprises: a first t-coil section defined by a first inductor mutually magnetically coupled and conductively coupled in series with a second inductor, and a first shunt capacitor coupled to a node between the first inductor and the second inductor; and a third inductor conductively coupled with the second inductor.

19. The method of claim 18, wherein values of the first, second, and third inductors are specified to provide a substantially linear phase response in a specified range of frequencies.

20. The method of claim 18, wherein a coupling coefficient corresponding to mutual magnetic coupling between the first inductor and the second inductor is established at an intermediate value between about 0.5 and about 0.7.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

[0011] FIG. 1A illustrates generally an example comprising an artificial transmission line that can include two or more unit cells, the unit cells comprising respective t-coil arrangements.

[0012] FIG. 1B illustrates generally an equivalent circuit representation of a unit cell comprising magnetically-coupled inductors forming a t-coil arrangement, such as corresponding to a unit cell from the artificial transmission line of FIG. 1A,

[0013] FIG. 2A shows illustrative examples comprising amplitude response plots obtained using simulation of an artificial transmission line having various coupling coefficients between magnetically-coupled inductors.

[0014] FIG. 2B shows illustrative examples comprising phase response plots obtained using simulation of an artificial transmission line having various coupling coefficients between magnetically-coupled inductors.

[0015] FIG. 3A illustrates generally an example comprising another unit cell topology that can be used to provide an artificial transmission line.

[0016] FIG. 3B illustrates generally an example comprising yet another unit cell topology that can be used to provide an artificial transmission line, similar to the unit cell of FIG. 3A, but including a second capacitor.

[0017] FIG. 4A illustrates generally an example comprising yet another unit cell topology that can be used to provide an artificial transmission line.

[0018] FIG. 4B illustrates generally an example comprising yet another unit cell topology that can be used to provide an artificial transmission line.

[0019] FIG. 5A illustrates generally an example comprising a differential inductor, such as can he fabricated as a portion of a monolithic integrated circuit, or included as a portion of an integrated module, such as to provide a portion of a unit cell S forming an artificial transmission line.

[0020] FIG. 5B shows an illustrative example of a layout of conductive layers that can be used to provide a differentiile of a phase shifter circuit topology, such as can include one or more artificial transmission lines as shown and described in relation to other examples in this document.

[0021] FIG. 7 illustrates generally a technique, such as a method, comprising receiving a control signal, and, in response, selectively coupling an electrical signal through a first electrical path or a second electrical path, such as using a phase shifter circuit topology as shown illustratively in FIG. 6.

DETAILED DESCRIPTION

[0022] Transmission line structures generally have associated electrical characteristics such as a time delay (e.g., group delay), phase shift, characteristic impedance, or other parameters. As mentioned above, an artificial transmission line structure can be formed using lumped or discrete elements to provide electrical behavior similar to an actual transmission line structure. In an actual transmission line structure, electrical characteristics such as capacitance per unit length, inductance per unit length, conductance, and shunt resistance, generally result from distributed electrical characteristics of the conductors and dielectric materials forming the transmission line structure. By contrast, in an artificial transmission line structure, at least some electrical elements are lumped components, such as inductors or capacitors. Various topologies can be used to provide an artificial transmission line. For example, a left-handed artificial transmission line can be established using series-connected capacitors with shunt-connected inductors. Similarly, a right-handed artificial transmission line can be established using series-connected inductors with shunt-connected capacitors. A composite right-handed and left handed structure can be formed using a combination of series-connected inductors and capacitors, and shunt networks comprising parallel-connected inductors and capacitors.

[0023] As mentioned briefly above, the present inventors have recognized, among other things, that an artificial transmission line structure can be formed using two or more cascaded unit cells, where the unit cells include respective t-coil sections. An artificial transmission line structure including such unit cells can provide electrical characteristics similar to an actual transmission line structure, including establishing a specified characteristic impedance (defined as a ratio of a voltage amplitude divided by a current amplitude of an electrical signal propagating through the line), group delay, or corresponding phase shift, as illustrative examples.

[0024] FIG. 1A illustrates generally an example comprising an artificial transmission line 100 that can include two or more unit cells 110A through 110N, the unit cells comprising respective t-coil sections. The t-coils can be defined by a first inductor, L1, and a second inductor L2, coupled in series, along with a shunt capacitor C coupled to a node between the first and second inductors L1 and L2 and a common node 106. The artificial transmission line 100 shown in FIG, 1 can represent a variation on a right handed artificial transmission line unit-cell topology. Coupled inductors L1 and L2 can be magnetically linked, and such flux linkage can be represented by a coefficient of mutual magnetic coupling k, having a value between zero and one. A value of zero indicates no mutual magnetic coupling between the inductors L1 and L2, and a value of one indicates perfect magnetic coupling. A first port 102 (e.g., an input port) can be defined by two terminals comprising a node 108 and the common node 106, and a second port 104 (e.g., an output port) can be defined by a node 112 and the common node 106. The example of FIG. 1 shows an unbalanced configuration but could also be implemented in a balanced configuration with corresponding inductances added along the line denoting the common node 106. Generally, the examples shown in this document are unbalanced configurations but could also be implemented using a balanced configuration. In part, a count of cascaded unit cells (e.g., comprising copies of unit cell 110A.) can be used to establish a specified phase shift or time delay (e.g., group delay).

[0025] FIG. 1B illustrates generally an equivalent circuit representation of a unit cell 110B comprising magnetically-coupled inductors forming a t-coil arrangement, such as corresponding to a unit cell 100A from the artificial transmission line 100 of FIG. 1A. Referring to FIG. 1B, if L1=L2=L/2, then a transfer function can be represented as the transmission scattering parameter, S.sub.21, and can be represented as follows:

[00001]$s_{21}=\frac{{\mathrm{jR}}_L\left(1+{}^2.Math.\mathrm{KLC}/2\right)}{{}^3.Math.L^2.Math.C/4.Math.\left(1-K^2\right)-.Math..Math.L\left(K+1\right)+{\mathrm{jR}}_L\left(1-{}^2.Math.\mathrm{LC}/4\right)},$

and when K=0, the transfer function can be simplified to provide a unit cell corresponding to a right-handed artificial transmission line having inductors that are not mutually magnetically coupled:

[00002]$s_{21}=\frac{{\mathrm{jR}}_L}{{}^3.Math.L^2.Math.C/4-.Math..Math.L+{\mathrm{jR}}_L\left(1-{}^2.Math.\mathrm{LC}/4\right)}.$

In the preceding expressions, can represent angular frequency value, f can represent an imaginary-valued coefficient corresponding to {square root over (1)}, C represents a shunt capacitor value, and R.sub.L can represent a load resistance value.

[0026] As can be shown from the expressions above, use of mutually-magnetically coupled inductors can provide bandwidth extension. As K approaches unity, bandwidth becomes greater, as shown illustratively in FIG. 2A, which shows illustrative examples comprising amplitude response plots obtained using simulation of an artificial transmission line having various coupling coefficients between magnetically-coupled inductors. As shown in FIG. 2A, when K is greater than zero, the 3 dB point, where the output amplitude is decreased by 3 dB relative to the OdB reference input amplitude, is extended to higher frequencies, with an idealized case of unlimited bandwidth when K=1. Such bandwidth extension illustrates generally that use of coupled inductors for t-coil sections in unit cells can provide an artificial transmission line structure providing at least one of greater usable bandwidth for the same physical circuit size, or reduced circuit size as compared to other approaches when provided a specified bandwidth.

[0027] FIG. 2B shows illustrative examples comprising phase response plots obtained using simulation of an artificial transmission line having various coupling coefficients between magnetically-coupled inductors, As shown in FIG. 213, use of non-coupled inductors provides a highly non-linear phase response (e.g., corresponding a right-handed structure having no mutual magnetic coupling where K=0). The present inventors have recognized, among other things, that a phase response can be substantially linearized such as by establishing a coupling coefficient, K, at an intermediate value between zero and one. For example, as shown in FIG. 2B, a value for the coupling coefficient, K can be established between about 0.5 and about 0.7, such as about 0.6. In this manner, a time delay (e.g., a group delay) through the artificial transmission line can be made constant across a specified range of operating frequencies (e.g., reducing dispersion of a signal propagating through the artificial transmission line structure). Other variations on the unit cell topology 110A of FIG. 1A can be used,

[0028] For example, FIG. 3A illustrates generally an example comprising another unit cell 310A topology that can be used to provide an artificial transmission line. As in the example of FIG. 1A, in FIG, 3A, a t-coil section can be established having two inductors, L1 and L2, and a capacitor C. In the example of the unit cell 310A of FIG. 3A, a third inductor, L3, can be coupled between the capacitor C and a node between inductors L1 and L2. A value of L3 can be established to at least partially cancel an equivalent negative inductance term (e.g., K(L/2) as shown in FIG. 1B), associated with a mutual inductance formed by magnetically coupling inductors L1 and L2. In addition, or instead, a value of L3 can also be used to adjust a phase response to help linearize such a phase response to provide, for example, a constant time delay (e.g., group delay). The third inductor L3 can be arranged to suppress or inhibit mutual magnetic coupling with the first inductor L1 and the second inductor L2 (e.g., by laterally offsetting L3 spatially from L1 or L2, or establishing L3 through parasitic inductance defining a loop that is substantially orthogonal to inductive loops defining L1 or L2).

[0029] FIG. 3B illustrates generally an example comprising yet another unit cell 3108 topology that can be used to provide an artificial transmission line, similar to the unit cell 310A of FIG. 3A, but including a second capacitor, CC, bypassing the first and second inductors L1 and L2. The addition of capacitor CC provides another degree of freedom to enable control of one or more characteristics of an artificial transmission line comprising two or more unit cells 310B.

[0030] FIG. 4A illustrates generally an example comprising yet another unit cell 410A topology that can be used to provide an artificial transmission line. In the example of FIG. 4A, first and second inductors L1 and L2 can be serially-connected, with a first capacitor C1 connected to the node between inductors L1 and L2. As in the examples mentioned above, L1 and L2 can be mutually magnetically coupled, such as having a magnetic coupling coefficient, K, as in other examples. A third inductor L3 can be connected in series with inductor L2. The third inductor need not be a discrete inductor. For example, if inductors L1 and L2 are co-integrated within an integrated circuit, inductor L3 can represent a specified parasitic inductance contribution corresponding to conductive couplings between an adjacent unit cell and the unit cell 410A. A second capacitor C2 can be coupled to the third inductor L3, such as at node distal to L2 as shown in the unit cell 410A. In this manner, a combination of the third inductor and a fourth inductor (e.g., representing the first inductor in the next cascaded unit cell) can be considered another t-coil section where the inductors comprising the t-coil are not mutually magnetically coupled, with the second capacitor C2 coupled to a node between the third and fourth inductors and a common node,

[0031] FIG. 4B illustrates generally an example comprising yet another unit cell 410B topology that can be used to provide an artificial transmission line, similar to the unit cell 410A, but having the second capacitor C2 coupled to a node between inductors L2 and L3.

[0032] In the illustrative examples of FIG. 4A and FIG. 4B, the third inductor L3 is not mutually magnetically coupled with either inductor L1 or inductor L2. In FIG. 4A and FIG, 413, the unit cells 410A and 410B provide several component values that can be specified to provide desired electrical characteristics. For example, if an integrated differential inductor topology is used (such as shown and described in the illustrative but non-limiting examples of FIG. 5A and FIG. 5B), a coefficient, K may be in a range from about 0.7 to about 0.8. A lower coupling coefficient, K, such as about 0.55, may be desired to provide enhanced phase linearity. To compensate for a difference between an actual K-value provided by an integrated circuit process, versus a desired value, other component parameters can be adjusted. For examples, values of one or more of L3, C1, C2, L1, and L2 can be varied parametrically to enhance performance across one or more electrical characteristics over a specified operating bandwidth, such as insertion loss, return loss e.g,, impedance matching performance), or phase linearity, as illustrative examples.

[0033] FIG. 5A illustrates generally an example 500 A comprising a differential inductor 515, such as can be fabricated as a portion of a monolithic integrated circuit, or included as a portion of an integrated module, such as to provide a portion of a unit cell forming an artificial transmission line. A t-coil section, such as mentioned in relation to other examples herein, can include two mutually magnetically-coupled inductors. Such inductors can be formed using a differential inductor 515, such as having a tap 520 to couple a capacitor (or other element) to a node between the two inductive portions of the differential inductor 515. In this manner, the example 500 A can provide a unit cell (or a portion of a unit cell) of an artificial transmission line, such as having a two-terminal input port comprising nod es 508 and 506, and an output port comprising a node 512 and the node 506. The output 512 can be coupled to another unit cell, or a series of cascaded unit cells, such as to provide a desired time delay value or phase shift, as an illustrative example.

[0034] FIG. 5B shows an illustrative example 500 B of a layout of conductive layers that can be used to provide a differential inductor 515. In the example 500 B, a first conductive layer (e.g., a metallization layer) of an integrated circuit can define portions of two or more concentric windings. A second conductive layer 525 can be used to conductive couple the portions of the two or more concentric windings, such as through respective via structures. A tap 520 can be provided, such as a center-tap (e.g., to define two equal-valued magnetically-coupled inductors), a capacitor, C, can be coupled between the tap 520 and a common node 506.

[0035] As mentioned in relation to other examples herein, the artificial transmission line structures described in this document can be used for a variety of applications. For example, FIG. 6 shows an illustrative example of a phase shifter circuit 660 topology, such as can include one or more artificial transmission lines as shown and described in relation to other examples in this document. in FIG. 6, an input signal 602 can be coupled to an input port having a first single-pole double-through (SPDT) switch 640A, to select between routing the input signal 602 through a first path 650A defining a first specified time delay (e.g., group delay) or a corresponding phase shift, and a second path 650B define a second, different specified time delay or corresponding phase shift. A second SPDT switch 640B can receive a delayed representation of the input signal 602, such as routing the delayed signal to an output port to provide an output signal 604. The states of the first and second SPDT switches 640A and 640B can be controlled using a control circuit 670. For example, the SPDT switches can include solid-state switching structures (e.g., field-effect transistors or other semiconductor switching devices) or mechanical switches (e.g., MEMS relay devices), and the control circuit 670 can receive a control signal and generate an appropriate drive signal (e.g., a gate drive signal or other signal) to actuate the first or second switches 640A or 640B. One or more of the first or second paths 650A or 650 B can include an artificial transmission line 600, such as shown and described in relation to other examples herein. For example, the artificial transmission line 600 can include two or more cascaded unit cells comprising respective t-coil sections including mutually magnetically-coupled inductors.

[0036] FIG. 7 illustrates generally a technique, such as a method, comprising receiving a control signal at 705, and, in response, at 710, selectively coupling an electrical signal through a first electrical path or a second electrical path, such as using a phase shifter circuit topology as shown illustratively in FIG. 6.

[0037] Each of the non-limiting aspects in this document can stand on its own, or can be combined in various permutations or combinations with one or more of the other aspects or other subject matter described in this document.

[0038] The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to generally as examples. Such examples can include elements in addition to those shown or described. However, the present inventors also contemplate examples in which only those elements shown or described are provided. Moreover, the present inventors also contemplate examples using any combination or permutation of those elements shown or described (or one or more aspects thereof), either with respect to a particular example (or one or more aspects thereof), or with respect to other examples (or one or more aspects thereof) shown or described herein.

[0039] In the event of inconsistent usages between this document and any documents so incorporated by reference, the usage in this document controls.

[0040] In this document, the terms a or an are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of at least one or one or more. In this document, the term or is used to refer to a nonexclusive or, such that A or B includes A but not B, B but not A, and A and B, unless otherwise indicated. In this document, the terms including and in which are used as the plain-English equivalents of the respective terms comprising and wherein. Also, in the following claims, the terms including and comprising are open-ended, that is, a system, device, article, composition, formulation, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms first, second, and third, etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

[0041] Method examples described herein can be machine or computer-implemented at least in part. Some examples can include a computer-readable medium or machine-readable medium encoded with instructions operable to configure an electronic device to perform methods as described in the above examples. An implementation of such methods can include code, such as microcode, assembly language code, a higher-level language code, or the like. Such code can include computer readable instructions for performing various methods. The code may form portions of computer program products. Further, in an example, the code can be tangibly stored on one or more volatile, non-transitory, or non-volatile tangible computer-readable media, such as during execution or at other times. Examples of these tangible computer-readable media can include, but are not limited to, hard disks, removable magnetic disks, removable optical disks (e.g., compact disks and digital video disks), magnetic cassettes, memory cards or sticks, random access memories (RAMs), read only memories (ROMs), and the like.

[0042] The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description as examples or embodiments, with each claim standing on its own as a separate embodiment, and it is contemplated that such embodiments can be combined with each other in various combinations or permutations. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.